Big bang

a theory that deduces a cataclysmic birth of the universe (big bang) from the observed expansion of the universe, cosmic background radiation, abundance of the elements, and the laws of physics.
Contemporary Examples

How Marine Le Pen and France’s Ultra-Right Won the Day Tracy McNicoll May 25, 2014
Three Top Lessons From ‘30 Rock’ Scholars Rachel Krantz January 29, 2013
TV Upfronts 2012: NBC, ABC, CBS, Fox, and the CW Announce Schedules Jace Lacob, Maria Elena Fernandez May 16, 2012
Partying With the Golden Globes Stars: Taylor Swift Cuts a Rug, Ben Affleck Holds Court, and More Marlow Stern January 12, 2014
Welcome to the Multiverse! Alexander Fabry February 10, 2011
Keanu Reeves on ‘Man of Tai Chi,’ ‘Bill & Ted’ & ‘Point Break’ Marlow Stern September 12, 2013
The Best Music Blogs Howard Wolfson January 25, 2014
Golden Globes 2011: Watch the Funniest Moments The Daily Beast Video January 16, 2011

Historical Examples

Through Space to Mars Roy Rockwood
An Onlooker in France 1917-1919 William Orpen

noun
any sudden forceful beginning or radical change
(modifier) of or relating to the big-bang theory
(sometimes capitals) the major modernization that took place on the London Stock Exchange on Oct 27 1986, after which the distinction between jobbers and brokers was abolished and operations became fully computerized
big bang
(bĭg)
The explosion of an extremely small, hot, and dense body of matter that, according to some cosmological theories, gave rise to the universe between 12 and 20 billion years ago. Compare big crunch, steady state theory. See also open universe.

Our Living Language : In the 1920s astronomer Edwin Hubble discovered that wherever one looked in space, distant galaxies were rapidly moving away from Earth, and the more distant the galaxy the greater its speed. Through this observation he determined that the universe was becoming larger. Hubble also found that the ratio between a galaxy’s distance and velocity (speed and direction of travel) was constant; this value is called the Hubble constant. By calculating the distance and velocity of various galaxies and working backward, astronomers could determine how long ago the expansion began—in other words, the age of the universe. The figure, which scientists are constantly refining, is currently thought to be between 12 and 20 billion years. According to the widely accepted theory of the big bang, the universe was originally smaller than a dime and almost infinitely dense. A massive explosion, which kicked off the expansion, was the origin of all known space, matter, energy, and time. Scientists are also attempting to calculate how much mass the universe contains in order to predict its future. If there is enough mass, the gravity attracting all its pieces to each other will eventually stop the expansion and pull the universe back together in a big crunch. There may not be enough mass, however, to result in an eventual collapse. If that is the case, then the universe will expand forever, and all galaxies and matter will drift apart, eventually becoming dark and cold.

Note: Scientists have recently found that the expansion of the universe is actually speeding up. This effect is attributed to the presence of dark energy.