The Early Universe - Cornell Universityhosting.astro.cornell.edu/.../30CosmoEarlyUniverse.pdf · Lec 30: The Early Universe 19 13T ~ 10 K proton, anti-proton T ~ 6 109 K electron,

Cosmology IV: The Early Universe

Lecture 30

Lec 30: The Early Universe 2

Announcement

Prelim #3 on Wednesday, Nov. 14 In class: 11:15am - 12:05pm (Uris Auditorium)

Will emphasize lectures 22-31 (Galactic Center to Habitability of Worlds)

Closed notes and closed book


Lecture Topics

Problems with the Big Bang

The Early Universe Theory of everything

Inflation

Pair-production

Nucleosynthesis

Pillars of the Big Bang

The Multiverse

The Anthropic Principle

What grade does Cosmology get?


Problems with Big Bang

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

Why is the CMB so uniform?

The Flatness problem

Why are we so close to Wk = 0 (a flat universe)?


What is a Horizon?

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.


The Horizon Problem

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

Earth

28 billion lightyears


The Horizon Problem

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”

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.

100,000 years after the Big Bang the separation would be 10

million lightyears


The Flatness problem

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!).


Epochs of the Universe

From the Big Bang until now, the universe can be viewed as proceeding through different “epochs” (time periods).

Distinguishing characteristics of epochs Each succeeding epoch is cooler and less dense.

Different “forces” and/or “particles” may dominate!


Epochs

10-50 10-30 10-10 1 1010 10-30 10-10 1 1010

Radius (cm)

GUT GUT = E-M, Weak, & Strong forces unified

Planck All four forces unified (Quantum Gravity) 10-45

10-35

10-25

10-15

10-5

105

1015

1032

1027

1022

1017

1012

107

102

Present t

(se

c)

T (

K)


Theory of Everything

Unite gravity with the other fundamental forces. 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).


Epochs

10-50 10-30 10-10 1 1010 10-30 10-10 1 1010

Radius (cm)


Planck All four forces unified (Quantum Gravity)

Hadron

Inflation

“Heavy particles in equilibrium with

the radiation field (Pair Production)

10-45

10-35

10-25

10-15

10-5

105

1015

1032

1027

1022

1017

1012

107

102

Present t

(sec)

T (

K)


Inflation (Part I)

At 10-35 sec after the Big Bang the Universe cooled to 1027 K!

This caused a “phase transition” 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!


Inflation (Part II) This rapid expansion phase is called inflation.

Universe causally connected before inflation CMB will be the same in all directions afterward

Solves Horizon Problem!

Universe becomes flat Because of stretching of space

Solves Flatness Problem!

Space will now be flat due to inflation


Epochs

10-50 10-30 10-10 1 1010 10-30 10-10 1 1010

Radius (cm)



Hadron

Inflation



Lepton Electron, muons, etc. in equilibrium

(Pair Production for low mass particles)

10-45

10-35

10-25

10-15

10-5

105

1015

1032

1027

1022

1017

1012

107

102

Present t

(se

c)

T (

K)


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).


Pair Production 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


T ~ 1013 K proton, anti-proton

T ~ 6109 K electron, positron

T < 109 K no pair production

Pair production (cont’d) 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


Pair Production (cont’d) 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. Still not fully understood


Epochs

10-50 10-30 10-10 1 1010 10-30 10-10 1 1010

Radius (cm)



Hadron

Inflation





Nuclear Formation of light elements

10-45

10-35

10-25

10-15

10-5

105

1015

1032

1027

1022

1017

1012

107

102

Present t

(se

c)

T (

K)


Deuterium

7Li

4He

10-32 10-31 10-30 10-29 10-28 10-12

10-9

10-5

10-1

Present density of baryons (g/cm3)

Fra

ction o

f to

tal m

ass in the u

niv

ers

e

3He

Big Bang Nucleosynthesis Predictions

Observations

Expected from CMB


Epochs Stellar

10-50 10-30 10-10 1 1010 10-30 10-10 1 1010

Radius (cm)



Hadron

Inflation





Nuclear Formation of light elements

Atomic Atoms form, matter photon decoupling

Galactic First Galaxies

10-45

10-35

10-25

10-15

10-5

105

1015

1032

1027

1022

1017

1012

107

102

Present t

(se

c)

T (

K)

Radiation

Dominated

Matter

Dominated

Dark Energy

Dominated


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

In-Class Question








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

In-Class Question

Sky is more uniform

than it should be (not

causally connected)

We are very near a 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

In-Class Question

Sky is more uniform

than it should be (not

causally connected)

We are very near a flat universe (W ~ 1)

Expansion of space due to “phase transition” in the early universe.


Pillars of the Big Bang

Hubble Expansion

Universe expanding in all directions

(necessary but not sufficient)

Cosmic Background Radiation

probes T ~ 1 eV, t ~ 105 years

Light Element Abundances

probes T ~ 1 MeV, t ~ 10 mins

These two

agree!!!

But how did

it all begin? Quantum gravity emergence:

Universe derives from

quantum fluctuations

The seeds of galaxies

cannot be infinitely close

together

Multiverse:

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

Our observable Universe extends

out to a distance of about 42 billion

light-years.

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

Cosmologists make educated

guesses as to what the rest of it

looks like. Observable Universe

Us

42 billion light-years

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.



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.



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?


Theory Report Card

From James Peebles (noted cosmologist), Sci. Am, Jan. 2001

Documents

The Early Universe - Cornell Universityhosting.astro.cornell.edu/.../30CosmoEarlyUniverse.pdf · Lec 30: The Early Universe 19 13T ~ 10 K proton, anti-proton T ~ 6 109 K electron,