Theory of Time Machine

Science or Fiction?

1st edition

Uday Hiwarale

IIT Indore

2012

The Theory of Time Machine

DisclaimerThis book is produced for a general reading and not for theeducational use. Most of the theories about universe and time arepurely hypothetical and pure fiction hence we do not aim any contextof this book to be use for research or any educational purpose.

This matter in this book is taken from all the references and internet.The ideas about anything which might look fiction and hypotheticalmay or may not be true in the real world and hence do not guaranteeabout any information which contradict the real scenarios in the realscientific world. The phrases or the world may look like to be quotedfrom the references directly but this book does not include anymaterial which might be copyrighted or published.

The matter, numbers or values mentioned in this book are roundedoff or taken on approximate scale. The values mentioned regardingany events or objects are taken from the references and hence wedo not provide a guarantee about those values or numbers.

The main aim behind production of this book is to provide overviewof the theories about universe and time concept. This book can beused to understand initials of the creation of the world or the conceptof beginning of time. This book also includes theory of relativity andthe theories of time travel. The special topic on construction of timemachine is also included but as it is a fiction, we request not to try itat educational level beside theoretical physics.

I thanks to all the readers and by collaborators for their help.

Note: This is not the final version of the book and this book maysubject to grammatical mistakes, incomplete sentences and othermistakes.

Dedicated to scientists and researchers of India

Index

1. Introduction

2. Theory of Relativity

3. Black Holes, White Holes, Wormholes

4. Time Travel1. Travelling to others time2. Travelling to owns 3.timeRule of time travel

5. The Time Machine

Chapter1: Introduction

Grandfather paradox – ©cartoonstock.com 2012

Time travel and time machine is not only interesting topics to discuss butit is a science fact. It has been proved that time dilation really occurs inthe systems that are travelling relative to us or objects that are in differentgravitational field relative to us.

The time dilation allows the traveller to travel into the future but not to thepast. If a person travel into the past then it will violates the principle ofcausality. Also a grandfather paradox telling quite literally that laws ofnature get broken if a person travels into the past.









‘The Time Machine’ been a most interesting, most discussed andfamous topic for science fiction movies and documentaries. But howmany of you believe in time machine? I mean in scientific way ratherthan science fiction.

Well many students of Astrophysics and Astrology denied thinkingabout it because it seems funny and foolish for them to constructtime machine or even think about time machine. Many of us believethan such things do not exist and cannot be developed ormanufactured in future. Perhaps it is true. But I don’t think so.

Albert Einstein, everybody knows about him. Sure we do. But whyhe is so famous? I think about 99% people knows this name do notknow what he has done making him so famous and one of thebrilliant mind in the world. In 1905 he introduce ‘Relative Theory’through a paper submitted by him ‘On the Electrodynamics ofMoving Bodies’ and in 1906 Max Plank introduced max plantsuggest ‘Theory of Relativity’ rather than ‘Relative theory’ and soonit became ‘Einstein theory of Relativity’. But that’s not all.

In 1916 Einstein published his second theory, ‘General theory ofrelativity’ describing law of gravitation and motion of bodies ingravitational field. Because of this theory his first theory waspronouns like ‘Special Theory of Relativity’ because it was used toexplain bodies in relative motion. The general theory of relativity wasbit difficult to understand and many people ware against it. But in1919 Sir Arthur Stanley Eddington, one of the brilliant astrophysicistand philosopher successfully proved Einstein general theory ofrelativity by experiment of observing deviation of light of stars duringsolar eclipse. At that time only two three people understood thistheory very well, Albert Einstein, Arthur Eddington and LudwigSilberstein. Ludwig Siberstein was physicist and member of royalsociety who defendant Einstein’s theory showing some degree of

scepticism. But even all, Einstein’s theory is fully understood andaccepted and used in modern physics and quantum mechanicscalculation.

It seems so strange that his special relativity theory explain that noone could travel faster than light and speed of light is same in inertialand non inertial frame of reference, mean speed of light will be samefor both observers at rest and in motion. This that time is not samefor all. Time ticks slower for observer in motion or in speed thanobserver in rest. His general relativity theory proposed that time isnot also same for observer in different gravitational field. Time ticksslower for people in more gravitational field or lower gravitationalpotential. This is known as time dilation or length contraction.

This theory also helps to understand the black holes, expansion ofuniverse and help to understand birth of universe. GPS andCommunication satellite need to be correct every time because oftime difference in space and on earth. This effect is due to timedilation, a consequence of Einstein’s theory and correction in timefactor is also done by using Einstein’s theory. This is like Einsteincasing the problem and Einstein fixing the problem.

This theory however seems very clumsy or rather difficult tounderstand because its sophistication and it never taught in school.Until 19th century people used to think that physics of the universe iscompleted. It was a shock for Newtonian physics when Einsteinproposed his theory because it was against it. Newton explainedhow gravity works and how a mass can influence the gravity. ButEinstein proposed that gravity is effect of space time curvature.Einstein had proposed ‘Time’ is fourth dimension and is differentfrom three spatial dimensions. Using these four dimensions heproposed system of partial differential equations which form space.His interventions in Newton theory are true at all but this doesn’tmean that Newton equation is useless. Gravity can be well

explained with good degree of accuracy using Newton’s theory inlower gravitational field like our solar system.

He also explained the particle nature of light by introducingexperiment of photoelectric effect. He has given Nobel Prize in 1921because his contribution in theoretical physics and developing lawsof photoelectric effect. Here interesting to note that is afterdeveloping ‘Theory of relativity’ he won Nobel Prize for somethingdifferent than it. Because his theory of relativity was bit controversialat that time.

That’s how Einstein became ‘The Einstein’. He is so famous by thiscontribution in theoretical physics and developing the most famousscience fiction idea ‘The Time Machine’. But Einstein doesn’tpropose anything like Time Machine or Time Travel. Well you mightbe interesting to know how idea of Time machine comes.

After Introducing General Relativity theory,Einstein began to talk about the curvedspace-time tunnels which are tunnels ofspace-time joins two universes. In 1935 heand his co-worker Nathan Rosen produce apaper governing questions of this type oftunnels known as ‘Wormhole’. Wormhole

are spatial tunnel can be described byEinstein-Rosen equation also known as

Einstein-Rosen Bridge. Fig.1 is showing 2D representation ofwormhole and in actual can be 3D. These wormholes allow fastertravel from one universe to another universe or one place to anotherplace of same universe. After few years Karl Schwarzschildsuccessfully proved that one of the solutions of Einstein-RosenBridge is satisfied by black holes. Actually wormholes are nothingbut the curved space-time between black hole and white hole.

Figure 1 : 2D wormhole

Black hole are stars with large masses and smaller radius less thanor equal to critical radius or Schwarzschild radius produced bysupernova explosions. This geometry makes these stars so densethat nothing can escape from the gravitational region around it, noteven light. Hence we cannot see them. Light get bended aroundblack hole due to stretched and curved space time fabric and henceit set into orbit around black hole.

Anything around black hole gets consumed or gets attracted towardcentre of black hole. Einstein-Rosen Bridge suggest that instead ofconsuming any matter, anything which falls into the black hole getstransported to the another universe or the places of same universe.In fig1. If top surface of bridge is black whole, mean things are fallinginto it, it needs to export things from bottom surface or hole. If welook from bottom side it will see like everything is coming out, evenlight too. Hence it seems like white hole.

Hence Karl Schwarzschild introduce that wormhole can be produceby joining black hole and white hole. But white hole seems to be onlya theoretical entity because it violates second law ofthermodynamics or simply law of nature.

It was very difficult for Einstein to introduce such thing which violatesits own theory. It was believed that if someone travels very fast fromone place to another in shorter time then, it must travel with the highspeed. But in worm holes, if anything is get transported from oneuniverse to another even light took thousands of light years to travelthis much of distance, traveller must break the speed of light. Hencetraveller must travel with the superluminal speed. This philosophyleads the contradiction and violation of Einstein Relativity Theory.

But in actual local speed of traveller is always subluminal that meanspeed of traveller is always less than that of speed of light insteadthe appears of speed of traveller is greater than speed of lightpropose that traveller is travelling backward in time. The postulate of

special relativity state that if any signal is travelling backward in timethen it appears to be travelling faster than light (FLT). This meansthat signal was received before it was sent.

But such wormholes known as traversable worm holes. Becauseequations of wormhole introduced by Einstein was unstable overtime. Narrow region of wormhole know as Throat was unstable and itopens at certain time and then vanishes. To allow the traveller topass through wormhole, wormhole must be open for the definitetime. To allow wormhole to open we need negative energy ornegative matter. Negative energy allows keeping wormhole open.Very small amount of negative energy can be created in laboratorybut not sufficient to keep wormholes open. We need tremendousamount of that energy.

After all of these theoretical evidences, it is proved that Einstein-Rosen Bridge or Wormholes are theoretical but scientific rather thanscience fiction and can be used for time travel.

American astronomer and author Carl Edward Sagan wrote‘Contact’, a science fiction novel and based on this novel Americanscience fiction drama film ‘Contact’ was produced. The concept of, awormhole can be used for time travelling was introduced by this film.But how the wormhole can be used to travel different part of spaceor different time wasn’t clearly explained though it was a sciencefiction.

But scientist and researchers not give up, not till now. With thiswhole new idea, many physicist established theoretical as well asmathematical model to explain time travel or space travel throughwormholes. Not a single back hole or wormhole have seen yet but itis believed that if we will unable to find naturally occurring back holeor wormhole, then we can make it artificially. Now if we make thiswormhole artificially without any bad consequences to life on earth,then it will be a revolutionary change in word, perhaps we will be

able to explore life on other planets and in other galaxies. Timetravel can be useful to understand the past history of mankind andlife on earth perhaps we will be able to stop unusual activity thathappened in past and we are suffering from that till now.

Time travel usually not simple as it looks. It introduces variousparadoxes that create unusual doubts about time travel. Just afterlistening to those paradoxes you may say that ‘Oh, time travelcannot be possible, not for me.’ Some problems cause a timetraveller not to go to past or future to save past or future.

To avoid these paradoxes, some people introduce self-consistencyprinciple of past that means that past is unchangeable. Some peopleintroduced theory of parallel universes that means that there aremany universes in the world with different timeline and to change inpresent can be allowed on changing scenario of past of sametimeline.

But many people believed that changes can be allowed in presentby going in past and changing something. Well, this seems veryunusual, for people who didn’t went to past. What happened if somechanged the past does the present change in a second?

Let’s discuss this in details in elaborated chapters.

Chapter2: Theory of Relativity

2D representation of space time - © volconvo.com 2012

Albert Einstein in 1916 published a theory about the gravitation whichknown a theory of general relativity. This theory precisely answers thequestion about gravity which Newtonian gravitational model failed toexplain. Einstein represented that heavier objects in space like planetsand star create indentations in space time fabric due to which otherobjects like satellites and meteoroids revolve around them. Image givenabove precisely explain why satellite revolve around earth.

Albert Einstein’s both Special and General theory is too important inmodern physics and quantum physics. GPS satellites and other particleaccelerator system needed to take care about these theories while doingthe measurements of time.

Albert Einstein was born at Ulm, in Württemberg, Germany, onMarch 14, 1879. In 1901, the year he gained his diploma, he acquiredSwiss citizenship and, as he was unable to find a teaching post, heaccepted a position as technical assistant in the Swiss Patent Office. Inspare time in Patent Office he did remarkable work about relativity andgravitation. His work made him so famous that we generally countEinstein as a world’s greatest power house of knowledge and thinking.Perhaps I use ‘Einstein’ to label most talented people.

Albert Einstein, the genius, proposed ideas of relativity whichchanged the image of everything we see and everything we about tosee. In his paper published in 1905 named ‘On Electrodynamics ofMoving Bodies’, he introduced strange ideas of relativity, well it wasstrange for people in that time and only few people had understoodthe concept of relativity proposed by Einstein but had not yetconvinced.

During the days at patent office, Einstein was really struggling tohimself not to propose something which people may cause people toconsider him as a fool. It was nothing but the speed of light isconstant for all observers and nothing can travel faster than light.

Consider you are in a bus, and a bus is travelling at a uniform speedV, an inertial observer is standing at bus stop and it is observingyou. Neither observer is moving nor you. But bus is moving. Whenbus is travelling at constant speed V, then you think that you aresteady bus actually you are moving at speed V with respect toobserver and observer can see you moving at constant speed V.What could happen if you are running in that bus with speed U, youthink that you are moving with velocity U, but in actual you aremoving at velocity U+V with respect to observer ate observer cansee you moving at velocity U+V. It’s like bus is giving you someextra push by V.

Now consider you are a light ray and you have a same situation. Ifyou are not moving then speed of light will be V, same as bus, butwhen you are moving at speed C then your speed will be C+V.Hence bus giving you, means light some extra push and hencespeed of light is C+V. I am sorry but it could not happen.

Einstein proposed that speed of light is constant for all source ofobserver. If person in bus is flashing a light in direction of motion ofbus and it observer speed of light is c. Observer on ground will alsoobserve speed of light c, not c + v.

Hence something extraordinary a speed must possess that makespeed of light always constant.

Many people, before his paper, ignore this idea because it was toounusual. But when Einstein asks for the answer to the simplequestion people were mute. ‘What happen if you are travelling at aspeed of light and you are holding mirror in front of you with yourhand? Will you see your image in it? People were used to say yes,why not. Einstein argued that ‘if you are saying speed of light is notconstant for sources of observers then you cannot see image of yourin your mirror. Mirror has already travelled the distance by sameamount light travelled. Hence no light is entering into the mirror andhence pretty obvious that no reflection occur. Hence no image ofyours is formed. But this do not happens.

Hence some factor either distance or time might be affected bysome supernatural thing. It is not supernatural thing, but naturalthing. It is space time. Einstein introduced that time is not same forall source of observers. Hence times is a not independent butdependent parameter and hence consider the fourth dimension andit is different from other three spatial dimension.

A point is has zero dimension and we are very familiar with points.Without points we cannot construct a line which is one dimensional

in space. Without lines we cannot construct a plane which is twodimensional. Without planes we cannot construct a 3d body. Andamazingly without time we cannot construct an event. Hence all 3spatial dimension with 4th fundamental dimension time we cannotspecify an event. Hence all 4 dimensions use to specify event inuniverse rather than a point in space.

The coordinate system formed by these 4 dimensions is known asspace time. As time is not constant for all source of observer,coordinate and/or coordinate system may changes as speed ofobserver change, like shifting of coordinates or rotation ofcoordinate.

After observing this entire phenomenon, Einstein comes toconclusion that time change as speed of traveller change. Whatdoes that means?This means that either time ticks slower or faster when travellerpicks up some speed. To understand what really happened to timewe need to go back to our previous example of bus and observer.To keep speed of light constant time scale must be change. Bysimple perception we assume that speed of light is c+v. thendistance travelled by light is (c+v)t where t is coordinate time, is localtime of observer. But by Einstein’s postulate it must be ct as c isconstant instead of c+v. Hence according to Einstein distancetravelled by light is ct*. Where t* is proper time. To equalize thedistance travelled according to traveller and observer as for botherperson if this event is took place between point A and B with finitedistance which is unchangeable. Hence {ct*} = {(c+v)t} hence t*>t if vis non zero. Hence time must ticks slower for fastest moving objects.What does really mean time must ticks slower?

Let say that you are leaving your home town and your brother comeyou with you to drop at bus stop. You have reached the bus stopand your bus is about to leave. Before that you ask your brother for

time as there was some fault in time of your clock. You set the timewith infinite accuracy or zero error as shown in your brother clock.Let sat both you have atomic clock with very good accuracy. Nowyou sat at your place in bus and you leaved the station. Your busdropped you somewhere about 500 km from the initial bus stop.After a year you return to your home you met your brother and checkthe clock again. What you saw was really unexpected, your brother’sclock and your clock is again mismatched. When both insist on thatthere wasn’t any fault in respective clock, I came to your house andinsist you to read Einstein relativity theory.

After all of this you come to conclusion that time slows down in yourclock and hence your time is lags behind your brother’s clock. Doesthat mean when you are in bus you can really see your clock tickingslower? No. Absolutely not. If there isn’t any technical fault in anyclocks then you will see time ticking at normal rate. Also stationaryobserver like your brother sees his clock ticking at normal rate. Butwhen stationary observer looks at your clock he sees your clockticking slower than normal rate. That also satisfy the example ofdistance equality we discussed.

This postulate of Einstein inspired many researcher of that decadeand many people began to think about it until Einstein published hissecond paper.

In 1916, Einstein proposed another strange theory known asEinstein’s theory of gravitation. This was modified version of spacetime which was already mentioned in old theory of relativity. In thistheory he proposed that instead of just plane space time, space timeis curved and heavy bodies in universe influence the curvature ofspace time.

Apposing Newton’s theory of gravitation of force between bodies,Einstein proposed new theory of gravitation. Einstein proposed thereis nothing like gravitation. According to Newton, planters are held

together in orbit or bodies experiences a force of attraction becauseof gravitation which is nothing but a force of attraction between twoor more bodies experience on each other and depend the amount ofmass they posses and how far they are from each other. But Newtondidn’t explain how this force is acting. And nobody attempt to thinkabout it.

Not until 1916. Einstein new idea of curved space time correctlyexplained how gravitation plays an important role in our life. Asdiscussed in earlier section we assume 4 dimensional coordinatesystem and we named it as space time. In space time, time changesas velocity of matter changes.

But in his new paper he proposed that time also changes due togravitation, instead we can say that time can be influence by thebodies in space. Heavier the body is more the time is affected. Thisidea can be visualize as consider the two dimensional version ofspace time.

As shown in fig. earth is located in space time. We can see that thespace time is little sinking down because of Earth. It just likes afabric like a stretched rubber sheet goes deeper when heavier objectput on it.

Some time students, scientist and researchers called 2d version ofspace time as space time fabric or fabric of space time or fabric ofcosmos because of its elastic nature. Heavier the object morecurved will be the space time fabric. In other way around denserplanets creates more curved space time around it. This isn’t at all.The rotation of planets also influences the space time fabric. Spacetime fabric is likely to swirl because of rotation of the planets andamount of swirl is more near the planet. This mean that space timeis curve near the planet in greater amount. Now how this theory ofstretched fabric explains the gravitation?

Look at the above fig. you can see the curve blue (for reference)fabric of space time is curved by earth and amount of curved is morenear earth. You can also see little curvature of space time nearmoon but amount is too little compare to earth. Hence heavier objectcreate more curved space time structure.

Consider space time, earth and moon your toys and you bring thistoys to your younger brother. Your brother took moon and throw incurved surface. You saw the moon rotate around Earth for some

time and then settle down. This means that if there weren’t anygravity and any friction moon couldn’t be sunk and keeps onrotating. And this is how the actual movement of moon around Earthis takes place. This theory also explains that only low mass planet orbody can travel massive object and other way around is notpossible. This theory also explains the elliptical orbits are possible.

This new theory was all about gravitation and explained motion ofplanets or bodies hence it was totally different form the old theory.Hence theory in traduced by Einstein in 1905 of relative motion ofbodies was more special and known as ‘Special Theory of Relativity’while the theory of gravitation was more general and hence knownas ‘General Theory of Relativity’.

The General Theory of Relativity changed the picture of Newtoniangravitational view and this new format correctly explains all thereason of gravitation which Newton failed to explained. Einsteingeneral relativity useful in modern astronomy and special relativity isused in modern physics and nuclear physics.

General Relativity, the concept of curved space time also explainthat time is not same for all observers in different gravitation. Thismeans that time is not same for observers in different gravitationalfield rather it ticks slower or faster in strong gravitation field. Tocorrectly explain if either ticks slower or faster we need to use someof Newton’s postulated. Newton said it is impossible to createpermanent gravity but we can experience artificially.

This means that in any gravitational field, we can create smallamount of temporary gravitational effect using centrifugal force orelevator. We feel gravity of 9.81m/s every day. You might be usingelevator every day. What happen when elevator start? Whileascending you feel that you become heavy or something is pushingyou downward and your weight is suddenly increase. While elevatoris descending you feel that you become too light and your weight is

decreased. This means that you are experiencing different gravitywhile ascending and descanting. To experience the weightlessnessyou need to break rope of elevator or perhaps take a ride in zero-gplane. This artificial effect of gravity perhaps explains thegravitational time dilation. I shall explain time dilation later but timedilation is nothing but phenomenon of producing time difference viarelativity. In more mathematic way more the speed difference moreyou feel the gravitation. If elevator is accelerating downward with g(case of free fall) you will feel weightlessness or zero gravity. If it isaccelerating upward with same amount you will feel 2g (twice thenormal Earth’s gravity).

In case if you are already in zero g and you want to producegravitational effect of g at same time. Then you need to accelerateyour vehicle at g. hence your speed must go on increasing andincreasing to produce acceleration g in any direction(as there is noother gravitational source). Special relativity theory stated that clockof traveller with some finite speed ticks slower. Hence more thegravitation is more the acceleration, more the velocity and henceslower the time ticks. Hence if we think that gravitation produce byplanet is equivalent to acceleration produce by moving objectartificial we come to conclusion that time ticks slower in case of moregravitational field.

Hence bigger the planet is larger the gravitation and hence slowerthe time ticks. We can visualize that our clock ticks slower compareto people in international space station because they are leaving inzero gravitational field and we are living in more gravitational fieldcompare to them if we neglect orbital field difference.

These two theories were revolutionary and that’s why many peopleand many institutions in the world consider Albert Einstein as fatherof modern physics. The quest for proof of those theories was

increase at that time because theories were so difficult tounderstand, people could hardly thought about the proofs.

Proofs of special relativity were too simple. The postulate of specialrelativity states that time ticks slower for object in speed than objectat rest. But in actual any vehicle build artificial not approach to thespeed by which we can actually experience the time dilation. Hencesome atomic clock is placed in rockets or shuttle as a part ofexperiments to calculate time dilation. These atomic clocks in shuttleare comparing with the atomic clocks in earth and hence calculatetime dilation.

It is observed that very little but finite time difference can beobserved in these clocks and hence it is experimental proof ofEinstein’s special relativity theory.

One thing must be remembered that if people in shuttle areobserving the clock, there won’t be any change in time and it ticks atnormal rate for people in shuttle but not for people on earth. It ticksslower for those people on Earth. Here gravitational time dilationalso plays an important role and hence the affect could beneglected.

It was little bit hard for Einstein to tell stories about general relativitybecause all the people at that time were follower of Newton. Peopleused to think that Newton’s gravitational law are true at any scaleand absolute. But that’s not true. Einstein’s model of gravitationrather explains the gravitation very wisely than Newton’s. Butscience needs proof and it was Sir Arthur Eddington who provesEinstein’s general relativity theory.

On May 29, 1919, Arthur Eddington went to Africa to observe andphotograph the solar eclipse. According to Einstein’s generalrelativity theory, massive objects create curved space time structureand hence it has ability to bend the light passes near by it. As we

know that light is compose of photons and it has particle nature aswell hence any matter that come near denser and massive objectget bended due to curvature of space time fabric. Based on this ideaEddington thought to take few pictures of solar eclipse so that due toshadow cast by moon, we can see stars around sun in sky andhence we can photograph it. Again on comparing this photographswith photographs of stars taken in night when sun is not there, if wecould see the mismatch of the stars near sun in both photographs,the means that light must have been bended due to suns curvedspace time fabric.

Based on observation of Arthur Eddington it was deviation of light ormismatch of stars in photographs.

As shown in fig. we can easily see how the light bends due to curvedspace time. This bending of light due to curvature of space timeknown as ‘Gravitational Lensing’. It is very common observablephenomenon. More massive the star is more the light bend.Sometime star is just behind the giant star let say sun, hence we cansee the disc ring like shape around sun. Black holes which are supermassive bodies can be identified using this phenomenon.

The work of Arthur Eddington was a giant step for Einstein andhence it was a good explanation of general relativity. It says that atthat time only two people fully understood general relativity theory.

After Arthur Eddington, many people were still unsatisfied with thetheory of twisting or swirl of space time created by rotator motion ofbodies.

Gravity Probe B (GP-B), was launched a satellite-based missionwhich launched on 20 April 2004 by NASA. This m

ission was for to proveEinstein’s general relativity theory of curved and twisted space time.Some smooth Gyroscopes were fitted and pointed at distant star. Ifthere wasn’t any curvature in space time, the gyroscope must havepointed in same direction. But they weren’t. The defection in thegyroscope were accurately measured and were exactly equal to thatwas calculated by Einstein. It was fantastic proof of GeneralRelativity.

And I would like to say that this is how the final form of specialrelativity and general relativity theory established. As we understoodtheoretical form of relativity, we must understand its mathematicalform.

A Dutch physicist Hendrik Lorentz, introduced Lorentztransformation and the term given below known as Lorentz factor (ᵞ)is term derived in his transformation to explain terms in relativitytheory.

Where v is normal speed of traveller and c is speed of light. Value ofLorentz factor is always less than 1. It becomes equal to one iftraveller is travelling at speed of light and special relativity says,

nothing can beat light hence there is no way to allow Lorentz factorto show real value for any speed that is more than light.

Time dilation is observable phenomenon and both special relativityand general relativity allow time dilation due to relative motion andgravitation respectively. We can exactly calculate the time dilation byatomic clocks placed in shuttle and one that is placed on earth. Youmay know about GPS (Global Positioning system) or might haveusing it now in your car. GPS is a system that tells you where youare right now on earth or where you are heading. It is also useful intracking a car, a person or might be a criminal who has GPSreceiver with accuracy of 5 to 10 metre.

GPS tracking device is fixed in satellite orbiting above few hundredkm from earth surface. These satellites are orbiting earth with someorbital speed with respect to us or earth surface. As we know thatrelative speed allows time dilation. As satellite is travelling fasterrelative to us, the clock present in satellite GPS must ticks slowercompared to ours on earth. By observation and calculation formspecial relativity theory clock in GPS lags behind clock on earth by 7microseconds per day. Hence in each 24 time period on earth only24 hr – 7 μs time had passed in clock of GPS.

We must not forget gravitational time dilation. As discuss earlier ingeneral relativity, time ticks slower in more intense gravitational field.This can be visualizing as gravitational field become weak as wemove away from the earth. In space we can actually experience zerogravity because there in no other thing that can produce gravitation.Space time is more curved near earth hence more time dilation andhence time ticks slower which in space time ticks faster as there isno gravitation.

As GPS satellite is far away from the earth hence experience lowergravitation than anything on earth. This makes sense that time mustticks slower on earth that in satellite. The gravitational time dilation

was accurately calculated and it was 45 microseconds. This meansthat our clock ticks slower by 45 microsecond a day than clock inGPS. Hence if 24 hr is passes in clock in GPS then our clock lagsbehind and only 24 hr – 45 μs is passed in our clock.

Now comparing the total effect or time dilation, we came toconclusion that because of relative motion of GPS relative to us timeticks slower by 7 μs in GPS and because of gravitation time ticksfaster by 45 seconds in GPS. This means that net effect is of 38 μsthat drives clock in GPS faster by 38 μs compared to time on earth.This means that if 24 hr is passed in GPS clock on 24 hr – 38 μs ispassed in clock on Earth.

Well you can say what a difference 38 μs makes? I would say, it cantake one’s life. Believe me, GPS request accuracy of nanosecondand hence it need to be matched with the time on earth in each 2min. to avoid difference of 10 km each day. As I said, the result ofnot adjusting time in GPS would be hazardous, is it really? Well, ifyou alone are on long journey on a road for a month and you don’tlike to drive hence you invented a car that drive itself automaticallyand follow the GPS orders and you went to giant sleep. If therewasn’t adjustment in time in GPS clock then perhaps you will seeyourself in volcano 300 km away from your destination. I am sorrybut I think, probably you will not see you actually dying becausevolcano is so hot that evaporate you as soon as you fall in it.

To understand how time dilation works in more mathematical wayyou need to understand a simple hypothetical experiment of twoplates at rest.

Assume you have photon pendulum (hypothetical). As shown in fig.photon move up with speed of light and reflect from top plate andagain come down and again come down and again reflect fromlower plate. This ticking of photon between two plate make it looklike a pendulum.

Distance between two plates is L. and onetime period is given by time taken by photonto strike same plate consecutively.

A stationary observer observes that timeperiod of clock is 2L/C.

Now consider these two plates are movingwith constant velocity v in one direction.

As shown in fig. below when both plate move in same direction withsame

Velocity v time taken by photon toemerge from plate A and come toplate C (final state of plate A) afterreflecting plate B is more than thattaken by two plate at rest.

Here time period is calculated as 2D/C. To understand moreprecisely we need to formulate D in term of L so that we cancompare time period of both clocks.

After geometrical calculation we arrived at this. We found thatchanged time period of clock is proper time ∆t multiplied by Lorentzfactor. Lorentz factor decrease with speed and hence as speed ofplates increase, lower the Lorentz factor more slowly time ticks.Hence from this derivation we understood how we perceive the timeticks slower for object in speed. This statement also allow time ticksslower in more gravitational field as I already explain the artificialgravity effect.















Not only time is affected by the speed but also the length of thetraveller. If L0 is the proper length (actual length of object that is atrest seen by stationary observer) then length of object travelling withsome finite speed as seen by stationary observer is less than properlength and given by

Which is nothing but proper length divided by Lorentz factor.

But it is very interesting to know that we cannot observe lengthcontraction with even speed of powerful rocket. At speed almostequal to 15% of speed of light length of object seem to be decreasedby only 1%. That means if 100m object is travelling at 0.15c then astationary observer will see it 99m. If a thief invented a car thantravel almost at speed of light then no police in the world could catchit because it will not visible to stationary observer. It will shrink tozero size and I will barely noticeable for anybody. Does it mean itreally shrink to zero size?

No. As we discussed about time dilation, local time for all observersare same that mean their own clocks are running at normal rate butwhen they see each other’s clock they see that it is not running atnormal rate. Stationary observer see clock of traveller with somefinite speed with respect to him running slower and almost stop atspeed of light.

Similarly, when objet is travelling its length shrink in the direction ofthe motion and extent of shrinkage depend on its speed. More thespeed more is the shrinkage. But remember that neither car shrinknor the person in car. They appear to be shrunk for stationaryobserver. In actual they are what they were mean their dimensionsare still the same as before. If you look at the car that travellingalmost at speed of light, you will say that its dimension does actually

change because you will see a vertical strip. As its horizontal lengthshrink while its height does not change as there is no motion of carin vertical direction.

But a person in car sees everything outside car is flattered orelongated along its length. If you are observing the car, a person callyou fatty even in actual you are skinned. But in actual it’s not true.Because you are not flattered and motion of car did not changeanything on earth. Conversely what you are saying is wrong andhence car did not shrink in actual, it did just appeared as it wasshirked.

The notion of length contraction is not useful in physics because itdoes not affect anything but still interesting. We can also say thatwhen time ticks slower for anything, its length must be decreases indirection of motion. It was pretty obvious.

E=mc2 is worlds most famous equation known as mass energyrelationship equation. Einstein’s this equation bring revolutionarychange in the worls and I can say that this was equtaion responsiblefor nuclear bomb or atom bomb. In this equation c is speed of lightand m is newtoniun mass of body (not weight). But this euation isvalid for those bodies whose momentum is zero. Means that if mv=othen E=mc2. Where v is velocity of that body. Here m in this formulais called ‘rest mass’ or ‘invarient mass’ as body is at rest.

But what is momentum of any object is non zero. What correctionsare needed in mass energy relationship equation? For that we needto understand relativistic energy-momentum equation. After suitableassumptions and calulation in this equation we arrived at final formof mass energy relationship as follows.











In short relativistic mass energy relationship can be formulated onlyby multiplying Lorentz factor to non relativistic mass energyrelationship.

Looking at above formula, energy of object increases as its speedincreases. Hence at almost speed of light energy of body is becomeinfinite. Again don’t take it literally because in actual its energy donot become infinite. It just appeared for stationary observer. (not sosure)

While explaining this Einstein’s propose that mass of body increaseif speed of body incraese. That menas now observer really feel thatit become so heavy that it can not travel more faster. The notion ofsaying this was for to avoid faster than light travel. As body movefatser, more the mass it gains and restist it to increase its speed. Atalmost speed of light, body became so heavy that it no loger havetendency to move faster than light. This can be given by

Where m0 is mass at rest or invarient mass. But it mus beremebered that it is not possible to increase mass to infinite level,because if it were then gravity created by that mass will be sointense such that it will produce a black hole hence it actual mass ofobject remain as it is and only increse in speed produce the effect ofincrease in mass. Increase in mass count for the increase inmomentum of object.

This formula exactly tells the ammount of negative energy requiredto completely destroy the body that is travelling some finite speed.This means that to make energy of isolated system (like universe)zero we need same ammount of negative energy that can bedescibe by relitivistic mass energy equation.

Time dilation is very important factor and very interesting too.Imporatnt because if you never understood time dilation well, youmight not have correct parameters to ajust the time in GPS clockand hence your GPS is no longer useful. Hence you mustunderstood how relative motion and gravity affect the time.

As I said that time dilation is very interesting perhaps you are sick ofmathematical formula of time dilation hence lets talk about inthoerotical way. As we know, more your speed is more your clockticks slower comapred to the clock at rest which can be explained byspecial relativity and more intence the gravitation is more your timeticks slower. This means your clock will tick slower in bullet train thanon bicycle. Similerely you time will slower on earth than on themoon.

What actually means time ticking slower? To answer of this questionI would like to explain twin paradox. When Einstein think of timedilation he began with wonderful idea. For that let us assume thattravelling in rocket with speed of light is possible. Two twins of sameage, I nammed them Al and Bert were brothers, of course they were.Bert was selected for space mission and hence he leaved earthsomeday. At that day his brother Al was really sad because hemissed Bert. Suddenly a news spread all over the world that Bert’sspceship lost in space because of some technical difficulties inrocket drived spaceship with speed of light. But Bert was safe andhe return to eath after a month and that was wonderful. Isn’t it? No, itwasn’t.

When he returned to earth he saw something very strange. When hefirst went to his home, he saw Al was too old and seek and he couldbarely breath. He thought that may be he is sleep and slap himslelfso hard but at last he convinced that that was real. What happenedis not a miracle but a pure science fact, the time dilation. As Bert

travelled at speed of light for a month according to his time manyyear had been past on earth according to time on earth. This ispretty obvious that time ticked slower for Bert as he travelled atspeed of light but he experienced time normally.

May be in more theortical way you can say that for a day in Bert’sspaceship more than a year is passed on earth. This story ofEinstein known as ‘Twin Paradox’. As a writer of this book I neededto think this twin paradox in different way to impress my reader andto show that I am wise too. So I took same two characters Al andBert and instead of being put them in relative motion I send Bert onjupiter. Jupiter is very large and massive planet and have gravityvery much larger than on earth. Hence Bert experience very largegravitational effect on him that Al on the Earth. Hence Bert’s clockticks slower compared to Al’s clock. After a month passed in Bert’sclock he feel himself little weak and ran out of food and water so hereturn to earth. As soon as he return to earth he paid visit to hisbrother at home but he wasn’t happy seeing his brother because hisbrother was too old compare to him.

Does that mean if you are tired of someone and hence you need himget older soon then you can travel at very high speed in space forsome time and come back to earth again? Does it mean that ifanybody in Earth is so beautiful that everybody agreed on statementthat she must be preserved trough many generations then she mustgo to space and travel at speed of light and pay visit every 50 years?

I would say, Yes. why not. If you want to see people around you aretoo lousy then you can go to space travel for finite time at speed oflight and come back. Perhaps you are so lucky, that people musthave been dead by getting older. If you want some lady which ismost beautiful and you are sure that the not will be any lady asbeautiful as her then you can think of some think different. Instead ofshowing her pictures to the people of next gereration why not show

her alive. For that you need to send her in space and she ordered totravel for some a month according to her time with speed of light andpay visit to earth every month. As in a month their wouldn’t be anychange in her but may be a generation is passed on Earth andhence people from new generation may be anle to see her alive.After a day she can go back to travel throught space for a month ofher time and people on earth must wait a generation to see heragain.

The main thing beyond these expamples is age difference. If you aretravelled in space with some finite speed then you are younger thatyour twin who travelled same disnace at speed less that yours or atrest comapre to you. But you are older than your twin who travelledsame distance but at speed more than yours. Well this difference isvery tiny for travellers on earths because speed at which a persontravel on earth is very very less and hence may create timedifference of 10-35 second in you clock and clock that were at rest.

Instead of twin if you consider any child on earth at rest comaped toyou and you travelled a journey speed equal to some fraction ofspeed of light. At intial before journey started if your and that child’sage difference was 20 year pehaps after journey you and that child’sage difference is 5 years. It can also happen that both of you arenow of same age or you are now younger than that child (which isman at the time of observation).

Nobody was expecting that relativity theory will intorduce suchphenomenon which before were used to considered as miracle orscience fiction. This theory inspired people to think about time travel.As we always travel from on place to other plate, would it bepossible to travel from time to another. As we discussed that bytravelling in space faster you will approach to you future faster. Butwould it be possible to go to initial condition if you don’t like yourfriends are now dead for sure by getting older? To answer these

questions we need to learn more about time travel which we aregoing to dicussed later.

Have you ever been think of tele transportation machine? Teletransporatation machine is concept of belief in science fiction thatone day man itself will be transported instaed being signals troughtmachine. We daily use machine like telephone or mobile orcomputer to conract your friend, parents or business couligs.Perhaps you say while talking to your friends on phone ‘I wish ifcould be there!’ or say ‘come here, we are having fun’. If you are inIndia and someone in Russia, it will be a madness if he made a planto come to you just to eat pizza with you by travelling a long journeyand wasting two days of his important life.

Consider a friend of yours is living in USA and you are in India. Oneday her grandpa fell ill and he is about to take leave from his life, sayit was a matter of few hours. Grandpa really willing to talk to yourfriend very imporatant (his grandson) but nobody can bring him toIndia in just few hours. Not jet rocket, for example.

If I will tell you that such machine exist by which you can travel fromone place to another place in matter of second, what you will think ofthose cases I mensioned above. Obviously, a your friend can comefrom Russia and you (India) in just just a minuit and possibly bothcan share a pizza together if you haven’t finished. If you are unwareof tele transportation machine then you may be die seeing yourfriend in front of you or you can say that he is lieing that he was inRussia. Or perhaps you will say ‘I didn’t expect that you will comethrough the phone’ and then die. Second, your friend who was inUSA will appear in front of you as soon as you say ‘oh my dearfriend, your grandpa who is about to leave us want to see you, but Iknow it won’t be possible for you to fly.’ Perhaps even if he had fly, ithad zero probablity to come to Indiaand meet his ‘Living Gravdpa’.

These type of machines are not possible for now and considered asa pure science faction. But we need to know what these type ofmachine to just for our interest. You are aware of email. When youemail someone text or image or sound or perhaps video thsesobjects are converted into a digital information code in yourcomputer and then through a telephone cable (let say that I amusing broadband internet though telephone cable) and send to aserver where your information is check, registered and then send tothe receiver’s email you have mensioned. When he open his emailhe can see what you have send to him upon downloading all theinformation cond is converted to the appropriate format.

Instead of video consider a man (or any animal), tele transportationmachine instead of computer. If you have teletransportation machineand you need to go to some place. At that place I consider ateletranspotation machine is also available. If you want to go thatplace just step in your tele transporation machine select destinationand click star. You will be converted to a code and code will travelthrough a telephone cable just like email and at destination machinewill convert code to you, a living man.

Well it look vey easy but it is not possible because a cell have maybe have 1.4 gega bites of information. And a normal man can haveten trillion (ten million million) cells in his body. Hence teletransportation menas more than ten trillion gega bites of informationtravel which is too heavy for a server to send in matter of seconds.Even if it is possible then what will happen if single bit of informationlost, if information is crash or corrupted, if power failure occur? Willthat man never gonna be normal?

Even if everything ok will that person even if he took human bodyshape be alive? This ideas are so strange even thinking about it willmake us feel bad. May be almost 99% of science fiction writerbelieves that it not gonna be real even in far future because of its

sophastication. Is that menas we never gonna get trasported fromone place to other in matter of second? I will say, I don’t think so.

Let me come to the point. What if other machine or other way ispossible to travel from one place to other in just seconds? I am notjoking, its real and known as Einstein Rosen bridge. In 1935 AlbertEinstein with an American-Israil physicist nammed Nathan Rosenwrote a paper on something called space time bridge. Theysuggested that electron are threaded by electic line of forces whichproduce tiny space tunnels. These space tunnels allows a electronto travel from one place to other place in space. Usually instaed oftaking long routes you always seek for shorcuts to save time.Einstein and Rosen represent a mathematical model which allow aelectron to travel from one place to another place in shorter timethrough shortcuts via a tunnel known as Einstein-Rosen bridge.

If you are travelling at speed of light in ordinary space between twoplaces in space. If you found some shortcut like E-R bridge will ittake shorter time than ordinary space travel to travel between sametwo place. If it is then it means that you are travelling more thanspeed of light. Travelling more than speed of light in inconsistentwith Einstein spacial relativity and violet Einsteinian causality.

Instead of promoting faster than light travel Enstein introducecompressed space structure. Take a piece of paper and fold it inbetween. Mark two point on edge of paper facing each other andmeasure the distace between them, let it is 20cm. Now fold thepaper but do not allow the points to overlap on each other hencemaintain small distance or gap in folds. Now by keeping handssteady tell someone to measure distance between these two points,let it is 1cm. what happended is if you want to go from on point toanother on the paper you need yo walk 20cm but when you fold thepaper their distence shrink and you needed to walk only 1cm whichis comparetevely very less.

Another way to think about compressed space is experiment doneballoon. Take a piece of balloon rubber and mark any two distictpont on it when it is unstreched. Now when you strech balloon pointson balloon go far from each other. Now strech the balloon upto somesafe level and look at those points. Now imagine two points two betwo places and ballon fabric (piece) as space. When balloon isstreched, two places are far apart. When you release forces on thebaloon rubber piece, rubber contract and hence two ponits comecloser. If you imagine this system in different view like two points tobe two places and balloon rubber as space. When space contractstwo place come closer and hence distence between two placesreduced.

If you think that two place are attched by two ways. On is ordinaryunstreched space and another is streched space which is shortcut.What which way will you choose? Obviously the shorter one.

But Einstein never think of material or any living species travelthrough the bridge. Many science fiction writer wrote that faster thanlight travel is possible and any material or living species can betransported throght this bridge they called these bridge as wormhole.You may think that what was bad in bridge and why they calledthese tunnels as wormhole?

I will suggest you to check apple before you eat. It could be worm init,hiding in wormhole. If you want to see what you will do is to turnapple around and see it. That your view sweeps entire halfcircumeference of apple. But what worm will do is it will dug a tunnelthroght apple streight to the point behind apple and this is how theseshortcut tunnel named as wormholes. The name wormholesuggested by American physicist John Archibald Wheeler in 1957.

You might be interested in wormholes in earth those are known asgravity train. But don’t get me wrong they are not wormholes butthery are like wormholes as they do not contract space but they

minimise time and consume no energy. You need to dig a tunnelthrough the Earth between any two place on the earth like India andUSA. If you travel from India to USA it will take a whole day but ifyou are travelling by a gravity gavity train which travel through thistunnel you will reach your destination in only 42.2 min. (neglectingthe effect if air resistence. Because of air restistance your train willnot come out of tunnel and go on dampped simple harmonic motingand eventually stop at centre of the earth. To cbrimg people toearth’s surface some rescue missioms need to be panned orpassengers need to climb the tunnel to come out). If you dig tunnelin earth between any two places it will always take 42.2 min to travelthrough tunnel. As gravity is pulling train inward and due to itsvelocity it oscilate in tunnel hence something which hold train attunnel mouth (we can say platform) required. Hence this type oftunnel minimises time of your jounrney but thery are not wormholes.

In actual wormhole are not ‘wormhole’s but scientists used theseterm to show that Einstein-Rosen bridge has tunnel like shape andlook like wormholes.

After a month when Alber Einstein propose general relativity, agerman phisicist Karl Schwarzschild found that one solution ofeinstein rosen bridge was satified by black holes. He explained howa tunnel shaped eisnetin rosen bridge can be constructed by warpedspace time by the influence of gravity produced by black hole andwhite hole pair.

Black hole and white hole are very small stars but possess very highmassive stars, in more scientific manner we can say that these arestars with very high density. What would happened if mass of earthincrease twice without changing its shape? According to newtoniungravity laws gravity on earth will be twice. That mean the rocketneed twice the drage to lift the payload. If we keep increasing massof the earth by holding it shape, a time will come that it is impossible

for rocket to produce a drag to lift itself up against the gaint gravity ofearth. Now consider earth so heavy that even light faild to escapethe earth.

If someone went to moon and see earth dark blue. Increase in massof earth to this limit may cause no light travel from earth to the moonand hence suddenly earth will disapper. What happens in nightwhen suddenly electricity gone. You see is all back beacsue there isno light that refect from the objects in room as there is no light thatfall on the object. But sun is the source of light for us, on the earth.We see moon because light from sun fall on the moon and refectson the earth hence we can see moon so bright.

Similerly people on moon (on mission) see earth because sun raysget reflected from the earth and travel to the moon. If there wasn’tincident ray like sunrays, earth wouldn’t be visible. But what is earthdid’t reflect back the sunrays? Obviously we couldn’t see the earth.Likewise if earth would be so dence that even light falling on earthwouldn’t get reflected back (trapped by the intence gravity) we wouldsee earth. What we will see is a back sphere. This back sphere isalso pronounced like back hole.

Due to intence gravity back holes attract everything around it, evenlight and consume it. Process of consuming means adding thingsarounf it to its mass. Hence anything that come in near blackholebelieved to be get consumed by backhole.

Black hole are so rare and very difficult to observe because space isback and it is very difficult to explore black in back. It just like to finda black cat in coal cellar. Hence we are unware of properties ofblackholes and how blackholes really consume things. Somephisicist believe that blackholes do not consume things, they attractthings and throw in space from behing. When you look a blackholefrom behind they will look like a volcano throwing thing from itsmouth. They are white holes which are so bright. Instead of

consuming they spread out everthing and hence they are antonymsof backholes.

Karl Schwarzschild explain that if a mass contracted to a radiuswhcih is known as schwarzschild’s radius then it get converted tobackhole. As blackhole are so massive and dense that even light failto espace from its gravity, you can imagine how itense its gravitymust be. According to einstein’s generel relativity theroy more themass of body more it streach or bend the space time fabric.

As shown in fig. above, we can see that backhole is warping spaceand hence produced well type structure in space time fabric. You willbe able to see the streched fabrick of space time of a white hole byplacing mirror at singlarity. White whole is purely hypotheticalconcept because no matter create such shape of space time. Whenyou will see combination of both you will see something like this.

This is known as Schwarzschild’s wormhole which is produce by oneback hole, one white hole and which can join two places or twouniverses.

Another theory concludes that there is no need to have white holealong with back hole to produce wormhole. As single backhole canproduce similer space time geometry and hence can be able to joindistinct universes. These wormholes are known as euclidien andlorentzian wornholes based on theroy of euclidean space time andlorentziun space time.

These type of wormholes are produced by black hole and cantransport things from one place to another, faster than light. Thissuggest that if you travel in space and come in contact with a backhole, you will get attracted toward it and fall in wormhole. It believedthat you might get transported to distinct place in a universe or placein another universe. This type of universe travel is known as intra orinter universal travel depend on in which universe you gettransported.

If a wormhole connect a place in our uinverse to the place in anotheruniverse, this type of of wormhole known as Inter-Universewormholes. If a wormhole connect places of same universe theyknown as Intra-Universe wormholes.

The mathematical calculation of Lorentzian wormholes show thatobjects passing through them would not only be moved spatially butalso temporally. This mean that if another universe exist that havesame people like us but at different time, like 500BC or like 2050ADthen using Lorentzian wormholes we can go to such places andmeet your past you or meet your future you. Even you can meetyour children and your future wife. This are purely hypothetical ideasand many paradoxes suggest that this type journey throught time isnot possible. Many ideas also suggest that these type of travel isalso possible if you followd some rules known and rules of timetravel. Hence ‘Time Travel’ has been a very discussed topic inscience fiction and theorotical physics.

We will discuss time travel in next chaperts but before that we needto understand how time travel is possible and what cause a personto travel throught time. Like if you want to win car race, you need tocover a minimum distance in very short time. To do that you need ageneously desined car which can fullfill your need. And to designsuch car you need marvolous engineering. This car can travelthrough space only but if you want to travel throught time, you needsonething which is impossible for human to construct, not yet. So tothink about time machine which can drive you through time you needto understand engineering behind it. But what if that machine isavailbale naturally but we haven’t tried to explore it.

Lets discuss it in our next chapter.

Chapter3: Black Hole, WormHoles and our Universe

Black hole fed by a star – wikipedia.com

Black hole is a massive dead star which has density greater than billionsof tons per cubic inch which almost create hole in space time fabric.Gravity of the black hole is so high such that escape velocity for anythingbecomes greater than speed of light. Hence nothing can escape from theblack hole, not even light. Black hole attracts everything that come closerto it. Many black hole fed by the massive stars in the universe.

For time travel we need to find wormholes and hence we need tofind back holes or white wholes which are believed to be essentialsfor producing Einstein Rosen bridge. But space is infinite and notjust few thousond kilometer in diameter. What we can see throughtadvanced engineering is perhaps a percent of the universe that existby now. So it is a big task for us to find those things in such a bigspace. It just like to find a gold atom in the sand covered on earth orperhaps more. Hence we need some techniques or some specialstrategies to find those things.

As I told you that finding black hole isn’t so easy, it just like to find ablack cat in coal cellar. Because it is black and most of the space isblack because it is not so dence by luminious matter like stars.

You might know that earth has been bumbarded by many meteroideveryday, we able to see luminious matter in sky every night.Meteroid or meteors are small rocks that are part of comets that tailof comet leaves behind. Coments are astronomica bodie which aremainly icy rocks and have a tail. Tail of comet is nothing but ashower of small rock that disintegrate from main body of comet dueto evaporation when comet come near sun. world witness howdistructive these comet could be when comet shoemaker levy 9broke apart and collided with Jupiter in july 1994. When these smallpart of rocks of tails leave in orbit of earth, one day these small rocksenter in earths atmosphere and egnite due to air friction and hencemany rocks get evaporated in atmosphere but few of them which arelarge could not get totally evaporated and hence collide with earth.Lonar reservoir is example of these type of meteroid crash. Thephenomenon of meteor fall known as meteor shower.

In india there is a belief that if you see a glowing object (these canbe meteor) in sky when wish for something your whish will befulfilled. If you are wishing for short long life, there is probablity ofthese meteor can hit your head and you will be dead just after you

have wished. I don’t like the idea of wishing for eternal life and Idon’t like to talk about it.

These meteor are very important for scientific study like evolution oflife and existance extra teristirial life. Hence when meteor showeroccur, many scientist began to search for these meteor rocks but asthey are visually same to the rocks on earth hence it is literaryimpossible to identify those rocks from the rocks on earth.

Hence meteor seekers go to icy land like antartica to find thoserocks because it is easy to detect these rocks on white surface andas therse is zero probablity of earth rocks to come out of thick icylayer. Hence if you see rock on ice in permant icy land, it isdefinetely meteor.

Similerly if you find such technique to explore black hole, it would belot easier to understand science behind it, it would be no loger tohave a time machine. It belived that there might be arround 0 to 300blackholes per cubic light year and hence as our galaxy is 100thousond light year in diameter hence there can be more than amillion black holes in our galaxy and nearest blackhole to us can beas far as pluto.

As pluto is observable for us but not the black hole. It is possible thatthere isn’t any black hole as far as pluto or since it is black we cannot see it by the instrument we have right now. So in which way wecan observe black holes?

To anser this question I will suggest you to understand the spaceand universe and study the evolution of universe. As we can tellprecisely how our sun is formed or how the earth is formed, perhapswe will be able to tell how black hole is formed and even we may beable to precisely locate them in our universe. If we found a blackhole near to us we will be able to understand it and other mysteriesof space will be known to us.

Universe is full of misteries. It has many things that we are unawareof and only 4% of universe is known to us. So the planet, stars,asteroids, comets, galaxies and all visible universe is contained inthis 4%. If we are going to study this 4%, might be this study couldnot anser the thing beyong this 4% or perhaps it will. If rest 96% ofuniverse have relation with visible universe then probably we willunderstand what we need to know.

So lets study the universe.

To understand something we need to know its origin. What is originof our universe? It is belive that god create our univers and manyscientific evidence tell us that universe is expanding. Why god wouldcreate expanding universe? Let’s remove the god’s intervention fromour study and think in more scientific manner.

Not literary god, but some one put a huge ammount of ennergy atinitial in space. Instead it had put by someone, we will say that it wasexisted long before about 14 billion years ago. At that time a globe ofinfinite enrgy and at about infinite temparature was symetric byforces. We are known of gravitational forces, magnetic forces,electric forces, neuclear forces etc but at that time these forces wasnot precesnt, actually they were balanced by each other and hencethee force which held the matter of infinite energy I called it singularforce or force of singularity. At the initial condition matter of infiniteenergy called as singularity. The singularity with infinite energy andinfinite temparature also had had infinite density. You can imagine ifall the visible matter in universe if assemble to for tiny football thenwhat could be its density.

This tiny singularity with high denisty was stable because of singularforces but as a paulies exclusive principle tell that no partical inunivese can have exactly same property, matter in sigularity was notall same hence they might have expericing different forces. As thematter experiencing difference forces it become unstable andsymmetry of forced began to break. As symmetry of all these forcedbroken, there were a huge explosion in matter of high energy. Justlike when balloon blast of if you pinned it due to unsymmery oftension in rubber.

Due to this explosion all compressed matter came out and spreadeverywhere in space. Many scientist call the time when thisexplosion occur as ‘big bang’ and some other call the actaulexplosion as ‘big bang’. I rather like to call this explosion as ‘big

bang’ and hence big bang occur nearely about 14 billion years ago.As big bang thrown out everything in space, it is not quite clear whatwas that ‘everything’. It belive that everything is nothing but thematter itself but these wasn’t matter like we see rather it wassubatomic particales like electron, nuetron, proton and theirantiparticle.

It is belived that when there was symmetry in forces then all thesingularity was composed of energy and no matter. When symmetrybroken and big bang occur then all the enery gathered and fromationof subatomic particales started. A matter can be converted into pairof matter and antimatter of same kind. Hene if electron is formedthen its antielectron is formed but it is impossible to antimatter inspace. It can be possible that rest of 96% of universe is made up ofanimatter.

When energy localised and began to from matter like subatomicparticals then at initial condition they were hot and had very highenergy hence they were moving away from each other. After certaintime after big band a new force started to dominate, nuclear force.This force start combining subatomic partical like nuetron and protonmaking nucleus of small atoms like dueterim, helium and lithium.Most of the matter that was formed was present in form nucleus ofatoms and this lead to cool the universe by millions of degrees.

As universe cooled further, another type of force began to dominatecalled electric force. This electric force attract the matter of oppositecharge. As in initial nuetrons, protons, electrons and nucleuses werepresent, electric forces bring nucleuses and electons to form atom ofduterum, helium and lithium while proton and electon combine toform atoms of hydrogen. Then what about nuetron? Nuetrondecayed to to form pair of proton and electron and hence a nuetronlead to form a hydrogen atom.

So at last there were huge clouds of hydrogen and few clouds ofother light elements. The clouds that were reseasonable to formstars called as stellar clouds or stellar medium. When huge ammoutof this clouds form and universe cooled to few degrees a new forcebegan to dominate and which is responcible for formation ofuniverse known as gravitation.

When we think about newtons gravitation, we remember a story ofhim and apple fell on it. Whiel studing in University of Cambridge,one day perhaps in different mood than usual he went to garden andsat in the shade of tree to read something. While reading a apple fellon his head and he shouted. He was distrurbed and stare at theapple in agree manner. But after some time he calm down and hepicked the apple and began to think, why instead of hitting the birdon the top of the tree, it hit him below it. His question was a simpleone but the answer was so long that even we study whole book ofgravitation.

He mad a marvolous conclusion that two massive objest attrct eachother and if many system of mass is present then net force will bevector sum of all forces. This means that earth produce moregravitation force on apple than the bird on it hence it fall toward theeath. If someone will stop it, then apple produce on reaction force onit equal to its weight.

This theory of newton answer the questions about what happened tothe clouds formed after big bang. As the gravitational force began todominate, all the cloud began to contract under its own gravitationalpull toward the centre of mass. As they began to contract, eachmolecule or atom was experiencing the force and hence theirvelocity increased. As they were attracted toward center they beganto come closer and hence relative distance between themdecreases. Due to velocity they began to collide on each otherresulted into increase in temparature. As they pull toward the centre

of mass, they get more velocity and experience more friction oneach other. At a certain time when the collison rate increased, theylose the tendensy of bouncing of each other and bagan to fused ineach other, in scientific language it called as fusion reaction.

When the hydrogen clouds began to contract by the gravitationalpull, collision between hydrogen and duterium atoms leads to thefusion reaction. When two hydrogen and dueterium atom fused theyform a helium atom with a nuetron. This single rection evolve about17.59 MeV of energy and hence in principle hydrogen bomb is verydangerous. Similar reaction occur on sun and give us energyproduced by the same reaction. It is belive that temparature of suncore is about 15 miliion degrees and it’s surface tempararture isabout 6000 degree celcius.

When the fusion reaction in clouds began to occur due to evolutionof such a tremendous energy, the temparature of gas rised andhence they began to experience outward pull and hence the starscompressing a lot. When the pressure inside gas due to nuclearreaction balanced the gravitatinal attraction, they become stable inshape and hence a final stable form of hot gas with fusion reactiontook place. Due to symettry of gravitational force they took shape ofsphere. This bodies what we call are stars. Our sun is a star andbased on same principle as discussed. In simple way, pressureinside the sun is balanced by gravitational force and if reaction willstart, gravity will dominate and start compressing sun.

Perhaps I think that earth and other planet form due to contraction ofdifferent gases like helium and lithium which on fusion reaction formother heavier eliments. Due to volcanoes inside matter come outand hence we have ununiform layer of eliments. If volcano wasn’tthere perhaps we had layer by layer of eliments, like on top surfacesilicon and then carbon and then helium (only for imagination). Butevolution of earth is not topic of our discussion.

When the stars formed in universe, then were not few but millionsand billions. These star began to form clustur which we now calledgalaxy. A galaxy has composed of many stars, planets, other bodiesand some unknown thing we called them dark matter. Theseclusture contain billions of stars and belive that as upermassiveblackhole exist at the centre of galaxy.

In ancient times, it was a belief that earth is at stationary and sunand other planets revolve around earth. But galilio observe that earthin actual rotate around sun but at that time technology wasn’t soadvanced hence they believed that everything were rotating aroundsun. In actual our solar systemis just a part of the galaxy and oursolar system in acutal is rotating about the the centre of galaxy. Ourgalaxy look like a milky river in night sky hence we call it ‘the milkyway’. Our galaxy have about few hundred billions stars and have100 thousond light years in diameter. Our sun is at a distace 25,000to 28,000 light years away from centre of galaxy and have timeperiod of 250 millions year.

When many advanced astronomical equipments were invented, itconclude that ours is not only a galaxy. But about 200 billions ofgalaxies are out there in observable universe and they are all ofdifferent kind. Some galaxies are like ours which we called BarredSpiral Galaxies, other all like normal spiral, some of them likeelliptical and others are irregular.

When began to understand what constist of galaxies it had foundthat dark matter accout for about 90% mass of a galaxy. Dark matteris nothing but the mass added to the galaxy so that all the propertylike spin and relative velocity of stars give correct value. If youassemble all the bodies in galaxy and weigh then perhaps it’s masswill be 90% less original than the mass of galaxy calculated by manyreserachers. Hence it has proved that something is there which ourinstrument can’t detect or perceive and which can not absorb oremmit or reflect light but that is there, hence we call it dark matter. Ifdark matter wouldn’t there, due to spin of galaxy, stars might haveescpaed.

But according to this theory we arrive at the point that ‘big bang’ isresponsible for creation of universe. If big band wouldn’t happen,nothing we see would be there and hence everything will be free forinfinite time. This concludes that only the big bang is theindependent reason for the creation of earth and nothing else. Manyphysicists didn’t agree with the statement and hence they refuse theidea of big bang. They thought that it is impossible to construct atsystem of infinite density in tiny shape known as big bangsingularity.

It was remarkable idea to refuse the theory of big bang because atsuch tiny singularity all the law of physics fails even laws of relativity.At such singularity space time curvature is infinite and no one knowwhat is going on such thing. Many scientist and researcher suggestnot to study anything that lie before the time of big bang because ofthis reason. Even Einstein didn’t like the idea of singularity hence hesuggested not to worry about it. Hence the people who weresupporter of big band started believing that it wasn’t big bang whichcreates everything.

But it was proven in middle of twentieth century, accidently. Twophysicists Arno Allan Penzias and Robert Woodrow Wilson wereworking on ultra-sensitive microwave receivers in Bell Labs in NewJersey. On a day in 1964 they found that their microwave receiverspicking up some radio noise which were not a part of theirexperiment. They tried to rotate their antenna but they found theradio noise were same in all direction. If the antenna is rotated atfixed angle to horizontal, noise were still the same. But when theantenna was pointed toward horizons intensity of noise was lowerwhen antenna was pointed right up. This happens becauseatmosphere is thicker when looking at horizon that straight up whichthe radiation get scattered in thick atmosphere (here noise).

This means that noise were coming from very long distance like maybe out of solar system perhaps may be from out of galaxy. Well ifyou think that what could be the source of such a strong and intensemicrowave radiation, then you will think of stars. But the microwaveradiation observed were not from a star or from galaxy rather it wasfrom different thing or different phenomenon. To understand thisphenomenon I would like to introduce ‘Doppler effect of lightproduced by moving objects’.

We are aware of Doppler Effect of sound. When object is comingtoward us with a speed, the sound emitted by that object seems to

be increased in pitch and vice versa. In case of light another visualeffect occurs.

As speed of light will be constant in vaccume hence when a objectwhich is source of visible white light (like our sun) run away from youat very high speed (some fraction of speed of light) then according tothe laws of physics its wavelength will increase. The increase inwavelength will depends on the speed at which source is movingaway from you. When a source of white light move away from you itlooks redder because all the components in white light hasundergone increase in wavelength and hence according to spectumof electomagnetic waves, red color has more wavelength. henceaccording to it, source must appear more redder and redder if it isaccelerarating. Exaclty oposite thing will happen if source of whitelight is moving toward you. Instead of increase in wavelength, now itwill decreases in wavelength and hence source will apper more blueand then turn violet according to spectrum.





There are specific names for those phenomenons according to thecolour that appears. When star or source of light moves away fromus, it looks redder to us than its original colour. This is known as ‘redshift’ because the colour is shifted toward red. Oppositely if star ismoving right toward us it looks bluer and hence this phenomenonknown as ‘blue shift’ of star.

But when the speed of separation of star from us is very high thenthe radiation is so red shifted that it lie in infrared or microwaveradiation of spectrum. And if the star is moving right toward us withvery high speed then radiation is so blue shifter that it will lie inultraviolet or X-ray region of spectrum.

From the time of Newton to the time when Hubble proposed his lawseveryone was interested in static universe. Even when Einstein’sgeneral theory of relativity was showing that universe is eithercontracting or expanding, he introduced ‘cosmological constant’ tomake universe stationary, at least in his calculation. But the staticmodel of universe wouldn’t last very longer.

Edwin Powell Hubble was a American astronomer who state that ouris not only galaxy. Galaxies move quite randomly like a swirl hencesome time at the part of another galaxy moving toward us whileanother moving away from us hence respective parts of galaxyshows blue shift and red shift in their radiation. When he observesthe galaxies and their spectra he was amazed by the fact theeverything in the galaxies in the universe were red shifted. Hence heproduced some laws for astronomical bodies known as Hubble’slaws. According to his laws, everything is moving away from us andalso we are not at fixed position in space. The entire universe isexpanding and the rate at which another galaxy move away from usis proportional to distance between them.

This expanding universe statement says that the red shift inradiation is obvious. This suggests that the noise observed by Arno

Penzias and Robert Wilson is in actual the radiation that was so redshifted by the speed of expansion of universe such that it lies inmicrowave band. But if you observe the red shift in the radiationfrom another galaxy it does not lie in the microwave region not evenin far infrared region. Hence radiation must not come from thenormal universe but the past universe when they were expanding atvery high speed almost at speed of light due to big bang explosion.This means that what Penzias and Wilson was not normal MWradiation but the radiation coming from far distance about 14 billionyear old.

When I heard the story about Penzias and Wilson, I was worriedabout the laws of special relativity. If the earth is impacted by theradiation that was coming from its birth place, the big band then howcould earth travel so far but not the light or radiation. This questionalmost blew me and hence I began to search for the answer. It wasso obvious that if this is not acceptable, who told you that big bangwas so unique. It is believed that not the big bang that wasresponsible for creation of our galaxy was alone but there weremany big bangs happed in the universe at same time.

The accidental discovery by Penzias and Wilson creates big bang asa standard model for creation of our universe at least forastronomical physicist. Therefore they were awarded by Nobel pricein 1978. Perhaps many religions will not be agreed with me but thatis other thing.

Now we understood the big bang and how the galaxies were bornbut we haven’t arrive at point, how black hole were formed. But forthat we need to discuss evolution of star because black holes arenothing but super massive stars.

We discussed how a star is formed from the hydrogen cloud butwhat drive the star to become so massive to form black hole? Whatare conditions for a star not to form black hole?

First of all I would like to share the idea of black hole. Black holesare astronomical bodies which are so dense that light even couldn’tescape from their gravity. According to Newtonian gravity a materialobject of mass M and radius R have acceleration due to gravity gequal to GM/R2. We will always refer g for gravity, so gravitydepends upon mass and radius for anything on surface.

On earth, if you want to throw a thing out of earth gravity of at aplace in space where earth’s gravity will not bring it back on earththen you need to through at velocity more than 11.2 km/sec, at leastequal to it. But what will happen if mass of earth become double ofits original mass. From formula gravity will double and hence escapevelocity will be doubles hence we need to throw a stone at speed22.4 km/sec. It is very difficult to add mass in any systeminstantaneously like planet but can reduce its shape (like bygravitation itself). If we decrease radius of earth by 100 time, gravitywill increase by 10000 time and hence escape velocity will beincrease by same factor. What if a star with mass 1000 time mass ofearth and have radius 1/1000 times radius of the earth. Fromformula gravity will be (1000) (1000000) =109. Hence escapevelocity will be 11.2 times 109.

But Einstein’s special relativity tells that no one can beat light thatmeans nothing can travel more than speed of light. As ourcalculation shows that to escape anything from the star ofconfiguration as mentioned we need a speed more than speed oflight. Hence it is impossible to escape anything from that star, evenlight. As if light fail to escape from that star, we have no light comingfrom that star and hence we cannot see it, in more certain term itappears black.

Hence to for black hole a star must need the gravity which producesescape velocity more than speed of light. But what parameters tellyou the escape velocity. If you know the mass of the planet and not

its radius then you cannot predict its gravity and if you know radiusbut not it’s mass then it is also complicated to tell about its gravity.Hence to tell about ones gravity you need mass and radius or if youknow the density then you can accurately predicts its gravity. Hencedenser the star, more its gravity and more the escape speed. Henceif a star or planet exceed the critical density of forming black hole,then it will form a black hole and it will not possible for light toescape from its gravity.

Formation of black hole is always a devastating experience becauseblack hole produce intense gravitational field and hence if sun isgoing to be a black hole in next year, we will not be there ontomorrow. Till tomorrow earth had already been consumed by sun.

To study formation of black hole we need to understand formation ofstar and then apply some conditions so that in last stage it willbecome black hole. As discussed, some finite time after big bang,there were huge clouds of hydrogen and helium, in astronomicallanguage these clouds that are responsible for forming star areknown as ‘Nebula’ which is region high density of clouds.

When they contract, friction and collisions between atoms increasethe temperature of gas up to 15 million degrees exactly same astemperature of suns core. But even at very high temperature densityand velocity of the gas is not high enough that hydrogen fuses toform helium. Hence star hasn’t achieved stable form. At thiscondition they glow due to the temperature of collision and friction.Hence they called as ‘Protostars’.

While contracting at certain condition the collision became sointense that now hydrogen barely bounce off from each other andhence they began to merge in each other producin helium. Due tothis reaction stars began to emmit more intense radiation and henceit look too bright. After finite time from fusion reaction started,pressure due to fusion reaction balances the the gravitational pull.

Hence the star achieved stable form and they are called as‘sequence stars’.

After few billion years like 10 billion year a star of a one solar massalomost uses the hydrogen and star began to ran out of the fuel. Atthis stage star glow less and star become completely composed ofhelium. But the core of the star is so hot that helium again fused toform higher elements like carbon. But the outer surface of starremain composed of helium because no fusion rection takes place.As helium started to convert into helium it began to contract asoutward pull became less due to less pressure created by this fusionreaction and gravitational force began to dominate over it.

Now as there is no place for the heat produced by the fusionreaction inside core, it start applying pressure on outer helium layerand hence outer layer began to expand. At this condition star appersdimmer and less shiny, at this stage it called as ‘Red Giant’.

After few thousond years all the helium is converted to carbon andhence it ran out of fuel for carbon formation. At that time outer layedis drift away from the core and it called as ‘planetory nebula’. Thecore has mass only 80% to 85% of that of original star. The core isnow seem like white but less luminius star called as ‘white dwarf’and it is it’s final state. As star colled down it become less luminiusand dims. At certain stage it became so dim that it called as ‘blackdwarf’.

Our sun will show similar scenarios. It is known as yelloe dwarfbecause it it yellow in color and it is very small in size comparatevelythan other star in our galaxy. It is belive that sun was formed 5 billionyear ago and will glow continiusly for more 5 billions years. Earth’smain source of energy is sun, if sun would’t there, perhaps we mightno be existed. But the enrgy coming from sun is produced bycontinious fusion reaction between hydrogen. After like 10 billionyear from the creation of sun or 5 billion years from now all the

hydrogen been converted to helium and sun will glow less brightly.But the temparature will cause helium to fuse forming carbon. After amillion years from the new fusion reaction all the helium will beconverted into carbon. But then carbon will star forming nitrogen andneon for another 100 thousond year. And then after few thousondyear sun will be so heavy that it will start collapsing on itselfproducing new fusion reaction in the core forming oxygen thensilicon and iron. At this time sun will be so heavy that it will dims andno sun no longer will be source of energy on earth. It will becomeuseless black dwarf. Perhaps we need to develop artificial sun orfind another sun.

But this things do not happen for all stars. Some stars having massmore one solar masses shows different scenarios. Such stars act insililar manner as the star less than one solar masses until it becomesequence star but after than it deviate from normal behavior. Afterstar ran out of fuel then due to high temparature it’s core began tofused to for carbon. But outer layer remain composed of helium andstars expanding due to pressure inside it. At this stage it known as‘red supergiant’

It must be remember that if star mass is high then it require morefuel to create more pressure to withstand under its own gravitationalpull. So more rapdly it uses its fuel and hence its age will be lowerthan those which are less massive. Hence massive stars of massesmore than one solar mass will be dead after few million years.

So in few million years star will be composed of many layer ofdifferent eliments and hence it will start contracting and becomemore denser. At the end of the life span the core become enrirelycomposed of heavier eliments and hence no fusion reaction willtakes place. Gravitatinal pull become so strong that core will collapson itself in time less than a second. This cause the huge explosionthat is so bright that it can shine entire galaxy. This explosion is

known as supernova. This supernova explosion are so strong that itproduce shock wave that blows out all matter in outer layer of star.

Some time the explosion also destroy the core of star and hence nostar will be there at the end and what will be is only the stellarremnant (small parts of star). But some time core of star survive inthe supernova. This core is very dense and bigger than core thatform at the end of star life of star less than a solar mass. This coresometime form nuetron star which are more massive, more denseand more luminious than white dwarf. Some time this core is sodense that it’s gravity do not allow to escape light from its surfaceand hence it form black hole.

(black hole name given by wheeler)

The star at the end always have mass less than mass it has beforethe nuclear reaction starts. As nuclear reaction stars fusion reactionproduce mass defect. As two hydrogen masses combinedproducing helium and nuetron, som mass is lost permanatly.Acoording to einstein’s energy mass relation, lost mass is exactlyequal to ebergy it produces.

Now we completely understood that how star is formed and whathappened at the end of the star life. We also get the picture howblack hole is created but in actual we do not get the exact conditionshow black hole in formed. Hence we need to understand the correctmass at which black hole is formed.

As discuss earlier, it was Karl Schwarzschild, a German physicistwho intoduced the black hole as a solution of general relativity justafter a month when einstein proposed the general relativity in 1916.

He had also published the ideas of black hole even before theEinstein introduced general relativity (1915).

According to his theory a non rotating mass with a radius lower thancritical radius can become so dense that it can produce a black hole.The critical radius he proposed in his calculation now known asSchwarzschild radius. This radius is nothing but the radius of eventhorizon of black hole. As black hole do not permit light to escapebeacsue of its gravitation. But as we move away from its surfacegravity decreasea just like on earth. Hence at some point in spacethere is a spherical surface on which gravity become so weak thatnot it is impossible for black hole to drag it back. Hence light out ofevent horizon can escape but inside it fails. We can not tell about thelight exacly on event horizon hence it assume to be stuck at thatplace. It neigher escpe nor dragged back.

If any astronaut intended to observe black hole from near then firsthe gonna need speed of light and he can observe it atleast from theevent horizon. If he went inside the event horizon, he will not comeout again.

Schwarzschild proposed if any star compressed to this radius then itwill turn into black hole. This radius can be given as follows.

.

The idea of black hole proposed by Schwarzschild was remarkableat that time. The black hole obtained from Schwarzschild’s solutionof GR were type of non rotating electrically uncharged black holesknown as Schwarzschild’s black holes.

For many years Schwarzschild black hole were standard model forany black hole for many physicist. But in 1965 a New Zealandmathematician Roy Patrick Kerr inroduce exact solution of GR

(general relativity) known as kerr vaccume solution which describe arotation uncharged black hole may exist in the universe. Hence notonly Schwarzschild black hole but Kerr black holes also exist whichhas spin. But after long long time due to expense of energy rotationof Kerr black hole stop and they become Schwarzschild black holes.Another solution to GR proposed that black holes with electricalcharge also exist and they are Reissner-Nordström (zero spin- nonrotating)and Kerr-Newman black (rotating) holes.

The reason why black hole forms was not cleared untill 1935.Subrahmanyan Chandrasekhar was an indian astrophysist who wonthe nobel price for his memorable work in life cycle of star.Chandrasekhar's most notable work was the astrophysicalChandrasekhar limit which can also describe the black holeformation.

While studing in Cambridge University he had mutual mutualacquaintance with Sir Arthur Eddington. He did study on theconsequence of star when it used up its fuel in other word we cansay it as a dying star. When the star ran out of fuel it become denseand star contracting under it’s own gravity. But the pressure insidethe dying star cause star material to stop contracting further. Thepressure inside the star is cause by pauli’s exclusion priciple saysthat the electrons in atom can not have same quantum state.Uncertainity princiople state that it is impossible to detect theposition of the partical if its momentum (or velocity) is known. Whenwe combine both laws we perhaps able to talk about stability ofmatter.

According to those laws it is not possible for any particle to havesame velocity at same position. Hence this reply that the expansionin star material is due to velocity difference of particles of star.Hence when a cold star (when star used up all its fuel it becomecold) balances the force of attracting produced by the gravity of it on

its matter with the force of expansion of exclusion principle, itachieve stable form.

Chandrashekar found that if the star has mass more than ~1.44times mass of sun will not support itself against its own gravitationalpull when it has used up its all fuel. This mass (1.44Msun) known asChandrashekar Limit.

If a star have mass less than chandrashekar limit then it will settle instable form with smaller radius than original star. they are known as‘white dwarf’. The radius of such star will be about few thousondmile. The stable form of such star are due to balance beween forceof gravitation and force caused by the repulsion of electrons in thematter according to exclusion principle.

It has been found that another stable state is also possible for a starwhen it used up all its fuel. The stable state is due to repulsionbetween proton and neutron in the matter rather than electrons.Hence this is known as ‘Nuetron stars’ and has radius of few miles.Hence Nuetron stars are more denser than white dwarfs. Our sun isknown as yellow dwarf but it hasn’t used up it’s fuel and hence it willlast another 5 billion years hence not need worry about it right now.

But it has a serious problem for a cold star of mass more thanchandrashekar limit. A cold star of mass more than chandrashekarrlimit would not produce enough repulsive thrust to balance the massaginst its own gravity hence it is impossible for such star to maintainstable form. Then what will happen to such star. one answer is that itwill collaps due to its own gravity and become so dense and tiny thatthe gravity will not allow the light to escpe. Hence the star is not ablack hole.

This conclusion lead that if any cold star is near around you withmass more than chandrashekhar limit, then perhaps you need start

enjoying your life right now because may be the day will be thetomorrow when you will get consumed by the black hole it forms.

Interesting to know that untill 1968 black holes were known as‘frozen stars’ or ‘black stars’ but in 1968 John Archibald Wheelersuggested alternative name ‘black hole’. What makes him think togive name ‘black hole’ to this star. Well let assume you and yourfriend is holding a space time fabrick, in other way we can replace itby a thin rubber sheett to make two dimensional analogy. If someone put hevy but very tiny ball on it, what will happen is the fabric willsink down. The curvature the ball created is more near it and hencethe fabric will be flat near your hands. But if you increase mass ofthe ball, more it will sink down producing more curvature. Due to thinsheet the ball is about to tear down the fabrick. If you increase massfurther, ball will drop from the fabrick making a hole into it. This iswhat happen in case of black hole. They makes hole in fabrick ofspace time which allow light to enter into it but do not allow it toescpe hence they look dark and black.

This idea lead Wheeler to suggest and alernative name for darkstars. But is that star really black? I would say you can give answerto that question when you think a red ball in your hand. The red ballhaving infinite compressiblity, that means yopu can make it infinitelydense. Assume that you have make it infinitely dense by justcompressing by your hands. The gravity surrounding by it do notallow light to escpe. If you are like a superman having capability tohold that ball in your hand then what you will see it a black ball inyour hands. But how could a red turn black. I would say it is notblack, it appers black. hence black holes are not so black, as said bystephen hawking in his book ‘the theoty of everything’.

Now we understood everything about black holes but what are whiteholes in actual?

White holes are astronomical bodies which act opposite of blackholes. Black holes are high dense dead stars that can not allow lightto escape from it. Hence anything falling into event horizon of blackhole in actual can not come out. White hole also have evnt horizonbut they act in different manner. As black hole consume everythingwhite hole throw everything out from its event horizon. Hence theyappers white luminious and have a tail like shape which is burst ofpartical it throwing out. In more simpler way we can say that nothingcan go inside white hole even light but everything come out of it.

Does this mean that white hole are repulsive? No, in actual they areattractive like black holes but they attracts thing only up to the eventhorizon. When anything reach event horizon it experiences outwardpull and hence it thrown out. It has no clear explaination forformation of white hole as we have for black hole.

Until 1980s nature of Quasars was controversial. Many astronomerbelived that they have found the white hole but in actual theyweren’t. after 1980s with more precised instruments and deep studyit has found that Quasras is Quasi-Stellar-Radio Source is veryenergetic and they appers to be throwing everything out as radiationcoming out of it. Radiation involve radio waves and visible light.They found in centre of galaxy. Quasars can be seen like below.

In real it is impossible for white hole to servive in nature. Accordingto Stephen Hawking and many astrophysicist suggest that whiteholes are purely hyphothetical object and can not exist in real aswhite holes violate laws of physics. Nature of white hole do violate2nd law of thermodynamics producing perpectual motion machine ofsecond kind. 2nd law of thermodynamics state that for any process inisolated system, entropy must increase. But white hole violate thisstatement.(explain)

Now it has serious problem about black hole that once it created itwill not destroyed fro infinite time becaude it will not allow anythingto escape from it, not even light. Hence it will lose its mass as nomass can escape from it and no chance to lose its mass throughradiation as even radiation can not escape from its gravity.

In 1974 Stephen Hawking, one of the brilliant theorotical physicistargued that black holes in actual emmits particles like photons,electrons, quarks, gluons near its event horizon due to quantumeffect. The radiation which created by the emission of these particleknown as ‘hawking radiation’. As black holes emmit particles itsmass decreases, hawking called the process of decrease of massas black hole evapration. Based on the mathematical model heclaimed, he explained how the evaporation is depend on the mass ofthe black hole. He suggested that lesser the mass of black holefaster it evaporate. This statement suggest that as black holeevaporate it losses its mass, as it losses mass faster it evaporate.Hence evaporate of black hole accelerate with time but it will notdestroyed completely. Due to evaporation it will evaporate until it willnot attain minimum mass known as ‘planck mass’.

‘Primoridial black hole’ are black hole that from at the begaining ofuniverse. Some people even suggest that big bang was a explosionin black hole but it seem impossible. When big bang occur materialdensity was so huge that permits formation of black holes. But due

to uniform density all the matter was not able to form black holes.These black hole can exist till now. But hawking calculation suggestthat a black hole of mass about 1015 grams is already evaporateyesterday or may be going to completely evaporate today. And otherlow mass black holes already benn evaporated due to highevaporation rate. The black hole which which are going to evaporatetoday are on their last moment but their mass is very low that we cannot even observe it by naked eye even they are in front of you. Suchblack hole may existed in universe.

We always imagine a deep black large and dense body when wethink of black holes. They are huge and do not allow anything toescape from its gravitational pull. But are all the black holes too big?Some computer simulations on GR tells that black hole can havesize raise from few micrograms to infinte. Besed on calculation itsaid that a black hole can have mass 22 micrograms and below it nomass produce density that induce gravity to trap light. This mass isknown as ‘planck mass’ and hence it is belied that such tiny blackhole can exist. Due to such tiny size they known as mini black holeor Micro black hole. Main reason behind production of such blackhole can be explained by quantum mechanics and hence they sometime called as ‘quantum black holes’ or ‘quantum mechanical blackholes’. Size of such black holes can be calculated by Schwarzschildradius.

Such mini black holes are child black hole produce by their parentsuper massive black hole but here child will die instead of grow. Sono generation of black hole will remain for eternal. Mini black holenot by only produced by the evaporation of super massive blackholes but also exist naturally. Computer simulation suggest thatprobablity of formation of black hole is inversely proportional to themass of black hole. This suggest that super massive black holes are

less in number than mini black holes. But as there is good probablityof existence of primoridial black hole in universe but no primoridialmini black hole exist in universe due to Hawking’s evaporation law.As evaporation rate is of black hole is inversely proportional to itmass mini black hole evaporate so quickly that no one can observeit after it was produced.

Hence it is very difficult to observe mini black hole by any means.Many people suggest that mini black hole created eveywhere inspace out of earths atmosphre and earth always bumbarded by it.When mini black hole penetrate through earth it produce ‘seismicsignals’ which are observable in microscopic signal receiver butdifficult to defferential from the signal earth produce.

Many peple suggested by their calculation that mini black holes areharmless, then it is possible to create such balck holes artificially? Ifit is possible then it will help us to understand about macroscopicblack holes. The artificial black holes known as ‘man made blackholes’.

You might have heard story about LHC. LHC (large hydron collider)is world’s largest paricle accerlartor planted at Jeneva inSwitzerland.. The main idea behind such a huge project was tounderstand and study the misteries of formation of our universe. Butfew rumors spread evrywhere that instead of studying the formationit will destroy the universe. A girl in India had committed suicide afterwatching TV reports that the physics experiments in HLC could bringabout the end of the world.

But after all what was the reason behind the belife of end of theworld scenario? It was about formation of black hole in LHC. Thecollsion between two particle in particle acclerator can create hugedensity in particle which can allow to increase gravity such that nolight will ecape from it. But as planck mass says that its mass will be

about 22 μg and hawking evaporation laws says it will not last forlonger. Hence they are harmless.

This suggest that mad made black holes are possible and hence itshould be formed in particle accelerator in large scale. But no suchblack holes observed in LHC, not yet. Calculation state that theminimum energy of a microscopic black hole is about 1019 GeVhence to produce such black hole a particle accelerator need toaccelerate particles at such huge energy but it is not quite attinable.Hence perhaps we can not able to produce such black hole inlaboratory. If we really want to create such mini black holes inlaboratory we need to develop particle accelerator of ring shapeabout 1000 light years in diameter which is not seems to possibleeven in human future.

then we don’t care about it. Hence why then we should care aboutthe black holes that form in HLC?

But the theory of multi-dimension state that In higher-dimensionalspacetime, the strength of gravity increases more rapidly withdecreasing distance than in three dimensions. Hence if we allowmore dimension to be present in particle accelerator then may be itwill be possible to produce such tiny black holes with minimumenergy.

Interestingly cosmis rays also impact the earth’s atmosphere withvery high energy and they are composed of mainly super atomicparticles and their antiparticles. As we know antiparticles are verydangerous as it can evaporate its congecutive particle, we evendon’t care about it. This cosmic rays thought to be more powerfulthan mini black holes but even

As mini black hole is not possible to observe due to their quickevaporation we need to find massive black hole to study. But it is

very difficult to observe it because it is black. As I told you it is justlike to find a black cat in coal cellar. Then how to find them?

Black holes are very misterius object that produce signal to let usknow about then but they are too far away from us, their signal cannot reach us and if it is, then its intensity is barely noticable for ourinstruments. Black holes are very heavy object if we are not talkingabout mini black holes, which can create gravitational waves, highredshifted micro waves, gamaa rays by hawking radiation, or theymay form in supernova explosion or they are still out there at verycentre of galaxies. Lets study all the menthod to detect them indetails.

Gravitational waves theory:

As I said, black holes produce gravitational waves, then what aregravitational waves? You might heard of electromagnetic waves,seismic waves, longitudinal waves but you might not heard aboutgravitational waves that much. Any waves beside gravitationalwaves travels through spece time but gravitational waves are rippleof space time itself. To understand gravitational waves I havedifferent anology. Consider still water in a pond, when you drop amarbal into it, the still water disturbs and waves are produce, in factthe waves produces on water known as gravity waves (which aredifferent from gravitational waves). Sometime we see similar waveson clouds, such waves are called gravity waves beacause gravityinduce such wave in contact of two medium like air and water orcloud and air. But similar waves also form on space time fabrick dueto motion of mass known as gravitational waves.

If you have fabrick streched like streched rubber sheet and whenyou drop some thing on it like a heavy marbel, waves are produceon fabrick which travel outer from the source (the point where wedrop marbel) and its strength decrease as it travel furter and aftersome time it disppears same as ripples on water. But in space no

such thing happen like dropping of planet or star. but when they aremoving in acceleratory manner they produce ripples on space timefabric known as gravitational waves.

When binary star system orbits in elliptical orbit, some time theycome near (perigee) and some time they are at maximum distance(apogee). So at perigee, according to kepler’s second law ofplanetory motion speed of planet near sun will be more than when itwhen it if far away, at apogee. So when a binary star system orbitaround each other about they centre of mass, some time when theyare both far away from each other their orbital velocities aredecellerating and when close enough their orbital velocities areaccelerating. This consequeces of acceleratory motion producegravitational fluctualtion in space time fabrick.

It must be remember that gravitational waves are produced byacceleratiory motion only and if anthing produced is travelling,orbitting or spiining at constant speed it will not produce gravitationalwaves. The gravitational waves produce by masses in acceleratoryor decceleratoty motion are like elecromagnetic waves travellingalways travelling at speed of light but their effect dimished as theytravell far away. Some time scientist reffers gravitational waves asgravitaional radiation same as electromagnetic radiation.

So gravitational radiation can be radiated from binary stars orbitingeach other in elliptical or irregular orbit such as nuetron stars orblack holes. Gravitational waves alos induce from black hole collaps.When two or more black holes come closed they first orbit eachother at high velocity and very irregular orbit and then mergetogether. This phenomenon of merging produce huge gravitationalradiation. Onather source of gravitational radiation is supernovaexplosion. When a stars collaps in fraction of second under its owngravity, a shock wave drift away all the masses outward. This shockwave produce ripples on space time.

But as I said, as these waves travells its effect become neglisiblesame as water on ripple as travels diminished after some time. Butvelocity of gravitational waves never decrese, in fact its frequencydecrease. Eath impacted by gravitational waves of frequency lessthan 10-7 Hz which is very small to detect. We have no suchinstruments to observe such tiny fluctuations and hence we are faraway from seeking black holes.

When moon come close to earth, gravity produce tidalm waves insea. According to Einstein’s general theory of relativity gravity wavesare nothing but curvature of sapce time. Hence moon is changingcuraveture of space time that earth produce. But better belive me itis not possible to measere such tiny changes in space timecurvature because earth has very low mass and hence it bendspace time curvature so little and which is very difiicult to measureas I gave expample of Gravity Probe B, so it is far beyond ourtechnology to find changes in such small curvature in space time.

But to understand how these gravity waves works and propogatethrough space time must studied because it can bring new era ofcommunication perhaps something extraordinary. But do you nowwhat happen if these waves travel thorugh any material? Consider apaper boat on a still water pond, if you drop some thing near it,ripples will travel toward it and boat will oscillate up and down orperhaps began a motion of tilting and coming to rest. But whengravitational waves travel through that boat when it is steady, itsdiamenision will change. Eather it elongate in length and compressin height or vice versa.

To understand how it happens condier a square paper in your handand gravitational wave travelling perpendicular to it. When you lookat the paper you will see that thight of paper increase and width isdecrease making it verticle rectangle again gaining maximum heightits height compress and width will increase. Passing through original

square dimension now it will began to copress in height andelongate along its width and again attaing maximum width it beganto compress in width and elongate along height. These oscillationwill continue till gravitational waves stops. If the gravitational wavesis decreasing in strength, the amplitude of oscillation of paper isdecrease. But it must remember that their won’t be any fluctuation inthickness of paper as it is parallel to the motion of gravitationalwave.

In 1974, Russell Alan Hulse and Joseph Hooton Taylor Jr.discovered binary pulsar. They use high precision test on thesebinary pulsar to measeure tiny flucuations in gravity but ofcoursefailed. But they stars a new are of research and experiments tostudy gravitational radiation on the philosophy of albert enisteinproposen in 1918 through his GR theory. In 1993, they awardednobel price in physics for they contribution in astrophysics andgravitation.

But now, all over the world, gravitation has been a very interirstingtopic for reseachers and scientist and hence we can see manygravitational wave observatoy all over the world. Theseobservatories are LIGO (USA), VIRGO (Italy/France), GEO(Germany/Great Britain), and TAMA (Japan).

The observatory located at Livingston, U.S.A. known as ‘Laserinterferometer gravitational waves observatory’ (LIGO)) detects tinyfluctuations in distance between two test masses like atoms withhelp of interference of light rays such as laser. If the distancebetween two masses increase or decrease if a gravitational wavepass through it, laser will sense it and will alarm that gravitationalwave has passes.

But to detect such changes in distance between two atoms, we needhigh precision laser interferometer which can sense change indimension up to 1/100 part of nucleus of atom. No such high

precision wave observatory has been built yet but will be one day infuture. Other than ground based observatory, NASA planned forspace observatory for Gravitational radiation study. They give name‘LISA’ to the space observatory means Laser Interferometer spaceantenna which is not yet launched.

After all in future, I hope technology will be more advanced such thatit will be easy to detect gravitational waves on microscopic level. Ifthis happens, the day will not be far when we find black holes in ourmilky way perhaps beyond the milky way. But if we fail to achievethis then what could be other technique to detect black hole? I wouldlike say, what do you think about gravitational lensing?

Gravitational Lensing:

Gravitational lensing is very interesting phenomenon, even onces in1919 Eddington use this to prove Einstein’s GR. You know what isoptical lensing (like convex lense), when a optical lens is held in theway of parallel rays, the rays will bend and converge to its focus. Inour childhood or in school we experience the power of solar energyby converging rays of light on the paper. When we place a convexlense between paper and sun, parellel sun rays coming behind lensepasses through the lense and get bend to single point on paper. Asconcentated beam of light fall on the paper, due to increase intempereture it burn. Similerly gravity also plays important role inbending of light. Hence gravitation field act as a lense which havecapability of bending of light, known as gravitational lense and thebenomenon of bending of light known as gravitational lensing.

To understand how gravity bends rays of light, we need to picturisespce time fabric. As a heavy mass if we put on rubber sheet createdent, similerely heavy bodies like sun create similer dent in spacetime fabric. When a ray of light is passes through such dent, it will

bend and then escape. You can imagine a hemisperical bowl and amarbel ball. If you held bowl fixed and when you though a ball in itwith very high speed, first it will pass though bowl and sweep insidealong curve surface and then emerge out due to its high speed. Ifyou notice path of travel, it will never parallel. You will see it isslightly bend inward which is due to curvature of bowl. Sameanalogy applied to space time which get bended by heavy mass inspace.

When you see stars in night, the rays of light coming from star isperfectly parallel and unbended. But when you see stars in dayduring solar elipse they seems to be slightly shifed. This happensdue to gravitation lensing. When there is no sun, rays reach youeyes is directly coming from star but when sun in between stars andyou, due to bend space time near sun, rays coming from light getslighly bended and what you see is star shifted from originalpossition, in fact this is not true.

As seen from picture, a massive star or galaxy or black hole are ableto bend light coming from distance star or any astronomical bodiesin space.

In fact this is an illusion, we can see ring around star as shown, but itis not true. This illusion also happen in deserts due to difference inair density, known as Mirage. Due to this fact, illusion created bygravitation also known as gravitational mirage. Gravitational lensing

is different from optical lensing as gravitaional lensing do not involvea real lense like in optical lensing. Second the light get more bendedat the point far away from the centre of the lense that near the centreof lense which do not happen in gravitational lensing due to fact thatspace time curvature is more near object due to gravitation. Third allthe parallel rays of light meet at focus on principle axis of opticallense but this do not happen in case of gravitational lensing while itdepends on position of souce of light relative to the centre of the starthat bend the light.

Small scale experiment of Eddington of beding of light of stars insolar eclipse was a satisfactory explaination of general relativity butno one was able to find real case gravitational lensing effect likeEinstein’s ring or Einstein’s cross. But with the help of HST (hubblespace telescope) it become possible to to observe gravitationallensing effect on macropic level without any trouble. Fist Enstein ringwas discovered in 1998 by astronomers of University of Manchesterwith the help of NASA and HST.

When a super massive object come beween a galaxy then the lightcoming from the galaxy get bended and what you will see is ringaround that object. As shown in picture above, the ring is formedaround the star is not the ring in actual but galaxy right behind thestar. the ring formation only occurs when the galaxy is right behindthe star means their centres and the observer must be in same line.Slightly mis lignment will distort the ring and some some time onlyarc of circle will be visible. Some time due to shape of bending starmultiple images of galaxy can form, if four images is formed then it isknown as Einstein’s cross.

Anything can create Gravitational lensing like star, galaxy or blackhole. The and angle of bending depend on the gravity that objectcreate. If you observe the bending of light of distance star by moon,it will be neglisible because the moon create little bend in space time

fabric due to its weak gravity. In fact black hole are so dense that willbend light more angle that anything else in the universe. On basis ofthe angle of bending gravitational lensing is divided into threedivisions viz. Strong lensing, weak lensing and microlensing. Stronlensing is produce by high gravity objects like nuetron stars andblack holes while weak lensing produce by stars of few solar massesand heavy planets while micro lensing almost do not produce anyangle of bending.

The space time fabric is infinitely curved near the black hole andhence it produce strong gravitational lensing effect. If you observethe ring around the star then it is obvious that the star casinggravitational lensing. But if you found the ring but not star, then is itinstrument fault? No, it could be a black hole which creating Einsteinring. But so such system has been descoverd yet, but if some oneobserve it, it would be a great discovery.

Galactic Center:

Galactic centre is cenrte of milky way galaxy, in other word it isrotational entre of milky way galaxy. Our galaxy is Barred SpiralGalaxy which rotate about galactic centre at velocity 552 to 630 kmper second and have period of 15 to 50 million years. It has about200 billion stars and have diameter of 100,000 light years. Our solarsystem is far away from galactic centre and distance from sun andgalactic centre is about 25 thousand to 28 thousand light years.

Many astronomers have been observing Milky Way for many yearsbut they were very confused about strange behaviour of centre ofMilky Way. They found stars near galactic centre behave verystrange in nature. The stars near galactic centre were seemed likeorbiting some invisible thing at galactic centre at very high speedabout 5,000 kilometres a second. In comparison sun have orbital

speed of 220 kilometres a second about galactic centre. As we arealready aware of fact that the farthest point on rotating discexperiences more orbital velocity than the point near the centre butin the case above if we treat galaxy as rotating disc and sun andthese stars as farthest and closest point then sun would have moreorbital speed but it do not happens. Hence there must be somethingabout which stars orbits.

In 1974, British astronomer Sir Martin Rees proposed thatsupermassive black holes might exist within the centers of milkyways and also at the centre of other galaxies. Upon observing thestrange paths followed by stars near galactic centre manyastronomer and astrophysicist belived that our galaxy is powered bya super massive black hole at galactc centre or perhaps thissupermassive black hole is responsible for birth of our galaxy. Ifblack hole really exist at the centre of galaxy then it must nearly beas old as galaxy. The universe is 14 billion year old and our galaxythought to be 13 billion years and hence the black holes must beabout 13.5 billion old. But according to Hawking calculations a blackhole of 1015 grams must evaporate today because of hawkingradiation. Mass of sun is about 2× 1033 grams hence a black holewith mass 1/1020 times mass of sun need to evaporate today. Butapproximate calculations and observation by scientists, it wasbelived that the mass of super massive black hole could be aboutmillions or billions solar mass.

But the observations by telescopes and other ground based opticalobservatories was not satisfactory and hence radio wavesobservatories plays important role in observation of misterius thingsin space. Scientists at the Max Planck Institute, Germany radiotelescopes have confirmed the existence of a supermassive blackhole at the galactic center. This black hole is on the order of 4 millionsolar masses, which is quite huge. Many radio observatory observedthat galactic centre is huge source of radio waves and it had found

that radio waves are coming from the Sagittarius constellation.There is region of radio sources in that constollation given name asSagittarius A, but using high resolution radio telescope a compactregion in Sagittarius A is souce of intense radio radiation, hence theregion called as Sagittarius A* (Sagittarius A star).

Many people believed that Sagittarius A* is a super massive blackhole while few peoplw believed that Sagittarius A* is lieing on thesupermassive black hole causing radio waves to emmit fromSagittarius A*. But how can a black hole induce Sagittarius A* toemmit radio waves.

Your answer is doppler effect of light. If you see electromagneticspectrum (given) then you will notice that radio wave lieing very leftof sprectrum. They are low frequency radiation having very longwavelength. As I already explained doppler effect of light due torelative motion but gravitation also effect the light.

Consider than you are on very massive planet whose mass is twicethe mass of sun and you have torch in your hand. Your friend withthe shuttle are orbitting the planet in GTO (geostationary orbit) inweak gravitational field that mean they can observe you any time.When you press on button on your torch and point the torch towardthem, light emmit from the torch reach shuttle after some time. Ifyour torch is source of blue light, then your friends in shuttle will notbe able to seeblue light, instead they will see red light.

Why this happens is very usual. When lighttravels from high gravity field toward zerogravity or low gravity field, its wavelengthincrease. As ray travel from massive object itfeel inward pull due to which its frequencydecrease if you treat the light wave asphotons will some mass oscillating but duringoscilations its speed will not decrease. As











seen from fig. it easy to understnd that if light is travelling frommassive object to very low mass objects, light become more redder.This is known as gravitational red shift. Opposite is also true, if youconsider ray travelling in opposite direction. When you persive bluelight from your shuttle, in fact it is actually red but due to gravitation itfeels like it is blue due to increase in frequency.

This changes in frequency due to gravitation known as gravitationaldoppler effect. Just like if train is approaching you, you feel the pitchof the whistel increases and when it goes, sound peach decrease.Similerly if you are standing on massive body, ray travelling towardyou pick up more frequency and when it goes, it decrese infrequency. This doppler effect is very usual perhaps you will begin tothink about color of sun but believe me, sun’s gravitational field isvery weak to produce any doppler effect.

But when you think of black hole with 4 million solar masses, then itmake rather difficult to negelct gravitational doppler effect of lightcoming from stars nearby it. If for a moment you consider such blackhole just fail to trap light and a ray of light escape from it, which wasso lucky. If this light ray travelled to earth, will it be detectable. Toundertsnd what would happened with light, consider same exaplethat you are standing on massive planet but in this can you are notstanding on just a planet but planet of 4 million solar masses henceit will be rather difficult you to be there, but I am assuming that youare superman. And you are holdin source of blue light in your hand.When some one from earth looks at you, will it see red light torch inyour hand? You perhaps answer, of couce not it will see blue lightbut in fact he will not see any light. In actual you are standing onblack hole which harding permit a single ray to travel from it and dueto doppler iffect of light it frequency must decrease but when ittravels from a huge massive object like black hole, it wave length willincrease such that receiver on earth receive aradio wave. So thedoppler effect of light due to black hole in actual turn red light wave

into radio wave. Radio wave are very low frequency wave andhuman eye can not see it but other indtruments can observe it.

Hence if black hole is really standing at the centre of galaxy then itmust produce huge radiation of radio waves and hence we can saythat black hole must be there. But the fact is Sagittarius A* can notbe a black hole because black hole do not emmit any radiation andhawking radiation emmitted by black holes lie in X rays and gammaray region. Hence we can alternatively say that Sagittarius A* islieing above or belove supermassive black hole. But no perfectanser have been suggested yet based on string proof.

Just for better understanding of graviational doppler effect, I wouldlike to suggset you to do househole experiment. If you have longplastic spring then tie one end to the ceiling of your house and otherto the floor. They you will see spring is bit streched but it is uniformthrough out. Not divide spring into four half by marking three line bymarker on it. Now consider that a spring is a light ray travelling fromfloor to the ceiling with uniform frequency and distance between ofloops in each division are same. If you conder that fllor is verymassive object and ceiling is very low massive object then the effectof floor on the spring will be more than ceiling. Hence we hang amass of 1 kg at 1st mark from ground and 0.5 at 2nd mark and 0.1 kgat 3rd mark, condisering spring is drag back due to graviation of floorwhich is decrese as we move away from it toward ceiling. Nowobserve the distance between loops of spring. In 1st division (nearfloor) you will see than distance between loops are very lesscompare to 2nd division and closeness of loops decrese down as wemove upward. Spring will be more streched at ceiling but will becompressed near floore. This suggest that as gravity decreases, thedistance between loops get increase in analogous to frequency oflight must decrease as it travel far away from the massive object.

Hawking radiation:

Stephen hawking is one of the brilliant physicist and his contributionin therotical physis and astronomical physics is appreciatable. He isvery famous in the world because of his theories related to big bangand black holes. But before 1970s no one was so familiar with blackholes and thought to be a body with infinite mass and infinitetemparature and entropy. But in 1972 the Israeli physicist JacobBekenstein suggested that black holes must have finite temparatureand entropy. Based on this statement, Hawking began to search foranswer base in his calculation he come to a devastating conclusionthat black holes must emmits the particles like photons, electrons,quarks, gluons. Many people defended this statement because theythought if black hole do not permit any radiation to escape from it,how could be it suppose to emmit particles. To satify this statementhe suggested that black hole do not emmit radiate anything from itssurface rather the emmision it takes place from the event horizon.He tell that at event horizon a pair of particle and antipartcle createswhich particle travel in the universe while antiparticle travel towardblack hole which reduce mass of black hole and hence result intorapid evaporation of black holes.

To support his idea he took statement of Jacob Bekenstein of finiteentropy which suggest that black holes must have then finitetemparature. Using plank’s black body radiation theory he suggestedthat black holes are more or less black bodies which emmits thermalradiation which depends on the temparature of black holes. As Ialredy stated that as black hole decrese it mass, rate of evaporationincrease means that particle emmision by black hole must increasewith time. This also support the black body radiation as radiation rateincrease because its temparature increase which lead to increaseradiation rate black hole. hence as black body evaporate itstemparature increases.

As black hole radiate, it evaporates which lead to decrese it mass.One moment will come such that it will be so tiny that hugeevaporation rate evaporate all the mass in just fraction of secondradiating gamma ray in the space. This phenomenon known as‘gamma ray’ brust. This type of gamma ray brust can also be seen in‘superova explosions’. The radiation cause by black hole at the endof their life is quite noticable to detect the black holes.

This radiation emmited by black hole known as ‘hawking radiation’ or‘Hawking-Bekenstein radiation’. The frequency of radiation dependon temaparture of black holes but manily premoridial black holesmay be so hot that they will emmit X-rays and gamma rays andhence be must search the source of this radiation may be one daywe will find black hole.

But seeking balck hole is not so easy because maby stars and otherastronomical event emmits x rays and gamma rays and hence wecan not be so sure about the black hole as a source of theseradiation we just observe. We must not forget that we live on theearth and not in the vaccume. We have a major probel inastronomical observation which is our thick atmosphere. Ouratmosphere do not allow Microwave, X rays and gamma rayradiation to pass thorught it and hence we can not experiment withdish antenna receiver on the earth. Hence for further study on thisradiationwe need some space observatory. And hence in June 2008NASA luanched gamma ray observatory satelite nammed as GLAST(gamma-ray large area space telescope) to observe flashed of thegamma ray coming from distant black holes.

But not only by the experiments and observation by telescope youcan say that earth is bumbarded by huge gamma ray radiation butyou can see it. If you look at the horizon at the evening perhaps youmight be able to see some colorful flashesh which are nothinng butthe effect of gamma ray collision on the atmoshpere. When a

gamma ray collide with the atom in upper atmosphere, it producespair of electron and positron. When high velocity electrons travelthough atmposhere, it emmits light rays with different frequencywhich seems like colorful spotlights in the sky (do not confuse withrainbows). Some time this event called as ‘electron shower’ whichwas first explained by Russian scientist Pavel AlekseyevichCherenkov (Nobel Prize-1958). hence some time it also reffer as‘Cerenkov rdiation’. Cerenkov rdiation are emmited when highvelocity charged particle travel through dielectric medium.

Suernova explosions:

We have discuss inough on supernova and we know the criterion offormation of black holes by this supernova explosion based ontheory of S. Chandrashekhar but what we need to know is how todetect them.

As I told you earlier that supernova are brilliantly bright explosions inspace which can shine entire galaxy. It drift away huge ammount ofenergy in less than a second which sun will radiate in its entire lifetime of 10 billion years. It just like millions and billions of hydrogenbombs explosion occur in space. When a cold star of few solarmasses explode due to supernova it drift away it mass in space. Astar form layer of elements due to fusion reaction on it but can notform heavier element than iron because iron require more energy tofuse which the cold star can not provide but when supernovaexplosions occurs the enerhy of explosion rapidly produce heavierelements. Based on this theory most of the people believe that weare made of star dust formed from the supernova explosions.

Leaving funny part, people observe that super nova explosion aresource of gamma rays and hence some time supernova explsionseems like burst of gamma rays in space. If we able to detect suchsupernova explosion, we may be able to find what happened to thestar after explosion. If the core of star survived in the explosion, it

has probablity to turn into black holes. Hence we must seek for suchexplosions in the universe.

Now we have understood different methods to explore the universefor black holes but if we found any, how can we use it for time travelor space travel? Lets discuss wormholes.

Wormholes:

Wormholes are one of the greatest theorotiv physics conspiracy.Some people say wormhole exist and some people don’t eventhinnk about it because it seems useless for them. Many peoplebelieve it is impossible to travel through worm holes and somepeople believe that matter had travelled so far because somewormhole were existed at the time of big band. But are they reallyexist?

No one knows the answer but everyone is trying to realise the worldthat they can exist and other are trying to defend it. Wormholes aretunnels of space time. It will be difficult for train to cross the hill bytravelling around it and hence tunnels had been made in the hills sothat train will take less time to cross it and journey will be easier.Same tunnel shape can exist in space time making your journeyshort. Wormhols are exact solutions of Einstein’s general relativityand hence they are no more fiction.

In 1916 when Albert Einstein published his general theory ofrelativity after barely a month later Karl Schwarzschild found exactsolution of GR is satisfied by black holes. It was a great moment forEinstein but he was worried about it. As black hole has singularity atthe centre of it where infinite density mass do not allow light toescape from it, all the law of physics breaks down at singularity.Infinite curvature of space time made by black holes trouble einstein.After studing deeply with his collaborator Nathan Rosen he found

that space time fabrick can be shaped into tunnel like shape whichactually join to pint in space time called as Einstein-Rosen bridge.

Karl Schwarzschild figured out that this bridges are produced byblack holes may not allow anything to travel through it because ifsomeone juped through it then he will hit singularity and no longerget exported to another point. Hence other end of the wormholemust be connected to the white hole such that if some one jumped inthe black hole it will expoted to another region through white hole.and hence this time of wormholes are black hole and white holecombination. If black hole and white holes comes toghter then it willproduce wormholes.

If any astronaut jumped into such wormholes it will no longer hit thesingularity and hence it will safe throuout its journey. Suchwormholes produce by BH-WH (black hole - white hole) pair areknown as Schwarzschild wormholes. in 1962 collaborative workbetween John A. Wheeler and Robert W. Fuller suugest thatSchwarzschild are unstable. Lorentzian wormholes are a category ofwormholes which do not support the theory of travel thorugh thewormholes. If any partcles is enter in the mouth of wormhole beforeit get transported to other end of the wormhole, the throat ofwormhole will destroy and hence bridge will break. No body canactually predict the scenario of the particle which entered in thewormhole but few theorotical physicist say that it will get crushed.Schwarzschild black hole was showing same phenomenon andhence some time it reffered as Lorentziun wormholes.

I have shown how bridge break when a particle is trying to cross it. Itjust like someone at other end denying to enter into their region. Butthat means wormholes are only for a show and are useless?

An American theoretical physicist Kip Thorne known for his work ingravitation physics and astrophysics. He suggest that universe is stillexpanding because of exotic matter present in our universe whichproduce antigravity. Exotic matter is some kind of negative matter orantimatter which have negative energy. You wouldn’t believe thatsuch matter exist but experiment done in 1948 by Hendrik Casimirwhich suggest existence of exotic matter and some scientist claimedthat they have produce minute scale of exotic matter in lab.

Thorne also proposed that if a exotic matter shell is placed at thethroat of wormhole then it will stabalised wormhole and do not allowto pinch off. So if any particle travel throught wormhole, bridge willnot break and hence particle will get successfully transported toother place. Such black holes through which space or time travel ispossible called as traversible wormholes. But when we think of placein space, what could be other end of black hole?

The place at the other end of black hole depens on what kind ofblack hole is. There are two types of worm hole viz. Lorentzian wormhole and Euclidean worm hole.

Lorentzian worm holes are unstabilize black hole and hence theyneed exotic matter to stabalize it for safe travel. They join distantplaces of same universes and also join places of different universes.When a wormhole join places of same universe it is known as intra-universe worm hole. In this type of wormholes other end will bepresent in the same universe. Like if a mouth intra-universe wormhole present near moon, if a astronaut jumped into it, it may gettransported on mars or may be on pluto. It will help us to coverlongest distance in shorter time hence no need to worry about fuelfor your rocket.

Other type of Lorentziun wormhole is inter-universe wormhole andwhich join distant places of different universes. You might getconfused with the term ‘different universes’. Let me explain. Somephilosopher thought that we are living in the universe is not only theuniverse but other universe also exist which have everything like ouruniverse but they are behaving slightly different than us. This manthat second you also exist in the universe but he might be doingother stuff than what you do everyday like he might be a begger. Sothere can be a possibility of many such universe to be existed inspace but we are very far to think about it. In science it called asmultiple universe.

If you consider a tree with apple everywhere. If you considerindividual apple as separate universe then the it is possible to travelfrom one universe to other universe through the tree itself. Here, ifsuch universes exist, wormhole may act as a tree which joins theseuniverses. In 1895 the term parallel universe was first introduced byamerical philosopher. William James. Parallel universes consideredas are hypothetical or science fiction and hence inter-universewormhole are trated as fiction than Intra-universe wormholes.

But the solution of Lorentzian black hole show that the particlatravelling through it not onlt get transpoted to distant places but todifferent time also. If you enter in the mouth of such wormhole youmay get back to earth but in the present time but may be in past like10,000 BC where the dinosorses was still alive or future like 3012.

The concept of baby universe was introduced by stephen hawking.He stated that a pinching wormhole created baby universes andinstead of particle get crushed in black hole it get transpoted in babyuniverse of its own. When a black hole alone produce such type oftunnels where other end is is very tiny which can bee seen in spacetime geometry created by single black hole.

If the black hole is present in universe and a particle enter the mouthof space time curvature of black hole. Instead of hitting singularity ofblack hole, the bottom of space time form a buble and when theparticle reach the end it will get separated from the paraent universe.The baby universe have different time than ours and which has nobeginning and no end. Hawking coined the name ‘Imaginary Time’for it which run perpendicular to our time. Such wormholes whichjoin places in which imaginary time exist known as Euclideanwormholes. Euclidean wormholes are more complicated thanLorentzian wormholes and are of interst to the quantum fieldtheories.

But traversible wormhole are very difficult to construct because firstit need a lot of exotic matter to stabilise the worm hole and secondno one is sure about that the traveller will get evaporated. If blackhole is creating such wormhole, a traveller must need to toleratehuge gravity as he traveller toward throat of wormhole. If even if youhave a good will power and belief that you will face such gravity thenyou are wrong. Black holes creates tidal forces on object fallingtoward it. Tidal Force is nonuniform forces extered on the body dueto gravitation. When a comet come very close to Sun or Jupiter, itexperience different forces on the different parts of it. As gravitydecreases as we move far from the souce of gravity. If you build ahotel that is about 100 km tall then person on ground will experiencenormal gravity but the person on the top floor will experience poorgravity. If person of 100km tall were exited on the earth, their legwere experiencd huge force than their head. Hence when a comentcome near massive planet or star, the part of comet which is

heading or near to it will experinece more force than the part far fromit. If the gravity is high enough the difference of forces beats thestrength of the force holding matter of comet together and hnececomet breaks into pieces. This was first wintness when ShoemakerLevy 9 was colide with Jupiter.

Then you can guess what could happen with the traveller who isentering the wormhole. When the traveller is come near throat, theforce experience by the diffeent parts of body will be different andhence it will cause pain, not just pain but after some time the bodyget tear apart. The tidal forces will be so intense at the throat ofwormhole that even the atoms of his body experience such a hugedifference in forces such that it will get separated. Hence it will notjust unsafe but a nonsence to jump into worm hole untill unless yougive some protection like ‘wormhole suit’ wich have enough strengthto overcome such a huge tidal forces of black hole.

Suppose if some day we able to find such wormhole near by us thenwill it be safe to travel though such wormhole, even we have allsafaty arrangements? I will suggest you not to go up there. Becauseif nobody haven’t been dare to enter through it, then why are youdoing it. Who know what is at the end of that wormholes. May theend of the wormhole is present near a hot star where thetemparature is so huge that it will makes you think that you havenade a mistake or perhaps the end of wormhole lies at the core ofthe star where you will not even get time to think about that. Sometime if the end is near the black hole then who knows what willhappen to you.

In 1960s the space race between Soviets and American change thepicture of universe and moon became the first celestial body visitedby human. The revolutionary change is stronomy open windows ofknowledge and may be that’s why we are talking about it. Justassume for a moment that with the help of probes and other modern

robot, it has found that the real world exist at the end of wormhole,then it would be a revolutionary day for human being. we mayachieve something that we never think of. It is taking a lot ofhardwork for a human to just get to the mars but using wormholesmay be one day we will be wintnessing our astronauts in othergalaxies.

Many people have been thinking that we are alone in the universebut it will be no longer when we will still say we are alone. Usingworm hole we can travells to such places at which life may exist. Willmay see such things which is not possible for HST to see.

Not only the space travel but time travel is also possible throughsuch wormholes. perhaps instead of just travel through space we willable to meet your own youngr you. If you need to seed some thing inthe past no need to watch video, you can witness that event live. Ifyou want to change something in your life, then go to your pastchange the course of scenarios and then ome back, perhaps yousee oyur life is completely canged. Not only the past but futuretravels is also possible. If you are suffereing from the world then noneed to die, just go to the future and live there may be you getadjusted there. Using future tike travel you can visit your old you oryour children or perhaps seek for your wife in the world.

This things may be makes you so exited or feel you wacky. Somepeople just laugh when they think of time travel. How could it bepossibel to go past and stop some one’s assasination?. How could itbe so easy to say about the future that you have never seen? Howcould be a person which is dead can bee exported to the presentfrom the past? This questing are really worthy to think about butwhat we need to know is how the time travel takes place. If youagainst the time travel then first you should note that one way timetravel is possible incertain ways and proved by science.

Before we start debate on it we must need to know about time travel.So lets discuss tikme travel in details.

Chapter4: Time Travel

A artist’s representation of wormhole– © dailymail.co.uk

Wormholes are hypothetical bridge which is tunnels of space time thatallow anything to cover longer distance in shorter time take by the light totravel same distance.

Lorentziun wormholes are unstable wormhole that not only allows aobject to travel spatially but temporally and hence wormhole can work astime machine. Theoretical physics speaks about multiple universessystem that is connected by wormholes.

Time travel has been a very popular topic for science fiction writer.From documentries to movies people have been waching sciencefiction as a part of virtual reality and time travel have been awondeful topic for production houses. But besides science fictionpeople are not really interested about the reality of time travelbecause they think that it is just a fiction but can’t be real. Well,when I was a child I used to inimitate the ‘mantras’ but I knew thatnothing catches fire by just few word but time travel is not that kindof thing. Some part of time travel thoery is proved by science andsome is still conspirious.

Time machine is a machine through which we can travel throughtime. Suppose a car which is usuful to travel distance in miles, timemachine is just like car but instead of distace it cover time. If youhave seen planes, it has already programmed and autopilot can takeyou from one place to another just by selecting the destination andspeed. Time machine is highly sophasticated and programmed suchthat selecting the time like past or future you can reach yourdestination. Hence Time Machine is used for time travel rather thanjust a distance.

In fact no such machine is invented yet but may be it will some day.It is more thorotical that sciece and hence no great research is goingto develop it. As time machine is thoerotical doesn’t mean that timetravel is theorotical too. Time can be travelled by many methods, butthose methods are too complicated to apply such that no singleexperiment have took place to experience time travel phenomenon.Time travel by wormhole, gravitation, relative speed are goodmethods but too complicated to use. Based on phenomenon of timedilation no such machine is produced that can actually travel throughtime.

There are two ways a person can travel through time. Past orFuture. Just like a road, if you are travelling on a road then you have

only two way to go, farward or backward. Anologous to time travelfaward time travel can take you to the future and backward timetravel can take you to the past. Faward time travel is most discusstopic in time travel thoery and sciece can prove that faward timetravel is possible but backward time travel or travelling to past haveno scientific evidence and it believed that trevel to the past is notpossibel and against the law of nature.

Forward time travel:

Forward time travel is possible and science had proven it on smallscale. What happen on forward time travel is very intersting.Perhaps if some day you buy a ticket of time machine and youdecided to go to future, no one will stop you from exploring futuregeneration cars flying over the head, tall bulding floating in sky andteletransporation machine on roads like phone booth availableanywhere. But as long as someone invent time machine, you canonly imagine in your mind.

Fprward time travel can be used to predict and accurately guess thereason behind some event. But for that someone need to go forwardin time, inverstimgate the cause and comeback to this time and tellthe truth about the cause so that we can prevent it from happening.But to do so travel in past is incountered as to come back fromfuture to this time is actually travelling in past according to the timeat the future and as we are not talnking about backward time travel,we need to skip such situations.

When Albert Enstein published his paper about relativity (both SRand GR) he didn’t mean to establish theory of time travelling but thetime dilation factor make him think about time travel. In case ofspecial relativity the relatiistng speed cahnge the rate of passage oftime while general relativity tell that graviational field also bringchange in rate of passage of time. The difference of time due tochanged rate is known as time dilation.

Time dilation is not the cause of relativity but it is effect. AlbertEnstein develop Special theory of relativity on just one statementthat speed of light is same for all source of oberver that mean lightalways beat traveller. If you are in space ship which are travelling atspeed of light. You lights will be no longer usful because the beforethe light travel certain distance, your space ship already covered thatdistance and hence light seems steady. But in real this does nothappen and hence light travels at the same speed anywhere.

The time dilation is very important to understand because it used inmany communication satelites. If you are not ajusting time regularlyit may happen that the clock that present in the satelite get so backin time that the information it had to provide yesterday, it is providingtoday. What happens is when satelite is rotate around earth then thepoint where the imformation is received and the ponit on satelitewhere information is provided is in relativitic speed difference due toorbital speed. Hence they experience different different time elsapedin their clock. If orbital speed is very high that orbital speed of pointon earth then the clock in satelite get older and older and one daydifference will be so huge such that if a clock on earth showing 25december the perhaps clock in satelite showing 24 december. Ifsatelite is programmed to send some information on 24 december, itwill follow tha order but the information on earth will be send on 25december. Hence satelite sent information late by 24 hr of earth.

But in real this do not happen. The concept of warp space timefabric in Einstein General relativity suggest that time ticks slower indifferent gravitational field. As we discusse more massive objectscreate more dent in space time fabrick and hence 4D space timefabrick get bended and streched by some ammount depend on themass that it created. If you consider earth then as we move awayfrom earth, gravity seems to be decreasing but according to Einsteingravity picture, it is not the force but the effect of curve spce timeand more gravity can be experience in more curve space time.

Reversely, more curves space time create more gravitation. Hencethe space time is more curved near the earth surface and decresseas we move away from it.

The space time is cordinate system that have 3 spatial dimensionand 1 teporal dimension. Hence the curved space time actuall chngethe rate at which time elapsed. As already explained artificialgravitational effect by accelarating the frame of reference canactually tell that to create more gravity we need to accelerate it moreand hence special relativity says that time must ticks slower. Thisanology can connect SR to GR and hence time ticks slower in moregraviational field. This means that satelite at very high alititude mustbe in weak gravitational field hence time must tick faster than our. Asdiscussed in case of GPS, time dilation by gravitation is 45 μs whichcan change course of a traveller.

As satellite is travelling at higher speed, times must ticks slower in itsclock. But as it is orbiting at high altitude time must tick faster.Combining both the result we get net time dilation. In case of GPStime dilation due to relative speed is 7 μs but time dilation due togravitation is -45μs and combining both the result we can say thattime dilation is -38 μs which mean that clock in satellite get ahead ofour clock by 38 μs every day. In more general time ticks slower onearth than in satellite.

You may have understood the scenario of time effect or time dilationoccurs due to both SR and GR. What is means travel in future? Itmeans that when you wake up, you find yourself in different time like2050 but your age is still same as were before you went to sleep.Now if this is time travel in future how could we travel to future usingtime dilation?

It can be possible by what we called ‘Twin Paradox’. Twin paradox isthe example explained by Albert Einstein to explain how agedifference takes place due to time dilation. Consider two twin brother

of same age. One of them got selected for experimental flight ofNASA to travel for two minutes in space at some fraction of speed oflight. So he went to space, travel for two minutes at such a highspeed and after two minutes of his clock he successfully land onearth. It was a proudest moment for him and mankind that man hastravelled at speed nearly equal to speed of light but unfortunately itwas not happiest moment for him. As he reached home he foundthat his old parents were dead and his twin brother is now too old towalk.

At the beginning before flight, twin was of same age but after onetravelled in space and come back there age difference werenoticeable like can say 40 years. The one who stayed on earth isnow older than his twin who went to space. This means that the onewho went to space count two minutes in his clock but many yearspassed on earth. In different way we can say that in space less timeis passed compared to earth and hence the age difference tookplace.

We cannot really observe the clock in space which is travellingalmost some fraction of speed of light but if we able to then we cansee that it ticks slower than our clocks on earth. This means that weneed to wait for moths to observe change of one second in themoving clock. As time appears slower in space doesn’t mean that itactually runs slower locally. The man in space ship always feels thesame time rate as earth. The time dilation takes place due torelativistic speed difference. The faster the spaceship moves, slowerthe time ticks and younger it gets. Younger in sense that the agedifference in twin get bigger and bigger but the age of the twin inship always increase. It will not happen that the twin in the shipbecame child when he came back to earth. This will be against thelaws of nature.

As we learned that more the speed of the ship, slower time ticks butgeneral relativity says that time perception can also change if we putclocks in different gravitational field. As discussed that moregravitational field slow down the perception of time, the clockpresent on earth ticks slower than the clock on moon. As earthproduce more gravitation than moon on its surface, the clock mustrun slower in more gravitational field and hence our time must passslowly than on the moon. Also sun is biggest object in our solarsystem and Pluto is smallest. Hence time must tick slower on sunthan on the Pluto. If one twin went to sun and another to Pluto, aftera month of their own time went to earth, the twin on Pluto will comeback to earth quickly but it will take years for twin who went to sunbecause a month has to pass in his clock. If he came back and meethis twin who went to Pluto, of course the twin who went to sun willbe younger.

Now you can imagine the future time travel without any objection.Suppose you are sick of this time and you feel that I wanted to live inthe future generation then no need to invent machine which canhibernate you or preserve you for generation. You need to go tospace travel there for some time of your clock but always rememberthat you need to travel about some fraction of light. When you willtravel to such speed, time will tick slower and you will get youngerthan people of your edge. Not only the people of you age but thepeople who were younger than you is now growing older. It will lookfunny but the child who was just born when you were leaving theearth is now older than you. How funny it is.

Calculation in special relativity says that if you travel at speed oflight, Lorentz factor will be zero and time will be stopped. This meanto tick 1 sec in your clock, few generation need to pass on earth.Hence as a minute is passes in your clock and you decide to comeback on earth, and then you will see about thousands of years haspassed. Many the future is so advanced that you need to take

permission to land on earth. Unless you have proper authority, itwon’t be possible or they might shoot you in the air.

It is not possible for anybody to travel at the speed of light. Sciencesuggests that it take infinite amount of energy to set rocket at speedof light. It takes years for hypothetical machine to travel at speed oflight by using nuclear propulsion. So it seems impossible to traveltime by using relativistic motion. Speed of 10,000m/sec also do notmake any sense for time travel because to reach future then youneed to wait more and hence you will get older. When you will touchdown on earth, perhaps you will be so older that you will not able toenjoy the future.

But this doesn’t mean that future time travel is not possible. Generalrelativity says that the time ticks slower in more gravitational field.Hence if someone went to a planet produce higher gravity than theearth then it will be possible for than person to travel to future ofearth. Suppose that you went to Jupiter which has gravity about100g. Then what general relativity says is time must ticks slower inyour clocks. As time pass on earth your clocks get behind the clockon earth. After a year’s pass on the on Jupiter, if you came back toearth you will see that people are older than you which wereyounger before your went to space.

But believe me this not going to happen because gravity on theJupiter is about 2.5 g, which is not so good to produce gravitationaltime dilation between earth and Jupiter so that time difference will beof years. But we have stars and black hole which can satisfy thisproblem. If you went to star like sun which have gravity 27.94 g onthe surface which is quite good and black hole which produce ∞gravity on its surface such that even light cannot escape from it. Butto went on black hole is rather difficult because of problems arises injourney like tidal forces of black hole and getting trapped in babyuniverse so it is better to stay at event horizon. But still it is not so

simple because to escape from event horizon you need to havespeed of light hence you need to keep far distance as you can. Thegravity due to black hole is so tremendous that can bringappreciable effect of time dilation to travel in time. If you spend amonth in the orbit around the black hole and come back to earth,you can see that generation must have pass on the earth.

In case if a technology has developed so to keep man safe on thesurface of black hole then physicist suggest that time will come to anend. This means that it will produce same effect like space ship istravelling at the speed of light and hence time will stop in the clock ofman on the black hole. It will take hundreds of years on earth to seethe clock on the black hole ticked by one second. Hence one minuteof your time on black hole can take you travel thousands of years onthe earth.

But not only relativistic speed, black hole or stars can take you to thedifferent time. We have discussed that wormholes can also take youto different time. Some solutions to Einstein Rosen Bridge orwormhole suggest that a astronaut travelling wormholes not onlymove in space but also in the time. Consider a wormhole joining toplace in universes. If you enter one mouth of it, it will take you theother place lie near second mouth. As we discussed that black holewhite hole can produced wormhole like Schwarzschild wormhole orblack hole can also produce wormhole tunnels alone hence theremust be a point in the wormhole at which gravity will be so intensethat cannot allow light to escape. Suppose that a wormhole hassemicircle ring shaped structure which can allow you to travel fromone half of the earth to the second half. Then as you enter thewormhole, you will pass through the field of high gravity and hencefor certain time your time ticks slower and hence when you come outof it from second mouth, less time has passed in your clock that theclock on the earth. Hence we can use wormhole to travel to the

future. Wormholes can also get you to the past and hence you canalso go to first place if you want.

When people think of wormhole, then they think of tunnel of spacetime through space and don’t think about the anything which itforms. But as the space time is folded into tunnel like shape theremust be a heavier object which it created and hence we need toconsider the time dilation it creates. Hence a person travellingdistance galaxies also travel time and his journey always take longertime than the expected.

Hibernation is also a way through which a time travel can beperceived but it is very difficult to achieve. The age of human can beincrease by reducing the metabolism and other reaction speed inhuman bodies. Hence human can preserve for many years alive butit is not the part of the relativity theory and this process of perceptiontime travel not consistent with time travel itself.

Forward time travel is not just a hypothetical concept but scientifictruth and hence it make very different from backward time travel.The clocks on the space flights run little bit faster due to lowgravitational field which is direct evidence of future time travel ispossible. Time dilation is only known and scientifically proved way toachieve future in more rapid rate, not at least the normal rate.

But the forward time travel that science explains is different fromwhat science fiction writer write about. What science fiction speaksabout is type of multiverse future time travel. In this case of forwardtime travel, your future you also exist in the world and time whereyou will land. This means that you can actually see your old version.But how could this be possible in real? When you leave the earth,you completely disappear from the earth and if long time spends onearth and you came back then is this possible that your old one stillexist? Yes, it is possible for time travel trough wormholes.

Wormhole can connect not the places of same universes but placesof different universes too. These universes contain everything sameas our universes, like earth and all the stuff on it but all stuff aregoing in different way. That means a person running in our universemay be watching TV in other universes and eating apple in thirduniverse. Such systems of universes are called parallel universes ormultiple universes or multiverse. When a person travels from oneend to other end of wormhole, he get transported to anotheruniverse. In this way he can actually see his duplicated old versionby multiverse forward time travel. If someone come to you sayingthat he is your young one then don’t slap him, he might be comingfrom different universes.

But travelling multiverse is purely hypothetical concept and no suchstrong theory or model is developed to explain it or prove it. Hencetravelling to such future where your old one still exist is impossiblefor now, but in future if traversable wormhole discovered then wemight be understood mysteries of multiverse time travel.

Perhaps one day tourism industries will evolve which not just provideluxuries travel through space, but also time. People alwaysinterested to know about their future and what future world may looklike hence future time travel is always first choice for time traveller.

Backward time travel is purely hypothetical concept because ofparadoxes it formed and there is no scientific proof which can tellwhether voyage to the past is possible. This means that once youreach the future there is no way to change your mind to come toinitial time again where you had started your journey. Once youreach the future, you have to stay there. Noting in the universes cantake you back to the past but theoretical physicists never give up.

Many theories in fiction suggest that time travel to the past ispossible and there are many ways to avoid ‘Causality’, paradoxescan be neutralised and history can be changed but there is no way

to explain it on the paper like Einstein did in form of Time Dilation.Although, the past is already happened and we remember it thenhow come one could change it by going into past? Will it affect thereal world?

These questions are really important for science because it cannothappen in real because law of nature cannot allow it to happen. Butthere is no such rules and law for fiction writers and theoreticalphysicists, hence many people has been developing theory ofbackward time travel. Let’s discuss it.

Backward Time Travel:

According to Albert Einstein time is not same for all sources ofobservers. This make sense that two observes at different place canhave their own time rates if externally viewed from some referenceframe. Because of this Einstein suggest to take 4th dimension astime to define an even in the universe. The unit of 4th dimension maychange from place to place in cosmos. If any event happen in aparticular universe then it is not label as three coordinate where theevent happen but also by time to denote when the event happen.This can be use to form a ‘Worldine’ of object to see path traced bythat object in 4D coordinate system. ‘Timeline’ refer as all the eventsthat have already happened. I can say timeline is just past of wholeuniverse where worldline represent past of single object.

The belief of time travel was first born in beginning of 20th centurywhen Albert Einstein published theory of special relativity andgeneral relativity. Time Dilation is the interesting thing to notice andthe clock change the relative speed or region of gravity. But theconcept of wormhole allow physicist to think about time travel to thepast as well.

Travelling to the past is completely different thing from travelling tothe initial point of our journey like generally happen in sports. If younotice that the earth travels around the sun in circular orbit (almost)and hence after 365 day it comes to the initial place where thejourney around the sun was started on 1st day. But as the earthmoved around the sun and come back to the initial place, the time ofalmost 365 day has passes. This means that it earth is coming to theinitial point in the orbit spatially but not temporally. We do notexperience same day on every 1st January and hence we do notcome to same time where the earth started it journey. This suggeststhat earth travel around sun only spatially.

Kurt Gödel in 1949 showed that a close time like curve can exist.Which sate that if earth travel around sun in circular orbit can comenot only to its initial place but also at the initial time and hence wewill experience to be moved back in time? Close time like curve isworldline which form a circular loop. When someone starts hisjourney from some point on the loop, he will come to the same pointafter some time at same time. The close times like curves aresolution of general relativity introduced by Gödel. These close loopsof space time proved to be existed in wormhole solution and alsotheory of quantum gravity.

I feel really strange about someone who trapped in the closetimeline curve. Actually when someone travelled the whole loop andcome to initial point, his clock showing exactly same time when hewas started his journey when look by the observer from somereference frame. But whatever it is, such close timelike curves areinessentials for backward time travel. If earth travelled in CTC then Idon’t know what will happen to the life on earth. Perhaps for sometime things will go as usual and for some time it will be reversed likedead men become alive as time passes.

Albert Einstein’s special theory tells that nothing can travel fasterthan light but the black hole radiation effect tell that due to quantumeffect some subatomic particles break the speed of light andsuccessfully escape from black hole. The contraction between BHradiation and SR lead to think about what happen if anything travelsfaster than light. Recently an unusual scenario of particle acceleratorat LHC conclude that they have broke the speed of light, but thescientist working there speak that it was a instrument malfunctionbecause of cable loose.

The particle if travelling faster than light called as ‘tachyon’. Atachyon is a hypothetical particle which travel faster than light andsend information to the past. Special relativity tells that no suchparticle can exist in nature because it violates Einstein’s Causality.SR tells that if particle travel faster than light then it travelling to thepast rather than to the future. Hence if you travel faster than speedof light and arrive to the past, you can change everything in theworld if you want.

If you went to space and orbit the earth at subluminal speed may bethe time passes on earth faster compare to your clock and when youreach the speed of light your time become almost constant if lookfrom earth. But once you star travelling faster than speed of light, thescenarios become more complicated. When you travel faster thanspeed of light, you began to travel in the past. This means that if youbegan to travel at the speed twice that of the speed of light, theworld you perceive began to travel backward in time. If you startyour journey to the space at 2012 and travel for a month in space atthe speed 2c, then perhaps you may return to the earth on 1009 orperhaps on the day when there were no humans on the earth.

It is very complicated to understand a system which travels back intime. Does that mean that a system is acting in reverse manner?When you return to earth from such journey, the time is moved

backward or you can say you moved in the past. People began tothink that this is impossible because ‘if no man was ever existed onthe earth at that time when a traveller landed on the earth in the pastthen that will violet rules of evolution of life.’ Of course it is true but ifyou think more theoretically then perhaps this is the answer we arelooking for.

When traveller is travelling in the past, things on the earth is going inreverse manner. The breaking cup may be gathering together on thetable and form original cup. The bullet coming from the gun nowgoing inside the gun and may be dead person is now alive. Thesethings look quite inconsistent to what we generally perceive, everyday in reality. According to science and philosophy of free will, aperson who is dead cannot be alive in the same universe.

Stephen hawking in his book ‘The Theory of Everything’ suggest thatthe time can have three directions viz. Psychological thermodynamicand cosmological. Psychological array of time tells that tings mustgo on in such a manner that a person must not doubt about thedirection in which it going. Like a bullet going in barrel of a gun,which is unusual and a person can tell that it is not possible. If youshow someone a video of gun fire in backward manner, it looks likethat bullet is going in the barrel but he can accurately tell that youhave just played the video backward. The person if feel that thethings he perceiving is running backward the he is travelling in thepast, which is not consistent with the psychological array of the time.

Secondly, thermodynamic array also tell that the time always passesin the direction where entropy of the universe increases. Entropy isthe term in the thermodynamic which tell about the extent by whichthe system is disordered. The entropy also uses to explain why theisolated system looses the ability to do work. Thermodynamic arrayof the time tell that the isolated system must go in the manner ofincreasing entropy. Like a cup when broke occupy more disorder

state than the initial when it was single whole cup. If there isdecrease in entropy of isolated system as time passes, then thesystem is running backward in time, which the fact of violation of 2nd

law of thermodynamic. Our universe is a type of isolated systemwhich always tends to increase its entropy.

Cosmological array of time is quite different from that of other as itdo not actually tells about how should a time pass but it explain thatif time reversed its directing then cosmological assumption will getcontradicted. The universe is expanding and can be explained byred shift of the part of galaxy that is moving toward. Hubble’sexperiments and his law about the universes are worth noting andtell that universe is expanding with increasing rate of expansion.There are many conspiracies behind the expansion of the universebecause what we perceive is not sufficient to expand universe withincreasing rate. If universe is expanding then rate of expansionneeded to be decrease with time because of gravitational attractionbetween matters. But in fact that increasing rate of expansionsuggests that there must be something in the universe perhaps aenergy which we cannot be perceived but exist in space to opposethe gravitational attraction between matter and tend to accelerateuniverse to expand. Such energy called as dark energy and it isbelieved that 74% of universe is composed of dark energy.

If the time reverses its direction then perhaps the expandinguniverse begins to contract and the laws of everything becomeuseless. If big bang tend to throw off mass from the tiny singularityperhaps upon reversing the direction of time, the universe we seewill began to collapse to form singularity again. If you look at thismore seriously then perhaps you begin to support the reversing thedirection of time. If we believe in the recycling universe which cancollapse and again give birth to universe through big bang then theremust be a time period in which time traverse its direction. Well this

will look quite terrible to think about must most of the theoreticalphysicists are agree with this.

Some time arrays support that time can be reversed and somestrongly defend but what is reality is still unknown. But what wediscussed is the time travel by time dilation but we have wormholewhich can allow a traveller to travel not only through space but allowthrough time. As we have been discussing the wormhole sciencefrom beginning of our discussion, there must be a constant source ofexotic matter at the throat to keep wormhole open. Such wormholeswhich allow traveller to travel through it are known as traversablewormholes.

If a wormhole is joining the earth and the galactic centre thenaccording to GR time must pass quite slowly at galactic centre.Hence if you travel through the wormhole, then you can reachgalactic centre more quickly and in the past. May be you canexperiment on the thing that went during the big bang or formation ofgalaxies because in the present that things are not existed. But suchwormhole which can join distant places of the same universescannot allow the traveller to travel in the past of his own world. Likesuch wormhole cannot allow traveller to travel to the past of earth.

But theoretical physicists believe that the time travel to the past ofhis own universe may be possible by allowing the wormhole to joindistance universes. As explained about parallel universes, if thewormhole joining different places of different universes then it will beeasy to travel to the past of the same world. Such wormhole calledas inter universe wormholes.

Parallel universe theory is a fiction and science does not agree withit. Theoretical physicist argues that universes are like fruits whichare connected to each other by branches of the tree. Thesebranches are nothing but wormholes. Travelling to the other placesby journey through space using conventional vehicle is not possible.

If intra universe wormhole joins places in our universe like earth andmoon then that does not mean we can’t travel to the moon if we donot use wormhole. Wormhole uses to reduce the time of the journey.But this does not happen in case of inter universal travel.

May people suggest that universes are trapped in the sphere ofimaginary boundaries which do not allow things to escape from it. Ifyou travel long distance in the space considering that you areinternal then there is a probability coming to the initial place whereyou have started your journey. If will not feel even not for a momentthat you are travelling in circular orbit around some reference point.This is a hypothetical model of universes but if we assume it is to betrue then wormhole must need to travel from one universe to otheruniverse.

If we assume that such parallel universes exist then what is goingout there? The parallel universe are the mirror universes but withdifferent timeline. The timeline refers for all physical events in historyand hence the parallel universes have different history just like adrama where the story can change but the character remain same.Everything including life is same between those universes andhence there is no need to fear about the lives in parallel universes.

Now for a moment we forget about everything about what sciencebelieve and defend and try to be more hypothetical. If some saysomeone invent the time machine which is able to travel thing in hispats then what could happen? Will the traveller actually gettransported to his past alive? Will he be able to change the historyand stop doing wrong deeds? Let if someone went to past and he isstill alive there when he stepped on the earth then first it is possiblethat he went such a world where his young self was never existedlike the future travel by time dilation where the world without him ismoved forward and when he land on the earth in the future there isno question of existence of his old version. Second case could be he

went to the world where his duplicate young is present where he canmeet his self young version.

First case looks to simple and according to special relativity ifsomeone travels at the speed much higher than speed of light thenhe will be travelling in the past. There is no scientific evidence andproof for backward time travel using superluminal speed but stilltheoretical physicists believe that this could be possible. But if youassume that a person went to the past and stay there affecting allthe physical event which can kill him there, then the timeline will bechanged and the person who is dead out there can effect wholeworld. But Novikov self-consistency principle that history is uniqueand self-consistent. This mean that a person who went to the pastcannot change the history but this principle also give rise to thequestions about free will.

For the second case where his young version is alive then it allow aparadox of free will. There is a belief in religion and science fictionthat a will is unique in the world. So how could be two person withsame will can exist in the same world? Even if we speak morehypothetically, saying it is ok to have such two people in the sameuniverse then there is a problem. Suppose the person who went tothe past, killed his young self then the person cannot be alive till thedate where he intended to go to the past. Hence there is no suchperson who travelled to the past. To understand it more clearly, weneed to understand grandfather paradox.

Grandfather paradox was first described by the science fiction writerRené Barjavel in his 1943. He explained that if a person went to thepast and kill his grandfather before his grandfather met hisgrandmother then his father and mother never would have born andhence he wouldn’t have born. This makes sense that he never havegone to the past and killed his grandfather.

Despite of this is we strongly allow the paradoxes not have tohappen then it is impossible to go to the past and change thehistory. There are few other ways to eliminate such paradoxes likeparallel universes.

The travelling to the past encounters many question and manyparadoxes making the journey to the past more complicated. Peopleargue that the change in timeline due to a person who went to thepast is obvious but no such machine will be invented that wouldallow a traveller to travel in the same universe which have sametimeline.

Dr. Igor Dmitrievich Novikov, is a professor of Astrophysics atCopenhagen University who stated that the history is self consistentand unique and hence nobody can change it. This make sense thattimeline is unique for a universe but not for all universe. If a travelleris travelling through the time, then he is moving in the past of theparallel universe. The parallel universes are universes with samecharacters but different timeline. If someone goes in the past andsave M.Gandhi being assassinated then of course it will createdifferent sequence of event i.e. timeline but this is this is real timelineof that universe and in fate of that universe it was fixed thatsomeone will come from other universe and same the Gandhi.

It will look funny but it is what many people think in order to makebackward time travel possible. There are so many rules and law aperson must need to follow during his journey to the past. Such rulesare known as rules of time travel. What I believed is a person thatwent to past is so emotionally attached to the things that he willnever think of anything which allows the paradoxes. In philosophysome rule that a person is always abide with known as ‘CategoricalImperatives’. Categorical imperatives always tell that what is wrongand what is right. A person if doing wrong deed then his mind alwaystell him that he is doing wrong but the situation prevail him to do

wrong. May be in the past such thinking dominate over wrong deedsand hence keep history clean and self consistent.

Some rules of time travel tell that history is flexible and hence it canbe change but then what about the causality. Causality tell thatcause always produce effect and without cause effect cannot beachieved like if you won’t pull the trigger, bullet will not be fired. Ifyou go to past and killed the person who pull the trigger, there is noquestion of firing but as in the present bullet is fired, this will arisethe question that who fired it? As the cause was pulling the triggerand effect were bullet coming from the gun then this condition statethere only effect was occur and not the cause.

Special relativity believes that if a particle if travelling faster than lightthen it is travelling in the past. If there are two reference frame inwhich A and B is sitting. If A send a single to B which travel fasterthan light and B send a signal to A which travel faster than light toshow that he got his signal then A we receive reply from B before Ahad sent a signal to B. his look impossible because how could aperson on the phone answer before you ask particular question?

The base of the backward time travel is weak and no strong theoryhas been developed to explain it. There need infinite amount ofenergy to accelerate a thing to speed of light and hence it lookimpossible to accelerate such thing a speed more than that of light.No wormholes have been found yet and existence of wormhole isalso somehow impossible. Even if the wormholes found, there nosource of exotic matter in our universe which can stabilisewormholes. The paradoxes and other conspiracies suggest that it isnot possible to travel in pass even if someone claims that he hasinvented the time machine. Hence it will be useless to think aboutthe past but theoretical physicists never stop thinking about it.

Chapter5: The Time Machine

A still from 1960 film ‘The Time Machine’– © nationalgeographic.com

Time machine is a one of the most used topic for discussion in sciencefiction and theoretical physics. Most of the people wrote science fictionnovels and many Hollywood blockbuster films have been produced.

Science truly believes on forward time travel and hence forward timetravel machine is possible but backward time travel seems to beimpossible. No scientific models ever have been developed to explainabout possibility of backward time machine.

Time machine is one of the most discussed and used topic inscience fiction. I saw some movies based on Time machine and timetravel. recently in Bollywood one film was released named ‘LoveStory 2050’ where a lover go to future in 2050 and seek for his lostlove. There are many other movies that are really based on timemachine. There are some movies based on the time machine inwhich they showed that they have invented a time machine throughwhich time travel can be achieved. In the American science fictionfilm “the time machine’, a scientist develops a time machine bymodifying his car.

Time machine is also an interesting topic of science fiction writersand hence there are many novels available. Time machine is a verygood topic to produce documentaries and discuss about it taking fewseminars or general talks. But after all there is no such thing liketime machine existed by now.

Stephen hawking also argue that Time Machine will never beproduce. His stunning idea about the future is worth noting. He saidas we don’t have the time machine so we can’t go back to our pastand show the time machine to the people of that time let say 1009AD. Similarly if our future generation is still lives then they don’t havetime machine because it were then they could come to their pastmean to our present. This also suggests that their future generationalso haven’t invented the time machine. Hence no time machine isever invented and won’t be invented.

Backward time travel is looks rather difficult and impossible butfuture time travel is bit more easy to achieve. As the forward timetravel is took good care of causality, science and direction of time,there are no other issues about it to say it is hypothetical. Actuallyscience also has proved that forward time travel is possible throughthe time dilation. Clocks on the satellites and space shuttles tells thattime travel is possible. Forward time travel can easily achieved by

theory of special relativity and general relativity and hence the futureis very near to us if we develop such system which actually allowsthe traveller to be more affected by time dilation created by SR andGR.

Hence we need to think separately about the machine that travels tothe past and to the future due to their sophistication. Perhaps it ispossible that the time machine which can get anyone to the future isinvented but not the time machine which travels backward in time.Hence there is no way that our future generations can come hereand introduce the time machine.

According to my conventions, if a time machine is allowed to travelto the future it called as ‘α type time machine’ or ‘α time machine’. Ifthe time machine used to travel to the past it called as ‘β type timemachine’ or ‘β time machine’. But if the time machine has both thefacility to travel to the future and to the past then the time machinewill be called as ‘γ type time machine’ or ‘γ time machine’. So let’sdiscuss the theory behind possibility of such time machines.

α Time Machine:

α time machine is a vehicle that not only travels through the spacebut also through the time in forward direction. α time machine isused to travel future only and if traveller change his mind to not tostay in future and go to original time then α time machine will notserve the purpose. α time machine always follow the principle ofcausality and hence past time travel cannot be achieved using it.

According to many philosophers and science fiction writers suggestthat forward time travel machine can take you to the place and timewhere your old self will still alive, so that you can actually meet him

and know what things you have done in the future but in reality αtime machine not used to travel distant universes and follows theparallel universes theorem. Hence you cannot meet your old selfwhen go to the future, because you. The basic principle of α timemachine is to take you to the future of the same universe.

So basically α time machine is science fact and can bemanufactured. α time machine works on the principle of time dilationthrough theory of Special Relativity and General Relativity. Hence αtime machine need to have some relativistic speed or it must creategravity difference between the traveller and the universe in which hewant to travel into the future.

If α time machine has to manufactured on the principle of specialrelativity then it is obvious that it must need a relativistic speed tothat of some reference frame into which the time change need to beallowed. Example of such system would be the Earth and Train. Ifwe suppose that train is time machine and we need to travel to thefuture of earth then it can be easily achieved by travelling in thetrain. But as to account sufficient time dilation to create timedifference of years between train and earth then no such train isavailable right now.

More or less earth’s circumference at equator is about 25000 milesor about 40,000 km and hence a high constant speed train can bemade to travel around it without affecting effect of gravity. But it mustbe noted that fastest speed of a train ever recorded was about 515km/h which is about is 143 m/s while comparing speed of light Ithought I did a mistake about the calculation or source of speed oftrain but believe me this is real. I thought what if a person travels foryear in such train? So I tried to do calculations of special relativity forthis case but my scientific calculator is not able to compute such atiny value and showing that no time dilation had take place. Fromthis we come to conclusion that is it literally impossible to travel

through such train in order to achieve effective time dilation. If Iconsider a jet plane which orbit around earth at the speed of aboutMach 6 which is about 2050m/s at (near sea level and at roomtemperature) then jet pilot hardly get moved in the future by 1second per year which is ridiculous.

LHC accelerate the subatomic like proton and electron at the speedof light. If one day scientist made a tiny clock which can be placedover that high speed particles then perhaps we can see actuallyclock is stopped. The clock will take infinite time of the clock presenton the earth to tick for just one second in it. As no human can beplaced in particle accelerator to travel at the speed of light, conceptof time travel to the future looks impossible for now.

But if you take this more seriously and placed the human travellerinside some sort of accelerator which rounds the earth (I called‘Human Accelerator’) to accelerate him to the speed of light thenhow amazing it would be. A person sitting inside a case which isnothing but the time machine travels at the speed of light through thetunnel of accelerator around the earth. There is no harm travellingat the speed of light. Only at the moment when he get accelerated tospeed of light, he can feel little uncomfortable as we feel when trainget accelerated suddenly but after the speed of train becomeconstant then there is no problem.

But if such system is build where a person can travel inside hollowcylindrical accelerator with speed almost about speed of light thenwe need power to drive it. It amazing to now that HLC almostconsume 800000 megawatt a year which is 2.2 terawatt a day. Thisshows that if a subatomic particle has to travel from subluminalspeed to that of light, it need huge amount of power. Many scientistsalso suggest that it need infinite amount of energy to accelerateanything like a human body to speed of light. Such a infinite amountof energy cannot be stored or continuously supplied and hence aman cannot be accelerated to the speed of light and hence no such‘human accelerator’ can be made.

These numbers are quite huge and seem like no time machine canbe made on the principle of SR but we have alternative method.Albert Einstein through his calculation showed that Time dilation canalso be achieved through General Relativity.

As discussed earlier that if a clock place near the more gravity fieldthen it tick slower than those clocks that placed in lower gravitationalfield compare to it. An example of it could be a clock on the earthtick faster than the clock on the moon or any satellite orbiting earth.More the time dilation, faster you move toward the future. A clock inthe satellite orbiting earth about 36,000km above earth (GSO) ticks

45microsecond faster a day because it is in weak gravitational field.But this is not sufficient to travel to the future. If you went to staysatellite for a month, then upon landing on the earth you will findsame time.

As we discussed about the black holes, if a person stay closeenough to the event horizon then time dilation will be more than theprevious case. Gravity near event horizon is so high that even lighthas to struggle to escape from it. In such gravity if a traveller stayedfor a minute, about thousands of years has been passed on theearth. This means when Hubble space telescopes look at thetraveller’s clock, it will seem like that clock has stopped from ticking.Reversely if traveller sees the clock on the earth, it looks like that itis ticking at infinite rate; perhaps he will not be able to identify thedifferent hand of clock because of high velocity of ticking.

But as we are talking about the time machine, it must be morecompact and safe and hence we cannot allow anything to travel nearblack holes. Also a machine must be produced to minimise theefforts but if the time machine needed to reside on high gravityobject temporarily then it is not comfortable because first we need toprepare launching system so that time machine travel to such hugeplanet or stars and second no such planet or star exist in solarsystem and even if it exist in anywhere in milky way then travellingthat distance is impossible for now.

But in order to travel future using time machine which based on theprinciple of GR, we actually do not need to go to such place wheregravity is intense. We can also achieve forward time travel byplacing time machine on the earth. How can this happen? Theanswer is lie beneath the concept of quantum gravity.

Quantum gravity is field of theoretical physics (for now) whichbelieves that gravity can be explained on quantum level. You knowthat there are four forces in the world viz. Electrical force, Magnetic

Force, Nuclear force and Gravitational force and we are acted by allthese forces every day but there is a problem. First three forced canbe explained on macroscopic level or cosmological level and also onmicroscopic level or quantum level. But there are few problems withgravitational force. Gravitational force can be explained oncosmological level like heavy bodies but not on quantum level.

Quantum gravity attempts to develop scientific model that canreplace both Newtonian gravity and Einsteinium gravity. If Quantumgravity able to build such model which can describe gravity to beeffect produced by some sort of sub atomic particles then all theforces can be explained by the quantum mechanics. The electricforce is created due to attraction and repulsion between subatomicparticles like protons and electron and others. Magnetic force is alsocreated by subatomic particles too. Nuclear force is the interactionbetween subatomic particles and hence all these three forces can beexplained on subatomic level or quantum level. But there is no suchsub atomic particles that can mediate gravitational force.

Quantum gravity suggest that gravitational force can also explainedon subatomic level or quantum level if we assume that there is exista particle in the atom called ‘graviton’. Graviton is hypothetical andmass less particle that mediate gravitational force. If somedayscientist found that such particles exist then maybe we can describethe gravity on microscopic level and build a frame work which candescribe all the fundamental forces together.

We can separate proton, neutron and electrons from their individualatom like a CRT use in the TV which throw the beam of electrons onfluorescent screen where we can see picture. Neutron is used toinitiate the reaction in uranium atom bomb. Protons used in particleaccelerator to study various property of nano scale. If you collect somany electrons then the charge will be so high that will produce

potential difference of thousands of megawatt between earth andyou which can burn you by travelling current through you.

If perhaps one day these particle found to be existed in atom andpeople succeed to separate it from the atom then the artificial gravitycan be created. If someone store very large number of gravitons in abox then everything will get attracted to it or perhaps it will go insideearth by drilling hole in the ground. Hence produce strong gravitydifference on the earth will be so easy and can be used to test GRtheory.

If a person allows staying inside a case that have thick layer ofgravitons and outer layer is made up of some kind of insulationwhich nullify the effect of gravitons as shown below.

.

If such insulation invented for gravitons (like there are insulations forelectric charges and current) then we can create two regions ofdifferent gravity. Place inside of the time machine known as systemwhich is region of high gravitational field, while the universe is theplace outside the insulation in which the change is expected. Henceif traveller sits inside system then his time will appear to be travel

more slowly compare to the time in the universe due to gravitydifference.

If we assume that gravity inside time machine is about 10,000g thentidal force created by such strong gravity will break traveller intopieces. Well this seems dangerous and I don’t think that anyone willdare to experience it for the first time. But if somehow if we able tocancel the forces created by opposite walls of time machine (just likeat the centre of the earth) then perhaps it will be safe ride throughtime machine.

Construction of such α type time machine using gravitons is purelyhypothetical and hence we can only think about time travel ratherthan to experience. Many people in the world claimed that they havecreated time machine or some people argue that their model of timemachine will work well but nothing of it is true. But perhaps one daywill come when present and future will be close enough to see inreality.

β Time Machine:

β time machine is purely theoretical machine which is morecontroversial since from the beginning of relativity. Relativity hatedanything that travels faster than light which β time machine runs onthe principle of FLT (faster than light travel). Relativity tells that noobject can travel faster than light and if then it is travelling inimaginary time in space time. Relativity argue that a tachyon cannotexist and if then they are travelling in the past.

A collaborative experiment between CERN, Geneva and LNGS, Italycalled OPERA experiment took place in Sept. 2011 to study neutrinooscillation. While they experimenting they have found that their

sensors found that neutrinos travelling at the speed faster than light.Many people started believing that faster than light speed ispossible. The result of this experiment were devastating andcontroversial but after experimenting in other labs it was found that itwas instrumental problems in OPERA experiments. Afterinvestigating closely it was found that optical cable was lookbetween GPS receivers and computer. Hence it also known as looscable experiment or Faster-than-light neutrino anomaly.

A story about black hole radiation also makes us thing about theparticles that radiate from the black hole might be travelling fasterthan light. If a black hole is evaporating then it must emits particlesor photons, but how a black hole could can emit radiation that do notallow any radiation to escape. In fact Black holes do not emitradiation rather it produce pair of matter in antimatter (people believein pair of photon and antiphoton) at event horizon. This happens dueto quantum mechanical principle and hence black holes evaporateupon combining antimatter that travels toward it.

After all of this, we found that have no such postulate than can tellprecisely that backward time travel machine or β time travel machineis literally impossible using SR. But would GR allow backward timetravel? Nobody knows about it and calculations tells that gravitationnever create such phenomenon where Pauli’s exclusion principleallow two different atoms at same place with speed differencegreater than speed of light. Hence according to me β time machineis fiction and can’t be made.

But let’s say, hypothetically say that our generations in the futurewith their advanced technology (ultra modern technology) made atime machine which actually works in reality then haven’t they madea dare to go to their past means our present world? If β timemachine really existed in the future then must have come here in our

present time but as there are no travellers from the future there is nohope that β time machine existed and will exist.

But my brain tells me to remain in favour of possibility of β timemachine. What I thought was is there is possibility of a particle thatcan travel faster than speed of light. In case of Big bang about 14billion years ago, when all the matter were compressed in tinysingularity went unstable which lead to imminent explosion burstingall the matter in the space. Some theory does believe that there wasa time when the expansion rate of universe too high called asinflationary model of the universes. What I thought was what if thematter in such explosion travelled faster than speed of light for somefinite time? This will not suggest anything or there is no other way toprove it right here but if we think about, hypothetical speaking thematter travelled in the past for some time. This suggests that bigbang acted like a time machine, for some time. But even if it getsproved then there is no application in the construction of timemachine.

But wormhole theory makes us think about possibility of time travelto the past. Many scientist tell that a wormhole can be used to travelinto the past but the fact is you can only travel into the past of others but not into the world where you are starting your journey.Consider a wormhole joining the earth and centre of our galaxy. Thehigher gravitational field at galactic centre allow low passage of timecompare to us. Hence if the galactic centre and earth formed at thesame time but now there ages is quite different. GR tells thatgalactic centre must be younger than the earth if we neglect timedilation caused by relative speed.

Hence the time near galactic centre must be old compare to the timehere on the earth. Therefore you can travel into the past, like whereis the matter aged 7 billion year old from the big band as we areabout 13 billion year old since from the big band. But if you are

willing to go to owns past like the time where ancient people werebuilding pyramids or Tajmahal then it is not possible usingwormholes. Only one hope of existence of parallel universes whichmight be running at different time rates can serve this purpose. Butas parallel universes or multiverses is madness to think about (forme), I don’t think we will be able to create wormhole even atlaboratory scale to join distance universes.

γ Time Machine:

β time machine is a time machine which can be used to achieveboth past and present. As there is facility of going in both thedirection of the time and hence not to worry about the travelling tothe initial time when you change your mind in the future or in thepast. But as β time machine seems impossible then there is nopossibility that γ time machine will be invented. But if some day βtime travel machine is invented then perhaps it will be possible tocombine both forward and backward time travel system to puttogether effectively forming β time machine.

Theory of Time Machine

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