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Turn in cosmology questions!
Starting in 1917, Vesto Slipher noted that most galaxies were
receding away from us. In 1927, using Einstein’s equations in
the Theory of Relativity, Georges Lemaître developed the
equations to describe that expansion and the constant that
defines the rate of expansion. In 1929, Edwin Hubble,
confirmed the relationship and refined the value of the
constant now known as Hubble’s Constant (H0).
In 1927, Georges Lemaître also noted that if the universe is expanding now,
then it must have been smaller in the past. If you trace backwards further,
there is a point where all of the galaxies in the universe start as a single point,
a Singularity. At the time, most scientists believed that the universe was
in a Steady State. Einstein himself believed this to be the case.
In 1949 Fred Hoyle mockingly referred to this new theory as the Big Bang
Theory. It turns out, that in light of the evidence, there appears to have been a
Big Bang in the past and the universe is not in a Steady State. If the universe
started as a singularity, then there is no center of the universe, or perhaps it is
better to say that everywhere is the center of the universe.
The Big Bang is defined as the start of time, space, matter, and energy.
Based on this definition, there was nothing before the Big Bang, and
therefore nothing to discuss as far as what existed before the Big Bang.
The answer is – nothing!
If we combine all of the information for the universe we see today, it is
possible to determine when in the past everything was a singularity. This is the
Big Bang itself. It appears to be 13.8 billion years ago.
HUBBLE’S LAW
The first evidence that supports the Big Bang Theory is Hubble’s Law.
Observations of distant galaxies and quasars show that there is a significant
redshift in their spectral lines. This evidence clearly demonstrates that the
universe was smaller in the past and has a time of origin.
CMBR
The second piece of evidence is the Cosmic Microwave Background
Radiation. The frequency of this radiation matches the theoretical frequency we
should see for electromagnetic radiation when the universe first became
transparent to photons. The fact that the radiation is essentially the same
frequency everywhere in the universe means we are looking at evidence
for a single event.
More evidence: Gravitational waves are 'ripples' in the fabric of space-time caused
by some of the most violent and energetic processes in the Universe. Albert
Einstein predicted the existence of gravitational waves in 1916 in his general
theory of relativity. Einstein's mathematics showed that massive accelerating
objects (such as neutron stars or black holes orbiting each other) would disrupt
space-time in such a way that 'waves' of distorted space would radiate from the
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