Transcript of 1 Stephen Hawking and the Universe a fascinating story Stephen Hawking and the Universe a...
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- 1 Stephen Hawking and the Universe a fascinating story Stephen
Hawking and the Universe a fascinating story Dr. Mounib Eid AUB,
Physics Department meid@aub.edu.lb CVSP204: Spring 2014-2015 Spiral
Galaxy
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- 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
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- 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?
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- 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)
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- 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
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- 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
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- 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
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- 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
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- 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
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- 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
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- 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
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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
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- 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
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- 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.
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- 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.
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- 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.
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- 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
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- 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
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- 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 !!
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- 20 Relativity for me is so beautiful, because it challenges my
imagination
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- 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
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- Light conein 2 dimensions x y In case of 2 space dimension, we
hav a light cone time 22
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- 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
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- 24 Part II: Universe This part is challenging. But challenging
is the best way for learning
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- 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
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- 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
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- 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
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- 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
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- 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
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- 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
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- 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)
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- 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
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- 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 !
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- 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
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- 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.
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- 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
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- 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
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- 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.
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- 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)
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- 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
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- 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
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- 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.
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- 43 Cosmic History You see 3 symmetry breakings to separate the
forces 1 2 3
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- 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
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- 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