the evolution of the universe topic 1: the early universe big bang, black holes, no math 1 big bang,...

The Evolution of the UniverseTopic 1: The Early Universe

Big Bang, Black Holes, No Math

1


ASTR/PHYS 109

Dr. David TobackLecture 19



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Was due Today – L19• Reading:

– (Unit 4)• Pre-Lecture Reading Questions:

– Unit 4: Stage 2• End-of-Chapter Quizzes:

– Chapter 12• Papers:

– Paper 2 Revision (if desired): Stage 1 was due today

– Paper 3: Stage 1 due Monday before class• Honors Papers:

– (Stage 2)– Final paper due on the last day of class



3

Unit 4: Evolution of the Universe

•Big Picture of the Evolution of the Universe: Temperature and Time

•Collisions and how they explain what we see

•The First Three Minutes•After the First Three Minutes



4

Getting Started

We now have a basic understanding of the evidence for the Big Bang

Lets look at the Origin and Evolution of the Universe



5

The Big Bang

•Ideally we’d start telling the story at the Big Bang itself and then move forward•Maybe even talk about what came BEFORE the Big Bang•Unfortunately, we don’t REALLY understand the Bang part or if there even was a bang



6

Best We Can Do

•The best we can do with confidence is start describing the Universe a short time AFTER its beginning

•Start there, then work our way forward and backward in time

What happened RIGHT AFTER the Big Bang?

Then what happened after that? Then what? Etc.



7

The Big Bang Theory

• A Big Bang occurs and the early Universe comes into thermal equilibrium with lots of high energy particles

• Then the Universe gets –Bigger–Older and –Colder

• As time goes by it changes over time–Often we use the word evolves



8

The History of the Universe

Universe expands as time passes

Un

ivers

e c

ools

dow

n a

s t

ime

passes

1 second

10 billion years

10 billion degrees

1 degree

Bigger wavelengths Smaller energies

Smaller Temperature



9

What happens at Different Times?

Particles, nuclei and atoms interact in different ways at early times and later times–Early Times

High Temperature High energy collisions

–Later Times Low Temperature Low energy collisions



10

Various TimesExplain what happens during each of

a number of different periods in time– The VERY early universe– The first three Minutes– The next 300,000 years– The next billion years– ~13 billion years later (now)– The ultimate fate

of the universe?• The first four will take a couple of

lectures

} Chap 14} Chaps 15-17} Unit 6

} Chap 13



11

What Happening?

What happens to the particles at each of these times?

Collisions!



12

CollisionsIn each collision a number of things can

happen• Can create new particles

» Only in high energy collisions– Particles can combine to form

composite objects» Protons, neutrons, atoms etc.

– Composite particles can get broken up– Collisions can transfer energy

Thus, the energy of the particles and what particles CAN exist in nature has a HUGE impact on the evolution of the early universe

Should also say that particles can decay



13

A Brief History of Time• Zero• Well before a

trillionth of a second• One millionth of one

second

• A few minutes

• A few hundred thousand years

• 100 million to 1 billion years

• 9 billion years• ~13.5 billion years

• The Big Bang (?)• Universe comes into

Thermal Equilibrium• Quarks and gluons

combine to form protons and neutrons

• Protons and Neutrons combine to form deuterium and helium nuclei

• Protons and electrons combine to form hydrogen atoms

• Stars and galaxies begin to form

• Our solar system forms• You take ASTR/PHYS

109



14

More detail



Confidence in this Story?

•How do we know this is what happened back then?

•What is the evidence for it?

•Will walk through the reasons next… It’s all about the energy of the collisions…

15



16

The Evolution of the Universe

Overview1. The Early Universe2. The First Three Minutes3. The next 300,000 years4. The next billion years5. The next ~13 billion years, until

todayThe particles have the same

temperature everywhere–Once the Universe comes into Thermal Equilibrium, it doesn’t really depend too much on what came before it



17

Not exactly sure how it all starts… Call it a Big Bang

Artists conception…



18

Before a Millionth of a Second

Lots of free particles at VERY high energies

• Quarks• Photons• Electrons• OthersBack when the Universe was very

small it quickly came into Thermal Equilibrium



19

Before a millionth of a Second

Lots of free particles, all with the same temperature…



20

Quarks can combine in the Early Universe to make a proton, but

are quickly broken apart by high energy photons in the Universe

Quark

Quark

ProtonNuclear Reaction

Quark

qqq Proton

High Energy Photon

Photon + Proton qqq



21

Before a millionth of a second very high energy collisions

• Lots of free quarks to make protons

• Not many protons in the Universe because they are quickly busted apart

Protons-in-The-Early-Universe Bathtub

Particles in the Universe: The Bathtub analogy



22

Time passes

•The Universe Expands and Cools

•Our story starts at a millionth of a second after the Big Bang

•Cool enough that when quarks combine to form a proton or neutron they stay together–Said differently, other particles aren’t energetic enough to bust them apart



23

A Millionth of a Second after the Big Bang

The quarks have combined to form Protons and Neutrons



The Evolving Universe

The Univer

se changes from this to

this

24

Early Universe Later Times



25

Protons after a Millionth of a Sceond

After a millionth of a second

• No more free quarks to make more protons

• Number of protons doesn’t decrease because they aren’t getting busted apart by high energy photons– Don’t exist



26

Very Early Universe is Still Very Complicated

•The other fundamental and composite particles also have a big impact

•One example is a Muon which is (for our purposes) just a heavier version of an electron–Discuss them more in Chapter 19



27

Photons and Muons

At very high energies photons can also turn into

Muon pairs

Muon pairs can turn into Photons

+ -

-+



28

Electron

Anti-ElectronPhoton

Muon pairs can always produce photon pairs

If the photons are energetic enough they

can interact and create muon pairs (or

vice versa) muons, electrons

and photons all have the same temperature

Muons are an Important Part of the Early Universe

Muon

Anti-Muon



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Why Aren’t They Around anymore?

• Most particles, except protons, electrons and photons decay REALLY quickly–Some at 10-24 sec, some 10-10 sec–Muons can live for 10-6 sec

• Can study lots of different types of particles here in experiments on Earth

• Need an accelerator to produce most new ones if you want to study them

• The photons in Today’s Universe aren’t energetic enough to produce new ones



30

Muons can also decay

-

-

Muon

Electron

Neutrino

Neutrino



31

Muons in the Universe

Early Universe Later Times



32

Very Early Universe is Very Complicated

What particles CAN exist determine what’s going on in the Very Early Universe

Problem: We don’t know if we have

discovered all the fundamental particles yet!

• Good reasons to believe there are new ones out that we just haven’t found yet–Need bigger accelerators and/or

Other tools–More on this later also



33

Nuclei in the Early Universe

Proton

Proton

DeuteriumNuclear Reaction

High Energy Photon

A high energy photon can break apart the Nucleus before it can find an electron to create an Atom or find another nucleon to form a bigger nucleus

Proton + Proton Deuterium

Deuterium + Photon Proton + Neutron



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What’s happening at about a millionth of a second after the

Bang?• Lots of protons–photons can’t break them apart

any more• Not many heavy nuclei: every time

one forms a photon busts it apart• Not many atoms: every time one

forms a photon busts it apart• Few “fancy” particles since most

would have decayed already, new ones not being produced



35

Moving towards later times…

•Universe gets bigger, older and colder

•By one hundredth of a second after the Big Bang there are basically no fancy particles left and the story is simpler to tell

•Protons, Neutrons, Electrons, Photons etc.



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Where are we?

Fancy particles gone by this time



37

Electron

PositronLow Energy photon

Electron pairs and interact and

annihilate but photon pairs no longer turn into

particle pairs

No easy way to produce more

positrons

Photons and Electrons at Later Times



38

Approaching the Three Minute Mark

•By three minutes after the bang the Universe is cool enough for Helium nuclei to form (4He) even though it doesn’t happen too much…

•Complicated to produce 4He, lots of intermediate steps that are easier to break apart



39

Nuclei at Lower Temperatures

Proton

Proton


Photon

At these lower energies the photon can’t often break apart the Nucleus

Amount of Deuterium in the Universe rises



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For Next Time– L19• Reading:

– (Unit 4)• Pre-Lecture Reading Questions:

– Unit 4 Revision (if Desired): Will open after Regrades

• End-of-Chapter Quizzes:– Chapter 13 (if we finished Chapter 13, else just 12)

• Papers:– Paper 2 Revision (if desired): Stage 2 due next

Wednesday– Paper 3: Stage 1 due Monday

• Honors Papers:– (Stage 2)– Final paper due on the last day of class



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1 Paragraph Essay Question

Why are there so many more hydrogen and helium atoms in the universe than any other type of atom?

42



Clicker Question

Why is hydrogen the most abundant element in the universe today?

a)It is the lightest elementb)Any heavy elements that

might have been present would have been broken apart by high energy photons in the early universe

c)Both of these contribute43



Clicker Question

Why do the photons in the universe appear to be in thermal equilibrium?

a)Because they all have exactly the same energy

b)They are in thermal equilibriumc)The universe has the same

temperature in all directions, and the photons are just one of the particles in the Universe

44



Clicker QuestionLet's say I have two galaxies in space

and they are exactly stationary relative to each other. What will happen next?

a)Since they are so massive that they will attract each other by gravity and start moving towards each other.

b)Since space-time is expanding, the distance between them will grow as space-time expands so they will start moving away from each other.

c)It depends on the overall distance between them. 45



Clicker Question

What was the last thing a typical photon in the universe (part of the Cosmic Background Radiation) did before we detected it?

a)Broke apart a hydrogen atom

b)Broke apart a helium nucleic)Broke apart a Proton

46



Clicker Question

If the universe were contracting, which of the following would be evidence for it?

a)Distant galaxies would be less red-shifted

b)The Cosmic Background Radiation would have a lower temperature

c)Distant galaxies would be blue shifted

d)The Earth would be getting closer to the Sun

e)Atoms would start shrinking

47



Clicker QuestionQ: Which of the following statements is

MOST correct?a)The photons in the cosmic background

radiation are there because the Universe has been expanding for ~13 billion years

b)The photons in the cosmic background radiation are there because the universe was in thermal equilibrium

c)The photons in the cosmic background radiation are there because photons can exist forever 48



Clicker QuestionIf space-time is expanding, is our galaxy

expanding?a)Yes. Everything in the universe is

moving away from everything else. b)No. It isn't expanding because the

gravitational attraction of masses pulls the galaxy back together again

49



Clicker Question

If space-time is expanding, are atoms expanding?

a)Yes. Everything in the universe is moving away from everything else.

b)No, they aren't expanding because the electric charge attraction and quantum mechanics keep the atoms the same size in space

50



Clicker QuestionIf the universe stated contracting, which

of the following would be evidence for it?

a)Distant galaxies would be less red-shifted

b)The CMB would have a lower temperature

c)We would start seeing distant galaxies have blue shifts

d)The Earth would start getting closer to the Sun

e)Atoms would start shrinking 51



Clicker QuestionWhy do we think that the Universe is an

expansion of space-time and not an explosion? Fix me.

a)Because distant galaxies are moving away from us.

b)Because the farther away a galaxy is, the faster it is moving away

c)Because hydrogen and helium are most of the atoms in the universe

d)Because of the Cosmic Background Radiation

e)Not great... 52



53

For Next Time– L15• Reading:

– Unit 4• Pre-Lecture Reading Questions:

– Unit 3 Revision in CPR (if desired): Stage 1– Unit 4: Stage 1

• End-of-Chapter Quizzes:– If we finished Chapter 12, then Chapter 12 (if not,

Chapter 11)• Papers:

– Paper 1 Revision (if desired): • Stage 2 due Monday March 17 by 11:55PM

– Paper 2: • Stage 2 due Monday March 17 by 11:55PM

– Paper 3:• If we finished Chapter 12, Stage 1 due Monday

before class



54

Prep For Next Time – L19•Note: May change depending on how far we

get in lecture•Reading:

– BBBHNM: All reading through Chapter 15•Reading Questions:

– All reading questions through 15•End-of-Chapter Quizzes:

– If we finished Chapter 13 then end-of-chapter quiz 13 (else just through Chapter 12)



55


get in lecture•Reading:

– BBBHNM: All reading through Chapter 16•Reading Questions:

– All reading questions through 16•End-of-Chapter Quizzes:

– If we finished Chapter 13 then end-of-chapter quiz 13 (else just through Chapter 12)



Papers

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•Papers:–Paper 0 Revision: Still working on re-grades.

–Paper 1: All regrades now done. Let us know if you see any further mistakes.

–Paper 1 Revision: Assignment closed before class. Let us know if you were misgraded

–Paper 2: Working on re-grades–Paper 2 Revision: Posted. New due date is Monday Nov 4th before class

–Paper 3: Posted, text due Wed Nov 6th before class



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Was due for Today – L20• Reading:

– BBBHNM: 15• Pre-Lecture Reading Questions:

– Chapter 15• End of Chapter Quizzes:

– Chapter 12• Papers:

– Paper 0 Revision: Still working on re-grades. – Paper 1: All regrades now done. Let us know if you

see any further mistakes. – Paper 1 Revision: Assignment closed before class.

Let us know if you were misgraded– Paper 2: Working on re-grades– Paper 2 Revision: Posted. New due date is Monday

Nov 4th before class– Paper 3: Posted, text due Wed Nov 6th before class



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Was Due Today – L9•Reading– BBBHNM: All reading through

Chapter 14•Reading Questions:– All reading questions through 14

• eLearning Quizzes:– All quizzes through Chapter 12

•Papers:– Paper 2 calibrations, reviews and

self-assessment due before class– Paper 3 text due in CPR and

turnitin.com due Wednesday!



Tentative Due Dates – L9

•Wednesday March 27th

–Paper 3 text due in CPR and turnitin (2-day extension)

•Monday April 1st

–Paper 3 Calibrations, Reviews and self-assessment due in CPR

–Paper 2 Revisions (if desired) due in CPR and turnitin

59



60


get in lecture•Reading:–BBBHNM: All reading through Chapter 17

•Reading Questions:–All reading questions through 17

•eLearning Quizzes:–If we finished Chapter 13 then end-of-chapter quiz 13 (else just through Chapter 12)

•Papers:–Paper 3 text due in CPR and turnitin.com before class on Tuesday



Prep for Next Time – P17

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• Reading– BBBHNM 14

• Reading questions– Chapter 14

• End-of-Chapter Quizzes– If we finished Chapter 13 then end-

of-chapter quiz 13 (else just 12) • Papers

– Paper 2 Revision: Text due Monday before class

– Paper 3: Text due Monday before class



Prep for Next Time – P18

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• Reading– BBBHNM 14

• Reading questions– Chapter 14

• End-of-Chapter Quizzes– If we finished Chapter 13 then end-of-

chapter quiz 13 (else just 12) • Papers

– Paper 1: Misgraded? Let us know– Paper 2: Misgraded? Let us know.

Revisions due Monday– Paper 3: Due Wednesday



Full set of Readings So Far•Required:–BBBHNM: Chaps. 1-14

•Recommended:–TFTM: Chaps. 1-5–BHOT: Chaps. 1-7, 8 (68-76), 9 and 11 (117-122)–SHU: Chaps. 1-3, 4(77-86), 5(95-114), 6, 7 (up-to-page 159) –TOE: Chaps. 1 & 2

63



Paper 3

What is the evidence for the Big Bang?

•Make sure to read all the instructions in CPR•Due 1 week from today (Wednesday)

– If you want TA feedback, must be submitted by Friday

– After that it’s best-effort by TA’s and first-come-first-served

•Same format at Paper 264



Paper 2 Revision• Will allow Paper 2 revisions• Not happy about some of the quality of

the papers and calibrations– If you are not going to submit a good

paper, then we aren’t going to give you a chance to revise

– If you aren’t doing well with calibrations, we expect you to ask for help

• If this doesn’t change, we won’t do revisions for the third paper

65



66

Prep for Today (Is now due) – L17

• Reading:–BBBHNM 13

• Reading questions:–Chapter 13

• End-of-Chapter Quizzes:–Chapter 12

• Paper Stuff–Paper 1: Misgraded? Let us know–Paper 2: Misgraded? Let us know–Paper 3: Due next Wednesday



67

Prep for Today (Is now due) – L18

• Reading:–BBBHNM 14

• Reading questions:–Chapter 14

• End-of-Chapter Quizzes:–Chapter 12

• Paper Stuff–Paper 1: Misgraded? Let us know–Paper 2: Misgraded? Let us know–Paper 3: Due Wednesday



68

Why not?

• General Relativity can’t be the entire story–Can’t make predictions at

infinitely small sizes• Quantum Mechanics doesn’t work

in curved space time• No good theory of Quantum-

Gravity yet• Universe went through thermal

equilibrium, can’t tell what happened before then

• Some other understanding?



69

The Reading So Far and For Unit 4

Full reading so far for Unit 4:• BBBHNM: Chaps. 1-14• TFTM: Chaps. 1-5• BHOT: Chaps. 1-7, 8 (68-76), 9 and

11 (117-122)• SHU: Chaps. 1-3, 4(77-86), 5(95-

114), 6, 7 (up-to-page 159) • TOE: Chaps. 1 & 2Lecture prep: Turn in on eLearning

Two questions from Chapter 14 you want to know the answer to



Papers 1 and 2• Done with grades for both

– Graded unfairly? Let us know!– Want to do better? We can help!

• Want to revise Paper 2?– CPR now open, due Friday at noon– You are required to do the

calibrations for the new papers– You are required to do the reviews

for your peers– Overall grade will reflect both

original paper and the revision70



Papers 3 and 4• Paper 3: –Due Wed. March 24th before

class–1 week after we finished

Chapter 12–Now open

• Paper 4:–Will be assigned after we start

Chapter 17

71



Other Stuff•Elearning:–Unit 3 now due, Unit 4 in progress

•Make sure you pick up the latest version of the online textbook!!!–Been updating it all semester

72



73

The Reading So Far

Full reading so far:•BBBHNM: Chaps. 1-13•TFTM: Chaps. 1-5•BHOT: Chaps. 1-7, 8 (68-76), 9

and 11 (117-122)•SHU: Chaps. 1-3, 4(77-86),

5(95-114), 6, 7 (up-to-page 159)

•TOE: Chaps. 1 & 2•Seeds (from the web)



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Writing Assignments1. Short Assignment 1

• Revised submissions were due last on Friday. Want to revise again? Talk to me. Still not getting the structure right? Need to get you to the writing center!

2. Short Assignment 2 is posted• Currently due Thursday Oct

29th, one week after we finish Chapter 12

eLearning:Unit 3 now due Need to be working on Unit 4



75

Papers AFTER Paper 2

Two options1. Research Paper

• If you want to do the research paper option you must turn in Stage 0 by Thurs Oct 29th

•Stage 1 due Thurs Nov 5th •Final paper due the last day of

class, Tuesday Dec 8th

2. Two short papers like the first one•One on Black Holes (due mid

Nov)•One on Dark Matter (due last

day of class)



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Part II

In class Quiz for Next Time: What is happening in each region? {



77

14 Second after the bang•At about 14 seconds after the

bang the temperature has dropped to ~3 Billion degrees

•Now low enough temperatures that photons are not energetic enough to produce electron pairs

•Since electrons and positrons can still annihilate, the number of electrons and positrons is dropping rapidly!



78

One Second after the bang

Still 10 billion degrees

too hot for protons and neutrons to bind into a nucleus and stay that way



79

Electron

Positron

High energy photon

Still high enough

energy for electrons, positrons,

and photons to be in

equilibrium between pair production

and annihilation

The Early History of the Universe



80

100th of a Second after the Bang

•100 Billion degrees•A Universe of matter (protons, neutrons, electrons, neutrinos) and photons (also known as radiation)

•All colliding with each other and interacting the way they usually do



81

Very Early Universe is Very Complicated

Above 1.5 Trillion degrees (0.1 seconds after the Big Bang) the presence of all the other “fancy” fundamental particles makes things very complicated

Why aren’t they around any more?



82

Electron

PositronLow Energy Photon

Electron pairs and interact and annihilate but

photon pairs no longer turn into particle pairs Fewer positrons

and electrons

Later Times and Lower Energies



83

Electron

PositronPhoton

Electron pairs can always produce photon

pairs

If the photons are energetic enough they can interact and create

electron pairs

electrons and photons in thermal

equilibrium

Photons and Electrons above 6 Billion Degrees



84

Note…

There are lots of numbers in The First Three Minutes

While they’re really important to the physicists (and why we believe the story), they aren’t important for telling the story…

I’ll try to stay away from them in general, but some of them are important…

Also, TFTM was written in 1988 so the particle physics is fairly out of date…



85

Quarks Combine to Form Nucleons

Quark

Quark

ProtonNuclear Reaction

Quark

qqq Proton



86

Photon Energies at Various Times


Un

ivers

e c

ools

dow

n a

s t

ime

passes

10.8 Trillion Degrees 1 GeV photons (proton mass)

6 Billion Degrees 0.5 MeV photons (electron mass and nuclear binding energy)

1.2 Trillion Degrees 105 MeV photons (muon mass)

3000 Degrees 10 eV photons (atom binding energy)

Second FrameThird Frame



87

Photons

As we’ve seen photons turn out to be one of the most important particles in the universe… focus on them for now

Remember E=MC2

Some numbers: –1 Giga-electron Volt = 1 GeV –1 GeV ≈ Mass of the proton



88

Photon Energies at Various Times


Un

ivers

e c

ools

dow

n a

s t

ime

passes

10.8 Trillion Degrees 1 GeV photons (proton mass)

6 Billion Degrees 0.5 MeV photons (electron mass and nuclear binding energy)

1.2 Trillion Degrees 105 MeV photons (muon mass)

3000 Degrees 10 eV photons (atom binding energy)

Will point

out why each of these

energies/masses

are importa

ntas we

move on



89

•Lecture 1 is 1-36•Lecture 2 is 1-6, 13-16 and then from 36-57

•Lecture 3 is 1-6, 13-16, 51-71



90

Switching The Order of the Syllabus

•New Section 5: The VERY Early Universe and the Fate of the Universe

•New Section 6: Big Objects: The formation of Galaxies, Stars and Black Holes

•New version of the reading order on the Web



91

In class Quiz

What is happening in this region?

{



92

3 Lectures

Today: • Big Picture of the Evolution of the

Universe: Temperature and Time• Collisions and how they explain

what we seeNext Time:• The First Three Minutes• After the First Three MinutesAfter that:• Stellar and Galaxy Formation



93

Why not lots of Heavier Nuclei?

Protons and neutrons Combine to Form a few

helium nuclei

Almost no elements

heavier than helium are produced

Nuclear Physics No stable nuclei with 5 – 8 protons

These decay so quickly its hard to produce heavier nuclei

~90% are hydrogen (~75% by mass)

~10% in helium



94

Another Crappy Word: Reionization

After less than ~ 1 billion years, the first stars form

Formation of the first stars

and Heavy elements

Ultraviolet radiation from the first stars re-ionizes gas in the early universe

Reionization

universe becomes

opaque again



95

TFTM Chapter 4

•Recipe for a Hot Universe•The CMB appears to be ~3

degrees now and leftover from a time when the universe was opaque, 1000 times smaller and hotter than now.

•At really early times, the energy of the photons was SO HIGH that collisions between photons could produce particles!



96

• Question: Why do we believe the Universe went through a period of thermal equilibrium?

• Is this the only way it could have happened?

• Actually, this is an assumption and it makes predictions that are consistent with observations–Uniform everywhere…

• Other models, but none work (yet?)



97

TFTM 3 cont…

•Since the universe was in equilibrium at some point it retains little of the conditions about what happened BEFORE it went into equilibrium



98

Cool pictures

•TCP Page 635: Evolution of the universe

•TCP 22.1 (634). Temperature vs. time

•Feynman diagrams 22.3



99

SHU 6

•When matter and anti-matter meet they annihilate and disappear in a burst of energy

•Evidence for anti-electrons (positrons) in 1932



100

•How could all the matter in the universe exist and be easily detectible if theoretically there should be just as much antimatter around?

•Either the matter and antimatter should have annihilated each other, or we ought to be able to detect as much antimatter in the universe, which we clearly do not



101

Neutron Fraction vs. Time



102

•This



103

PHOTON SCATTERING ELECTRON FROM ATOM

e-

p+

n

PHOTON



104


e-

p+

n

PHOTON



105


e-

p+

n

PHOTON



106


e-

p+

n

ELECTRON ABSORBS ENERGY OF PHOTON TO

ESCAPE



107

PHOTON BREAKING A NUCLEUS

PHOTON (γ)

HELIUM (He)



108


PHOTON (γ)

HELIUM (He)



109


PHOTON (γ)

HELIUM (He)



110


PHOTON (γ)

HYDROGEN

(H)

HYDROGEN

(H)



111

TFTM 3: Cont…

• Quantized energies: photons are particles!

• Don’t want to spend too long on this, but smaller wavelength is the same as high energy! Hard to make high energy (i.e., hard to make small wavelength) photons.

• Random number: It takes 13.6 electron volts to knock an electron out of a hydrogen atom.

• Nuclear interactions are a million times more powerful. Picture?



112

TFTM 3 cont…

•However, since the photons are in thermal equilibrium as the universe expands they stay one wavelength apart, so the wavelength goes up (i.e., they are red-shifted) and the energy goes down to what we see today.



113

•Penzias and Wilson found a radiation temperature of 3 degrees Kelvin, which is what would be expected if the universe had expanded by a factor of a 1000 since the time when the temperature was high enough (3000 degrees K) to keep matter and radiation in thermal equilibrium



114

Blackbody Radiation• Blackbody radiation: "Any body at

a temperature above absolute zero will always emit radio noise produced by thermal motion of electrons within the body.

• Inside a box with opaque walls, the intensity of the radio waves at any given wavelength depends only on the temperature of the walls - the higher the temperature, the more intense the static“

• Need this?



115

•Define nucleosynthesis?



116

•Distribution



117

•Text



118

TFTM 3 cont…

• "This radiation would have survived the subsequent expansion of the universe, only that its equivalent temperature would continue to fall (to cool) as the universe expanded. "

• In other words, the "present universe should also be filled with radiation (photons), but with an equivalent temperature vastly less than it was in the first few minutes"



119

•We still see the glow of the early universe because the light from very distant parts of it would only now be reaching us

•However, the expansion of the universe meant that this light would appear so greatly red-shifted that it would appear as low-energy light



120

TFTM 3 cont…

• At a time in the past, the universe was so dense (lets call it 700,000 years after the big bang) that light couldn't travel very far before it interacted with SOMETHING

• In fact, when it interacted with something like an atom it would typically break it apart

• Thus, atoms couldn’t form and stay formed for very long. Thus, stars (and galaxies and such) could not be created



121

TFTM 3: Continued

• “There must have been a time when the universe was so hot and dense that atoms were dissociated into their nuclei and electrons, and the scattering of photons by free electrons maintained a thermal equilibrium between matter and radiation

• As time passed the universe expanded and cooled, eventually reaching a temperature (about 3000 degrees Kelvin) cool enough to allow the combination of nuclei and electrons into atoms



122

TFTM 3 cont…

• The sudden disappearance of free electrons broke the thermal contact between radiation and matter, and the radiation continued thereafter to expand freely.”

• What happened to the photons since then?

• Individual photons would not be created or destroyed, so the average distance between photons would simply increase in proportion to the size of the universe



123

TFTM 3 Cont…

•Big picture: the differentiation of matter into galaxies and stars could not have begun until the time when the cosmic temperature became low enough for electrons to be captured into atoms.

•Picture of this? Video clip?



124

TFTM 3 cont…

• When electrons are free they “feel” the photons and there is lots of “pressure” on them

• But when they are in atoms they stop feeling the pressure (Quantum Mechanics) and its now easier for atoms to stop getting blown apart and start clumping into stars and galaxies

• All this “shifts” at 3000 degrees K



125

Above 4000 K, most of the energy in the universe was in the photons “radiation dominated” and now it’s matter dominated (i.e., the mass of the proton using E=Mc2) gives us most of the energy in the universe



126

TFTM Chapter 4

•Recipe for a Hot Universe•The CMB appears to be ~3

degrees now and leftover from a time when the universe was opaque, 1000 times smaller and hotter than now.

•At really early times, the energy of the photons was SO HIGH that collisions between photons could produce particles!



127

Stuff

•Stuff about anti-particle and the matter excess…



128

TFTM 4 cont…

• “If the universe in the first few minutes was really composed of precisely equal numbers of particles and anti-particles, they would have all annihilated as the temperature dropped below a billion degrees and nothing would be left but radiation

• However, there is good evidence against this possibility – we are here!” There must have been some excess of electrons over anti-electrons, protons over anti-protons etc…



129

TFTM 4 Cont…

•Conservation laws?•Energy•Electric charge (Maxwell’s

equations)•Baryon number (Why is this

conserved? Is it conserved?)•Lepton number (why is this

conserved? Is it conserved)?•Neutron decay (page 93?)



130

So what?

• Since in the early universe there were LOTS of protons and anti-protons as the universe

• How many more protons than anti-protons? Only 1 part in a billion more.

• However, as the universe cooled and the protons annihilated with the anti-protons all that was left was this small fractional excess… however this small fractional excess is all the stuff in the the universe as we know it now!!!



131

•The same is true for electrons and neutrons.

•Random note: 87% of nuclear particles are protons (not exactly sure why…)



132

Comments about Neutrinos?



133

TFTM 4: Cont…

•Random fact about neutrinos: They interact so “weakly” that in order to have an interaction with ordinary matter we would need it to pass through several light years of lead!!



134

•Put Figure 8 in here somewhere… Page 87



135

•Recipe for a Hot Universe



136

TFTM 4 final

• Recipe for a hot universe:• “Take a charge per photon equal to

zero, a baryon number per photon number equal to one part in a billion, and a lepton number per photon uncertain but small. Take the temperature at any given time to be greater than 3000 degrees of the present radiation background by the ratio of the present size of the universe to the size at that time



137

•Stir well so that the detailed distributions are determined by the requirement of thermal equilibrium. Place in an expanding universe, with a rate of expansion governed by the gravitational field produced by this medium. After a long enough wait, this concoction should turn into our present universe”



138

•How do we deal with this aside?



139

TFTM 4 cont…

• Why don’t we believe there are anti-matter galaxies out there?

• Two reasons:–No signs of anti-matter in the

universe–Most cosmic rays hitting the

earth are matter (rarely antimatter)

–Where are the photons from matter-antimatter collision out in space? They should have a specific energy from the annihilation mass!



140



141

Nuclei in the Early Universe

Proton

Proton


Photon Breaks up Nucleus before it

can find an electron to create an Atom

or find another nucleon to form a

bigger nucleus Free soup of

protons and neutrons

High Energy Photon



142

Atoms in the Early Universe

Proton

Electron

HydrogenAtom

ElectroMagnetic Reaction

High Energy Photon Breaks up Atoms

quickly Free soup of

electrons and protons

High Energy Photon



143

Photons and Electrons

Photons turn into Electron pairs

Electron pairs turn into Photons



144

Electron

PositronGamma-ray photon

Electron pairs and photon pairs interact and annihilate electron and photon Soup

Electron Photon Soup



145

Electron and Photon Soup

• If we have lots of electrons they will interact and create more photons

• If there are lots of high energy photons they will interact and create more electrons

•Eventually the two come into equilibrium. I.e., the market clears



146



147

Fundamental Building Blocks

What does the Universe look like a second after the big bang?

What are the things that happen at different temperatures as the Universe expands and cools?

Many things COULD happen• Quarks could combine to form protons

and neutrons• Protons/neutrons could combine to form

nuclei• Nuclei and electrons could combine to

form atoms– We’ll talk about earlier times and later

times in a future lecture…



148



149

•With these types of interactions dominating what happens how do we explain what we see?



150

•For the first million years radiation and matter were in thermal equilibrium and the universe must have been filled with photons with a temperature equal to that of the material contents of the universe



151

Cosmic Background Radiation

•Its this photon “gas” that is what we see as the Cosmic Background Radiation



152

• Give average energies of the two following photons–10 eV to break apart an atom–1MeV to break apart a nucleus?–0.5 MeV per photon to create an

electron-positron pair• What temperatures would those

correspond to?–What times do these correspond

to?



153

Preview of Particle Physics

•As we said before when two photons collide they can produce a pair of electrons



154

•Feynman diagram!•Question: Why don’t they

produce neutrinos? Too small a production cross section at those energies?

•However, this is a HUGE energy, ~0.5 Million eV or translating this to energy, that’s 6 billion degrees!! (center of the sun is only 15 million degrees)

•Muons here?



155

•More examples: muons Mass of 105 MeV Can be created at temperatures of 1.2 trillion degrees.

•Protons 1 GeV 10.8 trillion degrees

•More high mass particles later!



156

TFTM 4 Cont…

• Again, thermal equilibrium–Rate of production of electrons is

the same as the rate of electrons annihilating with positrons.

• I know the math starts getting bad here… Don’t sweat it… Lets just get the ideas…

• Bottom line: It took about 700,000 years for the universe to cool from 100 million degrees (below electron-pair production) to 3000 degrees (opacity)



157

•Reminder: at 3000 K the average photon energy is just enough to keep atoms from forming (eV energies)



158

Too Complicated For Now…

• In this chapter we’re going to move from RIGHT AFTER the big bang through… awhile later…

• Right after the Big Bang we had (we think) HUGE energy (temperature) and density

• Note: TFTM was written in 1988 so it’s a bit out of date, I’ll point out places where we know more here and we’ll get back to it later. They don’t really affect the story for now



159

Why start at 0.1 Sec?• I’m going to start at 0.1 sec because

that’s the time where I don’t have to worry about the creation of the heavy elementary particles– More on them later…

• At really early times, the energy of the photons was SO HIGH that collisions between photons could produce particles E=MC2 holds here!

• If the energy is high enough to create the rest mass of the particle, then we can create them



160

First Frame Stuff on Neutrinos

•The density is so thick that the neutrinos are constantly interacting –remember they typically need to travel through light years of lead to have, on average, a single interaction



161

Need Size for Anything Yet?



162

A long Aside

As we go back in time and the universe gets hotter and hotter, pairs of photons can start producing the heavy fundamental particles

Thus, what particles CAN exist in nature has a HUGE impact on the evolution of the early universe

Say a little about this…



163

Third Frame and Neutrinos…

•Neutrinos are long longer important to the story…

the evolution of the universe topic 1: the early universe big bang, black holes, no math 1 big bang,...

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