big bang, black holes, no...

Physics We NeedTopic 4: Nuclear Physics & Chemistry

Big Bang, Black Holes, No Math

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ASTR/PHYS 109Dr. David Toback

Lectures 13, 14 & 15



Was due Today – L15• Reading:

– (Unit 2) • Pre-Lecture Reading Questions:

– (Unit 2 Text Submission and Unit 2 Quiz)• End-of-Chapter Quizzes:

– (Chapter 7a and 7b)• Feynman Diagram Drawing Assignment

– (Feynman Diagram Assignment 1)– Likely assign Feynman Diagram Assignment 2 (in eCampus) today– http://people.physics.tamu.edu/toback/109/Diagrams/FeynmanDiagramAssignments.pdf– http://people.physics.tamu.edu/toback/109/Diagrams/DrawingFeynmanDiagrams.pdf

• Papers– Paper 1:

• Most grades posted. Let me know if you need help.• You should do your Reviews right after submitting. Can do all 3 separately, but you should finish any that

you start in a single sitting or Peerceptiv has problems • You will get Reviews (may take awhile to get the third), but you only have 72 hours to finish each after it

arrives or you will time out • You can submit a revision at any time, but you have to do a new set of Reviews and Feedbacks for it to

count. Instructions at http://people.physics.tamu.edu/toback/109/WritingAssignments/Papers_and_Peerceptiv.pdf

– Paper 2: • Will most likely assign Paper 2. If so, Text will be due in Peerceptiv on Wednesday Oct 14th at 11:55PM.• For feedback, due before Sunday October 11th• Stages same as Paper 1

• Honors Section:– Stage 1 Final Draft is due Wednesday– Need to hear from you at least once every 7 days

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Heads Up: Paper 2• What is the evidence that Stars are made of Atoms?

• This will be the topic of Paper 2

• In order to understand the evidence, we next talk about Atoms and how they work

• Will be assigned after we finish Chapter 8

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Outline for Unit 2: Physics We Need

1. Light and Doppler Shifts Done2. Gravity, General Relativity and

Dark MatterDone3. Atomic Physics and Quantum

Mechanics Done4. Nuclear Physics and Chemistry

This time5. Temperature and Thermal

Equilibrium



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Learning about Stars from their Light•Can look at the light from the stars to learn about them•Are they made of atoms?•If so, what TYPE of atoms? •How are stars formed?•What makes them shine?



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What is a Star?

• Our best understanding is that stars are giant balls of (mostly) hydrogen atoms

• The hydrogen interacts and produces the light we see– Makes them shine…

• What is the evidence for this?



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Stars• What would happen inside a giant ball of hydrogen?– Atoms would fall to the center (due to gravity) and bash into each other

• What would that look like to us?– Light from their interactions

– Next look at interactions



Proton + Proton Deuterium + Anti-Electron + Neutrino

Hydrogen Interactions produce energy

Proton

Proton

DeuteriumNuclear Reaction

Anti-Electron

Neutrino

The Deuterium, neutrino and the Anti-Electron get energy in the reaction26



Where does the energy come from?

•Mass of Deuterium is smaller than the mass of two protons

• So what? E=mc2, so the “mass energy” gets converted into kinetic energy in the collision (and light)

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Proton + Deuterium Helium3 + Photon

More interactions More Energy

Deuterium

Proton

Helium3

Nuclear Reaction

Photon

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Helium3 + Helium3 Helium4 + 2 Protons

Creating Stable Helium produces more…

Helium3

Helium3

Helium4

Nuclear Reaction

Proton

Proton



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Stars Shining

•Nuclear interactions in the center of the star create lots of energy which is eventually emitted as light from the surface of the star–Shines white (or yellow)



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What else can we learn from the light?

•This light passes through other atoms of the star–Light is “absorbed” by the outer atoms Spectral lines

•Tells us what the stars are made of



Looking at the Stars

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Analyzing Absorption Spectra• Each element produces a specific set of absorption (and emission) lines

• Using this information, we can study the composition of stars

See only spectral lines for known atoms



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Remarkable…• The Sun and stars are mostly made of Helium and Hydrogen

• Our Sun is made of the same stuff as all the other stars!

• The stuff out in the universe is made of the same stuff that is found here on Earth!



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Even More RemarkableIf all the stuff “out there” looks the same as the stuff here on Earth then: –The particles out there (electrons, protons, photons etc.) are the same as they are here

–The laws of physics that govern putting together protons, nuclei and atoms are likely to be the same everywhere!

–Strong evidence that the laws of physics have been the same for billions of years!



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Now that we know what stars are made of and

what they are SUPPOSED to look like, can we learn

anything else?



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•What if the stars were MOVING? •Can we tell? Yes!

Doppler effectHow?



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Atoms with Different Speeds

• If an atom emits a photon it will correspond to an energy that reflects the change of two energy levels

• However if the atom is MOVING the light will be shifted to a different color



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Observing an Atom

Atom Emitting Light

Not MovingMoving to the right

Can use this to study the motions of the stars



Looking at the Stars

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Provides additional evidence stars are made

of atoms



Lecture on Chapter 8 now complete

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Paper 2

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• Abbreviated description: What is the evidence that Stars are made of Atoms? – More detail on Peerceptiv, you REALLY need to

read ALL the instructions• Explain it to someone who isn’t taking the class (no

jargon)• Format:

– Introduction paragraph • Lawyers opening arguments at a Trial

– ~1 paragraph per piece of evidence/talking point• The case at a Trial

– Conclusion paragraph that ties it together• Lawyers closing arguments at a Trial

http://people.physics.tamu.edu/toback/109/WritingAssignments/samplepaper.shtml

Physics We NeedTopic 5: Temperature and Equilibrium


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Where we are…Topics1. Light and Doppler Shifts Done2. Gravity, General Relativity and Dark

MatterDone3. Atomic Physics and Quantum

Mechanics Done4. Nuclear Physics and Chemistry Done5. Temperature and Thermal Equilibrium This

Time



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Looking at the Lights in the SkyWhat we know about the universe comes from multiple places

So far:•Learned about the light coming from the Sun and the other stars

•The evidence that stars are made of atoms



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Other Stuff Out There… • We don’t just look at the stars…

• We can learn a lot from looking at light in other ways too…–Talk about this today…



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The World in a JarAs we’ll see, in many ways

when we look at the stuff in the sky (other than the stars) it looks like we’re sitting in a giant jar of stuff, like atoms

What does it look like to sit inside a jar of atoms or photons?

Why should you care?



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Start Simple: Atoms in a Jar• Since we can see how atoms interact in a jar on Earth, we can predict what would happen on Universe sizes

• Next: learn what it’s like to be inside a jar filled with atoms

• Gas (bunch of atoms) is well described by its Temperature and will eventually come into Thermal Equilibrium– Describe both these ideas next



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Overview of Today’s Material1. Temperature: Photons and Atoms2. Thermal Equilibrium3. Moving in a Gas4. Different types of Equilibrium5. What we can, and can’t, learn

from a system in Thermal Equilibrium



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Temperature

What do we mean when we use the word temperature?



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TemperatureHow do we typically “think” about Temperature?

• When we’re outside and we “feel” cold, the thermometer reads a small number

• When we’re outside and we “feel” hot, the thermometer reads a large number

What is the thermometer measuring?



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“Feeling” Cold•What is hitting you when you are outside? 1.Photons2.Atoms

Can think of temperature as the energy of the particles hitting you



Temperature of AtomsSame number, and type, of atoms in both

(small arrow = small energy, large arrow=large energy)

Low Energy:Cold Gas

High Energy: Hot Gas

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Prep for Next Time – L15• Reading:

– Will assign Unit 3 soon• Pre-Lecture Reading Questions Quiz:

– Will assign Unit 3 soon• End-of-Chapter Quizzes:

– If we finished Chapter 9 then end-of-chapter quiz 9 (else just quizzes 8a and 8b)• eynman Diagram Drawing Assignment

– (Feynman Diagram Assignment 1)– Feynman Diagram Assignment 2 due before next class– http://people.physics.tamu.edu/toback/109/Diagrams/FeynmanDiagramAssignments.pdf– http://people.physics.tamu.edu/toback/109/Diagrams/DrawingFeynmanDiagrams.pdf

• Papers– Paper 1:

• Most grades posted. Let me know if you need help.• You should do your Reviews right after submitting. Can do all 3 separately, but you should finish any

that you start in a single sitting or Peerceptiv has problems • You will get Reviews (may take awhile to get the third), but you only have 72 hours to finish each after

it arrives or you will time out • You can submit a revision at any time, but you have to do a new set of Reviews and Feedbacks for it to

count. Instructions at http://people.physics.tamu.edu/toback/109/WritingAssignments/Papers_and_Peerceptiv.pdf

– Paper 2: • Text is be due in Peerceptiv on Wednesday Oct 14th at 11:55PM.• For feedback, due before Sunday October 11th• Stages same as Paper 1

• Honors Section:– Stage 1 Final Draft is due Wednesday– Need to hear from you at least once every 7 days 53

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