THE
INFLATIONARY UNIVERSE
Before discussing what inflation actually is, let us consider what are the
problems facing the Big Bang theory. There exists three main problems: 1) the homogeneity
and isotropy of the Universe, 2) the matter density of the Universe (the curvature of space-time), and
3) the absence of magnetic monopoles.
The homogeneity and isotropy of the Universe. Consider the following:
because the light travels at 300000 kms/sec., the farther we look at in the Universe
farther in time we see. Now, if look at both directions totally opposed to each other in the sky,
we see regions that are separated by a distance of up to 30 million light years. Such regions could not
have time to communicate between them, since a beam of light would take longer than the
age of the Universe to reach the other region. However, it seems that the matter distribution in the
whole Universe has the same matter density. So, how could these separate regions could
influence each other?
The matter density of the Universe (the curvature of space-time). The
Universe had three options in the way it expands. It could have been a parabolic Universe, an hyperbolic Universe,
or a closed Universe. But it seems we live in a parabolic Universe which is an
unstable solution. This means that the conditions at its origins must have been
extremely precise. How to explain this precision?
The absence of magnetic monopoles. All modern particle physics theories predict
the existence of magnetic monopoles. However, none has been discovered so far.
These three problems we have mentioned above have a possible solution (a walk around kind of solution).
The solution is a new version of the Big Bang theory: the Inflationary Universe. This
theory was first proposed by A. Guth back in 1981. According with this theory, the
Universe suffered a violent expansion (inflation) when its age was of 10E-35 seconds
and its temperature 10E28 Kelvin due to a real phase transition. The expansion was
so violent that the size of any region grew by a factor of 10E50 in just 10E-35 sec.
This huge expansion can explain the isotropy of the Universe since initially
all the points of our visible Universe were closer between them than what is
predicted by the classic Big Bang theory. This also implies that the matter
density has to be closer to the critical density. Finally, it can explain the
dilution of the magnetic monopoles since there were not so many defects in our
region of the Universe.
Although this theory can explain the three major issues of the standard Big Bang
cosmology, it has shortcomings on its own. One is the fact that the amount of
inflation has to be fine tuned by hand, and again the question of why it has
to be so precisely set rises.
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