Big Bang

noun

• 1 Astronomy the rapid expansion of matter from a state of extremely high density and temperature which according to current cosmological theories marked the origin of the universe.

A fireball of radiation at extremely high temperature and density, but occupying a tiny volume, is believed to have formed around 13.7 billion years ago. This expanded and cooled, extremely fast at first, but more slowly as subatomic particles condensed into matter which later accumulated to form galaxies and stars. The galaxies are currently still retreating from one another. What was left of the original radiation continued to cool and has been detected as a uniform background of weak microwave radiation

• 2(in the UK) the introduction in 1986 of major changes in trading on the Stock Exchange, principally involving widening of membership, relaxation of rules for brokers, and computerization.