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• Big Bang
  Big Bang

  noun

  the sudden, instantaneous expansion of space from an exploding point of dense energy, starting the universe.
• big bang
  big bang

  noun

  any sudden forceful beginning or radical change

Big Bang

American  

[big bang] / ˈbɪg ˈbæŋ /

Or big bang

noun

1. the sudden, instantaneous expansion of space from an exploding point of dense energy, starting the universe.

   In the first seconds following the Big Bang, the universe expanded faster than the speed of light.

2. Astrophysics. the model or theory that explains the start of the universe by a sudden, instantaneous expansion of space from an exploding point of dense energy (often used attributively).

   The Big Bang cannot be tested via experiment, but it can be used to make testable predictions.

   The current cosmological model, called the Big Bang, is explained below.

3. big bang, any event or action that represents a sudden and massive development (often used attributively).

   The Prime Minister's commitment is being seen as one of the big bang decisions of this century.

   After spending $750 million on a redesign big bang, the Operations Center had nothing to show for it.

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big bang British  

noun

1. any sudden forceful beginning or radical change

2. (modifier) of or relating to the big-bang theory

3. (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

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big bang Scientific  

/ bĭg /

1. 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.

2. Compare big crunch steady state theory See also open universe

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Closer Look

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.

Etymology

Origin of Big Bang

Coined in 1949 by British astronomer Sir Fred Hoyle (1915–2001)

Example Sentences

See Examples For:

Big Bang big bang

It likely formed less than one and a half billion years after the Big Bang and could be as much as four times more massive than previous calculations suggested.

From Science Daily ● Aug. 22, 2026

Meanwhile, theorists such as Russian cosmologist Alexander Friedmann took Einstein's equations more literally and developed the theoretical foundation that would help support the Big Bang theory.

From Science Daily ● Aug. 18, 2026

Being part of the Big Bang Universe, no pun intended, means a star shower of guest shots throughout the series.

From The Wall Street Journal ● Jul. 22, 2026

‘Stuart Fails to Save the Universe’ is a wildly different series from ‘The Big Bang Theory’ and its prequels, elevating Kevin Sussman, Brian Posehn, Lauren Lapkus and John Ross Bowie to leads.

From Los Angeles Times ● Jul. 22, 2026

Very likely, the universe has been expanding since the Big Bang, but it is by no means clear that it will continue to expand forever.

From "Cosmos" by Carl Sagan

"We're just hoping it was just a mortar that went off underneath but definitely felt a big bang."

From BBC ● Jul. 5, 2026

The big bang theory may have triumphed among most cosmologists, but the persistence of unanswered questions—what came before that explosive moment? could our universe be one of many?—leaves plenty of room for speculation and dissent.

From The Wall Street Journal ● May 19, 2026

A chipper melodicist who never attempted to disguise his sentimental streak, Sedaka emerged at the moment rock ’n’ roll’s initial big bang started to fizzle.

From Los Angeles Times ● Feb. 27, 2026

Then came the Cambrian explosion, known as evolution's "big bang", roughly 540 million years ago.

From Barron's ● Jan. 28, 2026

The deflation would get faster and faster, the universe would get hotter and hotter, and it would eventually end in a backward big bang: the big crunch.

From "Zero: The Biography of a Dangerous Idea" by Charles Seife