A100 Exploring the Universe Big Bang Theory and the Early Universe. Martin D. Weinberg UMass Astronomy

Transcription

1 A100 Exploring the Universe and the Martin D. Weinberg UMass Astronomy December 02, 2014 Read: Chap 23 12/04/14 slide 1

2 Assignment on Chaps 22 23, at the end of next week, is optional and will count as extra credit Read: Chap 23 12/04/14 slide 2

3 Assignment on Chaps 22 23, at the end of next week, is optional and will count as extra credit Exam 3 on Thursday 4 Dec Covers Chapters Read: Chap 23 12/04/14 slide 2

4 Assignment on Chaps 22 23, at the end of next week, is optional and will count as extra credit Exam 3 on Thursday 4 Dec Covers Chapters Final exam: Hasbrouck 20 (here!) on Thursday 11 December at 1:00pm Covers everything in the course Read: Chap 23 12/04/14 slide 2

5 Assignment on Chaps 22 23, at the end of next week, is optional and will count as extra credit Exam 3 on Thursday 4 Dec Covers Chapters Final exam: Hasbrouck 20 (here!) on Thursday 11 December at 1:00pm Covers everything in the course The implied history of the universe Bang theory? Evidence for the Big Bang theory? Read: Chap 23 12/04/14 slide 2

6 Assignment on Chaps 22 23, at the end of next week, is optional and will count as extra credit Exam 3 on Thursday 4 Dec Covers Chapters Final exam: Hasbrouck 20 (here!) on Thursday 11 December at 1:00pm Covers everything in the course The implied history of the universe Bang theory? Evidence for the Big Bang theory? Questions? Read: Chap 23 12/04/14 slide 2

7 Extrapolate the expansion back in time The Universe is current expanding. Imagine reversing the arrow of time so that the Universe is then contracting... What happens? Read: Chap 23 12/04/14 slide 3

8 Extrapolate the expansion back in time The Universe is current expanding. Imagine reversing the arrow of time so that the Universe is then contracting... What happens? The density increases. The temperature increases. Read: Chap 23 12/04/14 slide 3

9 Extrapolate the expansion back in time The Universe is current expanding. Imagine reversing the arrow of time so that the Universe is then contracting... What happens? The density increases. The temperature increases. Universe becomes ionized, like the inside of a star Read: Chap 23 12/04/14 slide 3

10 Extrapolate the expansion back in time The Universe is current expanding. Imagine reversing the arrow of time so that the Universe is then contracting... What happens? The density increases. The temperature increases. Universe becomes ionized, like the inside of a star As we keep going, fusion may occur. Read: Chap 23 12/04/14 slide 3

11 Extrapolate the expansion back in time The Universe is current expanding. Imagine reversing the arrow of time so that the Universe is then contracting... What happens? The density increases. The temperature increases. Universe becomes ionized, like the inside of a star As we keep going, fusion may occur. Still later, the temperatures get so high that the baryons break up into constituent sub-particles (quarks). Read: Chap 23 12/04/14 slide 3

12 Extrapolate the expansion back in time The Universe is current expanding. Imagine reversing the arrow of time so that the Universe is then contracting... What happens? The density increases. The temperature increases. Universe becomes ionized, like the inside of a star As we keep going, fusion may occur. Still later, the temperatures get so high that the baryons break up into constituent sub-particles (quarks).???? Read: Chap 23 12/04/14 slide 3

13 Extrapolate the expansion back in time The Universe is current expanding. Imagine reversing the arrow of time so that the Universe is then contracting... What happens? The density increases. The temperature increases. Universe becomes ionized, like the inside of a star As we keep going, fusion may occur. Still later, the temperatures get so high that the baryons break up into constituent sub-particles (quarks).???? Realm of the Read: Chap 23 12/04/14 slide 3

14 Extrapolate the expansion back in time Read: Chap 23 12/04/14 slide 4

15 The early universe must have been extremely hot and dense Read: Chap 23 12/04/14 slide 5

16 Photons converted into particle-antiparticle pairs and vice-versa E = mc 2 Early universe was full of particles and radiation because of its high temperature Read: Chap 23 12/04/14 slide 6

17 Unification of fundamental physical forces Four known forces in Universe: (1) Strong Force (2) Electromagnetism (3) Weak Force (4) Gravity Read: Chap 23 12/04/14 slide 7

18 Unification Do the forces unify at high temperatures? Four known forces in the Universe: (1) Strong Force (2) Electromagnetism (3) Weak Force (4) Gravity Read: Chap 23 12/04/14 slide 8

19 Unification Do the forces unify at high temperatures? Four known forces in the Universe: (1) Strong Force (2) Electromagnetism (3) Weak Force (4) Gravity Electroweak (Yes!) Read: Chap 23 12/04/14 slide 8

20 Unification Do the forces unify at high temperatures? Four known forces in the Universe: (1) Strong Force (2) Electromagnetism (3) Weak Force (4) Gravity Electroweak (Yes!) GUT (Maybe) Read: Chap 23 12/04/14 slide 8

21 Unification Do the forces unify at high temperatures? Four known forces in the Universe: (1) Strong Force (2) Electromagnetism (3) Weak Force (4) Gravity Electroweak (Yes!) GUT (Maybe) String theory (???) Read: Chap 23 12/04/14 slide 8

22 Particle colliders attempt to create early-universe conditions Read: Chap 23 12/04/14 slide 9

23 Running the clock forward from the beginning... Read: Chap 23 12/04/14 slide 10

24 1. Planck Era 2. GUT Era Before Planck time ( sec) No theory of quantum gravity Lasts from Planck time ( sec) to end of GUT force ( sec) 3. Electroweak Era Lasts from end of GUT force ( sec) to end of electroweak force ( sec) Read: Chap 23 12/04/14 slide 11

25 4. Particle Era Matter and antimatter nearly equal 1 extra proton for 10 9 protonantiproton 5. Era of Begins when matter annihilates remaining antimatter at sec Nuclei begin to fuse 6. Era of Nuclei Helium nuclei form at this age 3 minutes Universe too cool to blast helium apart Read: Chap 23 12/04/14 slide 12

26 7. Era of Atoms Atoms form at age 380,000 years Background radiation released 8. Era of Galaxies Galaxies form at age 1 billion years Read: Chap 23 12/04/14 slide 13

27 Evidence for the Big Bang The Evidence Detected the leftover radiation from the Big Bang! Read: Chap 23 12/04/14 slide 14

28 Evidence for the Big Bang The Evidence Detected the leftover radiation from the Big Bang! Radiation from the last photon scattering with matter (like photosphere of star) Radiation from this epoch will shift to larger wavelength as Universe expands Black body temperature radiation will decrease Read: Chap 23 12/04/14 slide 14

29 Evidence for the Big Bang The Evidence Detected the leftover radiation from the Big Bang! 2. The Big Bang theory correctly predicts the abundance of helium and other light elements. Read: Chap 23 12/04/14 slide 14

30 Evidence for the Big Bang The Evidence Detected the leftover radiation from the Big Bang! 2. The Big Bang theory correctly predicts the abundance of helium and other light elements. Observed helium abundance too large to be the result of supernovae Extrapolate backwards in time At some point: Universe as hot as star center Fuse H to He! Read: Chap 23 12/04/14 slide 14

31 Universe now consists of protons and electrons (some He,... ): ionized H Universe continues to expand and cool At t = 300,000 years with T = 3000K: Photons no longer sufficiently energetic to keep H ionized Atoms form! Universe becomes transparent! Read: Chap 23 12/04/14 slide 15

32 Background radiation from Big Bang has been freely streaming across Universe since atoms formed at temperature 3,000 K: visible/ir Read: Chap 23 12/04/14 slide 16

33 Cosmic Microwave Background: Discovery CMB = Cosmic Microwave Background Engineers designed first microwave satellite uplink Signal independent of pointing antenna Assumed additional noise in their receivers that they could not understand Discovered relic cosmic radiation: T=2.73 K Read: Chap 23 12/04/14 slide 17

34 Cosmic Background Explorer The microwave background is a precise blackbody! Expansion of universe has redshifted thermal radiation from that time to 1000 times longer wavelength: microwaves Read: Chap 23 12/04/14 slide 18

35 Cosmic Background Explorer The microwave background is a precise blackbody! Temperature profile close to isotropic but not quite Read: Chap 23 12/04/14 slide 18

36 BB temperature on the sky WMAP gives us detailed baby pictures of structure in the universe Read: Chap 23 12/04/14 slide 19

37 Read: Chap 23 12/04/14 slide 20

38 Abundance of the elements Protons and neutrons combined to make long-lasting helium nuclei when universe was 3 minutes old Read: Chap 23 12/04/14 slide 21

39 Abundance of the elements Big Bang theory prediction: 75% H, 25% He (by mass) Matches observations of nearly primordial gases Read: Chap 23 12/04/14 slide 22

40 Abundance of the elements Abundances of other light elements agree with Big Bang model having 4.4% normal matter more evidence for WIMPS! Read: Chap 23 12/04/14 slide 23

41 : How do we observe the radiation left over from the Big Bang? Radiation left over from the Big Bang is now in the form of microwaves the cosmic microwave background which we can observe with a radio telescope. How do the abundances of elements support the Big Bang theory? Observations of helium and other light elements agree with the predictions for fusion in the Big Bang theory Read: Chap 23 12/04/14 slide 24

42 Cosmological problems 1. Horizon or Isotropy problem Microwave background is extremely uniform But, photons reaching us today were emitted beyond their particle horizon Read: Chap 23 12/04/14 slide 25

43 Cosmological problems 1. Horizon or Isotropy problem Microwave background is extremely uniform But, photons reaching us today were emitted beyond their particle horizon 2. Flatness problem: why is Ω o = 1? Unlikely to be random Must be a physical cause Read: Chap 23 12/04/14 slide 25

44 of the Universe The Universe is flat with only a 0.4% margin of error This implies an infinite volume The Universe is much larger than the volume we can directly observe Read: Chap 23 12/04/14 slide 26

45 ary Universe Rapid period of expansion: Lasted sec Scale factor R(t) increased by factor of Speculation: some change in the nature of physical laws created large amount of energy Like latent heat from in freezing water to ice Read: Chap 23 12/04/14 slide 27

46 ary Universe Rapid period of expansion: Lasted sec Scale factor R(t) increased by factor of Speculation: some change in the nature of physical laws created large amount of energy Like latent heat from in freezing water to ice Read: Chap 23 12/04/14 slide 27