Big Crunch

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An animation of the expected behavior of a Big Crunch Big Crunch.gif
An animation of the expected behavior of a Big Crunch

The Big crunch is one of the theoretical scenarios for the ultimate fate of the universe, in which the metric expansion of space eventually reverses and the universe recollapses, ultimately causing the cosmic scale factor to reach zero or causing a reformation of the universe starting with another Big Bang.

Ultimate fate of the universe topic in physical cosmology

The ultimate fate of the universe is a topic in physical cosmology, whose theoretical restrictions allow possible scenarios for the evolution and ultimate fate of the universe to be described and evaluated. Based on available observational evidence, deciding the fate and evolution of the universe have now become valid cosmological questions, being beyond the mostly untestable constraints of mythological or theological beliefs. Many possible dark futures have been predicted by rival scientific hypotheses, including that the universe might have existed for a finite and infinite duration, or towards explaining the manner and circumstances of its beginning.

The relative expansion of the universe is parametrized by a dimensionless scale factor . Also known as the cosmic scale factor or sometimes the Robertson–Walker scale factor, this is a key parameter of the Friedmann equations.

Big Bang The prevailing cosmological model for the observable universe

The Big Bang theory is the prevailing cosmological model for the observable universe from the earliest known periods through its subsequent large-scale evolution. The model describes how the universe expanded from a very high-density and high-temperature state, and offers a comprehensive explanation for a broad range of phenomena, including the abundance of light elements, the cosmic microwave background (CMB), large scale structure and Hubble's law. If the observed conditions are extrapolated backwards in time using the known laws of physics, the prediction is that just before a period of very high density there was a singularity which is typically associated with the Big Bang. Physicists are undecided whether this means the universe began from a singularity, or that current knowledge is insufficient to describe the universe at that time. Detailed measurements of the expansion rate of the universe place the Big Bang at around 13.8 billion years ago, which is thus considered the age of the universe. After its initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, and later simple atoms. Giant clouds of these primordial elements later coalesced through gravity, eventually forming early stars and galaxies, the descendants of which are visible today. Astronomers also observe the gravitational effects of dark matter surrounding galaxies. Though most of the mass in the universe seems to be in the form of dark matter, Big Bang theory and various observations seem to indicate that it is not made out of conventional baryonic matter but it is unclear exactly what it is made out of.


Some experimental evidence casts doubt on this theory and suggests that the expansion of the universe is accelerating, rather than being slowed down by gravity. However, more recent research has called this conclusion into question.

Accelerating expansion of the universe rate of increase in the expansion of the universe

The accelerating expansion of the universe is the observation that the expansion of the universe is such that the velocity at which a distant galaxy is receding from the observer is continuously increasing with time.


If the universe's 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. [1] Eventually all matter would collapse into black holes, which would then coalesce, producing a unified black hole or Big Crunch singularity.

In physics, escape velocity is the minimum speed needed for a free object to escape from the gravitational influence of a massive body. It is slower the further away from the body an object is, and slower for less massive bodies.

Gravity Curvature of spacetime attracting uneven distribution of masses together

Gravity, or gravitation, is a natural phenomenon by which all things with mass or energy—including planets, stars, galaxies, and even light—are brought toward one another. On Earth, gravity gives weight to physical objects, and the Moon's gravity causes the ocean tides. The gravitational attraction of the original gaseous matter present in the Universe caused it to begin coalescing, forming stars – and for the stars to group together into galaxies – so gravity is responsible for many of the large-scale structures in the Universe. Gravity has an infinite range, although its effects become increasingly weaker on farther objects.

Matter substance that has rest mass and volume, or several other definitions

In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic particles, and in everyday as well as scientific usage, "matter" generally includes atoms and anything made up of them, and any particles that act as if they have both rest mass and volume. However it does not include massless particles such as photons, or other energy phenomena or waves such as light or sound. Matter exists in various states. These include classical everyday phases such as solid, liquid, and gas – for example water exists as ice, liquid water, and gaseous steam – but other states are possible, including plasma, Bose–Einstein condensates, fermionic condensates, and quark–gluon plasma.

The idea behind the theory is that the expansion of the universe is linked to the energy released in the Big Bang, therefore the expansion would decrease over time due to gravity (mutual attraction). This would act as ballast and would eventually lead to a halt of the expansion. As matter attracts and there is no matter beyond the maximum expansion point, eventually all matter would begin to travel inwards again, accelerating as time passes.

Expansion of the universe increase in distance between parts of the universe over time

The expansion of the universe is the increase of the distance between two distant parts of the universe with time. It is an intrinsic expansion whereby the scale of space itself changes. The universe does not expand "into" anything and does not require space to exist "outside" it. Technically, neither space nor objects in space move. Instead it is the metric governing the size and geometry of spacetime itself that changes in scale. Although light and objects within spacetime cannot travel faster than the speed of light, this limitation does not restrict the metric itself. To an observer it appears that space is expanding and all but the nearest galaxies are receding into the distance.

Deceleration parameter dimensionless measure of the cosmic acceleration of the expansion of space

The deceleration parameter in cosmology is a dimensionless measure of the cosmic acceleration of the expansion of space in a Friedmann–Lemaître–Robertson–Walker universe. It is defined by:

The exact details of the events that would take place before such final collapse depend on the length of both the expansion phase as well as the previous contraction phase; the longer both lasted, the more events expected to take place in an ever-expanding universe would happen; nonetheless it's expected that the contraction phase would not immediately be noticed by hypothetical observers because of the delay caused by the speed of light, that the temperature of the cosmic microwave background would rise during contraction symmetrically compared to the previous expansion phase, and that the events that took place during the Big Bang would occur in opposite order. [2] For a contracting Universe similar to ours in composition it's expected that superclusters would merge among themselves followed by galaxy clusters and later galaxies. By the time stars were so close together that collisions among them were frequent, the temperature of the cosmic microwave background would have increased so much that stars would be unable to expel their internal heat, slowly cooking until they exploded, leaving behind a hot and highly heterogeneous gas, whose atoms would break down into their constituent subatomic particles because of the increasing temperature, that would be absorbed by the already coalescing black holes before the Big Crunch itself. [2]

Future of an expanding universe Future scenario assuming that the expansion of the universe will continue forever

Observations suggest that the expansion of the universe will continue forever. If so, then a popular theory is that the universe will cool as it expands, eventually becoming too cold to sustain life. For this reason, this future scenario once popularly called "heat death" is now known as the Big Chill or Big Freeze.

Speed of light speed at which all massless particles and associated fields travel in vacuum

The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its exact value is 299,792,458 metres per second. It is exact because by international agreement a metre is defined as the length of the path travelled by light in vacuum during a time interval of 1/299792458 second. According to special relativity, c is the maximum speed at which all conventional matter and hence all known forms of information in the universe can travel. Though this speed is most commonly associated with light, it is in fact the speed at which all massless particles and changes of the associated fields travel in vacuum. Such particles and waves travel at c regardless of the motion of the source or the inertial reference frame of the observer. In the special and general theories of relativity, c interrelates space and time, and also appears in the famous equation of mass–energy equivalence E = mc2.

Cosmic microwave background Electromagnetic radiation as a remnant from an early stage of the universe in Big Bang cosmology

The cosmic microwave background is electromagnetic radiation as a remnant from an early stage of the universe in Big Bang cosmology. In older literature, the CMB is also variously known as cosmic microwave background radiation (CMBR) or "relic radiation". The CMB is a faint cosmic background radiation filling all space that is an important source of data on the early universe because it is the oldest electromagnetic radiation in the universe, dating to the epoch of recombination. With a traditional optical telescope, the space between stars and galaxies is completely dark. However, a sufficiently sensitive radio telescope shows a faint background noise, or glow, almost isotropic, that is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum. The accidental discovery of the CMB in 1964 by American radio astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s, and earned the discoverers the 1978 Nobel Prize in Physics.

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 matter 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 [1] —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 heat death of the universe, where the universe reaches the maximum state of entropy that is thermodynamic equilibrium. In the state of thermodynamic equilibrium energy in the universe is evenly distributed so heat transfer or any other energy transfer is impossible so no reactions can happen in such universe making it "dead". [3] [ not in citation given ] One theory proposes that the universe could collapse to the state where it began and then initiate another Big Bang, [1] so in this way the universe would last forever, but would pass through phases of expansion (Big Bang) and contraction (Big Crunch). [4] Another scenario results in a flat universe which occurs when the critical density is just right. In this state the universe would always be slowing down, and eventually come to a stop in an interminable amount of time. Although, it is now understood that the critical density has been measured and determined to be a flat universe. [5]

Cosmological constant constant representing stress-energy density of the vacuum in Einsteins equation

In cosmology, the cosmological constant is the energy density of space, or vacuum energy, that arises in Albert Einstein's field equations of general relativity. It is closely associated to the concepts of dark energy and quintessence.

Heat death of the universe A possible end of the universe

The heat death of the universe, also known as the Big Chill or Big Freeze, is an idea of an ultimate fate of the universe in which the universe has evolved to a state of no thermodynamic free energy and therefore can no longer sustain processes that increase entropy. Heat death does not imply any particular absolute temperature; it only requires that temperature differences or other processes may no longer be exploited to perform work. In the language of physics, this is when the universe reaches thermodynamic equilibrium.

Entropy physical property of the state of a system, measure of disorder

In statistical mechanics, entropy is an extensive property of a thermodynamic system. It is closely related to the number Ω of microscopic configurations that are consistent with the macroscopic quantities that characterize the system. Under the assumption that each microstate is equally probable, the entropy is the natural logarithm of the number of microstates, multiplied by the Boltzmann constant kB. Formally,

Experimental evidence in the late 1990s and early 2000s (namely the observation of distant supernovae as standard candles, and the well-resolved mapping of the cosmic microwave background) [6] [7] led to the conclusion that the expansion of the universe is not being slowed down by gravity but rather accelerating. However, more recent research, based on larger datasets, has cast doubt on this conclusion. [8]

See also

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Physical cosmology branch of astronomy

Physical cosmology is a branch of cosmology concerned with the studies of the largest-scale structures and dynamics of the Universe and with fundamental questions about its origin, structure, evolution, and ultimate fate. Cosmology as a science originated with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on Earth, and Newtonian mechanics, which first allowed us to understand those physical laws. Physical cosmology, as it is now understood, began with the development in 1915 of Albert Einstein's general theory of relativity, followed by major observational discoveries in the 1920s: first, Edwin Hubble discovered that the universe contains a huge number of external galaxies beyond our own Milky Way; then, work by Vesto Slipher and others showed that the universe is expanding. These advances made it possible to speculate about the origin of the universe, and allowed the establishment of the Big Bang Theory, by Georges Lemaître, as the leading cosmological model. A few researchers still advocate a handful of alternative cosmologies; however, most cosmologists agree that the Big Bang theory explains the observations better.

Inflation (cosmology) rapid expansion of the universe

In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from 10−36 seconds after the conjectured Big Bang singularity to some time between 10−33 and 10−32 seconds after the singularity. Following the inflationary period, the universe continues to expand, but at a less rapid rate.

Dark matter Hypothetical form of matter comprising most of the matter in the universe

Dark matter is a hypothetical form of matter that is thought to account for approximately 85% of the matter in the universe and about a quarter of its total energy density. The majority of dark matter is thought to be non-baryonic in nature, possibly being composed of some as-yet undiscovered subatomic particles. Its presence is implied in a variety of astrophysical observations, including gravitational effects that cannot be explained by accepted theories of gravity unless more matter is present than can be seen. For this reason, most experts think dark matter to be ubiquitous in the universe and to have had a strong influence on its structure and evolution. Dark matter is called dark because it does not appear to interact with observable electromagnetic radiation, such as light, and is thus invisible to the entire electromagnetic spectrum, making it extremely difficult to detect using usual astronomical equipment.

Big Rip A cosmological model based on an exponentially increasing rate of expansion

In physical cosmology, the Big Rip is a hypothetical cosmological model concerning the ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, and even spacetime itself, is progressively torn apart by the expansion of the universe at a certain time in the future. According to the standard model of cosmology the scale factor of the universe is known to be accelerating and, in the future era of cosmological constant dominance, will increase exponentially. However, this expansion is similar for every moment of time, and is characterized by an unchanging, small Hubble constant, effectively ignored by any bound material structures. By contrast in the Big Rip scenario the Hubble constant increases to infinity in a finite time.

Non-standard cosmology

A non-standard cosmology is any physical cosmological model of the universe that was, or still is, proposed as an alternative to the then-current standard model of cosmology. The term non-standard is applied to any theory that does not conform to the scientific consensus. Because the term depends on the prevailing consensus, the meaning of the term changes over time. For example, hot dark matter would not have been considered non-standard in 1990, but would be in 2010. Conversely, a non-zero cosmological constant resulting in an accelerating universe would have been considered non-standard in 1990, but is part of the standard cosmology in 2010.

Big Bounce A hypothetical cosmological model for the origin of the known universe

The Big Bounce is a hypothetical cosmological model for the origin of the known universe. It was originally suggested as a phase of 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. It receded from serious consideration in the early 1980s after inflation theory emerged as a solution to the horizon problem, which had arisen from advances in observations revealing the large-scale structure of the universe. In the early 2000s, inflation was found by some theorists to be problematic and unfalsifiable in that its various parameters could be adjusted to fit any observations, so that the properties of the observable universe are a matter of chance. Alternative pictures including a Big Bounce may provide a predictive and falsifiable possible solution to the horizon problem, and are under active investigation as of 2017.

Cyclic model

A cyclic model is any of several cosmological models in which the universe follows infinite, or indefinite, self-sustaining cycles. For example, the oscillating universe theory briefly considered by Albert Einstein in 1930 theorized a universe following an eternal series of oscillations, each beginning with a big bang and ending with a big crunch; in the interim, the universe would expand for a period of time before the gravitational attraction of matter causes it to collapse back in and undergo a bounce.

Lambda-CDM model Model of big-bang cosmology

The ΛCDM or Lambda-CDM model is a parametrization of the Big Bang cosmological model in which the universe contains three major components: first, a cosmological constant denoted by Lambda and associated with dark energy; second, the postulated cold dark matter ; and third, ordinary matter. It is frequently referred to as the standard model of Big Bang cosmology because it is the simplest model that provides a reasonably good account of the following properties of the cosmos:

Flatness problem

The flatness problem is a cosmological fine-tuning problem within the Big Bang model of the universe. Such problems arise from the observation that some of the initial conditions of the universe appear to be fine-tuned to very 'special' values, and that small deviations from these values would have extreme effects on the appearance of the universe at the current time.

Structure formation The formation of galaxies, galaxy clusters and larger structures from small early density fluctuations

In physical cosmology, structure formation is the formation of galaxies, galaxy clusters and larger structures from small early density fluctuations. The universe, as is now known from observations of the cosmic microwave background radiation, began in a hot, dense, nearly uniform state approximately 13.8 billion years ago. However, looking in the sky today, we see structures on all scales, from stars and planets to galaxies and, on still larger scales, galaxy clusters and sheet-like structures of galaxies separated by enormous voids containing few galaxies. Structure formation attempts to model how these structures formed by gravitational instability of small early density ripples.

Paul Steinhardt American cosmologist

Paul Joseph Steinhardt is an American theoretical physicist and cosmologist who is currently the Albert Einstein Professor in Science at Princeton University.

History of the Big Bang theory

The history of the Big Bang theory began with the Big Bang's development from observations and theoretical considerations. Much of the theoretical work in cosmology now involves extensions and refinements to the basic Big Bang model.

Chronology of the universe The history and future of the universe according to Big Bang cosmology

The chronology of the universe describes the history and future of the universe according to Big Bang cosmology. The earliest stages of the universe's existence are estimated as taking place 13.8 billion years ago, with an uncertainty of around 21 million years at the 68% confidence level.

Dark energy unknown property in cosmology that causes the expansion of the universe to accelerate.

In physical cosmology and astronomy, dark energy is an unknown form of energy which is hypothesized to permeate all of space, tending to accelerate the expansion of the universe. Dark energy is the most accepted hypothesis to explain the observations since the 1990s indicating that the universe is expanding at an accelerating rate.

The Hoyle–Narlikar theory of gravity is a Machian and conformal theory of gravity proposed by Fred Hoyle and Jayant Narlikar that originally fits into the quasi steady state model of the universe.


  1. 1 2 3 How the Universe Works 3. End of the Universe. Discovery Channel. 2014.
  2. 1 2 Davies, Paul (January 9, 1997). The Last Three Minutes: Conjectures About The Ultimate Fate Of The Universe. Basic Books. ISBN   978-0-465-03851-0.
  3. Dr. Gary F. Hinshaw, WMAP Introduction to Cosmology. NASA (2008)
  4. Jennifer Bergman, The Big Crunch, Windows to the Universe (2003)
  5. Fraser Cain (2013-10-17), How Will The Universe End? , retrieved 2016-06-13
  6. Y Wang, J M Kratochvil, A Linde, and M Shmakova, Current Observational Constraints on Cosmic Doomsday. JCAP 0412 (2004) 006, astro-ph/0409264
  7. McSween, Stephen A. "Dark Energy and the Red Shift in a Contracting Universe."
  8. J. T. Nielsen, A. Guffanti & S. Sarkar, Marginal evidence for cosmic acceleration from Type Ia supernovae. Nature (2016)