Big Crunch
In
physical cosmology, the
Big Crunch is a
hypothesized collapse of the
universe upon itself after its
expansion eventually stops — a counterpart to the
Big Bang.
If the
gravitational attraction of all the
matter within the observable horizon is high enough, it could slow the expansion of the universe, and then reverse it. The universe would then contract, with about the same duration as the expansion. Eventually, all matter and energy would be compressed back into a gravitational singularity. It is meaningless to ask what would happen
after this, because time, as we know it, would end in this singularity.
 |
Lensing due to gravity. |
For this to occur, the average density of matter in the universe has to be sufficient so that the overall spatial curvature of the universe is positive, like the surface of a
sphere. If the matter density is less than a certain value, called the
critical density, the curvature is negative (like a hyperbolic surface, which is a mathematical
manifold often compared to the form of a saddle) and gravitation will be too feeble to completely counter inertia, so that expansion will continue to slow down but never come to an end. These two cases, and the limiting case in between in which space is flat, are called the three
Friedmann models. They assume the
cosmological constant to be zero.
However, recent experimental evidence (namely the observation of distant
supernovae as
standard candles, and the well-resolved mapping of the
cosmic microwave background) have—to most scientists' considerable surprise—shown that the expansion of the universe is
not being slowed down by gravity, but instead,
accelerating, suggesting that the universe will not end with a Big Crunch, but will instead expand forever, though some scientists have contested this theory.[
1] (The evidence of an accelerating universe has been considered conclusive by most cosmologists since
2002.)
In the framework of the field equations of the
General Theory of Relativity, the simplest model of an accelerating expansion corresponds to a positive value of the
cosmological constant, which can be attributed to the quantum vacuum itself exerting a force that repels gravitationally on large scales. More generally, the accelerating expansion is attributed to
dark energy, which could be the cosmological constant, or a dynamical field with negative "pressure", leading to an effective cosmological constant that could be time-varying. In such cases, it is theoretically possible that the cosmological constant need not remain positive, leaving open the possibility of a Big Crunch as the
ultimate fate of the universe. A Big Crunch is also still theoretically possible if Einstein's theory of general relativity were found not to apply on large scales. The current evidence neither favors nor rules out dark energy, or modifications of general relativity, of a form that could halt or reverse an eternal expansion; it does, however set lower bounds on the duration collapse (approximately 42 billion years from now, or more than 24 billion years at the 95% confidence level, according to one group led by
Andrei Linde).
The computer game
Marathon uses the Big Crunch as a basis for the actions of a main character, the
rampant AI Durandal. This character believes that, if one leaves the universe as it is being "crunched", that person would reach a form of
godhood—either by existing in a reality without the limits imposed by the universe itself, or by being the first sentient creature in a new universe (following another
Big Bang).
The computer game
Anachronoxs story features the destruction and creation of subsequent universes.
The Big Crunch is also referred to as the Gnab Gib' ("Big Bang" read backwards).
The first documentation of a cyclical expanding and contracting universe comes from the poetic writings of
Erasmus Darwin in
1791.
The British television show
Red Dwarf, the episode "Backwards" deals with a
parallel universe going through the Big Crunch by going reverse in time and space that would eventually descend into a singularity point in the universe before the
Big Bang.
In the second season of the television series
LEXX, an evil scientist called
Mantrid proceeds to convert all matter in the "light" universe into one-armed "Mantrid
drones". Mantrid succeeds, but not without causing the universe to collapse in on itself â€" which results from the rapid convergence of remaining matter to its center â€" and sending the
starship Lexx through a
singularity to an
alternate "dark" universe.
In the
The Simpsons episode "
Treehouse of Horror XVI", the universe collapses into a singularity when
Kang and Kodos activate an accelator-beam at a
baseball game. As the acceleration continues, the baseball stadium is drawn in to a specific point where the gravity is high. Afterwards the stadium's surroundings are drawn into this point and then the whole city, then Earth's
oceans, the whole
Earth, the
solar system, numerous
galaxies and finally
God is drawn into this point. When this happens, Kang leaves a note saying: "Treehouse of Horror XVI".
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. After spending a lengthy but indeterminate time in gestation, Galactus emerged and began his relentless feeding upon the life energy of numerous planets, destroying them in the process.
The Polish science-fiction book
Paroxysm number minus one (
Paroksyzm numer minus jeden) by
Ryszard GÅ‚owacki features beings that survived the last Big Crunch (called "paroxysm") and await the next one.
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 Erectrons wrote a song called "Big Crunch" that uses the concept as a metaphor for a relationship that has gone sour.
*
Big Rip*
Heat death of the Universe*
Omega point*
Ultimate fate of the Universe*
Arrow of time*
Entropy (arrow of time)*
"Cosmic doomsday delayed" (news@nature.com)
*
"Current Observational Constraints on Cosmic Doomsday" (Wang, Kratochvil, Linde, and Shmakova)
*
"How to destroy the earth @ Things of Interest"
