big bang, black holes, no math astr/phys 109 dr. david toback lectures 20

Evolution of the UniverseTopic 2: After The First Three

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Big Bang, Black Holes, No Math

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ASTR/PHYS 109

Dr. David TobackLectures 20 & 21


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Was due Today – L20• Reading:

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

– Unit 4 Revision (if Desired): Stage 1, due Wednesday

• End-of-Chapter Quizzes:– Chapter 13

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

Wednesday– Paper 3: Stage 1, due today

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


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Was due Today – L21• Reading:

– Unit 5• Pre-Lecture Reading Questions:

– Unit 4 Revision (if Desired), Stage 1: Due before class today

– Unit 5, Stage 1: Due before class today• End-of-Chapter Quizzes:

– Chapter 13• Papers:

– Paper 2 Revision (if desired), Stage 2: due before Class Wednesday

– Paper 3, Stage 2: due before class Wednesday• Honors Paper:

– Stages 1 & 2 must be approved explicitly– Final paper due on the last day of class


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A Big Bang Occurs… Then What?

Universe goes through a phase of being hot and small

As the universe evolves it gets bigger, older and colder


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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


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Where are we now in the history?

3 Minutes


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After the First Three Minutes

•At about the 3 minute mark the temperature of the Universe is about 1 billion degrees

•Electrons and positrons have mostly annihilated each other–No particles energetic enough to produce new ones

~1 electron for every proton


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What else?

•The temperature drops so that the photons, on average, can’t even break up deuterium–Easier to start building up the heavier nuclei


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Proton + Proton Deuterium + Electron + Neutrino

Forming Heavy Nuclei in the Early Universe

Proton

Proton

DeuteriumNuclear Reaction

Electron

Neutrino


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Nuclei and Low Energy Photons

Deuterium

Low Energy Photon

At the 3 minute mark, low energy photons only

“bump” nuclei


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Proton + Deuterium 3He + Photon

Can Now Build Heavier Nuclei

Deuterium

Proton

3He

Nuclear Reaction

Photon


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3He + 3He 4He + 2 Protons

Creating Stable Helium

3He

3He

4He

Nuclear Reaction

Proton

Proton

Replenishes the hydrogen in the Universe


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Why so few atoms Heavier than Helium?

Nuclear Physics

Can build up Hydrogen and Helium one at a time

So What? Since 5He and 5Li decay quickly they don’t have enough time to find another proton to become 6Li and be stable

Almost no elements heavier than helium are produced in the early Universe

• Will happen in stars later

Next possibility, 5He or 5Li, isn’t stable


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Time marches on…

•Universe continues to expand and cool

•Number of protons goes up and number of neutrons goes down–Why? Neutrons can decay into protons


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Neutron Proton + Electron + Neutrino

Neutron Decay

Neutron

ProtonDecay

Electron

Neutrino


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The End of an Era

•For the next couple hundred thousand years things don’t change much

•Nuclear processes eventually stop making new heavy nuclei since the Universe gets so big

•But it’s still MUCH too hot for atoms to form


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The beginning of a new Era

•From 200,000-700,000 years the universe expands and cools

•All the protons, neutrons and electron combine to form atoms–Translation: Universe cools until the photons in the universe can’t knock all the electrons out of the atoms any more


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Atoms in a Lower Temperature Universe

Proton

Electron

HydrogenAtom

ElectroMagnetic Reaction

At these lower temperatures photons can’t easily break up

atoms

Photon


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Where are we now in the history?

200,000-700,000 years


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Some Time Passes

The Transition From a Hot Universe to a Cool Universe


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The Universe at ~700,000 Years Old

•At a temperature of about 3000K photons, on average, can’t knock apart atoms

•Stable atoms can form and most electrons become part of atoms

•The atoms are now free to form into stars and galaxies


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Give this special time in history a name

Call this time “Recombination” Crappy

Word!Atoms are combining for the first time, not

recombining!


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Atoms in the Universe

Early Universe A couple hundredThousand Years Later

These days


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Before and After the Creation of Atoms

Lots of electrons and protons in the UniversePhotons scatter from

charged particles

Protons and electrons combine

to form atoms Universe becomes

transparent for photons


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Transparent Universe

The Universe now LOOKS different!•The light (photons) have no free

electrons to interact with •Since all the electrons are in atoms,

because of Quantum Mechanics, they largely ignore the photons

•Photons just travel in a straight line Like traveling through glass


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Atoms in the UniverseEarly UniversePhotons bust apart atoms

A couple hundredThousand Years Later

Photons can only excite atoms

These daysUniverse is transparent to photons

Hydrogen

High energy photon


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A Cartoon…

Before Recombination: Photons interact with charged particles Scatter and change directions

+

++

+

+

+

++

After Recombination: Atoms ignore the photons Photons travel in straight lines forever


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Cosmic Background Radiation

•The photons we see in the cosmic background radiation are essentially the photons AFTER they interacted with their last charged particle

•Well… they’ve been traveling for awhile so they’ve changed a little 28


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Photons in the UniverseAfter recombination, photons can travel freely through spaceTheir wavelength is only stretched (red shifted) by cosmic expansionObserve most photons as the cosmic background radiation! Also can observe photons emitted from Galaxies a billion years ago (just reaching us now) as being red-shifted


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A Neutral Universe• After the electrons and protons

combine to form atoms the Universe is almost completely neutral i.e., neutrally charged

• Why is this so important? All the particles in the Universe stop attracting each other due to their electric charge–Not completely true, just true

outside the atoms –Basically can ignore electric charge

from here on out


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Some Time Passes

The Transition From a “Charged” Universe to a “Neutral” Universe


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Aside on Dark Matter• Dark matter is a BIG part of this story

because there is 5 times more mass in the Universe in dark matter than in atoms–Will come back to this in Chapter 15

• However, the story doesn’t change much with Dark Matter since we think it is just another neutral particle

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A Gravity Dominated Universe

•The only thing left is gravity! •The gravitational attraction between massive things ONLY makes them move towards each other

•Any single atom would be most attracted to the closest place with lots of mass


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Wait a Half Billion Years•As the years go by, mass clumps together

•By a half a billion years after the bang, most of the mass is in one of a large number of “clumps”

•Billions of these clumps, each becomes part of a galaxy!


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The Next Few Billion Years

After less than ~0.5 billion years, the first stars form Stars produce heavy elements (“Stellar Cooking”)


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Fast Forward…

•Fast forward 13 billion years –Temperature of space is now ~3Kelvin

–Cosmic Background Radiation•We get people…•More on Stellar and Galaxy

Formation next


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Looking Forward

•Finished Unit 4–Evolution of the Universe

•Starting Unit 5–Big Objects and Black Holes


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For Next Time – L20• Reading:


– Unit 4 Revision (if Desired), Stage 1: Due before class Monday

– Unit 5, Stage 1: Due before class Monday• End-of-Chapter Quizzes:

– Chapter 14 (if we finished Chapter 14, else just 13)• Papers:

– Paper 2 Revision (if desired), Stage 2: due before Class Wednesday

– Paper 3, Stage 2: due before class Wednesday• Honors Paper:

– Stages 1 & 2 must be approved explicitly– Final paper due on the last day of class


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Full set of Readings So Far•Required:–BBBHNM: Chaps. 1-15

•Recommended:–TFTM: Chaps. 1-5–BHOT: Chaps. 1-7, 8 (68-85), 9 and 11 (117-122)–SHU: Chaps. 1-3, 4(77-93), 5(95-114), 6, 7 (up-to-page 159) –TOE: Chaps. 1-3

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Clicker Question

What is the electric charge of completely ionized hydrogen?

a)0 (Neutral)b)+1c)-1d)+2e)-2

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Clicker Question

What is the electric charge of completely ionized helium?

a)0 (Neutral)b)+1c)-1d)+2e)-2

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Clicker Question

Other questions to help with the EOC Chapter 14 quiz?

a)What is the difference between ionized atoms and fully formed atoms (better word for fully formed)

b)When do heavy nuclei enter the universe?

c)Do we ever have lots of ionized heavy nuclei? Re-ionization here is a bugger detail

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Clicker Question

Why can we only see so far back into space?

a)Because before recombination the light in the universe was scattering off of the charged particles

b)Because there are too many things in the way which block our ability to see

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Clicker QuestionOrder the following in the order of highest

required energy to lowest required energy

A.Breaking apart a ProtonB.Breaking apart a helium nucleiC.Breaking an electron out of a hydrogen

atoma) A>B>Cb) A>C>Bc) B>A>Cd) B>C>Ae) C>A>Bf) C>B>A

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Clicker QuestionHow far back in time can we “see” when

we look into space?a)To ~0.5 billion years after the bang

(time of creation of the first stars)b)To ~250,000 years after the bang (time

of “recombination”, creation of atoms)c)To ~3 minutes after the bang (creation

of heavy nuclei)d)To ~microsecond after the bang

(creation of protons)

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Clicker Question

Which of the following requires the highest energy photon?

a)Breaking apart a Protonb)Breaking apart a helium nuclei

c)Breaking an electron out of a hydrogen atom 47


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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 Protonb)Broke apart a helium nucleic)Broke the electron out of a

hydrogen atom 48


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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 was in thermal

equilibrium, and the photons are just one of the particles in the Universe

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Clicker Question

Why is hydrogen the most abundant element in the universe?

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 contribute

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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

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Papers

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•Papers:–Paper 0 Revision: Still working on re-grades. Will post in eCampus by Wednesday

–Paper 1 Revision: Let us know if you were misgraded

–Paper 2: •Bad Rubric fixed (everyone given credit for low-quality calibration)

•Working on re-grades–Paper 2 Revision: Changed due date to Wednesday before class

–Paper 3: Text due Wed before class


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Prep for Today (Is now due) – L19

• Reading:– BBBHNM 14

• Reading questions:– Chapter 14

• End-of-Chapter Quizzes:– Chapter 13

• Paper Stuff– Paper 2 Revision: Text was due

before class. Calibrations and Review due Monday

– Paper 3: Text was due before class. Calibrations and Review due Monday


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For Next Time – L19• Reading:


– Unit 4 Revision (if Desired): Stage 1 Due Monday before class

– Unit 5: Stage 1 due Monday before class• End-of-Chapter Quizzes:

– Chapter 14 (if we finished Chapter 14, else just 13)• Papers:

– Don’t forget that ALL papers must be submitted to turnitin.com

– Paper 2 Revision (if desired): Stage 2 due Monday before class

– Paper 3: Stage 2 due Wednesday before class• Honors Papers:

– Stage 1 Revision


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Prep For Next Time – L21•Note: May change depending on how far we get in lecture•Reading:–BBBHNM: All reading through Chapter 16

•Pre-Lecture Reading Questions:–All reading questions through 16

•End-of-Chapter Quizzes:–If we finished Chapter 14 then end-of-chapter quiz 14 (else just through Chapter 13)


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Prep for Next Time – P19

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• Reading– BBBHNM 15– Recommended:

• SHU: 4(87-93)• TOE: 3• BHOT: 8(76-85)

• Reading questions– Chapter 15

• End-of-Chapter Quizzes– If we finished Chapter 14 then end-of-chapter quiz

14 (else just 13) • Papers

– Paper 2 Revision: Text was due before class. Calibrations and Review due Monday

– Paper 3: Text was due before class. Calibrations and Review due Monday


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Prep For Next Time – L9• Note: May change depending on how far we get in

lecture• Reading:

–BBBHNM: All reading through Chapter 17• Reading Questions:

–All reading questions through 17• eLearning Quizzes:

–If we finished Chapter 14 then end-of-chapter quiz 14 (else just through Chapter 13)

• Papers:–Paper 3 text due in CPR and turnitin.com on Wednesday–Paper 3 calibrations, reviews and self-assessment before next class–Paper 2 revision: Text due Monday before class (if desired)


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Looking Back at the Early Universe

The more distant the objects we observe, the further back into the past of the universe we are looking


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Papers

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•Papers:–Paper 0 Revision: Still working on re-grades. Will post in eCampus by Wednesday

–Paper 1 Revision: Let us know if you were misgraded

–Paper 2: •Bad Rubric fixed (everyone given credit for low-quality calibration)

•Working on re-grades–Paper 2 Revision: Changed due date to Wednesday before class

–Paper 3: Text due Wed before class


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Part II

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


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Why not much Heavier than Helium?

Nuclear Physics

Can build up Hydrogen and Helium one at a time

So What? Since 5He and 5Li decay quickly they don’t have enough time to find another proton to become 6Li and be stable

Almost no elements heavier than helium are produced

Next possibility, 5He or 5Li, isn’t stable


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Aside on Helium

Why is Helium important to the story?

Explains two things:1. Why the atoms in the Universe

are mostly Hydrogen and Helium, and not much else

2. Why the Helium, like the photons is evenly distributed around the universe


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The Reading So Far and For Unit 5

Reading for Unit 5:• BBBHNM: Chaps. 15-17• SHU: 4(87-93)• TOE: 3• BHOT: 8(76-85)Full reading so far for Unit 5:• BBBHNM: Chaps. 1-17• TFTM: Chaps. 1-5• BHOT: Chaps. 1-7, 8 (68-85), 9 and 11 (117-

122)• SHU: Chaps. 1-3, 4(77-93), 5(95-114), 6, 7 (up-

to-page 159) • TOE: Chaps. 1-3Lecture prep: Turn in on eLearning

Two questions from Chapter 15 you want to know the answer to


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Some Time Passes

The Transition From a Hot Universe to a Cool Universe

Electrons

Protons

Photons

Photons

Atoms

Electrons

Protons

Photons


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Writing Assignments

1. Short Assignment 1•Want to revise again? Talk

to me. Still not getting it? Need to get you to the writing center!

2. Short Assignment 2 is posted•Due Today

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


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Papers AFTER Paper 2

Two options1. Research Paper

• If you want to do the research paper option you must turn in Stage 0 at the end of class today. Must be approved

•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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Before 700,000 years: Summary

Photons are incessantly scattered by free electrons; photons are in equilibrium

with matter

Radiation dominated era

Photons-electron soup have the

same temperature (energy)


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After 700,000 Years: “Recombination”

Protons and electrons combine to form atoms

universe becomes transparent for photons

Transition to matter dominated era

Crappy Word!Atoms are

combining for the first time,

not recombining!


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A cartoon of an atom and a photon

Mostly this is happening now since the photons are low energy


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The Cosmic Background Radiation

After recombination, photons can travel freely through space

Their wavelength is only stretched (red shifted) by cosmic expansion

This is what we can observe today as the cosmic background

radiation!


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Wait a Billion YearsAfter less than ~ 1 billion years, the first stars form Produce Heavy Elements in Stellar Cooking

Formation of the first stars


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The First Three Minutes

http://bigbang.physics.tamu.edu/Figures/StolenAnimations/first3minutes.swf

big bang, black holes, no math astr/phys 109 dr. david toback lectures 20

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