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

Topics Big Bang Cosmology The Accelerating Universe Summary

Big bang cosmology

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.

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.

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

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

Cosmic Background Explorer (COBE) Launched November 1989 T = 2.725 +/- 0.002 K

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.

Wilkinson Microwave Anisotropy Probe June 30, 2001 Kennedy Space Center http://map.gsfc.nasa.gov

(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

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 2003. 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.

Planck Mission to L2 (2009)

Planck Measurements (2013)

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.

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?

The accelerating universe

Breakthrough of the Year, 1998

The phantom menace

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?