Big Bang, Black Holes, No Mathpeople.physics.tamu.edu/toback/109/Lectures/ThisSemester/Lecture21.pdf · The Evolution of the Universe Topic 1: The Early Universe Big Bang, Black Holes,

Physics We NeedTopic 4: Nuclear Physics & Chemistry

Big Bang, Black Holes, No Math

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ASTR/PHYS 109Dr. David Toback

Lectures 19,20 & 21



Was due Today – L21• Reading:

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

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

– (Chapter 7a and 7b)• Papers

– Paper 1:• Text was due already in Peerceptive and TurnItIn (in eCampus) on Friday Feb

21st

• Please finish your Reviews if you haven’t done so already. Your fellow classmates cannot get a grade until they have 3 Reviews to Back-Evaluate

• If you want to do a revision, send me an email– Paper 2:

• Text: Currently set for Monday March 9th– Submit to Peerceptiv AND TurnItIn

• Draft for Feedback (Optional) – Currently due Wednesday March 4rd

– Will do our best for late submissions • Reviews and Back-evaluations: Same as before

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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



Clicker QuestionA neutral helium atom is sitting in space when a photon hits it. Depending on the photon energy, the following things can happen:A. An electron gets knocked out and the atom becomes ionizedB. A proton gets knocked out and it become a hydrogen atomC. A quark gets knocked out of the protonPlace the following in order from highest required energy to

lowest: a) A>B>Cb) A>C>Bc) B>A>Cd) C>A>Be) C>B>A

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Unique Fingerprints

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• Look at light from a light bulb with Hydrogen gas in the way

• Different lines will be absorbed by Helium

• Can now identify a mystery gas!



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Overview of the story• Big things are made from LOTS of small things • Small things: The Fundamental Building Blocks of Nature

– What is the “stuff” in atoms• ElectroMagnetism (electric charge)

– What holds electrons and protons together• Quantum Mechanics

– Why atoms form the way they do– Electron in orbits– Atoms absorbing and emitting photons (light)

• Different TYPES of Atoms– The Strong Force– Keeping protons and neutrons together (atomic nuclei)– Nuclear Physics and Chemistry– Different atoms Different light…

• Studying the Stars using their light– Spectral lines of the atoms – Atomic “fingerprints”– The light we see from the stars

LastLecture

ThisLecture



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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



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Outline for Unit 2: Physics We Need

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

Dark Matter Done3. Atomic Physics and Quantum

Mechanics Done4. Nuclear Physics and Chemistry

Done5. Temperature and Thermal

Equilibrium Next time



Prep For Next Time – L21• Reading:

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

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

– If we finished Chapter 8 then End-of-Chapter Quiz parts 8a and 8b (else, just 7a and 7b)

• Papers– Paper 1:

• Text was due already in Peerceptive and TurnItIn (in eCampus) on Friday Feb 21st

• Please finish your Reviews if you haven’t done so already. Your fellow classmates cannot get a grade until they have 3 Reviews to Back-Evaluate

• If you want to do a revision, send me an email– Paper 2:

• Text: Currently set for Monday March 9th– Submit to Peerceptiv AND TurnItIn

• Draft for Feedback (Optional) – Currently due Wednesday March 4rd

– Will do our best for late submissions • Reviews and Back-evaluations: Same as before

48

Documents

Big Bang, Black Holes, No Mathpeople.physics.tamu.edu/toback/109/Lectures/ThisSemester/Lecture21.pdf · The Evolution of the Universe Topic 1: The Early Universe Big Bang, Black Holes,