1. Lecture 28: Inflation Astronomy 1143 – Spring 2014

2. History of Inflation

3. Key Ideas Universe expanded very quickly in the early times thanks to inflation Energy released from phase transition? Inflation can explain The flatness problem The monopole problem The horizon problem The growth of quantum fluctuations Our lumpy Universe comes from these tiny fluctuations, thanks to gravity Detected of ripples in the CMB from gravity waves – predicted by inflation models

4. Inflation in the Early Universe Inflation Inflation = a brief period of highly accelerated expansion, early in the history of the universe. Space expanded much faster than the speed of light At t ≈ 10 -34 seconds, the universe started expanding exponentially, doubling in size every 10 -34 seconds. Inflation ended at t ≈ 10 -32 seconds, after expansion by a factor 10 30.

5. Beginning of Inflation What caused inflation to start? According to the particle physicists: universe underwent a phase transition at t ≈ 10 -35 s. Phase transition associated with the end of the GUT era – separation of strong from electroweak force dark energy The energy released by the phase transition at t ≈ 10 -35 s acts (temporarily) like dark energy.

6. Example of Phase Transition The freezing of water is an example of a phase transition Liquid water has no preferred orientation; ice does This is called symmetry breaking Idea is that the separation of the strong force from the electroweak force broke symmetries found in GUTs. This releases energy.

7. Liquid to Ice Transition

8. When water goes from liquid to solid, it goes from a random state to an ordered state. Energy is released.

9. During a freeze in Florida, orange trees are sprayed with water. Why? The energy released by freezing water warms the leaves & fruit.

10. Inflation to the Rescue If Inflation happened it would explain the flatness problem the monopole problem the horizon problem how quantum fluctuations became the seeds of large-scale structure

11. The Flatness Problem Why should the average density of the universe ( ρ ) be so close to the theoretical critical density ( ρ crit )? Ω There’s no law of nature that says Ω (= ρ/ρ crit ) must be equal to one. Why not Ω = 0.01 or Ω = 100? fairly insanely Since the universe is fairly close to flat today, it must have been insanely close to flat in its early history.

12. Really, Really Flat

13. Inflation greatly increases the radius of curvature of the Universe. How does inflation solve the flatness problem?

14. Suppose the radius of the universe was only one nanometer (10 -9 meter) before inflation. After inflation, the radius would be 30,000 parsecs; today, 3 trillion trillion megaparsecs. Really, really increases the radius

15. The Monopole Problem One of the frontiers of modern physics is to create the correct GUTs and TOEs A prediction of the best models at the present time is the existence of magnetic monopoles Just a North or South pole by itself Not yet detected in the laboratory Inflation solves this by diluting the density of magnetic monopoles After inflation, just 1 magnetic monopole every 1x10 61 Mpc 3, much bigger than our current horizon

16. The Horizon Problem The Universe is remarkably homogeneous and isotropic This is easy to do if the various parts of the observed Universe can share energy, etc. so that the temperature becomes uniform But without inflation, the whole observable Universe was never in contact 400,000 ly = 1 degree on the sky not 180 Nothing can travel faster than light!

17. The observed Universe was in contact thanks to Inflation

18. But, wait! Universe isn’t homogeneous today Inflation can help with that, too! Inflation

19. On subatomic scales, the universe is full of quantum fluctuations. A vacuum looks empty, but it’s full of particles & antiparticles being created & destroyed. Inflating Quantum Fluctuations

20. Ordinarily, these quantum fluctuations are on tiny scales.However, inflation increased tiny scales (1 nanometer) to galaxy-sized scales (30,000 parsecs)! Regions with higher density will start to grow by gravity. We can see these regions when the Universe is 400,000 years old

21. Seeds of Structure slightly much A region that was slightly denser than average will eventually become much denser than average; it’s compressed by its own gravity Low-amplitude density fluctuations at t ≈ 400,000 years give rise to high-amplitude fluctuations at t ≈ 13.7 billion years. Let’s look for density fluctuations in the Cosmic Microwave Background Radiation Density fluctuations will appear as temperature fluctuations because compressed gas heats up.

22. Spherical Earth can be projected onto a flat map: So can the celestial sphere: (visible light) Mapping the Sky

23. isotropic Observation: Temperature of CMB is nearly isotropic (the same in all directions). homogeneous Interpretation: early universe was nearly homogeneous (the same in all locations). T = 2.725 K Mapping the CMB (color = temperature)

24. hottercooler Observation: Temperature of CMB is slightly hotter toward Leo, cooler toward Aquarius (on opposite side of sky). cooler → ← hotter Temperature fluctuation = 1 part per 1000. mK = 0.001 Kelvin

25. News Flash: The Earth is Moving Doppler shift Interpretation: difference in temperature results from a Doppler shift. Earth orbits Sun (v ≈ 29 km/s) Sun orbits center of the Galaxy (v ≈ 220 km/s) Galaxy falls toward Andromeda Galaxy (v ≈ 50 km/s) Local Group falls toward Virgo Cluster (v ≈ 200 km/s)

26. blueshifted Cosmic light from direction of Leo is slightly blueshifted (shorter wavelength, higher temperature). blueshifted (Leo) redshifted (Aquarius) Net motion: toward Leo, with a speed v ≈ 300 km/s ≈ 0.001 c.

27. Observation: After subtracting the effect of our motion through space, CMB still shows hot & cold spots, about 1 degree across. Temperature fluctuation = 1 part per 100,000 ← hotter cooler →

28. Temperature Tells Us About Density Higher temperatures come from compressed gases density Regions that were compressed had higher density Hot cold Hot spots in the CMB are higher in temperature than cold spots by 1 part per 100,000. densityfluctuations Implication: the density fluctuations in the early universe were also small (about 1 part per 100,000).

29. The high-density (warm) and low-density (cool) spots on the CMB… …are tiny quantum fluctuations that have been blown up in scale.

31. denser more massive A dense region becomes denser & more massive with time; its gravity attracts surrounding matter. Quantum fluctuations blown up by inflation are the “acorns”. Great Oaks from Tiny Acorns Grow.

32. The Usefulness of Inflation But is it correct?

33. Gravity Waves & Inflation Inflation is predicted to have a strong influence on the spacetime of the early Universe Quantum overdensities – gravity pull Expansion of spacetime itself Disturbances in spacetime = gravity waves These gravity waves will be very difficult to detect with the gravity waves detector such as LIGO.

34. BICEP2 results

35. Polarization of Light

36. Gravity Waves & the CMB Gravity waves traveling at the time of recombination stretch & squeeze the space around electrons Therefore, those electrons see more energetic photons come from one direction than another

37. Gravity Waves & the CMB Remember: “hotter” photons have higher energy. Therefore, they “win” and their signal dominates

38. Polarization and Light

39. Polarization Unfortunately, hotter photons also come from hotter regions in space! So the signal is very difficult to detect and interpret. However, the polarization patterns are different for these two cases

40. What Density does to CMB Polarization

41. The Signal!