1916 - 1929 This decade saw the birth of cosmology –Einstein gave us a new theory of gravity (GR), that works for the whole Universe –Hubble discovered the Universe, and its expands!
FRW Equation Assuming homogeneous and isotropic universe (RW metric), then GR gives: Hubble Parameter Average density of matter a is the scale factor (radius) of the Universe relative to today k is the curvature of space-time of the Universe (a constant) Cosmological constant, but could be fn of time & space w=p/ =-1
3 Solutions to FRW equation ( =0) R time Bang Never stop! Stop at infinity Big crunch! Value of decides the fate of Universe! Like throwing a stone into space Larger universe Later in Universe
Search for two numbers (H 0 and 0 ) Subscript 0 means today (R=1), but formula holds at other cosmic times. Total energy density ( )
Luminosity Distance We cant measure distances in the Universe directly, so hard to measure geometry and expansion rate directly d L is the luminosity distance and depends on the cosmological parameters, z is the redshift
So is w=-1? 99.74% detection Percival et al. (2006) 143k + 465k 79k z~0.35 z~0.2 Percival et al. 2007 Measure ratio of angular- diameter distance between these redshifts (D 0.35 /D 0.2 ) D 0.35 /D 0.2 = 1.812 ± 0.060 (ratio should be 1.67 for cosmological constant)
Future Questions Is it a Cosmological Constant? Better measurements, specifically control of systematics (new experiments) Is it just a breakdown of GR on large scales? Probe universe using different measures (growth of structure). Again limited by systematics Better theory (any theory!) Parallels with HEP - large careful experiments worrying about large datasets and systematics DES, SDSS-III, WFMOS, DUNE, SPACE, SNAP, ADEPT