Big Bang
About the origin of the Universe exist various theories, at the moment most scientists accept the Big Bang theory as the start of the Universe.
The
Big Bang.
This theory states that the Universe in its current shape is only a
phase of a process that started with a gigantic explosion about 15 billion
years ago.
In the beginning the Universe was all in one point, all its matter
and energy where squished into an infinitely small volume, mathematically
expressed a singularity. From this singularity the Universe exploded
and by this native explosion not only matter and energy was created, however
also space and time.
The theory says that it is not of any use to speak of the period before
the Big Bang, there is no 'before' because time (and space) did not exist.
Science
assumes to have a good idea of the developemnts after the Big Bang.
Immediately after the explosion the small space was filled with energy
(as radiation) and had an extreme high temperature, one milion billion
billion billion (10 wtih 32 zeros) degrees Kelvin, this stage is called
the primordial fireball.
In a fraction of a second elementary matter came into existence: protons, neutrons and electrons, followed by a very fast expansion (inflation). Since the beginning the Universe cools down and expands more and more. This time is called the radiation era, as electromagnetic radiation was the most important thing in the Universe.
After several hundred thousand years the temperature drop was large enough for atoms to develop from elementary particles, in particular hydrogen and helium, this is called the matter era.
After 300,000 years the Universe had cooled down enough to become
transparent for radiation, at that time the first Galaxies arose.
The evidence
of the Big Bang.
The first observation that indicates the Big Bang is the fact that
the Universe is expanding. Edwin
Hubble noticed this in 1929.
|
If the Universe is expanding, than a simple conclusion may be that
it must have been smaller in the past. By imagening the expansion in a reversed direction astronomers can
determine how long ago the Universe was at size zero and the Big Bang must
have taken place: about 15 billion years ago.
The second observation is the presence of Cosmic Background Microwave Radiation. The cooling down and expansion of the Universe still continues. In case the Universe really started by the Big Bang about 15 billion years ago, then at present the Universe should to be cooled down to a temperature of about 3 Kelvin (this 3 degrees above the absolute zeropoint). Astronomers do indeed observe this in the entire Universe by means of radiotelescopes and distortion of radio signals that correspond with a temperature of 3 Kelvin. |
|
The third evidence is the presence of large quantities of Helium in the Universe (about 25% of all matter). The lifetime of the Universe is simply too short to explain these large quantities of Helium, except when the Universe has had a period of extreme heat and density. Under these conditions the Helium is formed from Hydrogen by nuclear reactions. Calculations indicate that during such a phase -an extremely hot Big Bang- about 25% of all the Universal matter would be turned into Helium. And that is what is observed.
The
end of the Universe
For the time being nobody is able to predict what will finally happen
to the Universe. Based upon the theory that the Universe is still expanding
from the Big Bang, two possibilities are the most likely.(Big
Crunch).