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{{Short description|Cosmological model}}
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{{cosmology}}
In [[physical cosmology]], the '''Big Rip''' is a [[hypothesis|hypothetical]] [[Physical cosmology|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, until distances between particles will infinitely increase.

According to the standard model of cosmology, the [[Scale factor (cosmology)|scale factor]] of the universe is [[Accelerating expansion of the universe|accelerating]], and, in the future era of cosmological constant dominance, will increase exponentially. But this expansion is similar for every moment of time (hence the exponential law—the expansion of a local volume is the same number of times over the same time interval), 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. According to recent studies, the universe is set for a constant expansion and [[Heat death of the universe|heat death]],<ref>{{Cite web |last=Sutter |first=Paul |date=2024-02-26 |title=What is the big rip, and can we stop it? |url=https://www.space.com/universe-the-big-rip-can-we-stop-it |access-date=2024-09-11 |website=Space.com |language=en}}</ref> because the [[Equation of state (cosmology)|equation of state]] parameter ''w'' = −1.

The possibility of sudden rip singularity occurs only for hypothetical matter ([[phantom energy]]) with implausible physical properties.<ref>{{cite book |title=Relativistic Cosmology |url=https://archive.org/details/relativisticcosm00elli |url-access=limited |first1=George F. R. |last1=Ellis |author-link1=George F. R. Ellis |first2=Roy |last2=Maartens |first3=Malcolm A. H. |last3=MacCallum |name-list-style=amp |year=2012 |location=Cambridge, UK |publisher=[[Cambridge University Press]] |pages=[https://archive.org/details/relativisticcosm00elli/page/n627 146]–147 |isbn=978-0-52138-115-4}}</ref>

==Overview==
[[File:Big-rip-proper.png|thumb|300px|Spacetime diagram of a hypothetical big rip universe in [[Comoving and proper distances|proper distance coordinates]]. Time goes up the vertical axis and space is on the horizontal axis.]]{{main|Future of an expanding universe|Heat death of the universe|Timeline of the far future|Ultimate fate of the universe}}

The truth of the hypothesis relies on the type of [[dark energy]] present in our [[universe]]. The type that could prove this hypothesis is a constantly increasing form of dark energy known as [[phantom energy]]. If the dark energy in the universe increases without limit, it could overcome all forces that hold the universe together. The key value is the [[equation of state (cosmology)|equation of state]] parameter ''w'', the [[ratio]] between the dark energy pressure and its [[energy density]]. If −1&nbsp;<&nbsp;''w''&nbsp;<&nbsp;0, the expansion of the universe tends to accelerate, but the dark energy tends to dissipate over time, and the Big Rip does not happen. Phantom energy has ''w''&nbsp;<&nbsp;−1, which means that its density increases as the universe expands.

A universe dominated by phantom energy is an [[Accelerating expansion of the universe|accelerating universe]], expanding at an ever-increasing rate. But this implies that the size of the [[observable universe]] and the [[Cosmological horizon|cosmological event horizon]] is continually shrinking—the distance at which objects can influence an observer becomes ever closer, and the distance over which interactions can propagate becomes ever shorter. When the size of the horizon becomes smaller than any particular structure, no interaction by any of the [[Fundamental interaction|fundamental forces]] can occur between the most remote parts of the structure, and the structure is "ripped apart". The progression of time itself will stop. The model implies that after a finite time there will be a final singularity, called the "Big Rip", in which the observable universe eventually reaches zero size and all distances diverge to infinite values.

The authors of this hypothesis, led by [[Robert R. Caldwell]] of [[Dartmouth College]], calculate the time from the present to the Big Rip to be

{{block indent|<math>t_\mathrm{rip} - t_{0} \approx \frac{2}{3\left|1+w\right|H_0\sqrt{1-\Omega_\mathrm{m}}}</math>}}

where ''w'' is defined above, ''H''<sub>0</sub> is [[Hubble's constant]] and ''Ω''<sub>m</sub> is the present value of the density of all the matter in the universe.

Observations of [[galaxy cluster]] speeds by the [[Chandra X-ray Observatory]] seem to suggest the value of ''w'' is between approximately −0.907 and −1.075, meaning the Big Rip cannot be ruled out. Based on the above equation, if the observation determines that ''w'' is less than −1 but greater than or equal to −1.075, the Big Rip would occur in approximately 152 billion years at the earliest.<ref name="chand">
{{cite journal | title = Chandra Cluster Cosmology Project III: Cosmological Parameter Constraints | last1 = Vikhlinin | first1 = A. | last2 = Kravtsov | first2 = A. V. | last3 = Burenin | first3 = R. A. | date = 2009 | display-authors = 3 | last4 = Ebeling | first4 = H. | last5 = Forman | first5 = W. R. | last6 = Hornstrup | first6 = A. | last7 = Jones | first7 = C. | last8 = Murray | first8 = S. S. | last9 = Nagai | first9 = D. | volume = 692 | pages = 1060–1074 | issue = 2 | doi = 10.1088/0004-637X/692/2/1060 | bibcode = 2009ApJ...692.1060V | journal = The Astrophysical Journal
|arxiv = 0812.2720 | s2cid = 15719158 }}</ref> More recent data from Planck mission indicates the value of ''w'' to be −1.028 (&pm;0.031), pushing the earliest possible time of Big Rip to approximately 200 billion years into the future.<ref name="plank">
{{cite journal |author1=The Planck Collaboration |title=Planck 2018 results. VI. Cosmological parameters |journal=Astronomy and Astrophysics |year=2020 |volume=641 |pages=A6 |doi=10.1051/0004-6361/201833910 |arxiv=1807.06209 |bibcode=2020A&A...641A...6P|s2cid=119335614 }}</ref>

==Authors' example==
In their paper, the authors consider a hypothetical example with ''w''&nbsp;=&nbsp;−1.5, ''H''<sub>0</sub>&nbsp;=&nbsp;70&nbsp;km/s/Mpc, and ''Ω''<sub>m</sub>&nbsp;=&nbsp;0.3, in which case the Big Rip would happen approximately 22 billion years from the present. In this scenario, [[Galaxy|galaxies]] would first be separated from each other about 200 million years before the Big Rip. About 60 million years before the Big Rip, galaxies would begin to disintegrate as gravity becomes too weak to hold them together. [[Planetary system]]s like the [[Solar System]] would become gravitationally unbound about three months before the Big Rip, and planets would fly off into the rapidly expanding universe. In the last minutes, stars and planets would be torn apart, and the now-dispersed [[atom]]s would be destroyed about 10<sup>−19</sup> seconds before the end (the atoms will first be [[ionization|ionized]] as [[electron]]s fly off, followed by the [[dissociation (chemistry)|dissociation]] of the [[atomic nucleus|atomic nuclei]]). At the time the Big Rip occurs, even spacetime itself would be ripped apart and the scale factor would be infinity.<ref>{{cite journal
| doi = 10.1103/PhysRevLett.91.071301
| last = Caldwell | first = Robert R. |author2=Kamionkowski, Marc |author3=Weinberg, Nevin N.
| title = Phantom Energy and Cosmic Doomsday
| journal = Physical Review Letters
| volume = 91
| pages = 071301
| year = 2003
| pmid=12935004
| arxiv=astro-ph/0302506
| bibcode=2003PhRvL..91g1301C
| issue = 7
| s2cid = 119498512 }}</ref>

==Observed universe==

Evidence indicates ''w'' to be very close to −1 in our universe, which makes ''w'' the dominating term in the equation. The closer ''w'' is to −1, the closer the denominator is to zero and the further the Big Rip is in the future. If ''w'' were exactly −1, the Big Rip could not happen, regardless of the values of ''H''<sub>0</sub> or ''Ω''<sub>m</sub>.

According to the latest cosmological data available, the uncertainties are still too large to discriminate among the three cases ''w''&nbsp;<&nbsp;−1, ''w''&nbsp;=&nbsp;−1, and ''w''&nbsp;>&nbsp;−1.<ref>{{cite web |url=http://wmap.gsfc.nasa.gov/news/ |title=WMAP 9 Year Mission Results |website=wmap.gsfc.nasa.gov |access-date=22 September 2017}}</ref><ref>{{Cite journal | bibcode = 2008MNRAS.383..879A | title = Improved constraints on dark energy from Chandra X-ray observations of the largest relaxed galaxy clusters | last1 = Allen | first1 = S. W. | last2 = Rapetti | first2 = D. A. | last3 = Schmidt | first3 = R. W. | last4 = Ebeling | first4 = H. | last5 = Morris | first5 = R. G. | last6 = Fabian | first6 = A. C. | volume = 383 | year = 2008 | pages = 879 | journal = [[Monthly Notices of the Royal Astronomical Society]] | doi = 10.1111/j.1365-2966.2007.12610.x | issue = 3| doi-access = free |arxiv = 0706.0033 | s2cid = 18200810 }}</ref>

Moreover, it is nearly impossible to measure ''w'' to be exactly at −1 due to statistical fluctuations. This means that the measured value of ''w'' can be arbitrarily close to −1 but not exactly at −1, hence the earliest possible date of the Big Rip can be pushed back further with more accurate measurements but the Big Rip is very difficult to completely rule out.<ref>{{Cite web |last=Mack |first=Katie |date=7 October 2020 |title=Tearing Apart the Universe |url=https://www.americanscientist.org/article/tearing-apart-the-universe |website=American Scientist}}</ref>

== See also ==
{{div col|colwidth=30em}}
* {{annotated link|Big Bounce}}
* {{annotated link|Big Crunch}}
* {{annotated link|Future of an expanding universe|Big Chill}}
* {{annotated link|Entropy as an arrow of time|Entropy (arrow of time)}}
* {{annotated link|False vacuum decay}}
* {{annotated link|Heat death of the universe}}
* "[[Last Contact]]" – A short story describing what Big Rip would be like from an everyday perspective

{{div col end}}

==References==
{{Reflist}}

==External links==
* {{cite news |url=https://www.nytimes.com/2004/02/17/science/from-space-a-new-view-of-doomsday.html?pagewanted=all |first=Dennis |last=Overbye |title=From Space, A New View Of Doomsday |newspaper=The New York Times |date=17 February 2004}}
* {{cite news |url=https://www.theguardian.com/science/2015/jul/02/not-with-a-bang-but-with-a-big-rip-how-the-world-will-end |first=Hannah |last=Devlin |title=This is the way the world ends: not with a bang, but with a Big Rip |newspaper=The Guardian |date=3 July 2015}}
* {{cite web |url=http://www.physicsoftheuniverse.com/topics_bigbang_bigcrunch.html |first=Luke |last=Mastin
|title=The Big Crunch, the Big Freeze and the Big Rip |work=Physics of the Universe |year=2009}}

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