The Big Bang

Astronomers use the term “the Big Bang” to describe the event that marked the
beginning of our universe; a tremendous explosion of energy from a single point.  
This explosion produced huge amounts of energy much of which was released in
the form of highly energetic photons of light.  These high energy photons were
actually powerful enough to transform into matter in the form of protons and
neutrons. These protons and neutrons exhibit a natural affinity for one another and
before long they began to form the atoms of some of the very lightest elements like
hydrogen and helium.  The large scale that this process operated at early in our
universe accounts for why hydrogen and helium are the two most plentiful elements
in the universe.

Scientists also use the same term, the big bang, to refer to the expansion and
cooling of the matter and energy that resulted from the initial explosion.  Since the
1920s scientists have become more and more convinced that our current model:
“the big bang model of the universe” accurately coincides with our observations of
the night sky.

In the 1920s Edwin Hubble observed that the majority of stars, and the galaxies
that they make up, are moving away from our own galaxy at very high speeds.  
Hubble also found that the speed of each observable galaxy is proportional to its
distance from us.  These two findings, expressed mathematically as Hubble’s Law,
have been captured in a simple equation that describes the inflation rate of the
expansion of our universe.

Many astronomers in the 1920s realized that in order to predict what happened in
our cosmological past, we must imagine what we would see if we could play out
this expansion backwards.  Newtonian physics and simple logic tell us that as we
turn back time all of the matter and energy in the universe would draw closer and
closer together.  Back in the 1920s and even still today we assume that at one
point, around 15 billion years ago, all of the matter and energy in the entire
universe was extremely “close together.”

The big bang is referred to as the first event in our universe because there was no
time or space before it.  If you are familiar with Einstein’s theory of Relativity, then
you know that time and space can be affected by two properties of physical matter:
energy and speed.  During the first few moments after the big bang the energy that
was released was so powerful, that our current laws of physics break down.  Time
and space were so warped by the tremendous amount of matter and energy that
relativity, quantum mechanics, and classical physics cannot make predictions
about the history of the early universe.

Before the Big Bang all that existed was a concept called a singularity.  A
singularity is basically a point with no physical dimensions; no time, zero volume
and infinite density.  This “concept” is seen by physicists as a state of rest, the very
opposite of our post big bang universe.

To read more about the big bang and its consequences
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