The Cosmic Perspective of Cosmology

1. The Cosmic Perspective of Cosmology NOTES: Cosmological Terminology: Cosmology: the study of the large scale structure and evolution of the universe. Homogeneity: the claim the universe has the same density in all locations at the largest scale. Isotropy: the claim the universe looks the same in all directions.

2. Cosmology is NOT cosmetology… though a cosmologist makes up the face of the universe.

3. Cosmology is the study of the large scale structure and evolution of the universe: in space & time.

4. Homogeneity: the claim the universe has the same density in all locations at the largest scale. (Center for Cosmological Physics at the University of Chicago)

5. Cosmological redshift z = redshift) = Δλ/λ = v/c (for small v = expansion speed)

6. Isotropy: the claim the universe looks the same in all directions. Counts of distant galaxies and radio-sources appear to provide evidence that the universe is isotropic.

7. Pre 1998 Cosmology --ignoring dark energy in space: In 1998, using Supernova Ia’s, universe was found to be ruled by dark energy, making it accelerate. We ignore this at first.

8. Ω (Omega) = density of universe/critical density critical density = 10-29 grams per cubic centimeter

9. Alexander Friedmann (Russian) 1920 (utilizing Einstein’s General Theory): gave us three possible expanding universes.

10. With no dark energy: Flat Universe: Curvature = 0 Omega = 1 Destiny = barely stop expanding, it reaches a maximum speed but with no collapse Closed Universe: Curvature > 0 Omega > 1 Destiny = collapse Open Universe: Curvature < 0 Omega < 1 Destiny = endless decelerating expansion

11. Graph of Friedmann’s three expansions:

12. Galaxies are not flying apart through space, they are being carried away by the expansion of space itself (like small marks in the surface on an inflating balloon). The Big Bang was not like an explosion in a pre-existing space, but rather an explosion of space itself.

13. However, there were problems with Friedmann’s universe which resulted in the Inflationary Universe of Andre Linde (Russia1979) and Alan Guth (US 1980). Guth got the Nobel Prize for a theory that didn’t work. Later, Linde adapted his own theory to one that worked.

14. Three problems led to a theory of early rapid inflation: 1. Horizon Problem  The isotropy of the microwave background indicates that regions A and B in the universe were very similar to each other when the radiation we observe left them, but there has not been enough time since the Big Bang for them ever to have interacted physically with one another. Why then should they look the same?

15. 2. Flatness Problem If the universe deviates even slightly from critical density, that deviation grows rapidly in time. For the universe to be as close to critical as it is today, it must have differed from the critical density in the past by only a tiny amount.

16. 3. Magnetic monopole problem: Universe is believed to produces North magnetic poles without a South, but we don’t observe any. Friedmann’s universe didn’t expand enough to make them far apart.

17. Inflation: Scale vs time (sec):

18. Just as ice takes up more volume than water, space was believed to have undergone a expanded phase change related to the Grand Unified Theory (GUT) of elementary particles. (Guth’s Theory). However, this meant that protons should decay and they don’t.

19. Chaotic Inflation: Among many parallel universes, one expands like ours with a bubble that bursts and explains the lumpy structure of the universe necessary to produce clusters, galaxies, and stars. This is called Scale-free lumpiness. Andrei Linde (now at Stanford) showed this.