Beyond the Big Bang
Inflation: A way to face the problems mentioned
in last section was proposed
by Alan Guth in the early 1980s.
The idea of Guth is that the universe went through a phase transition,
such as when water freezes into ice. If the freezing can be done fast enough,
then it is possible to obtain super cooled water, i.e. water at a
temperature where ice is the stable state of water. This is not a situation
of thermal equilibrium, but it is known to occur under special circumstances.
Similarly, the universe went through a stage of super cooling when it was
below the temperature of the phase transition. In that state the energy
of the false vacuum (which is positive) increased; this was accompanied
by an increase of negative energy (gravity) because matter flew apart,
so that the sum of the two energies stayed the same
(energy is conserved).
As in the case of super cooled water, the metastable state cannot survive long, because things tend to come to thermal equilibrium. Thus, eventually water becomes ice and a transition from one phase (liquid) to another (solid) would have occurred. In this case energy is released. In the case of the universe, a phase transition occurred and was symmetry breaking, in the sense that forces and particles started to differentiate (break the symmetry that existed before). As water when it freezes doesn't always make a perfect ice crystal, but voids, cracks and other defects are created, so in the phase transition of the universe defects such as mono-poles (an isolated magnetic charge that has never been observed but has been postulated to have been produced in quantity in the Big Bang), cosmic strings etc. were produced. Our universe is just one part of the entire universe, like a small patch of ice. In that patch of ice there are few defects (most of the defects are between patches), and in the universe we observe there are few mono-poles.
Bubble Universes. The fact that the visible universe came out of a small patch of the entire universe means that we live in one of the many existing universes. We can think of the original universe as a collection of bubbles and we live in one of the bubbles. Because each bubble at the beginning was not in causal relation wit the others, we will never be able to know about the other universes (because in order to send a light signal from one universe to the other it would require light signals to travel for a time longer than the age of the universe).
During the inflationary era, the universe expanded
in size by many billions of times between 10-35 and 10-33
sec. after the Big Bang.
Dark Matter: Astronomers can compute how much luminous
matter there is, that is, matter that is visible with telescopes. However,
this amount of matter is not enough to explain, for example, the existence
and stability of many galaxies. In this case, the motion of stars in the
galaxy is not consistent with the amount of mass that is producing light:
there must be more mass, by a factor at least 10. So, it is fair to say
that most mass in the universe is not seen, and only about 10% or so is
visible. The rest is non-luminous material, such as clouds of gas and dust,
and planets and stars to dim to see. Even postulating that there is 10
times more non-visible matter than luminous matter, we end up with a total
budget of mass of the universe that is