In GR cosmology, there is a big bang singularity. For every
particle, there was only a finite time in the past. During this
finite time, only a finite distance may have been reached. This
allows to define a horizon of influence for each event — all
events which may have had a common cause in the past. Now, in
standard GR cosmology this horizon is small. Too small to
explain some observable facts: The second problem is much more
serious — some homogeneous distribution may have caused by
something else, last but not least homogeneous initial values
seem to be a meaningful assumption, based on Ockham's razor. But
if initial fluctuations are greater than horizon size, this
requires a very strange conspiracy forbidden by current physics.
The GR solution of this problem is inflation in the early
universe. That means, some additional mechanism (with some
hypothetical origin in particle physics) has to give an
additional term in the early universe. This additional term
leads to an acceleration of the expansion of the