Big Bang Theory

The theory that the known universe originated in an explosive event the big bang in which all of the matter and energy of the universe was contained in a single point and began to rapidly expand and evolve starting as high energy particles and radiation and as it cooled over time evolving into ordinary subatomic particles atoms and then stars and galaxies According to this theory the four dimensional space time continuum which we perceive as our universe continues to expand to the present time but it is unknown whether the expansion will continue indefinitely or eventually stop or even reverse possibly leading to a contraction to a single point sometimes referred to as the ldquobig crunchrdquo The competing ldquoSteady state Theoryrdquo gradually lost favor in the 1980s and 1990s See also big bang