Big Bang

Big Bang

The Big Bang theory (or Big Bang model) is the prevailing cosmological theory of the early development of the universe. In this theory, the Big Bang is an event that took place at some finite time in the past, more than ten billion years ago. In the Big Bang, the universe, originally in an extremely hot and dense state, suddenly began to expand rapidly. It has since cooled by expanding to the present diluted state and continues to expand today. The theory is supported by the most comprehensive and accurate explanations from current scientific evidence and observation.[1][2] According to the best available measurements as of 2010[update], the initial conditions occurred around 13.3 to 13.9 billion years ago.[3][4]

Georges Lemaître proposed what became known as the Big Bang theory of the origin of the universe, although he called it his "hypothesis of the primeval atom". The framework for the model relies on Albert Einstein's general relativity and on simplifying assumptions (such as homogeneity and isotropy of space). The governing equations had been formulated by Alexander Friedmann. After Edwin Hubble discovered in 1929 that the distances to far away galaxies were generally proportional to their redshifts, as suggested by Lemaître in 1927, this observation was taken to indicate that all very distant galaxies and clusters have an apparent velocity directly away from our vantage point: the farther away, the higher the apparent velocity.[5] If the distance between galaxy clusters is increasing today, everything must have been closer together in the past. This idea has been considered in detail back in time to extreme densities and temperatures,[6][7][8] and large particle accelerators have been built to experiment on and test such conditions, resulting in significant confirmation of the theory, but these accelerators have limited capabilities to probe into such high energy regimes. Without any evidence associated with the earliest instant of the expansion, the...