A100H Exploring the Universe: Big Bang Theory. Martin D. Weinberg UMass Astronomy

Transcription

1 A100H Exploring the : Martin D. Weinberg UMass Astronomy astron100h-mdw@courses.umass.edu April 21, 2016 Read: Chap 23 04/26/16 slide 1

2 Early Final Exam: Friday 29 Apr at 10:30 am 12:30 pm, here! Emphasizes Chapters Some topics from entire course folded in... Same format: approximately 2/3 multiple choice, 1/3 short answer Read: Chap 23 04/26/16 slide 2

3 Early Final Exam: Friday 29 Apr at 10:30 am 12:30 pm, here! Today What are the features of the Big Bang theory? The Early What is the implied history of the according to the Big Bang theory? Evidence for the Big Bang theory? Read: Chap 23 04/26/16 slide 2

4 Early Final Exam: Friday 29 Apr at 10:30 am 12:30 pm, here! Today What are the features of the Big Bang theory? The Early What is the implied history of the according to the Big Bang theory? Evidence for the Big Bang theory? Your questions? Read: Chap 23 04/26/16 slide 2

5 Extrapolate the expansion back in time Early Read: Chap 23 04/26/16 slide 3

6 Early Early The early universe must have been extremely hot and dense Read: Chap 23 04/26/16 slide 4

7 Early Early Photons converted into particle-antiparticle pairs and vice-versa E = mc 2 E = hν = hc λ Early universe was full of particles and radiation because of its high temperature Read: Chap 23 04/26/16 slide 5

8 Unification of fundamental physical forces Early Four known forces in the present-day : (1) Strong Force (2) Electromagnetism (3) Weak Force (4) Gravity Read: Chap 23 04/26/16 slide 6

9 Unification Early Do the forces unify at high temperatures? suggests that they do! Four known forces in the : (1) Strong Force (2) Electromagnetism (3) Weak Force (4) Gravity Read: Chap 23 04/26/16 slide 7

10 Unification Early Do the forces unify at high temperatures? suggests that they do! Electroweak (Yes!) Four known forces in the : (1) Strong Force (2) Electromagnetism (3) Weak Force (4) Gravity Read: Chap 23 04/26/16 slide 7

11 Unification Early Do the forces unify at high temperatures? suggests that they do! Electroweak (Yes!) Four known forces in the : (1) Strong Force (2) Electromagnetism (3) Weak Force (4) Gravity GUT (Maybe) Read: Chap 23 04/26/16 slide 7

12 Unification Early Do the forces unify at high temperatures? suggests that they do! Electroweak (Yes!) GUT (Maybe) Four known forces in the : (1) Strong Force (2) Electromagnetism (3) Weak Force (4) Gravity String theory (???) Read: Chap 23 04/26/16 slide 7

13 Early Particle colliders attempt to create early-universe conditions Read: Chap 23 04/26/16 slide 8

14 Early Running the clock forward from the beginning... Read: Chap 23 04/26/16 slide 9

15 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 04/26/16 slide 10

16 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 too cool to blast helium apart Read: Chap 23 04/26/16 slide 11

17 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 04/26/16 slide 12

18 Evidence for the Big Bang Early The Evidence The Big Bang theory correctly predicts the abundance of helium and other light elements. Read: Chap 23 04/26/16 slide 13

19 Evidence for the Big Bang Early The Evidence 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: as hot as star center Fuse H to He! Read: Chap 23 04/26/16 slide 13

20 Evidence for the Big Bang Early The Evidence The Big Bang theory correctly predicts the abundance of helium and other light elements. 2. Detected the leftover radiation from the Big Bang! Read: Chap 23 04/26/16 slide 13

21 Evidence for the Big Bang Early The Evidence The Big Bang theory correctly predicts the abundance of helium and other light elements. 2. Detected the leftover radiation from the Big Bang! becomes transparent to radiation soon after electrons combine with nuclei Prediction: Cosmic Microwave Background Radiation from this epoch will shift to larger wavelength as expands Black body temperature radiation will decrease Read: Chap 23 04/26/16 slide 13

22 Evidence for the Big Bang Early The Evidence The Big Bang theory correctly predicts the abundance of helium and other light elements. 2. Detected the leftover radiation from the Big Bang! Read: Chap 23 04/26/16 slide 13

23 Abundance of the elements Early Protons and neutrons combined to make long-lasting helium nuclei when universe was 3 minutes old Read: Chap 23 04/26/16 slide 14

24 Abundance of the elements Early Big Bang theory prediction: 75% H, 25% He (by mass) Matches observations of nearly primordial gases Read: Chap 23 04/26/16 slide 15

25 Abundance of the elements Early Abundances of other light elements agree with Big Bang model having 4.4% normal matter more evidence for WIMPS! Read: Chap 23 04/26/16 slide 16

26 now consists of protons and electrons (some He,... ): ionized H continues to expand and cool At t = 300,000 years with T = 3000K: Photons no longer sufficiently energetic to keep H ionized Atoms form! becomes transparent! Read: Chap 23 04/26/16 slide 17

27 Early Background radiation from Big Bang has been freely streaming across since atoms formed at temperature 3,000 K: visible/ir Read: Chap 23 04/26/16 slide 18

28 Early Like photosphere of star Background radiation from Big Bang has been freely streaming across since atoms formed at temperature 3,000 K: visible/ir Read: Chap 23 04/26/16 slide 18

29 Cosmic Microwave Background: Discovery Early 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 04/26/16 slide 19

30 Cosmic Background Explorer Early 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 04/26/16 slide 20

31 Cosmic Background Explorer Early The microwave background is a precise blackbody! Temperature profile close to isotropic but not quite Read: Chap 23 04/26/16 slide 20

32 BB temperature on the sky Early WMAP gives us detailed baby pictures of structure in the universe Read: Chap 23 04/26/16 slide 21

33 Early Read: Chap 23 04/26/16 slide 22

34 Early 1. Why is the so close to close to the critical solution? Called the flatness problem Read: Chap 23 04/26/16 slide 23

35 Early 1. Why is the so close to close to the critical solution? Called the flatness problem 2. Why is the so isotropic? Photons we see from opposite directions could never have been in contact. Why is the temperature the same? Called the horizon problem Read: Chap 23 04/26/16 slide 23

36 Early The flatness problem Three types of s: Closed, open, and flat. Geometry of our universe appears flat Read: Chap 23 04/26/16 slide 24

37 Early The flatness problem Three types of s: Closed, open, and flat. Geometry of our universe appears flat Mass-energy density and expansion rate of the universe appear to be nearly perfectly balanced, even 14 billion years later when minor variations should have grown drastically! Why the minor variations haven t increased dramatically? Did the variations not exist? Did some unknown physics prevent their growth? Did some unknown physics smooth them out? Read: Chap 23 04/26/16 slide 24

38 Early The horizon problem Look in some direction = looking back in time There s a boundary of 14 billion (or so) light-years in all directions If there is anything farther away than that, there is no way for it to have ever communicated with us. This is called the horizon. Choose a direction and you observe CMB from 14 billion light-years away (call this Point A). Observe in opposite direction (call this Point B); you see exactly the same sort of CMB in that direction. Read: Chap 23 04/26/16 slide 25

39 Early The horizon problem This suggests the CMB in the has diffused throughout the, like heating up an oven The thermal information seems to be have been transferred Points A and B Physicists call this: thermal equilibrium But Points A and B are 28 billion light-years apart We only have 14 billion years to send a signal Therefore, Points A and B could not have communicated with each other in the age of the How did they become the same temperature if there s no way for heat to transfer between them? This is the horizon problem Read: Chap 23 04/26/16 slide 26

40 Early A period of rapid expansion early in the history of the solves both problems! Originally proposed by Alan Guth in 1980 This model asserts that the early Universal expanded at an exponential rate for a short period How is the horizon problem is solved? Different regions we see were close enough to communicate at early time During inflation, space expanded so rapidly that these close regions were spread out to cover the visible Read: Chap 23 04/26/16 slide 27

41 Early A period of rapid expansion early in the history of the solves both problems! Originally proposed by Alan Guth in 1980 This model asserts that the early Universal expanded at an exponential rate for a short period How is the horizon problem is solved? How is the flatness problem solved? Inflation actually flattens the universe! Picture an uninflated balloon. As the balloon expands, though, the surface smoothes out. According to inflation theory, this happens to the fabric of the as well. Read: Chap 23 04/26/16 slide 27

42 Early Other successes of the theory: Inflation also provides the seeds for the structure that we see in our universe today. Tiny energy variations during inflation, due simply to quantum uncertainty, become the sources for matter to clump together, eventually becoming galaxies and clusters of galaxies. Read: Chap 23 04/26/16 slide 28

43 Early Problems with the theory: The exact mechanism that would cause and turn off the inflationary period isn t known. Thought be energy generated in a phase transition. E.g. as water freezes it heats its surroundings. Many technical aspects of inflationary theory remain unanswered, though the models include a scalar field called an inflaton field and a corresponding theoretical particle called an inflaton. Most cosmologists today believe that some form of inflation likely took place in the early universe. Read: Chap 23 04/26/16 slide 28

44 Early Read: Chap 23 04/26/16 slide 29

45 Early 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 04/26/16 slide 30

46 Early How do we account for the geometry and isotropy of the? A rapid period of expansion called inflation makes the flat and allows regions that were in contact at early times to be spread over very large distances today. Read: Chap 23 04/26/16 slide 31

47 Early Read: Chap 23 04/26/16 slide 32