Big Bang, Black Holes, No Math ASTR/PHYS 109 Dr Big Bang, Black Holes, No Math ASTR/PHYS 109 Dr. David Toback Lectures 25, 26 & 27

Was due Today – L26 Reading: (Unit 4) Pre-Lecture Reading Questions (PLRQ) Unit 4: Grades posted soon Unit 4 Revision (if desired): Due Wednesday before class End-of-Chapter Quizzes: Chapter 12 parts A&B Papers Paper 2: Grades posted. Let us know if you believe you were misgraded Paper 2 Revision (if desired): Due Friday March 30 in TurnItIn Paper 3: Draft for TA (if desired): Friday at 11:55PM. Text: Due Wed March 28th

Was due Today – L27 Reading: (Unit 4) Pre-Lecture Reading Questions (PLRQ) Unit 4: Grades posted soon Unit 4 Revision (if desired): Due Friday before class time (no class) End-of-Chapter Quizzes: Do worksheet on class homepage to help prepare for EOC quizzes Does not need to be turned in Chapter 12 parts A&B Papers Paper 2: Grades posted. Let us know if you believe you were misgraded Paper 2 Revision (if desired): Due Friday March 30 in TurnItIn Paper 3: Text: Due Wed March 28th Reviews: Due Monday April 2nd Back-evaluations: Due Wed April 4th

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 Photons as “Bullies of the Universe” and “Bathtubs” of particles The First Three Minutes After the First Three Minutes

We now have a basic understanding of the evidence for the Big Bang Getting Started We now have a basic understanding of the evidence for the Big Bang Lets look at the Evolution of the Universe after the Big Bang in more detail

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

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.

The Big Bang Theory A Big Bang occurs and the early Universe has the same temperature everywhere and 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

The History of the Universe 10 billion degrees 1 degree Universe cools down as time passes 1 second 10 billion years Bigger wavelengths Smaller energies Smaller Temperature Universe expands as time passes

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

} Chap 13 } Chap 14 Various Times Explain 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 13 } Chap 14 } Chaps 15-17 } Unit 6

Collisions! What happens to the particles at each of these times? What Happening? What happens to the particles at each of these times? Collisions!

Collisions In 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

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 (?) All parts of the visible universe come to have the same temperature everywhere 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

Photons: The Bullies of the Universe In many ways, the history of the universe is the history of the energy of the photons Early Days: Energetic photons break apart anything formed (Bullies!) Later Days: They lose their ability to break things apart (no longer bullies!)

More detail Photons no longer energetic enough to bust apart protons Photons no longer energetic enough to bust apart nuclei Photons no longer energetic enough to bust apart atoms

Confidence in this Story? Why do we think it happened this way? Will walk through the reasons next… It’s all about the energy of the collisions…

The Evolution of the Universe Overview The Early Universe The First Three Minutes The next 300,000 years The next billion years The next ~13 billion years, until today The particles have the same temperature everywhere Once the Universe has the same temperature everywhere, only the details really depend on what came before it

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

Well before a Trillionth of a Second Particles at VERY high energies Small wavelengths What is now the visible universe was so small back then that it had the same temperature everywhere Which is why we see it having the same temperature everywhere now

Before a Millionth of a Second All particles will be FREE Composite particles would be broken apart No protons, neutrons or heavy nuclei No atoms Only FUNDAMENTAL particles Quarks Photons Electrons Muons Other from Chapter 3, plus others

Before a millionth of a Second Lots of free particles, same temperature everywhere

Quarks can combine in the Early Universe to make a proton, but are quickly broken apart by high-energy photons in the Universe qqq  Proton Photon + Proton  qqq Quark Nuclear Reaction Proton High Energy Photon Quark Quark

Particles in the Universe: The Bathtub Analogy 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

Time passes The Universe Expands and Cools Easier to tell the story after 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 anymore

A Millionth of a Second after the Big Bang The quarks have combined to form Protons and Neutrons

The Universe changes from this to this The Evolving Universe Early Universe The Universe changes from this to this Later Times

Protons 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 High enough energy photons don’t exist anymore

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

Photons and Muons At very high energies photons can also turn into Muon pairs + - Muon pairs can turn into Photons + -

Muons are an Important Part of the Early Universe Electron Anti-Electron Photon Muon Anti-Muon 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

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

Muon decay Electron - Neutrino Muon - Neutrino

Muons in the Universe Early Universe Later Times

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

Nuclei in the Early Universe Proton Proton + Proton  Deuterium Deuterium + Photon  Proton + Neutron Nuclear Reaction Deuterium A high energy photon can break apart a nucleus before it can find an electron to create an atom or find another nucleon to form a bigger nucleus High Energy Photon Proton

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 one formed gets quickly busted apart Not many neutral atoms Every one formed quickly gets busted apart Very few other fundamental particles Old ones would have decayed already, new ones not being produced

Moving towards later times… Universe gets bigger, older and colder By one hundredth of a second after the Big Bang there are basically no unstable fundamental particles left and the story is simpler to tell Protons, Neutrons, Electrons, Photons etc.

One hundredth of a second Fancy particles gone by this time Photons can break up nuclei and neutral atoms, but not protons

Photons and Electrons at Later Times Electron Positron Low Energy photon Electron pairs interact and annihilate but photon pairs no longer turn into particle pairs No easy way to produce more positrons

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

Nuclei at Lower Temperatures Proton Nuclear Reaction Deuterium At these lower energies the photon can’t often break apart the nucleus  Amount of Deuterium in the Universe rises Photon Proton

Lecture on Chapter 13 now complete

Chapter 13 and 14 worksheet One of the most important things to understand is How much of each type of “stuff” is found in the universe during its History (and why) Since many people struggle with this (especially for the EOC quizzes) we have made a handout and an Excel worksheet to help you On the main 109 page http://people.physics.tamu.edu/toback/109/ under “Chapter 13 and 14 Materials” Make sure you enter in “Negligible” or “Abundant” in all boxes There is feedback for you if you didn’t enter in things correctly

For Next Time – L25 Reading: (Unit 4) Pre-Lecture Reading Questions (PLRQ) Unit 4: Was due before class End-of-Chapter Quizzes: Chapter 13 parts A,B,C and D (if we finished Chapter 13, else just Chapter 12 parts A&B) Papers Paper 2: Text: Was due already in both TurnItIn and Peerceptiv Reviews: Was due Monday night. Back-evaluations: Due tonight Paper 3: Draft for TA (if desired): Friday at 11:55PM. Text: Due Wed March 28th

For Next Time – L25 Reading: (Unit 4) Pre-Lecture Reading Questions (PLRQ) Unit 4: Was due before class End-of-Chapter Quizzes: Chapter 12 parts A&B Papers Paper 2: Text: Was due already in both TurnItIn and Peerceptiv Reviews: Was due Monday night. Back-evaluations: Due tonight Paper 3: Draft for TA (if desired): Friday at 11:55PM. Text: Due Wed March 28th

For Next Time – L26 Reading: (Unit 4) Pre-Lecture Reading Questions (PLRQ) Unit 4: Grades posted soon Unit 4 Revision (if desired): Due Wednesday before class End-of-Chapter Quizzes: Do worksheet on class homepage to help prepare for EOC quizzes Does not need to be turned in Chapter 13 parts A,B,C and D (if we finished Chapter 13, else just Chapter 12 parts A&B) Papers Paper 2: Grades posted. Let us know if you believe you were misgraded Paper 2 Revision (if desired): Due Friday March 30 in TurnItIn Paper 3: Draft for TA (if desired): Tonight at 11:55PM Text: Due Wed March 28th

For Next Time – L26 Reading: (Unit 4) Pre-Lecture Reading Questions (PLRQ) Unit 4: Grades posted soon Unit 4 Revision (if desired): Due Wednesday before class End-of-Chapter Quizzes: Do worksheet on class homepage to help prepare for EOC quizzes Does not need to be turned in Chapter 12 parts A&B Papers Paper 2: Grades posted. Let us know if you believe you were misgraded Paper 2 Revision (if desired): Due Friday March 30 in TurnItIn Paper 3: Draft for TA (if desired): Tonight at 11:55PM Text: Due Wed March 28th

For Next Time – L27 Reading: (Unit 4) Pre-Lecture Reading Questions (PLRQ) Unit 4: Grades posted soon Unit 4 Revision (if desired): Due Friday before class time (no class) End-of-Chapter Quizzes: Do worksheet on class homepage to help prepare for EOC quizzes Does not need to be turned in Chapter 13 parts A,B,C and D (if we finished Chapter 13, else just Chapter 12 parts A&B) Papers Paper 2: Grades posted. Let us know if you believe you were misgraded Paper 2 Revision (if desired): Due Friday March 30 in TurnItIn Paper 3: Text: Due Wed March 28th Reviews: Due Monday April 2nd Back-evaluations: Due Wed April 4th

For Next Time – L27 Reading: (Unit 4) Pre-Lecture Reading Questions (PLRQ) Unit 4: Grades posted soon Unit 4 Revision (if desired): Due Friday before class time (no class) End-of-Chapter Quizzes: Do worksheet on class homepage to help prepare for EOC quizzes Does not need to be turned in Chapter 13 parts A,B,C and D Papers Paper 2: Grades posted. Let us know if you believe you were misgraded Paper 2 Revision (if desired): Due Friday March 30 in TurnItIn Paper 3: Text: Due Wed March 28th Reviews: Due Monday April 2nd Back-evaluations: Due Wed April 4th

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

End of Lecture

Clicker Question Which of the following is the best ranking for the speeds (from fastest to slowest) at which galaxies A, C, and D would be moving away from an observer in galaxy B? A > C > D D > A > C C > D > A D > C > A D A C B E Early Universe Universe Some Time Later

Clicker Question For the most distant galaxies, which is true? Most of the red-shift of their spectral lines is because they are moving very fast through space Most of the red-shift of their spectral lines is because space is expanding

Clicker Question Let's say I have two galaxies in space and they are exactly stationary relative to each other. What will happen next? Since they are so massive that they will attract each other by gravity and start moving towards each other. Since space-time is expanding, the distance between them will grow as space-time expands so they will start moving away from each other. It depends on the overall distance between them.

Clicker Question Let’s say you were the person observing the galaxies, but each other person in the room were a galaxy. Which person in the room is moving away from you most quickly? Back left Back right Front left Front right

Clicker Question Why is hydrogen the most abundant element in the universe? It is the lightest element Other elements were broken apart by high energy photons in the early universe Both of these contribute

Clicker Question What was the last thing a typical photon in the universe (part of the Cosmic Background Radiation) did before we detected it? Broke apart a neutral hydrogen atom Broke apart a helium nuclei Broke apart a Proton

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

What is the simplest evidence that we live in an expanding universe? Short Answer Quiz What is the simplest evidence that we live in an expanding universe?

Short Answer Quiz What is the evidence that the universe is an expansion of space and not an explosion of stuff into space?

Clicker Question If the universe were contracting, which of the following would be evidence for it? Distant galaxies would be less red-shifted The temperature of the Cosmic Background Radiation would be dropping Distant galaxies would be blue shifted

Clicker Question Why do the photons in the universe appear to be in thermal equilibrium? Because they all have exactly the same energy They are in thermal equilibrium The universe has the same temperature in all directions, and the photons are just one of the particles in the Universe

Clicker Question Q: Which of the following statements is MOST correct? The photons in the cosmic background radiation are there because the Universe has been expanding for ~13 billion years The photons in the cosmic background radiation are there because the universe was in thermal equilibrium The photons in the cosmic background radiation are there because photons can exist forever

Clicker Question If space-time is expanding, is our galaxy expanding? Yes. Everything in the universe is moving away from everything else. No. It isn't expanding because the gravitational attraction of masses pulls the galaxy back together again

Clicker Question If space-time is expanding, are atoms expanding? Yes. Everything in the universe is moving away from everything else. No, they aren't expanding because the electric charge attraction and quantum mechanics keep the atoms the same size in space

Clicker Question Why can electrons, positrons, and photons be in thermal equilibrium with each other, even if they are creating and annihilating one another? They can be the same temperature They are in thermal contact Can only become in thermal equilibrium when interactions cease A and B

Clicker Question Why do we think that the Universe is an expansion of space-time and not an explosion? Fix me. Because distant galaxies are moving away from us. Because the farther away a galaxy is, the faster it is moving away Because hydrogen and helium are most of the atoms in the universe Because of the Cosmic Background Radiation Not great...

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?

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 & 2 Lecture prep: Turn in on eLearning Two questions from Chapter 14 you want to know the answer to

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

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!

One Second after the bang Still 10 billion degrees too hot for protons and neutrons to bind into a nucleus and stay that way

The Early History of the Universe Electron Positron High energy photon Still high enough energy for electrons, positrons, and photons to be in equilibrium between pair production and annihilation

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

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?

Later Times and Lower Energies Electron Positron Low Energy Photon Electron pairs and interact and annihilate but photon pairs no longer turn into particle pairs Fewer positrons and electrons

Photons and Electrons above 6 Billion Degrees Electron Positron Photon 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

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…

Quarks Combine to Form Nucleons qqq  Proton Quark Nuclear Reaction Proton Quark Quark

Photon Energies at Various Times 10.8 Trillion Degrees  1 GeV photons (proton mass) 1.2 Trillion Degrees  105 MeV photons (muon mass) 6 Billion Degrees  0.5 MeV photons (electron mass and nuclear binding energy) Universe cools down as time passes 3000 Degrees  10 eV photons (atom binding energy) Second Frame Third Frame Universe expands as time passes

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

Photon Energies at Various Times 10.8 Trillion Degrees  1 GeV photons (proton mass) 1.2 Trillion Degrees  105 MeV photons (muon mass) Will point out why each of these energies/masses are important as we move on 6 Billion Degrees  0.5 MeV photons (electron mass and nuclear binding energy) Universe cools down as time passes 3000 Degrees  10 eV photons (atom binding energy) Universe expands as time passes

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

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

What is happening in this region? In class Quiz What is happening in this region? {

3 Lectures Today: Big Picture of the Evolution of the Universe: Temperature and Time Collisions and how they explain what we see Next Time: The First Three Minutes After the First Three Minutes After that: Stellar and Galaxy Formation

Why not lots of Heavier Nuclei? ~90% are hydrogen (~75% by mass) ~10% in helium Protons and neutrons Combine to Form a few helium nuclei Nuclear Physics  No stable nuclei with 5 – 8 protons These decay so quickly its hard to produce heavier nuclei  Almost no elements heavier than helium are produced

Another Crappy Word: Reionization After less than ~ 1 billion years, the first stars form Ultraviolet radiation from the first stars re-ionizes gas in the early universe Reionization Formation of the first stars and Heavy elements  universe becomes opaque again

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!

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?)

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

Cool pictures TCP Page 635: Evolution of the universe TCP 22.1 (634). Temperature vs. time Feynman diagrams 22.3

SHU 6 When matter and anti-matter meet they annihilate and disappear in a burst of energy Evidence for anti-electrons (positrons) in 1932

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

Neutron Fraction vs. Time

This

PHOTON SCATTERING ELECTRON FROM ATOM

PHOTON SCATTERING ELECTRON FROM ATOM

PHOTON SCATTERING ELECTRON FROM ATOM

PHOTON SCATTERING ELECTRON FROM ATOM ELECTRON ABSORBS ENERGY OF PHOTON TO ESCAPE p+ n e-

PHOTON BREAKING A NUCLEUS HELIUM (He) PHOTON (γ)

PHOTON BREAKING A NUCLEUS HELIUM (He) PHOTON (γ)

PHOTON BREAKING A NUCLEUS HELIUM (He) PHOTON (γ)

PHOTON BREAKING A NUCLEUS HYDROGEN (H) PHOTON (γ) HYDROGEN (H)

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?

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.

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

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?

Define nucleosynthesis?

Distribution

Text

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"

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

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

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

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

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?

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

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

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!

Stuff Stuff about anti-particle and the matter excess…

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…

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?)

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 universe as we know it now!!!

The same is true for electrons and neutrons. Random note: 87% of nuclear particles are protons (not exactly sure why…)

Comments about Neutrinos?

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!!

Put Figure 8 in here somewhere… Page 87

Recipe for a Hot Universe

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

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”

How do we deal with this aside?

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!

Nuclei in the Early Universe 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 Proton Nuclear Reaction Deuterium High Energy Photon Proton

Atoms in the Early Universe High Energy Photon Breaks up Atoms quickly  Free soup of electrons and protons Proton ElectroMagnetic Reaction Hydrogen Atom Electron High Energy Photon

Photons turn into Electron pairs Electron pairs turn into Photons Photons and Electrons Photons turn into Electron pairs Electron pairs turn into Photons

Electron Photon Soup Electron Positron Gamma-ray photon Electron Positron Gamma-ray photon Electron pairs and photon pairs interact and annihilate  electron and photon Soup

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

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…

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

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

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

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?

Preview of Particle Physics As we said before when two photons collide they can produce a pair of electrons

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?

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!

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)

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

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

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

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

Need Size for Anything Yet?

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…

Third Frame and Neutrinos… Neutrinos are long longer important to the story…