Big Bang, Black Holes, No Math ASTR/PHYS 109 Dr. David Toback Lecture 5

1. Big Bang, Black Holes, No MathASTR/PHYS 109Dr. David TobackLecture 5

2. Prep For Today (is now due) – L5 • Reading: • BBBHNM Unit 2 (Due Monday) • Pre-Lecture Reading Questions • Unit 1: done • Unit 1 Revision (if needed) now open, Stage 1 Due Monday before class • Unit 2, Stage 1 due Monday before class • End-of-Chapter Quizzes • Chapters 2 and 3

3. Next Topic: Scientific Methods Unit 1: • Introduction  Done • Going Big  Done • Going Small  Done • Evidence and the Scientific Method Today we move on to the Questions and How we go about answering them

4. Plan for the Next Few Weeks } • More on the Questions and How we go about answering them • Some of the history to teach us about the method • Need to learn some physics Today } Next Unit

5. Next few Weeks Continued… To learn Cosmology will need to learn a bit about: • Light and Doppler Shifts • Gravity, General Relativity and Dark Matter • Atomic Physics and Quantum Mechanics • Nuclear Physics and Chemistry • Temperature and Thermal Equilibrium Won’t spend too long on these, just enough to get back to the big picture…

6. Evidence and The Scientific Method • What are the Questions and how do we go about answering them? • Scientific Method • How do we know what we know? • What is the evidence for the stories we heard growing up? • Observation (looking at the heavens)

7. How do we know what we know? • We have a lot of experience in the world around us • Unfortunately, our experience is really lousy in guiding us to really understanding the bigger (and smaller) world around us unless we’re really careful • As you’ve already seen, the world is incredibly complex and much of it is different from what we experience

8. Single example to Show the Scientific Method in Action • People have watched the sky and noticed that the stars (the dots of light in the sky) basically all move together over the course of the night and over years • Five of them behave differently • Start this story in the 2nd century

9. Fun Videos of Just the Stars Video of stars moving with Polaris (north star) at the center https://www.youtube.com/watch?v=XTTDWhky9HY Video of stars moving including the Milky Way (from Chile) https://www.youtube.com/watch?v=JEHm-XUHwNw

10. Ptolemy’s Universe (2nd century) The Sun, Moon and Stars go around once a day, but the planets only move through the stars a little every night Appear to orbit the Earth in mostly circular paths Every so often the planets move backward for awhile Best guess: these are mini-orbits way out there (epicycles)… Hmmm…

11. Looking at Mars in the Stars

12. How Ptolemy envisioned it The big circle is the main orbit, and the little circle is the epicycle http://bigbang.physics.tamu.edu/Figures/StolenAnimations/ptolemy.model.swf

13. Cracks in the `early cosmology’ In 1514, Copernicus hypothesized that Planets and Earth orbit the Sun Much simpler in some ways  no epicycles More complicated in others  Says Earth is rotating

14. Epicycles??? A more modern view of the motion of the Earth and Mars and the stars behind them (from the point of view of the center) http://bigbang.physics.tamu.edu/Figures/StolenAnimations/mars_retrograde_motion.swf

15. If we lived in the 1500’s, should we believe Copernicus? The Earth isn’t at REST and rotates? • Shouldn’t we FEEL this? • If the Earth is rotating,,why don’t we fall off like an ant on a bicycle wheel? • Why don’t we feel a wind as we rotate?

16. Cracks in the `early cosmology’ Should his view have just “been accepted”? Perhaps his theory was just a “different interpretation” of the same data? • Both models are consistent with observations Need more evidence! Need a better TOOL to test, experimentally, which is correct Early 1600’s: Kepler and Galileo started gathering data from telescopes

17. Data Provides Evidence • Discover moons orbiting Jupiter!  Solid evidence that not EVERYTHING orbits the Earth!

18. Another Piece of Evidence • Can understand the phases of the Moon because of the locations of all three • Not eclipses

19. Venus • Consider the two different versions of how Venus is predicted to move in space

20. The Phases of Venus • Venus has a full set of phases, like the moon • Sunlight shining off Venus and to our eyes • No good way to explain this if Venus rotates around the Earth

21. More data • With better data Kepler realizes an even better description of the data is that all planet orbit the Sun in an ellipse, not a circle • Sun-centered model now agrees with the high-quality observed data, Earth centered does not • No good REASON for ellipses though…

22. The next generation…Newton • Newton puts forward his theory of Gravity and describes it as a Force • So what? The same force that pulls an apple to the ground from a tree ALSO pulls the Moon towards the Earth and keeps it in orbit • This “explains” the orbits as ellipses (and why we don’t fall off a spinning Earth) Isaac Newton 1687

23. Scientific Method The history is fun, but we have a problem: • How do we separate true stories from stories we’d like to believe, but aren’t actually true? • Need EVIDENCE and a good Scientific THEORY • Good hypothesis testing

24. Some words; “It’s a theory…” • Theory:“A set of rules that relate quantities in a model to observations we make” • Hypothesis:“A tentative assumption that is useful in that it predicts the outcome of an experiment and can be tested”

25. Science • For us to “believe” in a theory, or said better, to think it might correspond to truth, we agree that it has to be tested in such a way it can be tested over and over again such that the results must always confirm the theory • Does the world function in a “predictable” manner? • What happens when you test a hypothesis?

26. What Makes a Good Theory? Two requirements: • It must accurately describe a large class of observations, clues, or other pieces of evidence. • For example g, the acceleration due to gravity. Same everywhere on the Earth? • It must make DEFINTEPREDICTIONS about the results of FUTURE (not yet done) observations or experiments • Creates testable hypotheses • Path of a golf ball on the moon?

27. Yet more on Scientific Method • It also must be falsifiable • If we do an experiment and the results disagree with the predictions of the theory, then the theory is wrong or has to be modified • It has been said that “even the most beautiful theory can be slain by a single ugly fact” • If the theory makes predictions for a new experiment and the data agrees then it gives us really good reason to believe there really are underlying principles in the world we live in

28. What science does not promise Science does not promise eternal truths Only promises the systematic elimination of false hypotheses and the establishment of what is currently the most likely explanation of an aspect of reality…

29. Everyday Conversation • Explanations that stand the test of time and LOTS of experiments are what we call Theories • Gravity, Quantum Mechanics etc. • When someone says “Well… It’s a theory” we know what they mean. They mean “it’s a hypothesis” • We don’t yell at them for the same reason we don’t get upset when someone says the “Sun is setting”

30. Better experiments… At some point our experiments get so good that we can “observe” things that our eyes can’t see directly • The very small • The very faint and/or far away What happens if the theories that explain what we can see with our eyes don’t explain what we see in a microscope?

31. Weirdness… Have to try new weirder theories • What if we come up with a theory that accurately “predicts” the results of both the experiments we can do with our eyes AND the really sensitive ones we can do with really special microscopes? • What if that theory is counter to our intuition?

32. More weirdness • What if our weird theory then makes further weird predictions? • What if it predicts that if we do a simple experiment we will get crazy results? • What if we DO the experiment and GET the crazy results? At what point do start believing there is some “truth” to the theory?

33. Fact is Stranger than Fiction • Typically we have confidence in theories that do a good job of predicting the results of experiments have some basis in reality • In the 1920’s scientists starting coming up with such theories:General Relativity and Quantum Mechanics are good examples… Stood up to 90 years of experiments • Will talk in the next unit about what’s weird about them, and what weird things they predict and explain

34. Outline for Unit 2: Physics We Need Topics • Light and Doppler Shifts • Gravity, General Relativity and Dark Matter • Atomic Physics and Quantum Mechanics • Nuclear Physics and Chemistry • Temperature and Thermal Equilibrium

35. Prep For Next Time – L5 • Reading: • Required: BBBHNM Unit 2 (Chapters 5-9) • Recommended Reading: • See P3 of http://people.physics.tamu.edu/toback/109/Syllabus.pdf • Pre-Lecture Reading Questions • Unit 1 Revision (if Needed): Stage 1 in CPR due Monday before class • Let me know if you think you were misgraded • Unit 2: Stage 1 due Monday • End-of-Chapter Quizzes • If we finished Chapter 4 then End-of-Chapter Quiz 4

36. End of Lecture

37. Clicker Quiz A muon is observed to decay into an electron and two different neutrinos. Is a muon considered a fundamental particle? • No, because it has the electrons and neutrinos inside it so it can't be fundamental. • Yes, because it isn't composed of electrons and neutrinos, it just decays into them • No, because fundamental particles can't decay

38. Clicker Quiz Q: What does it mean for an electron to be "stable?" • It is balanced with exactly one proton • Its orbit ring exists in one plane (no wobble) • It has reached minimum size (10-19 m) • Undisturbed, it can go on living forever and ever • They don't appear to be made of anything smaller

39. Paper 0 Stuff • Want feedback before turning it in? • Post it in eCampus in .doc (or .pdf) for comments by the TA by 5PM Friday • Make sure you polish it • If you have lots of grammar and spelling mistakes we’ll just make you resubmit it

40. Another Piece of Evidence • Can understand the phases of the Moon because of the locations of all three • Not eclipses

41. The Phases of Venus • Venus has a full set of phases, like the moon • Sunlight shining off Venus and to our eyes • No good way to explain this if Venus rotates around the Earth

42. Class trip to Cyclotron Clicker question • Any interest in a class trip to the Cyclotron? If so, which day would you be most interested • A = Wednesday • B = Friday • C = Other day please!!! • D = Not likely to make it

43. Prep For Next Time – L5 • Reading: • BBBHNM: Chap 5 • Reading Questions: • Two questions from Chapter 5 or the recommended reading • End-of-Chapter Quizzes • If we finished Chapter 4 then end-of-chapter quiz 4 (else just 3)

44. Prep For Next Time – L4 • Note: May change depending on how far we get in lecture (some may have already been due) • Reading: • BBBHNM: All reading up to Chapter 6 • Pre-Lecture Reading Questions: • Two reading questions from Chapter 6 • End-of-Chapter Quizzes • If we finished Chapter 4 then end-of-chapter quiz 4 (else just 3) • Paper 0 • Paper 0 has been posted on CPR • If we finished Chapter 4, then Paper 0 is due one week from today

45. Full set of Readings So Far • Required: • BBBHNM: Chap 1-5 • Recommended: • BHOT: Chap. 1-3 • SHU: Chap. 1-3 (p55-69) • TOE: Chap. 1

46. Prep for Today (Is now due) – L5 • Reading: • BBBHNM: Chap 4 • Reading questions • Two questions from Chapter 4 • End-of-Chapter Quizzes: • Chapter 3

47. Phase I, Phase II and Phase III Phase I: (Paper due 1 week after we finish Chapter 4) • Turn in a polished draft to eCampus • TA’s will provide feedback, but not if there are multiple spelling/grammar mistakes • Pass/Fail grade Phase II: (Due one week after Phase I) • A revised version will be done 1 week later on CPR • When you submit to CPR (after revision), you will need to also submit a copy of your to the turnitin.com line on eCampus Phase III: (Due one week after Phase II) • Calibrations and Reviewing due one week after you submit

48. Paper 0 Stuff – L9 faculty.physics.tamu.edu/toback/109/WritingAssignments/ • Phase I: Due last Wednesday • You will get feedback soon, work on revisions now • Email if you need an extension • Phase II: • Due in CPR/Turnitin.com Wednesday • Phase III: • Will talk more about CPR and reviewing Wednesday • Following Wednesday

49. History and Just-So Stories State of our understanding 2500 years ago: “The earth is, obviously, flat…” So, how DID they figure out the earth is round? • Ships on the horizon: Top of the mast first • Aristotle (340 BC): The earth’s shadow on the moon

50. Worse… Actually, it’s even worse • What we “believe” can deceive us from understanding how things actually work • Unfortunately, our history is littered with “Just-so stories…” that have set back our understanding