Tests of Big Bang Cosmology
http://edu-observatory.org/olli/tobbc/Week7.html   or   index.html

Foundations of the Big Bang Model - Theory

Foundations of the Big Bang Model - Concepts

  To this point, the only assumption we have made about the                   
  universe is that its matter is distributed homogeneously and
  isotropically on large scales. There are a number of free
  parameters in this family of Big Bang models that must be fixed
  by observations of our universe. The most important ones are:
  the geometry of the universe (open, flat or closed); the
  present expansion rate (the Hubble constant); the overall
  course of expansion, past and future, which is determined by
  the fractional density of the different types of matter in the
  universe. Note that the present age of the universe follows
  from the expansion history and present expansion rate.

  Since both energy density and pressure contribute to the
  strength of gravity in General Relativity, cosmologists
  classify types of matter by its "equation of state" the
  relationship between its pressure and energy density. The basic
  classification scheme is:

  Radiation: composed of massless or nearly massless particles
  that move at the speed of light. Known examples include photons
  (light) and neutrinos. This form of matter is characterized by
  having a large positive pressure.

  Baryonic matter: In this cosmological context, this is
  "ordinary matter" composed primarily of protons, neutrons and
  electrons. This form of matter has essentially no pressure of
  cosmological importance.

  Dark matter: this generally refers to "exotic" non-baryonic
  matter that interacts only weakly with ordinary matter. While
  no such matter has ever been directly observed in the
  laboratory, its existence has long been suspected for reasons
  discussed in a subsequent page. This form of matter also has no
  cosmologically significant pressure.

  Dark energy: this is a truly bizarre form of matter, or perhaps
  a property of the vacuum itself, that is characterized by a
  large, negative pressure (repelling force). This is the only
  form of matter that can cause the expansion of the universe to
  accelerate, or speed up.

Tests of Big Bang Cosmology

  The Big Bang Model is supported by a number of important
  observations, each of which are described in more detail
  on separate pages:

  1. The expansion of the universe

  Edwin Hubble's 1929 observation that galaxies were generally
  receding from us provided the first clue that the Big Bang
  theory might be right.

  2. The abundance of the light elements H, He, Li

  The Big Bang theory predicts that these light elements should
  have been fused from protons and neutrons in the first few
  minutes after the Big Bang.

  3. The cosmic microwave background (CMB) radiation

  The early universe should have been very hot. The cosmic
  microwave background radiation is the remnant heat leftover
  from the Big Bang.

  These three measurable signatures strongly support the notion
  that the universe evolved from a dense, nearly featureless
  hot gas, just as the Big Bang model predicts.

Wilkinson Microwave Anisotropy Probe (WMAP) Results

WMAP Facts

WMAP Technical Papers