1 Stephen Hawking and the Universe a fascinating story Stephen Hawking and the Universe a...

1 Stephen Hawking and the Universe a fascinating story Stephen Hawking and the Universe a fascinating story Dr. Mounib Eid AUB, Physics Department [email protected] CVSP204: Spring 2014-2015 Spiral Galaxy

The Universe was not in hurry to form the first stars: about 440 million years after creation Dark age 2 380,000 years First atoms formed Microwave Background radiation escaped Timeline of the universe

The scientists does not study nature because it is useful; he/she studies it because he/she delights in it, and he/she delights in it because it is beautiful. If nature were not beautiful, it would not be worth knowing, and if nature were not worth knowing, life would not be worth living. Henry Poincare , My translation 1000000000000000000 km=10 18 km 100,000 light years Spiral Galaxy like ours 3 Who?

4 Short Outline Part I: Picture of the Universe Interesting History Space-Time & Relativity and Reality Part II: Universe Big Bang Inflation Cosmic History Anthropic Principle My aim in this lecture is three-fold: not to tell trivial things Avoid Equations Initiate interests and thinking Part III: Relativity & Black Hole (if time available)

Part I: Picture of the Universe 1. Interesting history Aristotle (340 B.C.) : Earth spherical. He realized that the Moon is eclipsed by the Earth and Earths shadow was round. He thought: Earth stationary, Sun and Moon circle the Earth- he believed in the perfection of the circles. This was a philosophical bias Eratosthenes (276-194 B.C.) : has determined the diameter of the Earth rather accurate (see details at the end of the file}. Human beings were always intelligent. This measurement was done 200 B.C. by this Greek Philosopher 5

Ptolemy: (100-170 A.D.) Almagest Geocentric model of the universe Epicycles and Planetary Motion Seven of these tortoise This model was suggested to resolve the retrograde motion 6 tortis

Heliocentric model of the Universe, 1514 removed Earth from the center, put the Sun instead. He was afraid of the church. Hundred years passed before the idea was take seriously. Great achievement: Sun at center (not the Earth) and at rest. Only the Moon orbits the Earth. Retrograde motion of planets a consequence of the Earths motion relative to a planet. All planets revolve around the sun. Copernicus model represents an exceptional turning point in the history of science and human thought. He once for all displaced us from our centric view of ourselves that our planet is a focal point. Copernicus writings on the heliocentric universe were placed on the Churchs index of prohibited books in 1616. They have been published after 73 years. scientific truth wins always. Well, meanwhile Vatican has observatory! It is a new relation between science and religion Copernicus: Polish (1473-1543): Wait for animation Mars Sun Earth 7

GALILEO GALILEI: Italian (1564- 1642) Has used a self-made telescope in 1604 and his observation led to a breakthrough. Galileo found: Moon shows mountains and craters, Dark spots on the surface of the sun (sunspots). He found that the Sun is rotating Galileo also observed Jupiter. He saw FOUR small moons orbiting Jupiter (invisible to the naked eye). This was another conflict with the Greeks model: The Earth is not the only center of rotation Amazing Galileo published his results, and this was a play with fire. The Church (Inquisition) put him under house arrest in 1633 until his death. Firstly, in 1992, Galileo was rehabilitated by the pope in Rome. A new era began having a healthy relation between science and religion. But why we have problems now??? 8

JOHANNES KEPLER: German: (1571-1630) Found a simple striking structure of the solar system He formulated three laws 1. he orbits of the planets are ellipses with the Sun at one focus 2. An imaginary line connecting the sun to any planet sweeps out equal areas of the ellipse in equal intervals of time. 3. The square of planets orbital period (p) is proportional to the cube of its semi- major axis (a). slow fast P in Earth's years A in unit of 150 million km, Earth-Sun distance Low of harmony 9

Isaac Newton : British, (1642-1727) Philosophiae Naturalis Principia Mathematica Most important single work in physical science 1. Every object remains at rest, or moves at constant speed in a straight line, unless an unbalanced force acts on it. He invented three laws: 2. The acceleration (a) produced by an applied force F on an object of mass m is: a = F/m or F = ma 3. If an object exerts a force on another object, the second objects exerts an equal and opposite force on the first: Action = Reaction Newton was a great physicist He invented the force of gravity 10

Newton laws in action The Sun attracts the planet due to the force of gravity at each position. It forces into a curved path The Sun is by far more massive, the planet tries to go straight (First law), but it becomes accelerated (Second law) Conclusions (so far): The insight through the works by Copernicus, Galileo, Kepler and Newtons laws helped to understand the solar system in a simple way. The motion of the planets is related to basic principles. The planets are not independent of each other as the Greeks thought. 11 Reality is now subject to experience

12 https://www.youtube.com/watch?v=DL1nepxj2F8https://www.youtube.com/watch?v=DL1nepxj2F8. 5:45 min Stimulation to relativity Brian Green, Colombia University, will be talking In short: Green says we have to deal with enormous range in lengths, mas or speed. Our experience is so restricted to a very small region in this 3-dim world Play 4 min

1. Space-Time and Special Relativity Aristotle and Newton both believed in absolute time and that time is separated from space. This is also usually our common sense But our common sense fails when dealing with high speeds if it is a significant fraction of the speed of light, or when dealing with subatomic particles. We need the theory of relativity and quantum mechanics in the hope to understand the Universe Why relativity? It is a striking fact in our universe that the speed of light is universal and given by c=2.99792458x10 8 m/s in vacuum, independent of the motion of the source or the observer. This is experimentally verified by the famous experiment by Michelson and Morley The theory of special relativity (Einstein 1905) is based on two fundamental postulates: 1. Universality of the speed of light 2. The description of physical reality is the same regardless of the constant velocity at which the observer s moving 13

14 Before Einstein, the believe was among physicists that there existed a frame of reference absolutely at rest, in which the aether sat motionless. Only in this frame, the speed of light was exactly c. Then, an observer in a frame can measure the velocity of light. If it is equal c, then her frame was absolutely at rest. Otherwise her velocity is with respect to the aether. Exactly this was the aim of the Michelson-Morley experiment, which has failed to detect any motion relative o the eather. This negative result opened the door to theory of relativity All motion is relative No frame of reference is preferred Einsteins principle of relativity removed the validity of absolute truth. Instead of one frame of reference at rest, any not accelerating frame may be considered at rest.

15 What about space According to relativity, space does not exist per se, it is rather a relationship between physical objects. If there were no objects, there will be no space. Outstretch your arms, put them down at your side. What happens to the space between them? That is really amazing: for Newton, space is still there, but not for Einstein. What about time Einstein's view: it is the relation between events. If there were no events in the universe, there would be no time. When nothing is happening to us, we loose our sense of time. Let us summarize: For Newton, time is what a clock tells. But how was the concept of time before the invention of a clock? Newton: time has an absolute status Einstein: relationship between events. We follow the order of events without necessarlyy agreeing on their durations: Whistle, stamp your feet, clamp you hands. Order is clear, but no agreement on the durations of the events.

16 The constancy of the speed of light has destroyed the Newtonian view of absolute time consequences 1. Time dilation 2. Length contraction 3. E=mc 2 (equivalence between mass and energy) Focusing on time dilation: A moving clock runs slower Suppose a clock is moving at a velocity v=0.866 c Then one hour on the moving clock will be on the stationary (Earth) clock equal to: This means: moving clocks appear to loose time. If the moving observer reaches the speed of light, time comes to standstill for the Earths observer.

17 This sounds like science fiction Reflection Although, the time in the moving frame appears to slow down for the stationary observer, the moving observer does not experience that slowing down. In fact, from the point view of this observe, the stationary frame is in motion. She thinks the time is slowing down in the other frame Strange: each observer believes that the time is dilated in the other frame. How can this be possible? Which clock is telling the correct time? Asking this question means assuming absolute time. But it is so that two observers moving relative to each other do not observe the same things. Example: The meson is an unstable elementary particle, it lives 10 -8 sec in it is frame at rest. But it lives longer when moving with high velocity by

18 This means, the meson projects its self into the future. We reach the point to talk about space travel and time machine Space travel Closest star, alpha Centauri is about 4 light years away (light year is a distance covered by the light traveling one year at a speed of 3x10 8 m/s and covers about 10 13 km. There are very few stars it in a instance of 50 light years, that is 100 light years for a round trip. Hopeless situation for us. But he time dilation helps. Suppose an astronaut can travel at 0.999 c to a star 99.9 light years away Then, in his frame of reference, he will need only: Or he will be aged about 9 yrs when he returned to Earth, where 100 yrs have elapsed

19 In other words, the astronaut has projected himself 91 yrs into the future So, we have a time machine, but not of the type imagined by H.G wells, traveling back an forth. Why not? You cannot travel into the past unless you travel faster than light. If you could, you overtake light signals and you could watch the Egyptians building the pyramids. No one can do that !!

20 Relativity for me is so beautiful, because it challenges my imagination

Future 0 0.2 0.4 0.6 0.8 0.9 1.0 1.2 1.4 1.6 Space-Time Diagram: 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 Time [min] x/(10 11 m) Distance But wait for 8.33 min Earth 150 million km Light propagation Sun Past Presence Not accessible Earth enters the future cone of the Sun x=ct 21 If the Sun would disappear you cannot know it immediately

Light conein 2 dimensions x y In case of 2 space dimension, we hav a light cone time 22

Message to the audience Science has the freedom of thoughts, but also the responsibility of proofs Religion is a believe, does not need a proof There is no terror in a religion, but there are terrorists in each religion 23 In Paris on Jan 2015, one Moslem killed the other, before he died he shouted: I am Ahmed, even this did not help

24 Part II: Universe This part is challenging. But challenging is the best way for learning

Expanding Universe Expansion of space does not affect the size of the material objects such as galaxies and even apples. Circle a galaxy on a balloon, the circle will not expand as the balloon is inflating Important to know this: We can detect the expansion only if our measuring instruments have fixed sizes. Otherwise, if everything changes size, we would not notice the difference interesting Even before Hubbles discovery of the expanding universe, the Russian Alexander Friedman, solving the Einstein's equations, proposed that the galaxies are moving away from each other, He proposed: The universe looks the same in each direction and for all observers wherever they are. How do we understand this? Analogy: If you look at a forest. Nearby, you see the space between the trees. But from far away every square meter is similar to another. 25

Friedmans model begins with zero size followed by expansion. But with what fate? Expanding forever, or crushing? The idea of the Big Bang was born, but not many believed it Fred Hoyle (Scottish) proposed a steady-state universe. But in 1965, a great discovery was made, the discovery of the cosmic Cosmic Microwave Background Radiation (CMBR) It is like in the microwave in your kitchen, but less powerful, and it is partially on your TV when no picture appears It was an accidental discovery by Penzias and Wilson (1965), It is a relic of a hot Big Bang (BB), But, why do we say hot? How do we know? Fingerprint At about 3 min after BB, the universe was a fusion reactor. The percentage of Helium in the Sun is 28%, But Helium cannot be produced in stars except of 3- 4%. Thus most of the helium was made during the first minutes and this needs at least 100 million degrees, really hot. 26

Interesting The relativity theory of Einstein does not provide a true picture about the origin of the Universe. Why? Einsteins theory of general relativity predicts infinite temperature, density and curvature, or singularity in mathematical sense. It is like dividing by zero. Reflection We are not saying that the general relativity is wrong, on the opposite it is beautiful. However, it cannot be applied to the Big Bang. It is after all a classical field theory. First Phase of expansion It is called cosmological Inflation: The Universe expanded by 50 order of magnitude between a time 10 -32 and 10 -30 seconds See Figure next page 27 Project for you: can you talk about MCBR with single temperature without inflation? This is called horiozon problem

28 We have a trouble! It looks as the Universe was expanding faster than light We calm down: The expansion of the universe is the expansion of space itself not the motion of objects through space. Concept of limited speed to the speed of light does not apply here

29 Three indicators in favor of the Big Bang 1.Cosmic microwave background radiation (CMBR) 2.Helium-production 3. Hubble Expansion (receding Galaxies) 1.Cosmic microwave background radiation (CMBR) 2.Helium-production 3. Hubble Expansion (receding Galaxies) Now, the theory of inflation is not well understood, it needs quantum gravity. But the inflation was not completely uniform. This means very small irregularities in temperature may exist. Indeed, the COBE (Cosmic Background Explorer) satellite, and also the WMAP (Wilkinson Microwave Anisotropy Probe) both discover this fluctuation T=(2.726 0.0013) K So it is experimentally verified that the CMBR temperature is This will not heat your food in the microwave more than -270 K The Universe is really cool in every respect So accurtate

30 Reflection: A uniform Universe would be boring. We are lucky to have these irregularities. The Universe having some irregularities mean that some regions would have slightly higher densities. Gravity would help the regions to collapse to form galaxies, stars and planets and finally we came out! If you think about this you could say we are product of quantum fluctuations in the very early Universe. WE ARE PTODUCT OF a GREAT DESIGN If you think about this you could say we are product of quantum fluctuations in the very early Universe. WE ARE PTODUCT OF a GREAT DESIGN

31 Most Challenging: The universe was a cataclysmic quantum event, because of the extremely small scales. To have the ambition of understanding the beginning, a combination of general relativity and quantum mechanics is needed But how does this work? Gravity wraps space and time Relativity easy to wrap space, but how to wrap time? Let us think: If you speak about space and time separately, you can do that in case of low speed and weak gravity But in general, space and time are intertwined. In case of space, you have no problem to go around like around the Earth, since it is not flat. But time is like a railway track, isnt ? If it has a beginning, then someone has to set the train going. But does this go on forever? When quantum mechanics is added, time becomes like another dimension of space, which means that the early inverse is at least four-dimensional. When we say beginning, we look backward to a time beyond our experience, but not beyond our imagination, it is still subject to Mathematics (this sounds very nice)

32 Project: what is Mathematics? More imagination than experience? The physicists have to add to their imagination their experience Very strange If time is another direction of space (say: spacetime), then we get rid of talking about the beginning of time. Simply, you cannot bring it into you experience! Question: Why religions can speak of beginning? Is it because the are not asked to bring it into the physical experience? Back to physics If we can combine general relativity with quantum mechanics, we stop asking about what was before the beginning Asking St Augustine: what was God doing before creating the Universe His Answer: he was preparing hell for you when asking this question

33 Historical Remarks Many believed including Aristotle: Universe must have always existed in order to avoid the problem of how it was set up Others believed: Universe had a beginning and used that to indicate existence of God Any alternative? Hawking: Universe governed by the laws of sciences and does not need to be set in motion by some God. This touches your and my believe !

34 Comments Einsteins general relativity predicts that space-time begins at Big Bang singularity. But this is a classical field theory. Then, what is the role of quantum mechanics? The problem is due to the very strong gravitational field Questions: Why the Early Universe so hot? Why the Universe so uniform on large scale? Why does it look the same in all directions and having the same temperature? we have Galaxies and stars owing to density fluctuations. What is their origin? Challenging thoughts How were the initial conditions been chosen? By God the omnipotent? But why God did choose to let the Universe evolve according to laws we undestand? There is a clear order in the Universe. Is that order divinely inspired? diveinly We arrive to talk about the Anthropic principle We see the Universe the way it is, because we exist- a problematic statement

35 Two versions of the anthropic principle: weak version and strong version Weak version: In a Universe that is large or infinite in space and/or time the conditions necessary for the development of intelligent life will occur in certain regions limited in space & time. No surprise It is like a rich person living in a wealthy area not seeing poverty Strong version: Either many different universes, or many different regions in a single universe. Our own universe would have the right conditions for the development of intelligent life. The strong statement is: Asking: Why the universe is the way we see it? Answer: if it were different, we would not exist. Well, we know that the fundamental constants (strength of the forces) are fine-tuned. Still there are objections to the strong version.

36 In what sense can many universes exist? We cannot know what happened in them. We tend to remove them from the theory If there are different regions of the same universe, the law of sciences would be the same in each region, so that we can move from one region to another. But the initial conditions would be different, and we are back to the weak version of the anthropic principle Another argument against the strong version is: It runs against the tide of the history of science. All what we have discovered from the geocentric model to the modern picture and all what is existing, hundred billion of galaxies, all this is for our sake? I hope you enjoyed the lecture. We are ready for your questions

Implication of the first postulate: Imagine you are in a spaceship moving toward a flashlight. You could be moving at 90% of the peed of light, you will measure the speed of light for the flashlight, as your spaceship were motionless. Implication of the second postulate: Suppose you were inside a railroad car moving due north in a straight line at 100 km/h. Any measurement you make inside the car, for example how long you can stand on one leg, will be the same as if the car is moving in any other direction or any other speed or not moving at all. Striking consequence of relativity Equivalence of energy and mass: E=mc 2 : energy of a moving object adds to its mass. This means it becomes harder and harder to increase its speed. Any normal object is forever confined by relativity to move at a speed less than the speed of light. Only light can travel at that speed Our ideas of space and time received a shock. Relativity put an end to the idea absolute time, every observer has own clock carried with him. And moving clocks run slower: Time dilation 1 2 37

Part III: Relativity and Black Holes The most dramatic prediction of general theory of relativity is the existence of black holes. As the matter is compressed to extreme densities the strength of gravity at the surface of the sphere increases dramatically. Consequence.

39 Gravitational bending of light (experimentally tested) How come that this bending happens at all? Newtonian description of gravity cannot be applied to light, because it has no mass (it is pure energy). But Einsteins description of gravity gives the answer. (see next page)

Curved spacetime around a black hole: no escape even for light. Gravity in the Einsteins theory is affecting the geometry of space, it corves the space in the vicinity of the mass

Black hole in general relativity The event horizon: or the entrance to the end of time. Doest the time flow in the hell? A B 12:00 p.m. Cross sections In a collapsing star Singularity Observer A: Never sees the light emitted at 12:00 p.m., when observer B enters the event horizon. His light signal propagates along the edge of the cylinder Observer B: his time runs normal. However he/she disappears for ever beyond the event horizon you astronaut Schwarzschlds radius

42 Psart I: details At the time one assumed that the distance Aswan-Alexandria is 5000 stadia, where one stadium is 0.16 km, or 800 km=5000x0.16 km. So, 800x50 km=40000 km very close to the diameter of the Earth These people had no electric lights and Iphones, but they were smart. To be smart, you should have a functioning brain not only a functioning cell phone.

43 Cosmic History You see 3 symmetry breakings to separate the forces 1 2 3

44 Some references: 1.A Brief History of Time S. Hawking 1988 Check chap. 1,2,3 and 8 (not easy to read) 2. The Grand Design S. Hawking and L. Mlodinow, 2010 3. Universe Freedman, Keller and Kaufmann 9 th edition, Freeman 2011 end chapters in the book

45 https://www.youtube.com/watch?v=8l_AqyHWxYMhttps://www.youtube.com/watch?v=8l_AqyHWxYM. All Israel 200 atomic bombs and more, cannot stop the desire for life of these young Palestinians Watch and wonder

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