Inflationary Cosmology
In the 60's it became accepted that the universe began with the Big Bang
that occured about 15 billion years ago. The standard model as it evolved
in the 70's could give a good account for the history from the first millionth
second to our present time (well there are quite a lot of issues left to explain like
the mechanism of galaxy formation and such).
However that first millionth second was troublesome. The very first 10^-43 seconds
known as the Planck era would of course have to wait for a quantum theory of gravity
to be understood. What was more disturbing for the cosmologists was that the GUT models
predicted the existence of large numbers of monopoles.
Then in the early 80's it was realised that symmetry breaking mechanisms could cause
a scalar field to momentarily give rise to an equation of state known as false vacuum.
This false vacuum would cause the universe to expand at an exponential rate, if the time
scale for the universe to double in size was say 10^-33 seconds and the era of false vacuum
persisted to 10^-31 seconds then the universe would grow a factor of 2^100 times (or in more
familiar decimal notation 10^30 times). This would explain why no monopoles are observed.
This inflation also explains why the universe is so homogeneous on a large scale.
More detailed studies of such scalar fields showed that the inflation was not an entirely
smooth process. Quantum fluctuations would cause the scalar field to have a larger
amplitude in some areas and thus inflate more than its surroundings, this was known as
chaotic inflation. In fact these quantum fluctuations could be so large for a
sufficiently strong scalar field that such a fluctuation would equal the decay of the false
vacuum causing it to have a constant or even growing value in some areas.
This scenario is known as eternal inflation.
In the view of such an inflationary theory the term 'Big Bang' ought to apply at the end
of inflation in our local part of the universe (that occured those 15 billion years ago).
The first troublesome millionth of a second is really a finite but arbitrarily large amount of
time that has expired between the Planck era described by a TOE and the later epoch of
an effective GUT derived from this larger theory.
The period of this GUT then describes how the prevalence of matter over anti-matter
was established, also some relics like cosmic strings may be left from this time.
In view of all this the modern scenario of inflation gives 3 scales to the universe.
On the largest global scale the universe is very inhomogeneous due to large
fluctuations in the scalar field driving inflation.
On an intermediate regional scale the universe has a fractal structure
where new 'children-universes' sprout from an inflating parent universe.
The observable cosmos is only a small part on the local scale of the
universe where the fluctuations at the end of the inflationary era was very small.
When scientist looked deeper into these issues they discovered a weird
twist to the story.