1. Harrison B. Prosper Florida State University YSP
Cosmology 2
Harrison B. Prosper
Florida State University
YSP

2. Topics
Big Bang Cosmology
The Accelerating Universe
Summary

3. Big bang cosmology

5. In the distant past the visible Universe was much smaller than it is today and therefore much, much hotter.
Therefore, the Universe must have been filled with very short wavelength photons.
As the universe expanded, it cooled and all wavelengths were stretched by the same factor by which the universe expanded.

6. Big Bang Cosmology – Predictions
The universe should be expanding
Prediction 2
The universe should be made of roughly ¾ hydrogen and ¼ helium and not much else
Prediction 3
Today, the universe should be filled with microwaves, with a perfect thermal spectrum.

7. The Abundance of Elements
Element Structure Abundance (%)
Hydrogen (p) 77
Helium-4 (2p,2n) 23
Deuterium (p,n) 10-3
Helium-3 (2p,n) 10-3
Lithium (3p,4n) 10-8

8. Cosmic Microwave Background (CMB)
Arno Penzias and Robert Wilson (1965)
While preparing a radio telescope at Bell Labs to observe the Milky Way they discovered the CMB!
1978 Nobel Prize

9. Cosmic Background Explorer (COBE)
Launched November 1989
T = / K

10. COBE – (1991) Measured temperature fluctuations of 1 part in 100,000.
Snapshot of universe when it was ~ 300,000 years old
when photons could finally travel freely.

11. Wilkinson Microwave Anisotropy Probe
June 30, 2001
Kennedy Space Center

12. (Optional) Challenge Problem!
Show that the distance of L1
from the Earth is given
by the implicit equation:
Assume circular orbits for which the centripetal acceleration in F = ma is v2 / r
Remember objects orbit about the center of mass, but the gravitational force depends on the objects separation
The orbital period T at L1 is the same as that of Earth

13. WMAP Measurements
Figure 19–12 Temperature fluctuations on the microkelvin level displayed on an all-sky map. (B) The higher resolution provided from NASA’s Wilkinson Microwave Anisotropy Probe. These data, based on the first year of observations, were released in early Many cosmological parameters were determined, including Hubble’s constant and the percentages of ordinary matter, dark matter, and dark energy. The following three years of data, and eventually the European Space Agency’s Planck Mission (to be launched in 2007), should do even better.
See the images opening Chapter 15 for WMAP images at three different microwave wavelengths, which were used to compile the image shown here.

14. Planck Mission to L2 (2009)

15. Planck Measurements (2013)

16. Figure 19–11 The relative number and amplitude of variations in the sky versus their angular size. Though variations appear over a wide range of scales, the most common ones appear to be about 1° in diameter, or twice the full moon. As of 2003, at least three peaks can be seen. The sizes and positions of the peaks in the graph indicate that the Universe is flat and allows the percentage of nuclear particles in the Universe to be calculated. The curves show theoretical fits to the data shown with error bars. Do not confuse such diagrams of fluctuation peaks with Planck curves, which graph intensity versus wavelength for a given temperature. (B) The experimental results based on the Wilkinson Microwave Anisotropy Probe (WMAP) observations and observations from the CBI and ACBAR telescopes, with a solid line drawn from the post-WMAP best model.

18. Big Bang Cosmology – Puzzles
The Flatness Problem
Why is the global geometry of space Euclidean?
The Horizon Problem
Why is the temperature of the CMB the same at opposite sides of the Universe?
The Smoothness Problem
Why, on very large scales is the Universe so smooth?
Why, on smaller scales, are galaxies distributed in huge sheets, separated by great voids?

19. The accelerating universe

20. Breakthrough of the Year, 1998

25. The phantom menace

31. Summary Big Bang Cosmology The universe began a finite time ago
The universe had a hot dense beginning
Space is globally flat
Galaxies were seeded by quantum fluctuations
Big Bang Puzzles
What caused the big bang?
Why this particular universe?
What is causing the accelerated expansion? Is it dark energy? If so, what is dark energy?