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In physical cosmology, the Big Crunch is one possible scenario for the ultimate fate of the universe, in which the metric expansion of space eventually reverses and the universe recollapses, ultimately ending as a black hole singularity or causing a reformation of the universe starting with another big bang. Sudden singularities and crunch or rip singularities at late times occur only for hypothetical matter with implausible physical properties.
If the universe is finite in extent and the cosmological principle (not to be confused with the cosmological constant) does not apply, and the expansion speed does not exceed the escape velocity, then the mutual gravitational attraction of all its matter will eventually cause it to contract. If entropy continues to increase in the contracting phase (see Ergodic hypothesis), the contraction would appear very different from the time reversal of the expansion. While the early universe was highly uniform, a contracting universe would become increasingly clumped. Eventually all matter would collapse into black holes, which would then coalesce producing a unified black hole or Big Crunch singularity.
The Hubble Constant measures the current state of expansion in the universe, and the strength of the gravitational force depends on the density and pressure of the matter and in the universe, or in other words, the critical density of the universe. If the density of the universe is greater than the critical density, then the strength of the gravitational force will stop the universe from expanding and the universe will collapse back on itself—assuming that there is no repulsive force such as a cosmological constant. Conversely, if the density of the universe is less than the critical density, the universe will continue to expand and the gravitational pull will not be enough to stop the universe from expanding. This scenario would result in the 'Big Freeze', where the universe cools as it expands and reaches a state of entropy. One theory proposes that the universe could collapse to the state where it began and then initiate another Big Bang, so in this way the universe would last forever, but would pass through phases of expansion (Big Bang) and contraction (Big Crunch).
Recent experimental evidence (namely the observation of distant supernovae as standard candles, and the well-resolved mapping of the cosmic microwave background) has led to speculation that the expansion of the universe is not being slowed down by gravity but rather accelerating. However, since the nature of the dark energy that is postulated to drive the acceleration is unknown, it is still possible (though not observationally supported as of today) that it might eventually reverse sign and cause a collapse.
In popular culture
- The first documentation of a cyclical expanding and contracting universe comes from the poetic writings of Erasmus Darwin in 1791.
- In The Restaurant at the End of the Universe, the big crunch is the floor show entertainment. It is referred to as "the Gnab Gib."
- The Polish science-fiction novel Paroxysm number minus one (Paroksyzm numer minus jeden) by Ryszard Głowacki features beings that survived the last Big Crunch (called "paroxysm") and await the next one.
- Poul Anderson's novel Tau Zero involves a starship that ultimately survives the Big Crunch at the end of the novel.
- In Super Mario Galaxy, Bowser builds a sun which collapses in on itself to form a supermassive black hole. The universe is sucked into it and ultimately destroyed via being crunched into a singularity, and is soon after reconstructed in a big bang.
- The computer game Marathon uses the Big Crunch as a basis for the actions of a main character, the rampant AI Durandal.
- The computer game Anachronox features the destruction and creation of subsequent universes.
- An episode of the third series of Red Dwarf, "Backwards", also (albeit comically) takes place on Earth during a big crunch, during which time runs in reverse along with the universe contracting.
- In the Doctor Who television series between the years 1980 and 1989 the various opening credits follow a "Big Bang" and expansion of the universe, while the closing credits show the reverse: a contraction and eventual "Big Crunch."
- In the second season of the television series LEXX, an evil scientist called Mantrid converts all matter in the "light" universe into one-armed "Mantrid drones" which causes the universe to collapse in on itself and sends the starship Lexx through a singularity to an alternate "dark" universe.
- In the The Simpsons episode "Treehouse of Horror XVI", the entire universe (including God) collapses into a singularity when Kang and Kodos activate an accelator-beam at a baseball game.
- The Marvel Comics character Galactus, a being of cosmic powers, is a reincarnation of "Galan", an intrepid space explorer of the planet Taa and the last survivor of the previous universe. Upon that universe's Big Crunch, Galan was transformed and then released into the newborn universe upon its Big Bang.
- The Marvel Comics Wolverine series included Mojo attempting to stop the Big Crunch.
- In the movie K-PAX, the lead character, an alleged alien named Prot, says that his race has long ago figured that the universe will one day contract into a singularity, then expand again, and repeat the process eternally. He also states that each cycle will be exactly the same, including everyone's actions.
- The band The Electrons wrote a song called "Big Crunch" that uses the concept as a metaphor for a relationship that has gone sour.
- Lyrics of the Bad Religion song "Big Bang" reference both the Big Bang and Big Crunch theories.
- Arrow of time
- Bentley's paradox
- Big Bounce
- Big Rip
- Chronology of the universe
- Cyclic model
- Entropy (arrow of time)
- Eternal return
- Gravitational collapse
- Heat death of the universe
- Timeline of the far future
- Timeline of the universe
- Ellis, George F. R., R. Maartens, and M. A. H. MacCallum. Relativistic Cosmology. Cambridge: Cambridge UP, 2012. 146–47. Print.
- Dr. Gary F. Hinshaw, WMAP Introduction to Cosmology. NASA (2008)
- Jennifer Bergman, The Big Crunch, Windows to the Universe (2003)
- Y Wang, J M Kratochvil, A Linde, and M Shmakova, Current Observational Constraints on Cosmic Doomsday. JCAP 0412 (2004) 006, astro-ph/0409264