The Big Bang Theory is the prevailing scientific theory for the beginning of the universe. The theory states that all matter in the universe was at one point held together in a very dense, hot form (composed of elementary particles). At some point, this condensed matter began to cool, and as the elementary particles clung together to form protons and neutrons, the mass exploded into smaller objects and the universe began to expand (and still is expanding today.)
This explosion is estimated to have occured some fifteen to twenty billion years ago. Some scientists theorize that the expansion of the universe would eventually slow down and that the gravity of its matter would eventually cause the universe to collapse on itself (the force of the explosion would run out and would be overtaken by the forces of gravity, slowly pulling the matter together again).
However, in recent studies, some scientists (seperately) performed tests on the speed of the expansion of the universe. By looking at the light emitted by supernovas at varying distances from the earth, they hoped to determine the rate at which the universe's expansion is slowing. The results: it isn't. Their research showed that the universe was actually speeding up in its expansion, which has led to several speculations. As of yet, no complete explanation exists.
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