COSMOLOGY 2 Harrison B. Prosper Florida State University YSP Topics Big Bang Cosmology The Accelerating Universe Summary BIG BANG COSMOLOGY 3 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 Prediction 1 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 Hydrogen Helium-4 Deuterium Helium-3 Lithium Structure (p) (2p,2n) (p,n) (2p,n) (3p,4n) Abundance (%) 77 23 10-3 10-3 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! Problem 9: Show that the distance of L1 from the Earth is given by the implicit equation: Me R3 M E Me r 2 2 (Me M E ) r R (R r)2 1. Assume circular orbits for which the centripetal acceleration in F = ma is v2 / r 2. Remember objects orbit about the center of mass, but the gravitational force depends on the objects separation 3. The orbital period T at L1 is the same as that of Earth 12 WMAP Measurements Planck Mission to L2 (2009) 14 Planck Measurements (2013) 15 17 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 19 Breakthrough of the Year, 1998 20 21 22 23 24 THE PHANTOM MENACE 25 26 27 28 29 30 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?