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In physical cosmology
Physical cosmology

Physical cosmology, as a branch of astronomy, is the study of the largest-scale structures and dynamics of our universe and is concerned with fundamental questions about its formation and evolution....
, the Big Crunch is one possible scenario for the ultimate fate of the universe
Ultimate fate of the universe

The ultimate fate of the universe is a topic in physical cosmology. Many possible fates are predicted by rival scientific theories, including futures of both finite and infinite duration....
, in which the metric expansion of space
Metric expansion of space

The metric expansion of space is the averaged increase of metric distance between objects in the universe with time. It is an intrinsic and extrinsic properties expansion?that is, it is defined by the relative separation of parts of the universe and not by motion "outward" into preexisting space....
 eventually reverses and the universe recollapses, ultimately ending as a black hole
Black hole

In general relativity, a black hole is a region of space in which the gravitational field is so powerful that nothing, including electromagnetic radiation , can escape its pull after having fallen past its event horizon....
 singularity
Naked singularity

In general relativity, a naked singularity is a gravitational singularity without an event horizon. The singularities inside black holes are always surrounded by event horizon, and therefore cannot be directly observed....
.

he universe is finite in extent and the cosmological principle
Cosmological Principle

In physical cosmology, the cosmological principle is an assumption, or working hypothesis, about the large scale structure of the cosmos, stating that:...
 (not to be confused with the cosmological constant
Cosmological constant

In physical cosmology, the cosmological constant was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a Einstein's universe....
) does not apply, and the expansion speed does not exceed the escape velocity, then the mutual gravitational attraction of all its matter
Matter

In common usage, matter is anything that has both mass and volume . A more rigorous definition is used in science: matter is what atoms and molecules are made of....
 will eventually cause it to contract.






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In physical cosmology
Physical cosmology

Physical cosmology, as a branch of astronomy, is the study of the largest-scale structures and dynamics of our universe and is concerned with fundamental questions about its formation and evolution....
, the Big Crunch is one possible scenario for the ultimate fate of the universe
Ultimate fate of the universe

The ultimate fate of the universe is a topic in physical cosmology. Many possible fates are predicted by rival scientific theories, including futures of both finite and infinite duration....
, in which the metric expansion of space
Metric expansion of space

The metric expansion of space is the averaged increase of metric distance between objects in the universe with time. It is an intrinsic and extrinsic properties expansion?that is, it is defined by the relative separation of parts of the universe and not by motion "outward" into preexisting space....
 eventually reverses and the universe recollapses, ultimately ending as a black hole
Black hole

In general relativity, a black hole is a region of space in which the gravitational field is so powerful that nothing, including electromagnetic radiation , can escape its pull after having fallen past its event horizon....
 singularity
Naked singularity

In general relativity, a naked singularity is a gravitational singularity without an event horizon. The singularities inside black holes are always surrounded by event horizon, and therefore cannot be directly observed....
.

Overview

If the universe is finite in extent and the cosmological principle
Cosmological Principle

In physical cosmology, the cosmological principle is an assumption, or working hypothesis, about the large scale structure of the cosmos, stating that:...
 (not to be confused with the cosmological constant
Cosmological constant

In physical cosmology, the cosmological constant was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a Einstein's universe....
) does not apply, and the expansion speed does not exceed the escape velocity, then the mutual gravitational attraction of all its matter
Matter

In common usage, matter is anything that has both mass and volume . A more rigorous definition is used in science: matter is what atoms and molecules are made of....
 will eventually cause it to contract. Because entropy
Entropy

In many branches of science, entropy is a measure of the disorder of a system. The concept of entropy is particularly notable as it is applied across physics, information theory and mathematics....
 continues to increase in the contracting phase, 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. 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
Entropy

In many branches of science, entropy is a measure of the disorder of a system. The concept of entropy is particularly notable as it is applied across physics, information theory and mathematics....
. Some theorize that the universe could collapse to the state where it began and then initate another Big Bang
Big Bang

The Big Bang is the physical cosmology model of the initial conditions and subsequent development of the universe supported by the most comprehensive and accurate explanations from current scientific method and observation....
, 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 supernova
Supernova

A supernova is a Astronomy#Stellar astronomy explosion. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months....
 as standard candles, and the well-resolved mapping of the cosmic microwave background) have led to speculation that the expansion of the universe is not being slowed down by gravity but rather accelerating
Accelerating universe

The accelerating universe is the observation that the universe appears to be expanding at an accelerating rate. In 1998 observations of Type Ia supernovae suggested that the expansion of the universe is speeding up....
. However, since the nature of the dark energy
Dark energy

In physical cosmology & astronomy dark energy is a hypothetical form of energy that permeates all of space and tends to increase the Hubble's law....
 that drives the acceleration is unknown, it is still possible that it might eventually reverse sign and cause a collapse.

See also

  • Big Bounce
    Big Bounce

    The Big Bounce is a theorized scientific model related to the formation of the known Universe. It derives from the cyclic model or oscillatory universe interpretation of the Big Bang where the first cosmological event was the result of the collapse of a previous universe....
  • Big Rip
    Big Rip

    The Big Rip is a physical cosmology hypothesis first published in 2003, about the ultimate fate of the universe, in which the matter of universe, from stars and galaxies to atoms and subatomic particles, are progressively torn apart by the metric expansion of space at a certain time in the future....
  • Heat death of the universe
    Heat death of the universe

    The heat death is a possible Fate of the universe, in which it has "Entropy" to a state of no thermodynamic free energy to sustain motion or life....
  • Oscillatory universe
    Oscillatory universe

    The oscillating universe theory is a cosmological model investigated briefly by Einstein in 1930 and critiqued by Richard Tolman in 1934, in which the universe undergoes a series of oscillations, each beginning with a big bang and ending with a big crunch....
  • Cyclic model
    Cyclic model

    Cyclic model refers to several cosmological models in which the universe follows infinite, self-sustaining cycles ....
  • Ultimate fate of the universe
    Ultimate fate of the universe

    The ultimate fate of the universe is a topic in physical cosmology. Many possible fates are predicted by rival scientific theories, including futures of both finite and infinite duration....
  • Arrow of time
    Arrow of time

    In the natural sciences, arrow of time, or time?s arrow, is a term coined in 1927 by British astronomer Arthur Eddington used to distinguish a direction of time on a four-dimensional relativistic map of the world, which, according to Eddington, can be determined by a study of organizations of atoms, molecules, and bodies....
  • Entropy (arrow of time)
    Entropy (arrow of time)

    Entropy is the only quantity in the physical sciences that "picks" a particular direction for time, sometimes called an arrow of time. As one goes "forward" in time, the second law of thermodynamics says that the entropy of an isolated system can only increase or remain the same; it cannot decrease....
  • Cosmological principle
    Cosmological Principle

    In physical cosmology, the cosmological principle is an assumption, or working hypothesis, about the large scale structure of the cosmos, stating that:...


External links

  • (news@nature.com)