Assumptions are important components of the models that we construct to represent atoms, electromagnetic radiation, planetary composition, and so forth One often makes numerous assumptions at the beginning of an investigation However, at the end of the investigation, the number of assumptions should be reduced,
The basic assumptions of Cosmology are 1) The Universe is homogeneous – every observer sees the same thing 2) The Universe is isotropic – there is no preferred direction in the universe The implication of these two statements is that the universe must either be static, or have purely radial motion (For example, if
Cosmology à la Newton • K ~ total energy of a comoving particle • K < 0, RHS > 0, since da/dt > 0 today, universe will expand forever • K = 0, RHS > 0, universe will expand forever but da/dt ? 0 as t ? ? • K > 0, RHS = 0 when a = 8?G? 0 /3Kc2, at this point expansion stops and universe starts to contract • Critical density
Fundamental Observations of Cosmology Hubble constant 70 km/s/Mpc ? age 14 billion year Geometry of Space-Time 1 It gets dark at night 2 The universe is expanding light from distant galaxies has red shifts ? distance no center 18-03a 18-03b Einstein's General Relativity matter ? local distortion Black Holes Large Scales ultimate fate
Assumptions of Randomness in Cosmology Models Leonid A Levin Boston University\ast Abstract Non-compact symmetries cannot be fully broken by randomness since non-compact groups have no invariant probability distributions In particular, this makes trickier the ``Copernican"" random choice of the place of the observer in infinite cosmology models
Mainstream cosmology currently sits on a few simple assumptions: about ^Hubble’s Law _, about ^redshift _, and about the universe beginning with a hot ^Big Bang Taken together, these ideas lead to models (like ^L-CDM _), and to predictions about the age and history of the universe