Download The Early Universe

Cosmology IV: The Early Universe
Lecture 30
Announcement
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Prelim #3 on Wednesday, Nov. 14
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In class: 11:15am - 12:05pm (Uris Auditorium)
Will emphasize lectures 22-31 (Galactic Center to
Habitability of Worlds)
Closed notes and closed book
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Lecture Topics
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Problems with the Big Bang
The Early Universe
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Theory of everything
Inflation
Pair-production
Nucleosynthesis
Pillars of the Big Bang
The Multiverse
The Anthropic Principle
What grade does Cosmology get?
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Problems with Big Bang
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The Big Bang described thus far is very
successful in may aspects.
However, there are two major problems that
need to be addressed
The Horizon problem
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Why is the CMB so uniform?
The Flatness problem
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Why are we so close to Wk = 0 (a flat universe)?
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What is a Horizon?
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Our horizon (in a Cosmological sense) is the
maximum distance we can see out to in the Universe.
More generally, for any point in the Universe, the
horizon is the maximum distance from which light
could have reached that point, within the age of the
Universe.
Nothing outside your horizon can have any effect on
you, because it has never been in causal contact.
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The Horizon Problem
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Looking at one part of the sky and looking in the
opposite direction radio telescopes see the same
CMB temperature to 1 part in 100,000
Suppose the Universe is 14 billion years old, then the
two directions are separated by 28 billion lightyears
28 billion lightyears
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The Horizon Problem
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Looking at one part of the sky and looking in the
opposite direction radio telescopes see the same
CMB temperature to 1 part in 100,000
Suppose the Universe is 14 billion years old, then the
two directions are separated by 28 billion lightyears
Thus they should not be “causally connected”
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That is, they don’t know about each other
The two regions should not have the same temperature
In the past the situation is even worse.
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100,000 years after the Big Bang the separation would be 10
million lightyears
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The Flatness problem
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Measurements of the curvature of the Universe indicate it is
almost exactly flat.
However, both the average density and critical density change
with time.
In the past, right after the BIG BANG if the average density was
slightly larger or smaller we would have a very obviously closed
or open Universe.
At the beginning of the Big Bang the density would have to be
very close to the critical value (1 part in 1060!).
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Epochs of the Universe
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From the Big Bang until now, the universe can
be viewed as proceeding through different
“epochs” (time periods).
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Distinguishing characteristics of epochs
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Each succeeding epoch is cooler and less dense.
Different “forces” and/or “particles” may dominate!
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Present
1015
102
105
107
10-5
1012
10-15
1017
10-25
1022
10-35
1027
Epochs
GUT
Planck
1032
T (K)
t (sec)
10-45
GUT = E-M, Weak, & Strong forces unified
All four forces unified (Quantum Gravity)
1010
1 10-10 10-30 10-50 10-30 10-10 1 1010
Radius (cm)
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Theory of Everything
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Unite gravity with the other
fundamental forces.
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Merging of gravity with quantum
mechanics and other forces.
We don’t have a theory yet but
the most promising ones
involves “string theory” and
“higher dimensions”
String Theory suggests there
are 11 dimensions (10 spatial
+ 1 time).
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Present
1015
102
105
107
10-5
1012
10-15
1017
10-25
1022
Epochs
“Heavy particles in equilibrium with
the radiation field (Pair Production)
Hadron
t (sec)
10-45
1027
Inflation
GUT
GUT = E-M, Weak, & Strong forces unified
Planck
1032
T (K)
10-35
All four forces unified (Quantum Gravity)
1010
1 10-10 10-30 10-50 10-30 10-10 1 1010
Radius (cm)
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Inflation (Part I)
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At 10-35 sec after the Big Bang
the Universe cooled to 1027 K!
This caused a “phase
transition”
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Like ice changing into water
The strong force split from the
other forces releasing
tremendous amounts of
energy
The Universe expanded by a
factor of 1050 in 10-33 sec!
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Inflation (Part II)
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This rapid expansion phase is called inflation.
Universe causally connected before inflation
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CMB will be the same in all directions afterward
Solves Horizon Problem!
Universe becomes flat
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Because of stretching of space
Space will now be flat due to inflation
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Solves Flatness Problem!
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Present
1015
102
105
107
10-5
1012
10-15
1017
Epochs
Lepton
10-25
Electron, muons, etc. in equilibrium
(Pair Production for low mass particles)
“Heavy particles in equilibrium with
the radiation field (Pair Production)
1022
Hadron
t (sec)
10-45
1027
Inflation
GUT
GUT = E-M, Weak, & Strong forces unified
Planck
1032
T (K)
10-35
All four forces unified (Quantum Gravity)
1010
1 10-10 10-30 10-50 10-30 10-10 1 1010
Radius (cm)
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What is Anti-Matter?
A particle and its anti-particle have the
same mass but opposite charge.
 Many antiparticles can be created in
laboratories.
 Positrons (anti-electrons) are used
routinely in medicine to imagine internal
organs using Positron Emission
Tomography (PET).
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Pair Production
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Particle-antiparticle annihilation occurs when
matter and anti-matter destroy each other in a
burst of g-rays.
The reverse is called pair production:
2 g  particle + anti-particle
Pair production happens spontaneously, and
depends upon the temperature.
 Higher T  more energetic photons
 more massive particles produced
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Pair production (cont’d)
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In the early universe temperatures were high
enough for pair production to take place.
There was a “sea” of photons, particles and
anti-particles.
The “threshold” temperatures are:
Temperature
Particles Pairs
T ~ 1013 K
proton, anti-proton
T ~ 6109 K
electron, positron
T < 109 K
no pair production
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Pair Production (cont’d)
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Above these threshold temperatures,
particles and anti-particles will exist in
equilibrium (as many created as destroyed).
As the universe expands and the “plasma”
cools, we expect particles and anti-particles
to annihilate one another leaving just
photons.
This didn’t happen! We are here.
This is because there are asymmetries
between matter and anti-matter.
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Still not fully understood
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Present
1015
102
105
107
10-5
1012
10-15
1017
Epochs
Formation of light elements
Nuclear
Lepton
10-25
Electron, muons, etc. in equilibrium
(Pair Production for low mass particles)
“Heavy particles in equilibrium with
the radiation field (Pair Production)
1022
Hadron
t (sec)
10-45
1027
Inflation
GUT
GUT = E-M, Weak, & Strong forces unified
Planck
1032
T (K)
10-35
All four forces unified (Quantum Gravity)
1010
1 10-10 10-30 10-50 10-30 10-10 1 1010
Radius (cm)
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Fraction of total mass in the universe
Big Bang Nucleosynthesis Predictions
10-1
4He
Observations
10-5
3He
7Li
10-9
Deuterium
Expected from CMB
10-12
10-32
10-31
10-30
10-29
10-28
Present density of baryons (g/cm3)
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Present
Dark Energy
Dominated
Stellar
Epochs
Galactic
First Galaxies
1015
102
Matter
Dominated
105
107
Atomic
Atoms form, matter photon decoupling
Nuclear
Formation of light elements
Lepton
10-5
1012
10-15
1017
10-35
t (sec)
10-45
1022
1027
Inflation
“Heavy particles in equilibrium with
the radiation field (Pair Production)
Hadron
GUT
GUT = E-M, Weak, & Strong forces unified
Planck
1032
T (K)
10-25
Radiation
Dominated
Electron, muons, etc. in equilibrium
(Pair Production for low mass particles)
All four forces unified (Quantum Gravity)
1010
1 10-10 10-30 10-50 10-30 10-10 1 1010
Radius (cm)
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In-Class Question
What were two problems with the Big Bang theory?
a) Horizon and Bigness
b) Flatness and Expansion
c) Expansion and Bigness
d) Horizon and Flatness
e) There were no problems
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In-Class Question
What were two problems with the Big Bang theory?
a) Horizon and Bigness
b) Flatness and Expansion
Sky is more uniform
than it should be (not
c) Expansion and Bigness
causally connected)
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d) Horizon and Flatness
We are very near a
e) There were no problems
flat universe (W ~ 1)
What is the answer to these problems?
a) Cosmic string theory
b) Inflation
c) Accelerating Universe
d) All of the above
e) None of the above
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In-Class Question
What were two problems with the Big Bang theory?
a) Horizon and Bigness
b) Flatness and Expansion
Sky is more uniform
than it should be (not
c) Expansion and Bigness
causally connected)

d) Horizon and Flatness
We are very near a
e) There were no problems
flat universe (W ~ 1)
What is the answer to these problems?
a) Cosmic string theory
Expansion of space due
 to “phase transition” in
b) Inflation
the early universe.
c) Accelerating Universe
d) All of the above
e) None of the above
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Pillars of the Big Bang
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Hubble Expansion
Universe expanding in all directions
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Cosmic Background Radiation
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probes T ~ 1 eV, t ~ 105 years
Light Element Abundances
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probes T ~ 1 MeV, t ~ 10 mins
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These two
agree!!!
But how did
it all begin?
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Quantum gravity emergence:
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Universe derives from
quantum fluctuations
The seeds of galaxies
cannot be infinitely close
together
Multiverse:
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Maybe we are one of many
universes continuously
being created
As above or intersection of
higher dimensional spaces
Laws of physics may be
different in each universe
See Michal Turner article in
Sep 2009 Scientific American
The Multiverse
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Our observable Universe extends
out to a distance of about 42 billion
light-years.
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Our cosmic horizon, which
represents how far light has been
able to travel since the big bang
(as well as how much the universe
has expanded in size since then).
Assuming that space does not just
stop there and may well be
infinitely big
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Cosmologists make educated
guesses as to what the rest of it
looks like.
Us
42 billion light-years
Observable Universe
See Scientific American - Aug. 2011
article by George Ellis
Level 1 Multiverse: Plausible:
Our volume of space is a
representative sample of the whole.
Distant alien beings see different
volumes‚ but all of these look
basically alike but we can’t see each
other.
Level 2 Multiverse: Questionable
Sufficiently far away, things look
quite different from what we see.
The laws of physics would differ
from bubble to bubble, leading to an
almost inconceivable variety of
outcomes.
The Anthropic Principle
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Philosophical position, rather than hard
science. (Not universally agreed on.)
Essential it states “we are here, so the
Universe must have formed in such a way as
to allow life”.
Can have powerful reasoning implications.
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The Anthropic Principle
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If any of a number of fundamental constants
were altered just slightly, the Universe
wouldn’t be capable of sustaining life.
It may seem that the Universe is very well
suited to us, but if it wasn’t then there
wouldn’t be anyone around to ask the
question, why is the Universe the way it is?
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Theory Report Card
From James Peebles (noted cosmologist), Sci. Am, Jan. 2001
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