Big Bang, Black Holes, No Math ASTR/PHYS 109 Dr. David Toback Lecture 10 & 11

1. Big Bang, Black Holes, No MathASTR/PHYS 109Dr. David TobackLecture 10 & 11

2. Was Due for Today – L10 • Reading: • None • Pre-Lecture Reading Questions: • Unit 1 Revision (if needed): Stage 2 • Unit 2 Revision (if desired): Stage 2 • End-of-Chapter Quizzes: • Chapter 6 • Paper 1: • Stage 1 due Wednesday before class • Also, submit to turnitin on eCampus

3. Was Due for Today – L11 • Reading: • None • Pre-Lecture Reading Questions: • None (Let us know if you were misgraded) • End-of-Chapter Quizzes: • Chapter 6 (already due) • Paper 1: • Stage 1 was due before class • Also, submit to turnitin on eCampus

4. Paper 1 • What is the evidence for Dark Matter? • Due Wednesday before class in CPR (Stage 1) • Also, in turnitin.com (in eCampus)

5. Papers in CPR/Schedule Schedule is Like PLRQ since it is in CPR: Each Paper has 4 (or 6) Steps: • Mentioned after we start the chapter (just did that) • Assigned after we finish the chapter • Submit text 1 week later (Stage 1) • Calibrations/Reviews/Self-Assessment due the week after that (Stage 2) • Revision (optional): Stage 1 due one week later • If you did a Stage 1, Calibrations/Reviews/Self-Assessment due one week after that

6. Style of the Paper • Explain it to someone who isn’t taking the class (no jargon) • ~600 words (This is the equivalent of both side of a sheet of paper, double spaced) • No citations! Use your own words • Text should be professional. You are “trusted guide” not a “buddy” or “comedian”

7. Paper Format • Must follow expected Format • Usually 5 paragraphs. Needs: • Introduction paragraph • 1 paragraph per piece of evidence (3 total?) • Conclusion paragraph that ties it together • http://faculty.physics.tamu.edu/toback/109/WritingAssignments/samplepaper.shtml

8. Help Available for Stage I • Submit a draft for feedback from the TA • Submit on eCampus in “Rough Drafts (Optional)” • Drafts were due Friday at midnight • If you submit late, we can try to give feedback but we can’t guarantee it • We also recommend going to the writing center

9. Updated Best Guess Schedule • Paper 1: Text due 2/19 (Ch 6) • Paper 2: Text due 3/3 (Ch 8) • Paper 3: Text due 3/17 (Ch 12) • Paper 4: Text due 4/9 (Ch 17) • Honors Stage 0 (not in CPR): Due 2/19

10. So Far Topics • Light and Doppler Shifts  Done • Gravity, General Relativity and Dark Matter Done • Atomic Physics and Quantum Mechanics  Now • Nuclear Physics and Chemistry • Temperature and Thermal Equilibrium

11. Where We Are Going Next In Chapter 3 we learned a little about how the stuff of the Universe is put together • Big things are made from LOTS of small things • Small things: The Fundamental Building Blocks of Nature • What is the “stuff” in atoms?

12. The Largest Stuff • Most of the light we see from space comes from stars • What are stars made of? • Stars are lots of atoms interacting • The ways they interact creates light we can see • Can study the distant stars by looking at the light from them • Can study atoms here on Earth. Are they the same?

13. How do Atoms work? • ElectroMagnetism (electric charge) • What holds electrons and protons together • Quantum Mechanics • The funny way atoms form • Electrons in orbits • Atoms absorbing and emitting photons (light) This Lecture, Chapter 7

14. Different Types of Atoms Next Lecture, Chapter 8 • The Strong Force • Keeps protons and neutrons together in the atomic nucleus • Different types of nuclei  different types of atoms • Different atoms  Different light… • Nuclear Physics and Chemistry • Studying the Stars using their light • Spectral lines of the atoms • Atomic “fingerprints” • The light we see from the stars

15. 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) • The Strong Force • Keeps protons and neutrons together • Different types of nuclei  different types of atoms • Different atoms  Different light… • Nuclear Physics and Chemistry Different TYPES of Atoms • Studying the Stars using their light • Spectral lines of the atoms • Atomic “fingerprints” • The light we see from the stars This Lecture Next Lecture

16. The Fundamental Building Blocks Our best understanding: The very BIG stuff is made up of LOTS of very small stuff Need to understand: • What are the fundamental building blocks of nature • How it’s all held together • How they “create” the light we see

17. Early evidence for the Atomic Model Experiment (1910’s): Shoot atoms at a “target” Theory: 1? Bag stuffed with cotton 2? Bag stuffed with cotton and a few small rocks The experiment gives results like #2! The positive charge in an atom and most of its mass is concentrated in a tiny, very dense center: The Nucleus

18. The Building Blocks of Nature In the 19-teens and 20’s experiments determined: • Atoms are made of a nucleus surrounded by electrons • Many types of nuclei • Only one kind of electron

19. Nuclear Physics Many years later (using many of the same methods): • Nucleus is composed of neutrons and protons • Number of protons and neutrons in the nucleus determines the atom type

20. The Fundamental Building Blocks of Nature • Electrons • Photons • Neutrons • Protons • Neutrons and Protons are really made of quarks • Discovered in the 1970’s • We’ll talk more about this in the next chapter Talked about this in Chapter 3 More in Chapter 8

21. Putting Them Together How do we put these fundamental building blocks together to form atoms?

22. 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) • The Strong Force • Keeping protons and neutrons together • Different kinds of nuclei • Nuclear Physics and Chemistry  different atoms • Spectral lines of the atoms • Atomic “fingerprints” • The light we see from the stars This Lecture Next Lecture

23. ElectroMagnetism • You probably already know that protons and electrons have “electric” charges • Positive charge and negative charge attract each other • Call this ElectroMagnetism + -

24. Weirdness… You probably never thought about it this way but in many ways the way things with electric charge attract is the same as in gravity + -

25. Gravity vs. ElectroMagnetism ElectroMagnetism • Every charged object in the universe “attracts” every other charged object in the universe • The bigger the charge, the bigger the attraction • The further the distance between the objects, the smaller the attraction • Gravity • Every object in the universe attracts every other object in the universe • The bigger the mass, the bigger the attraction • The further the distance between the objects, the smaller the attraction Physics 202 Physics 208 Physics 201 Physics 218

26. What’s different? • Gravity: • All objects attract no matter what • (As far as we know…) • ElectroMagnetism: • Ignores neutral particles

27. Other Differences • ElectroMagnetism is MUCH stronger than gravity • If I have two electrons, the electric force between them is so powerful that it is 1042 times stronger than gravity • Can “ignore” gravity inside atoms

28. Aside • ElectroMagnetism is MUCH weaker than the Strong Force • For two quarks inside a proton the Strong Force is ~100 times stronger than the EM force • Can almost “ignore” EM inside protons

29. Atomic Physics How do we make up atoms? • Start with a simple (partially wrong) atomic model • Positive Nucleus attracts the negatively charged electrons and keeps them in “orbit” • Then move to the weird world of Quantum Mechanics

30. A Hydrogen Atom Figure not to scale The simplest atom: Hydrogen One electron and one proton (Partially wrong) - + | | ~10-15 m | ~10-10 m |

31. Is the world this simple? • This is a nice simple model • Why does the electron stay in “orbit”? • Simple (partially wrong) answer: There is a “Force” that keeps it in orbit just like Gravity keeps the Earth orbiting the Sun

32. Problem • ElectroMagnitism says electrons slow down when they move in circles • Observe this for electrons moving in big circles • Should be true for electrons in small circles (atoms) also  Spiral down until they hit the nucleus and we’d have nothing: No atoms! • Would take 10 picoseconds (10-11s)

33. Another Problem • Stars can be in orbit any distance from the center of the galaxy • Depends only on their speed • Electrons should, depending on their speed, be able to be almost anywhere near the nucleus (like a planet or a comet) • Don’t observe this… Only specific distances from the nucleus

34. 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 This Lecture Next Lecture

35. Quantum Mechanics • How do we explain these weird features that we observe about Atoms? • Quantum Mechanics! • LOTS we COULD say about QM, but since we could spend years on this we’ll focus only on the most important points you need

36. Quantum Mechanics Two big issues: • All particles can be described both as particles AND waves • Saw this for photons • True for electrons (and protons etc.) also! • Electrons can ONLY be in one of the available energy states, and at certain distances from the nucleus • Keep atoms from collapsing! (Good!) • “Quantizes” the interactions with light i.e. only some energy photons interact with atoms

37. Energy of Electron Waves • Small energy electron have large wavelengths • Small wavelength electrons have large energy

38. Only Orbits with Specific Wavelengths Work • The electron “wave” has to go all the way around • Can have one peak/trough, two peaks/troughs, three peaks/troughts etc… • A quantized number • The Quantum in Quantum Mechanics

39. Only Orbits with Specific Wavelengths Work • Lower Energy and closer to the nucleus • Higher Energy and further away from the nucleus

40. Energy and Distance from The Nucleus Higher Energy and further away from the nucleus Lower Energy and closer to the nucleus Only these levels are allowed!

41. How Photons Interact with an Atom • To understand better how photons interact with the stuff in an atom, “how we’ll SEE atoms”, we need to say a bit more about Energy and about Quantum Mechanics • Lots of different ways they can interact… start with the simple interactions

42. Simple: Photon-Atom Collision • Before: Start with a high energy photon and a low energy atom • After: Lower energy photon, higher energy atom (like two billiard balls colliding) • Same TOTAL energy before and after collision • Conservation of Energy

43. Clicker Question After a collision with a stationary atom, the energy of a photon is • Higher • Lower • Same

44. Clicker Question After a collision with a stationary atom, the speed of a photon is • Higher • Lower • Same

45. Clicker Question After a collision with a stationary atom, the wavelength of a photon is • Longer • Shorter • Same

46. Atom-Photon Perspective • Photon’s perspective: I collide with a low energy atom and “transfer” some of my energy • Atom’s perspective: I collide with a high energy photon and “take” some of its energy

47. Quantum Mechanics and EM • In General Relativity we found that it is better to describe the “force” of gravity as the curvature of space-time • How do we “better” describe ElectroMagnetism, especially with Quantum Mechanics? • Electric fields • Answer: In ElectroMagnetism “Force” is essentially all about the “emission” and “absorption” of photons by charged particles like electrons and protons

48. Quantum Mechanics – Force Carriers • Think of the force between electrically charged things as being caused by the exchange of “virtual” photons • The force, or interaction, is “carried” by particles

49. Example with Two Electrons • First electron emits a “force-carrying” particle (a photon) • Causes a recoil of the first electron • You shoot a gun and lurch back • The other electron “catches” it and gets “banged” • Your friend gets hit with the bullet and falls backward • Net result:The two particles move differently, “as if” there were a force between them

50. Visualizing Our Analogy 1: Two electrons hanging out 2: electron on the right “emits” a photon and “recoils” - - 3: Photon bangs into the left electron and bumps it Both now move apart: Same sign charges “repel” each other