December 2, 2011 – 10am class

1. December 2, 2011 – 10am class Prizes for Planet Hunters Review for midterm: Sunday, 6-8pm Midterm 3: Wed. Dec. 7 Review for final: Sunday Dec. 11, 6-8pm Today: Cosmic Microwave Background

2. Horizons The Earth has a horizon: we can’t see beyond it because of the Earth’s curved surface. A black hole has an event horizon: we can’t see into it because photons can’t escape.

3. The Ultimate Horizon The universe has a cosmological horizon: we can’t see beyond it because photons from beyond haven’t had time to reach us. Distance to cosmological horizon is approximately equal to the Hubble distance (c/H0 = 4300 Mpc).

4. Since the Universe has a finite age, there is a cosmological horizon. We can't see farther than 13.7 billion light years, since light from a galaxy farther than that has not had enough time to reach us. However, we assume that the Universe is infinite, and that what we see is a fair sample of the Universe.

5. Olber’s Paradox Why is the sky dark at night? If the Universe is infinite in space and time, then you expect that in every direction you would see a star Heinrich Olbers (1758-1840)

6. Olber’s Paradox Illustration:

7. Olber’s Paradox The sky is dark at night. Explanation: Since the Universe is only 13.7 billion years old, we only see to the cosmological horizon.

8. The Cosmic Microwave BackgroundRelic Radiation from the Primeval Fireball

9. The Cosmic Microwave Background • If we run the Hubble Expansion backwards the Universe was hotter and denser in the past. • The point at which the Universe was infinitely dense is THE BIG BANG. • At about 380,000 years after the Big Bang, the Universe cooled enough for protons and electrons to recombine into neutral atoms. At that point, the Universe suddenly became transparent. • t= 38000 years is called “Recombination”

10. We see a background of photons that were freed at that time: the Cosmic Microwave Background.

11. Cosmic Microwave Background (CMB) discovered at Bell Labs in 1965 by Penzias and Wilson

12. The CMB has a blackbody spectrum, with T=2.7K today. It peaks at microwave wavelengths.

13. The CMB has been studied by spacecraft (COBE and WMAP) and ground-based radio telescopes, and balloon borne telescopes at the South Pole. The all-sky map of the CMB shows it is very nearly uniform in every direction

14. Map of T across sky, as measured by WMAP T = 2.725, very accurately Planckian. Uniform to 1 part in 105

15. Subtracting T=2.725, what you see is a DIPOLE The CMB temperature is 3.353 K hotter in one direction, and 3.353 mK cooler in the opposite direction. Milky Way The CMB defines a “cosmic reference frame”. The Earth is moving with a “peculiar velocity” with respect to the “Hubble flow” of galaxies.

16. The observed dipole indicates that the Solar System is moving at 368+/-2 km/sec relative to the observable Universe in the direction galactic longitude l=263.85o and latitude b=48.25o with an uncertainty slightly smaller than 0.1o

17. Earth’s Motions: Do they add up to the CMB velocity? (1) Earth spins on its axis V≈ 0.5 km/sec at equator (2) Earth orbits Sun V ≈ 30 km/sec “heliocentric velocity” (3) Sun orbits Galactic Center, in Milky Way Galaxy V ≈ 225 km/sec

18. (4) Milky Way falling towards M31 V ≈ 100 km/sec (Andromeda) in the Local Group M31, Andromeda

19. (5) Local Group is falling into the V ≈ 220 km/sec Virgo supercluster of galaxies “Virgocentricinfall” center of the Virgo Cluster of Galaxies

20. (6) Virgo Supercluster is falling V ≈ 600 km/sec towards the Hydro and Centaurus clusters of galaxies “The Great Attractor” ~1016solar masses at 50 Mpc

21. Galaxies in the direction of the Great Attractor

22. Map of T across sky, as measured by WMAP T = 2.725, very accurately Planckian. Uniform to 1 part in 105

23. Subtracting T=2.725, what you see is a DIPOLE The CMB temperature is 3.353 K hotter in one direction, and 3.353 mK cooler in the opposite direction. Milky Way The CMB defines a “cosmic reference frame”. The Earth is moving with a “peculiar velocity” with respect to the “Hubble flow” of galaxies.

24. COBE data of the Cosmic Microwave Background c. 1992 First detection of temperature fluctuations, i.e. CMBR anisotropies Milky Way Subtract dipole  temperature fluctuations indicates density fluctuations which later collapse to form galaxies, clusters, etc.

25. WMAP temperature fluctuations These slightly overdense regions at the time of CMB production later became gravitationally unstable and collapsed to form galaxies, clusters of galaxies and all other structures we see in the Universe today. What created the fluctuations? To talk about this, we need to talk about what happened before recombination.

26. The History of the Universe from t=0 to t=380,000 years 1.  t=0 to the Planck Time.The Planck Time = 10-43 seconds after the Big Bang.

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

28. At the Planck time, space “boils” in a frothy quantum foam (on very small scales): Smooth on “large” scales: 10-12 cm Slightly rough Quantum Foam

29. Quantum Fluctuations In space/time: Spacetime Foam Near the time of inflation

30. 2.  The GUT era;  Inflation. GUT = grand unified theory When the GUT divided into the strong/electroweak/gravity forces, the Universe INFLATED very very rapidly.   In 10-36 sec, a piece of the Universe the size of an atom expanded to the size of the Solar System.