Matter and radiation dominated universes

Cosmology (Winter, 2013)

January 21, 2013

After reviewing the basic equation for an expanding universe, Professor Susskind solves the equation explicitly for a zero energy universe, and then extends the derivation to universes with non-zero energy.  These universes can take two forms: matter-dominated universes, and radiation-dominated universes.  The radiation-dominated form characterizes our early universe, and the matter-dominated form characterizes our universe today - or so cosmologists believed until observations led to theories of dark energy in the 1990s.