7 Cosmic Inflation
The concordance FLRW Big Bang model describes a homogeneous and isotropic
adiabatically expanding Universe, having a beginning of space and time with very
problematic initial conditions: nearly infinite temperature and density, even more
homogeneous than now since inhomogeneities are unstable because of gravitation,
and tend to grow with time. Where did the 10^90 particles which make up the visible
Universe come from?
Aside from such shortcomings the FLRW model has, as so far presented, been
essentially a success story. We are now going to correct that optimistic picture and
present a remedy: cosmic inflation.
In Section 7.1 we shall discuss problems caused by the expansion of space-time: the
horizon problemrelated to its size at different epochs, themonopole problemassociated
with possible topological defects, and theflatness problemassociated with its metric.
There are a large number of models of cosmic inflation, the simplest being the
classical orconsensusslow-roll model based on a a single scalar field, which we shall
study in Section 7.2. It is characterized by a de Sitter-like expansion, terminating with
a huge entropy increase, in violation of the law of entropy conservation.
Most other models do not provide clear predictions regarding the nature of matter
created after inflation nor the mode of exiting inflation in a vacuum that can excite
the Standard Model degrees of freedom.
In Section 7.3 we discuss the scenario of thechaotic model, which introduces a
bubble universe where we inhabit one bubble, totally unaware of other bubbles. The
inflationary mechanism is the same in each bubble, but different parameter values
may produce totally different universes. Since our bubble must be just right for us to
exist in, this model is a version of theAnthropic Principle. We close this section with
a discussion of the predictions of inflation.
In Section 7.4 we turn our attention to an alternative to consensus inflation, a cyclic
or bouncing universe of five dimensions containing dark energy and gravity as driving
forces.
Introduction to Cosmology, Fourth Edition. Matts Roos
© 2015 John Wiley & Sons, Ltd. Published 2015 by John Wiley & Sons, Ltd.