Big Bang, Black Holes, No Math ASTR/PHYS 109 Dr. David Toback Lectures 14 & 15

1. Big Bang, Black Holes, No MathASTR/PHYS 109Dr. David TobackLectures 14 & 15

2. Was due Today – L14 • Reading: • Unit 3 • Pre-Lecture Reading Questions: • Unit 3 in CPR: Stage 1 • End-of-Chapter Quizzes: • Chapter 9 • Papers: • Paper 1: • Revision (if desired): Stage 1 due Wednesday • (Text needs to be in turnitin on eCampus) • Paper 2: • Stage 1 due Wednesday • Also due in turnitin

3. Was due Today – L15 • Reading: • Unit 3 • Pre-Lecture Reading Questions: • Unit 3 in CPR: Stage 2 • End-of-Chapter Quizzes: • Chapter 9 • Papers: • Paper 1: • Revision (if desired): Stage 1 due Friday • (Text needs to be in turnitin on eCampus) • Paper 2: • Stage 1 due THURSDAY at 5:45 • Also due in turnitin

4. Starting Unit 3 Finished Unit 2: Physics We Need • Light and Doppler Shifts • Gravity, General Relativity and Dark Matter • Atomic Physics and Quantum Mechanics • Nuclear Physics and Chemistry • Temperature and Thermal Equilibrium Starting Unit 3: Evidence for Big Bang • The Exploding Universe • Expanding Space-Time • Photons and Hydrogen in the Universe

5. Where we are going… • First give three pieces of evidence for the Big Bang • Don’t worry… you don’t need to memorize them now • Will keep coming back to them over and over again • Will be in the lecture notes • Then tell the story about how they all fit together • Will be the topic of Paper 3

6. Overview: Evidence for the Big Bang • We observe all distant galaxies to be moving away from us • The further away the galaxy is the faster it is moving away from us • True no matter which direction we look • We observe low energy photons (microwaves) uniformly distributed in all directions which are consistent with a temperature of about 2.7 degrees above absolute zero (Kelvin) • The atoms in the Universe are basically Hydrogen and Helium and not much else

7. 3 Lecture Outline • The Exploding Universe • Today • Expanding Space-Time • Next Lecture • Photons and Hydrogen in the Universe • The Lecture After That

8. Today’s Outline • Looking at Galaxies • Light from distant galaxies is Red Shifted and appears the same in all directions • The Exploding Universe • A problem…

9. Galaxies before 1920’s • Before the 20’s, when the telescopes became powerful enough, there was no convincing evidence that there was anything outside the Milky Way • When Einstein first wrote about the Universe, he meant “The Milky Way”

10. Edwin Hubble • In the 1920’s Hubble established that there are distant galaxies made of individual stars • VERY far away • Now know that in the same way that Sun is just one star of many, the Milky Way is just one of about a 100 billion galaxies

11. What can we Learn from Galaxies? Measure some important things: • How far away are they? • How fast are they moving? • What directions are they moving?

12. How do you measure the distance to a galaxy? Use a special Star called a “Cepheid Variable” • We know how much light they emit • Like a 100 Watt Light bulb • If we measure how much light we see, we can figure out how far away it is • If we can find a Cepheid in a galaxy, then we can figure out how far away that galaxy is

13. What is Their Velocity? • How fast are they moving? • What direction are they moving? Use the Doppler shift and measure their spectral lines!

14. Observing a Galaxy Galaxy Emitting Light Not Moving Moving away from us

15. Put it all together 0 Measure distance from how much light reaches us Measure speed from Doppler shift of Spectral lines

16. Distances • Andromeda (the closest galaxy to our own) is ~2 million light years away! • More than 10 times farther away than the furthest thing in our own galaxy • We see galaxies over 10 billion light years away

17. Speeds A fast star can travel a few hundred kilometers per second! Put this in perspective  Big: Can travel 10 billion kilometers in a year  Small: That’s less than a 1000th of the distance to the star nearest us

18. Is there a trend? • Most of the galaxies are red shifted • Moving away from us • More importantly: The further away they are the faster they are rushing away from us! • Perhaps even more important: Looks the same in all directions! Individual Galaxies Call this simple relationship “Hubble’s Law”

19. Put this in Perspective • They are traveling away from us really quickly • From New York to California in ~1 second • Can’t see this effect in our galaxy • Furthest stars in our galaxy are ~105 light years away • Thousand times smaller size

20. So What? • We live in a Universe where things are clearly moving! • Galaxies are moving away from us very quickly • Is something pushing them?

21. Why are Things Flying Apart? • The answer turns out to be complicated • We’ll start with a hypothesis that turns out to be wrong but helps us understand • Then we’ll go back and explain it more correctly

22. An Explosion? • Georges Lemaitre (1927): The galaxies are not flying apart because something is “forcing” them apart, they are moving apart because they were part of an explosion a long time ago

23. Is the data consistent with the simplest picture of an exploding Universe?

24. A Simple Explosion

25. A Snapshot in Time Fast Stuff is far from the explosion Slow Stuff is close to the explosion

26. A (wrong) Hypothesis… Fast Stuff is far from the location of the explosion Slow Stuff is close to the location of the explosion Consistent with this data

27. A Beginning? If galaxies are rushing apart from us then at some point in the past they must have all have been closer together

28. Running Backward in Time

29. Bottom Line The data about the velocities of the galaxies provides evidence that we live in a Universe that exploded into existence a long time ago We now know it was about 14 billion years ago

30. The Story is Always more Complicated Let’s think about our data a little more carefully Say it again: Galaxies are moving away from us AND moving the same way in EVERY direction Simple explanation? We’re located at the center of the explosion and we’re not moving!

31. We’re at the CENTER and NOT MOVING: Red Shifted Light Consistent with what we observe!

32. If We’re at the Center Equal amounts of stuff on each side Slow Stuff Medium Speed Fast Stuff Consistent with what we observe!

33. Another possibility: We’re at the center and MOVING Not what we observe!

34. If We’re Not At The Center Lots of stuff on this side Not much stuff on this side Medium Speed Slow Stuff Fast Stuff Not what we observe!

35. ??? • Do we REALLY believe we’re the center of the Universe AND that we’re not moving? • Is there a better explanation?

36. Was due Today – L14 • Reading: • Unit 3 (if not finished) • Pre-Lecture Reading Questions: • Unit 3 in CPR: Stage 2 due Wednesday • End-of-Chapter Quizzes: • Chapter 9 • Papers: • Paper 1: • Revision (if desired): Stage 1 due Wednesday • (Text needs to be in turnitin on eCampus) • Paper 2: • Stage 1 due Wednesday • Also due in turnitin

37. Full set of Readings So Far • Required: • BBBHNM: Chaps. 1-12 • Recommended: • TFTM: Chaps. 1-3 • BHOT: Chaps. 1-7, 9 and 11 (117-122) • SHU: Chaps. 1-3, 4(77-86), 5(95-104), 6, 7 (up-to-page 153) • TOE: Chaps. 1 & 2

38. End of Lecture

39. Clicker Question Which best describes the two galaxies below? Both are moving towards us, but the left one is moving faster than the one on the right Both are moving towards us, but the right one is moving faster than the one on the left Both are moving away from us, but the left one is moving faster than the one on the right Both are moving away from us, but the right one is moving faster than the one on the left

40. Clicker Question Two stars in the Milky Way have the same temperature. Are they in thermal equilibrium with each other? • Yes • No

41. Clicker Question True or False: Once a bunch of atoms are in thermal equilibrium, the energy of an individual atom doesn’t change • True • False

42. Clicker Question True or False: If I have a bunch of electrons, positrons and photons in thermal equilibrium, we will never have another positron annihilate with an electron and raise the number of photons • True • False

43. Clicker Question Why can electrons, positrons, and photons be in thermal equilibrium with each other, even if they are creating and annihilating one another? • They can be the same temperature • They are in thermal contact • Can only become in thermal equilibrium when interactions cease • A and B

44. Clicker Question On a cold winter morning, which is a lower temperature, a metal sign pole or a wooden bench? • The metal pole • The wooden bench • They are the same temperature • They are at absolute zero

45. Clicker Question Let’s say you were the person observing the galaxies, but each other person in the room were a galaxy. Which person in the room is moving away from you most quickly? • Back left • Back right • Front left • Front right

46. Prep For Next Time – L7 • Reading: • BBBHNM: All reading through Chapter 12 • Reading Questions: • All reading questions through 12, due before class • eLearning Quizzes: • Through Chapter 9, due before class • Papers: • Paper 2 text feedback (if desired) due Monday March 11th for guaranteed feedback. • Due Tuesday March 19th in CPR and turnitin.

47. Was due Today– L16 • Reading: • Chapter 10 • Pre-Lecture Reading Questions: • Chapter 10 • End of Chapter Quizzes: • Chapter 9 • Papers: • Paper 0 Revision (if you didn’t pass the first time – See eCampus score, not CPR Score): Calibrations/Reviews due Monday before class • Paper 1: Scores are on CPR (won’t go on eCampus). If you want to do a revision, that will be due next Wednesday before class. • Paper 2: Text due today before class, Calibrations/Reviews due next Wednesday before class • Honors Paper: Stage 0 due Today

48. Prep For Next Time – L16 • Note: May change depending on how far we get in lecture • Reading: • BBBHNM: Chapters 11 and 12 • Pre-Lecture Reading Questions: • Chapter 11 and 12 • End of Chapter Quizzes: • Chapter 10 if we finished 10 today, if not just 9 (already assigned) • Papers: • Paper 0 Revision (if you didn’t pass the first time – See eCampus score, not CPR Score): Calibrations/Reviews due Monday before class • Paper 1: Scores are on CPR (won’t go on eCampus). If you want to do a revision, that will be due next Wednesday before class. • Paper 2: Text due today before class, Calibrations/Reviews due next Wednesday before class • Honors Paper: Stage 0 due Today

49. Prep For Next Time – L7 • Note: May change depending on how far we get in lecture • Reading: • BBBHNM: All reading through Chapter 12 • Reading Questions: • All reading questions through 12 • eLearning Quizzes: • If we finished Chapter 10 then end-of-chapter quiz 10 (else just through Chapter 9) • Papers: • Paper 2 text feedback (if desired) due Monday March 11th for guaranteed feedback. • Due Tuesday March 19th in CPR and turnitin.

50. Was due Today – L8 • Reading: • BBBHNM: All reading through Chapter 12 • Reading Questions: • All reading questions through 12 • eLearning Quizzes: • Chapter 9 • Paper 2: • Due Tuesday March 19th (tomorrow) in CPR and turnitin