Cosmology and the Universe: The Big Bang, Dark Matter and Dark Energy 267
intergalactic space is unknown and, hence, it is still an open question as
to whether our universe is open and infinite or finite and closed. There is
also the issue of dark matter and dark energy that must be examined.
The Big Bang Theory
The General Theory of Relativity provides a general framework for
describing the universe as a whole. It does not, however, constitute a
complete description since the initial condition of the universe must be
specified in order to solve the field equations. There are literally an
infinite number of possibilities. Cosmologists attempt to hypothesize a
set of initial conditions that will provide a solution to the field equations,
which matches our astronomical observations. Each set of conditions
defines a model or a theory, which must be tested. The Big Bang theory
is one example of such a model, which we will soon discover, has many
different variations. The motivation of the Big Bang theory is that it
provides a simple explanation of the expansion of the universe, in
particular, the approximate linearity of velocity and separation.
Genesis
According to the Big Bang theory the universe or the present cycle of the
universe began 13.7 billion years ago as a singularity or point of energy.
A violent explosion occurred and the universe began to expand. Let us
refer to the time of this singularity as time zero (the beginning of the
universe or at least this phase of it). At time zero the universe had an
infinite density, an infinite temperature and an infinitesimal extension.
The energy of the universe was finite since by conservation of energy,
the energy then must be the same as it is now. The present universe is
estimated to have a total energy of 10^69 Joules based on an estimate of
the total number of stars and galaxies in the observable universe. A
description of the universe for times less than 10-44 seconds when the
density of the universe is 10^94 grams per cubic centimeter and the
temperature is 10^33 K is impossible because of quantum fluctuations and
the uncertainty principle.
The Hadron Era
It is believed that the universe began as pure light. “And God said:
‘Let there be light’ And there was light. And God saw that the light