The Big Bang

There are many different theories about the origin of the universe and none is thought to be completely correct. Many people in the scientific community regard the "Big Bang" as the best estimate of how the universe began.

The theory starts out by stating that the universe as it is today is only one phase, which started with a giant explosion. The universe began with one singular point, which is known as a singularity. All the matter and energy which is now present in the universe was squeezed into this singularity of infinitely small volume. From the singularity the Universe exploded and released an incredible amount of matter and energy. You may be asking what happened in the time before the explosion. Scientists say that there was no universe before the Big Bang and that from the singularity came not only matter and energy but also space and time. So there is no use in talking about before because time did not exist.

Immediately after the explosion a massive fireball formed called the primordial fireball which is thought to have been as hot as one million billion billion billion (10 with 32 zeros) degrees Kelvin. This fireball moved away from the singularity in all directions and from it came elementary particles like neutrons, protons, and electrons. For a long period of time these particles spread out across the universe at an incredible rate. This period in history is known as the radiation era which was very influential in the way the use universe is composed today.

These particles began to cool down and soon started to form elements like hydrogen and helium. These would serve as the building blocks for the stars and the planets. The universe continued to cool down and eventually galaxies formed and planets materialized.

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, then a simple conclusion may be that it must have been smaller in the past. By imagining 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 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 zero point). Astronomers do indeed observe this in the entire Universe by means of radio telescopes 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, which comprises 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 helium is formed from hydrogen by nuclear reactions. Scientist have calculated that the intense heat of the Big Band would turn about 25% of the particles into helium, and that is what we have observed.

The End of the Universe

Right now no one is sure how the universe will end. Some think that eventually it will start to contract and end up back into a singularity. This theory is known as the Big Crunch. Others believe it will continue to expand infinitely, but there is no evidence to support either hypothesis.