Problems with the Hot Big Bang (2) ...
In addition to the horizon problem, there are two other problems concerning initial conditions for
the big bang that are of concern: the flatness problem, and the
magnetic monopole problem.
The Flatness Problem
The experimental
evidence is that the present Universe has very low geometrical curvature
(its spacetime is nearly flat). Theoretical arguments that are well established but
too complex to go
into here suggest that this is a very unlikely result of the evolution of the
Universe from the big bang, unless the initial curvature is confined to an
incredibly narrow range of possibilities. While this is not impossible, it does
not seem very natural. The left-hand
figure illustrates. Even a tiny change in initial conditions
for the big bang would have led to Universe very far from flat. Although the geometry of the
Universe may just happen to be flat, it would be more satisfying scientifically if there were a
fundamental reason why it should be so flat.
The Monopole Problem
It is believed that very shortly after the big bang the Universe was described by
ideas from elementary particle physics that are called grand unified theories (GUTs).
In these theories, at very high temperatures such
as those found in the instants after the Universe was created the strong, weak, and
electromagnetic forces were (contrary to the situation today) indistinguishable
from each other. We say that they were unified into a single force.
The adjacent figure illustrates this unification of forces (about which we will have more to say
shortly).
Although there is as yet no certain evidence for
the validity of GUTs, there is strong theoretical reason to believe that
they will eventually turn out to be essentially correct.
These theories imply that the very early Universe should produce extremely
massive particles called
magnetic monopoles (which are much more massive than any presently known particles),
and that there should be many such monopoles in the Universe today. However,
no one has ever found evidence for such a particle. So the final problem is: where are
the monopoles?
Modifying the First Moments of Creation
The big bang theory has been very successful in describing the evolution of our Universe.
Detailed consideration of the correct predictions of the big bang indicates that they
depend primarily on conditions in the Universe after it was about one second old.
This suggests that we might retain the successful predictions of the big bang,
and perhaps be able to address the three preceding difficulties, if we modify our theory of
the first instants of creation. To do so though, we must first make a slight detour and
consider some basic ideas from elementary particle physics concerning
grand unified theories.
Animation:
Problems of the big bang and the inflationary solution.
