In 1929, Edwin Hubble discovered that the universe is expanding and that all galaxies are moving away from each other. Using a sort of reverse engineering, scientists postulated that since the universe is expanding, it must have originated from a very small point and it is from this point that the universe is expanding. This led to the development of the Big Bang Theory, which states that all matter was concentrated in a point until about 14 billion years ago, it suddenly started expanding, giving birth to various galaxies and other heavenly bodies. Atoms of various elements combined, giving rise to new elements by the process of fusion and ultimately to the universe that we see today.
The universe began by expanding from an infinitesimal volume with extremely high density and temperature. The universe was initially significantly smaller than even a pore on your skin.
This is called the singularity point, but there are stull specualtions about that. we do know for sure what happend at 10^-29s but not before. because the singularity goes against the laws of nature itself ^^. the hope to find this out at CERN(france) with their Large Hadron Collader.
About 15 billion years ago a tremendous explosion started the expansion of the universe. This explosion is known as the Big Bang. At the point of this event all of the matter and energy of space was contained at one point. What exisisted prior to this event is completely unknown and is a matter of pure speculation. This occurance was not a conventional explosion but rather an event filling all of space with all of the particles of the embryonic universe rushing away from each other. The Big Bang actually consisted of an explosion of space within itself unlike an explosion of a bomb were fragments are thrown outward. The galaxies were not all clumped together, but rather the Big Bang lay the foundations for the universe.
The universe began by expanding from an infinitesimal volume with extremely high density and temperature. The universe was initially significantly smaller than even a pore on your skin. With the big bang, the fabric of space itself began expanding like the surface of an inflating balloon – matter simply rode along the stretching space like dust on the balloon's surface. The big bang is not like an explosion of matter in otherwise empty space; rather, space itself began with the big bang and carried matter with it as it expanded.