1. 17.3 The Big Bang and Inflation 17.4 Observing the Big Bang for yourself Our Goals for Learning What aspects of the universe were originally unexplained by the Big Bang model? How does inflation explain these features of the universe? How can we test the idea of inflation? How is the darkness of the night sky evidence for the Big Bang?

2. Why is the darkness of the night sky evidence for the Big Bang?

3. Olbers’ Paradox If universe were 1) infinitely large and infinitely old

4. Olbers’ Paradox If universe were 1) infinitely large and infinitely old 2) unchanging

5. Olbers’ Paradox If universe were 1) infinitely large and infinitely old 2) unchanging 3) everywhere the same

6. Olbers’ Paradox If universe were 1) infinitely large and infinitely old 2) unchanging 3) everywhere the same Then stars would cover the night sky

7. Olbers’ Paradox If universe were 1) infinitely large and infinitely old 2) unchanging 3) everywhere the same Then stars would cover the night sky

8. Night sky is dark because the universe changes with time

9. Night sky is dark because the universe changes with time: it’s only 13.75 billion years old (only a finite # of stars in observable universe)

10. Night sky is dark because the universe changes with time: it’s only 13.75 billion years old (only a finite # of stars in observable universe), and expansion of universe shifts some light from visible to longer wavelengths invisible to the human eye.

11. What aspects of the universe were originally unexplained by the Big Bang model?

12. Questions Unanswered by the original Big Bang model 1)Why is the overall distribution of matter and temperature in the universe so uniform, even on opposite sides of the sky?

13. Questions Unanswered by the original Big Bang model 1)Why is the overall distribution of matter and temperature in the universe so uniform, even on opposite sides of the sky? 2)Where do the tiny non-uniformities in the cosmic microwave background come from?

14. Questions Unanswered by the original Big Bang model 1)Why is the overall distribution of matter and temperature in the universe so uniform, even on opposite sides of the sky? 2)Where do the tiny non-uniformities in the cosmic microwave background come from? 3) Why is the density of the universe so close to the critical density?

15. Questions Unanswered by the original Big Bang model 1)Why is the overall distribution of matter and temperature in the universe so uniform, even on opposite sides of the sky? 2)Where do the tiny non-uniformities in the cosmic microwave background come from? 3) Why is the density of the universe so close to the critical density? An early episode of rapid inflation of the universe can solve all three mysteries!

16. How can microwave temperature be nearly identical on opposite sides of the sky?

17. Regions now on opposite side of the sky were close together before rapid inflation of the universe pushed them far apart

18. What caused inflation? At high temperature, enough energy is available to keep strong & electroweak forces unified as the GUT force (Grand Unified Theory). [Example: energy can keep a pencil standing symmetrically on its end, in a state of high potential energy]

19. Four known forces in universe: Strong Force Electromagnetism Weak Force Gravity Recall that forces unify at high temperatures Separation of GUT force into strong force + electroweak force releases energy

20. What caused inflation? At high temperature, enough energy is available to keep strong & electroweak forces unified as the GUT force (Grand Unified Theory). [Example: energy can keep a pencil standing symmetrically on its end, in a state of high potential energy] As universe cooled, GUT force splits into strong and electroweak forces and releases energy [Example: without energy, pencil breaks symmetry and falls over, converting gravitational potential energy into kinetic energy]

21. GUT Era Lasts from Planck time (~10 -43 sec) to end of GUT force (~10 -38 sec)

22. What caused inflation? At high temperature, enough energy is available to keep strong & electroweak forces unified as the GUT force (Grand Unified Theory). [Example: energy can keep a pencil standing symmetrically on its end, in a state of high potential energy] As universe cooled, GUT force splits into strong and electroweak forces and releases energy [Example: without energy, pencil breaks symmetry and falls over, converting gravitational potential energy into kinetic energy] That energy powers inflation, expands the universe!

23. How did inflation create the structure seen in the cosmic microwave background radiation (the CMBR)?

24. Quantum fluctuations On the smallest possible scales, the universe doesn’t play by “normal” rules. Particle/antiparticle pairs can appear & disappear, if they last for a short enough time (example: write a check, then deposit money to cover it).

25. Quantum fluctuations On the smallest possible scales, the universe doesn’t play by “normal” rules. Particle/antiparticle pairs can appear & disappear, if they last for a short enough time (example: write a check, then deposit money to cover it). So on these extremely small scales, the amount of energy in existence at any given time is different from point to point, even though the total energy is well defined and doesn’t change with time. Note: energy = mass = spacetime curvature

26. Energy fluctuations = mass fluctuations = spacetime fluctuations (scales below: 10 -12 cm, 10 -20 cm, 10 -33 cm)

27. Inflation can make observed CMBR structure by stretching tiny quantum ripples to enormous size. New ripples also appear later, but inflation was too quick for old ones to disappear. These ripples in density then become the seeds for all structures.

28. Why is the energy density of our universe so close to the critical density? In other words, why is the universe so close to “flat”?

29. Why is the energy density of the universe nearly uniform, and so close to the critical density? Overall geometry of the universe is closely related to total density of matter & energy. Density = Critical Density > Critical Density < Critical

31. Inflation of universe flattens overall geometry like the inflation of a balloon, causing overall density of matter plus energy to be very close to critical density

32. Thinking about our universe Our three-dimensional universe appears very close to flat (1 part in 50 at the moment), as well as infinite (infinite in three spatial directions) (2-dimensional analogies: flat = zero curvature = infinite piece of paper; positive curvature = like a balloon; negative curvature = like a Pringle)

33. Thinking about our universe Our three-dimensional universe appears very close to flat (1 part in 50 at the moment), as well as infinite (infinite in three spatial directions) Inflation predicts our universe is very close to flat (probably at the level of 1 part in 100,000) (2-dimensional analogies: flat = zero curvature = infinite piece of paper; positive curvature = like a balloon; negative curvature = like a Pringle)

34. Thinking about our universe Our three-dimensional universe appears very close to flat (1 part in 50 at the moment), as well as infinite (infinite in three spatial directions) Inflation predicts our universe is very close to flat (probably at the level of 1 part in 100,000) If the universe is that flat, for all intents and purposes it is exactly flat, and we may never know whether our universe started out exactly flat or curved (positively or negatively) (2-dimensional analogies: flat = zero curvature = infinite piece of paper; positive curvature = like a balloon; negative curvature = like a Pringle)

35. Universe started out at a point in time, but not in space. It may have been much smaller prior to inflation, or it may have started out infinitely large in space, just getting less dense with time. (Infinity divided by anything is still infinity.)

36. How can we test the idea of inflation?

37. Cosmic background radiation structure patterns will be different for different values of the parameters of the universe (age, normal matter density, dark matter density, dark energy density, etc.); inflation predicts some of those parameters.

38. Observed patterns of structure in universe agree (so far) with what inflation predicts.

39. Our Universe’s Properties, as Inferred from the Cosmic Microwave Background Overall geometry is flat –Total mass+energy has critical energy density Ordinary matter ~ 4.56%+-0.16% of critical Dark matter is ~ 22.7%+-1.4% of critical Dark energy is ~ 72.8%+-1.6% of critical Age of 13.75+-0.11 billion years

40. Our Universe’s Properties, as Inferred from the Cosmic Microwave Background Overall geometry is flat –Total mass+energy has critical energy density Ordinary matter ~ 4.56%+-0.16% of critical Dark matter is ~ 22.7%+-1.4% of critical Dark energy is ~ 72.8%+-1.6% of critical Age of 13.75+-0.11 billion years In excellent agreement with observations of present-day universe and inflationary Big Bang models with WIMPs as dark matter!

41. Actual observed map of the sky at microwave wavelengths: redder means higher temperature, bluer means lower

42. The Doppler shift changes the peak wavelength λ of the cosmic background radiation (CBR) across the sky If you then convert the peak wavelength to a temperature using Wien’s law (lambda * T = constant), you’ll get different temperatures at different places in the sky. The amount by which the temperature changes across the sky is larger if you’re moving faster So by measuring the temperature change, we can figure out how fast the Milky Way is moving

43. The Milky Way IS moving at 555 km/sec towards a distant supercluster of galaxies in the constellation of Lyra the Lyre (which contains the bright star Vega). The Shapley Supercluster is located 600 million light years away towards Lyra. Knowing the distance d to that supercluster, we can use our estimate of the Milky Way’s acceleration a to estimate the supercluster’s mass M, since a=GM/d 2 =GM gal N gal /d 2