The Big Bang theory is the prevailing cosmological model for the universe from the earliest known periods through its subsequent large-scale evolution. The model accounts for the fact that the universe expanded from a very high density and high temperature state, and offers a comprehensive explanation for a broad range of observed phenomena, including the abundance of light elements, the cosmic microwave background, large scale structure, and Hubble's Law. If the known laws of physics are extrapolated beyond where they are valid, there is a singularity. Modern measurements place this moment at approximately 13.8 billion years ago, which is thus considered the age of the universe. After the initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, and later simple atoms. Giant clouds of these primordial elements later coalesced through gravity to form stars and galaxies.
The Big Bang is the cosmological model of the universe, originally conceived to describe its origins, that is best supported by all cosmological observations. The essential idea is that the universe has expanded from a primordial hot and dense initial condition at some finite time in the past and continues to expand to this day. Observational evidence for the expansion of the universe came first from Edwin Hubble's 1929 discovery that galactic distances are proportional to their redshifts. Since the universe is seen to be expanding today, theoretical cosmologists can make detailed predictions of the universe's denser and hotter past. A major feature of Big Bang cosmology is its prediction of the conditions of an early universe having extreme densities and temperatures that today can only be probed in high-energy environments. The results of Big Bang predictions have been found to conform accurately and precisely to a variety of astronomical observations.
Within fiction, a Big Bang is usually portrayed as a massive release of energy, instead of an expansion of space-time itself. A Big Bang is generally considered to be a universe level attack (however this should be evaluated on a case by case basis).
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