Big Rip

Inphysical cosmology,theBig Ripis ahypotheticalcosmological modelconcerning theultimate fate of the universe,in which thematterof theuniverse,from stars and galaxies to atoms and subatomic particles, and evenspacetimeitself, is progressively torn apart by theexpansion of the universeat a certain time in the future, until distances between particles will infinitely increase. According to the standard model of cosmology, thescale factorof the universe isaccelerating,and, in the future era of cosmological constant dominance, will increase exponentially. However, 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, smallHubble 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.

The possibility of sudden rip singularity occurs only for hypothetical matter (phantom energy) with implausible physical properties.

Overview

Main articles:Future of an expanding universe,Heat death of the universe,Timeline of the far future,andUltimate fate of the universe

The truth of the hypothesis relies on the type ofdark energypresent in ouruniverse.The type that could prove this hypothesis is a constantly increasing form of dark energy, known asphantom 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 theequation of stateparameterw,theratiobetween the dark energy pressure and itsenergy density.If −1 <w< 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 hasw< −1, which means that its density increases as the universe expands.

A universe dominated by phantom energy is anaccelerating universe,expanding at an ever-increasing rate. However, this implies that the size of theobservable universeand thecosmological event horizonis 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 thefundamental forcescan occur between the most remote parts of the structure, and the structure is "ripped apart". The progression oftimeitself 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 byRobert R. CaldwellofDartmouth College,calculate the time from the present to the Big Rip to be

$t_{\mathrm {rip} }-t_{0}\approx {\frac {2}{3\left|1+w\right|H_{0}{\sqrt {1-\Omega _{\mathrm {m} }}}}}$

wherewis defined above,H₀isHubble's constantandΩ_mis the present value of the density of all the matter in the universe.

Observations ofgalaxy clusterspeeds by theChandra X-ray Observatoryseem to suggest the value ofwis between approximately −0.907 and −1.075, meaning the Big Rip cannot be definitively ruled out. Based on the above equation, if the observation determines that the value ofwis less than −1, but greater than or equal to −1.075, the Big Rip would occur approximately 152 billion years into the future at the earliest.

Authors' example

In their paper, the authors consider a hypothetical example withw= −1.5,H₀= 70 km/s/Mpc, andΩ_m= 0.3, in which case the Big Rip would happen approximately 22 billion years from the present. In this scenario,galaxieswould 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 systemslike theSolar Systemwould 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-dispersedatomswould be destroyed about 10⁻¹⁹seconds before the end (the atoms will first beionizedaselectronsfly off, followed by thedissociationof theatomic nuclei). At the time the Big Rip occurs, even spacetime itself would be ripped apart and the scale factor would be infinity. Other universes and things made of universes would also be ripped apart and it would be infinite.

Observed universe

Evidence indicateswto be very close to −1 in our universe, which makeswthe dominating term in the equation. The closer thatwis to −1, the closer the denominator is to zero and the further the Big Rip is in the future. Ifwwere exactly equal to −1, the Big Rip could not happen, regardless of the values ofH₀orΩ_m.

According to the latest cosmological data available, the uncertainties are still too large to discriminate among the three casesw< −1,w= −1, andw> −1.

Moreover, it is nearly impossible to measurewto be exactly at −1 due to statistical fluctuations. This means that the measured value ofwcan 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.

See also

• Big Bounce– Model for the origin of the universe
• Big Crunch– Theoretical scenario for the ultimate fate of the universe
• Big Chill– Future scenario if the expansion of the universe will continue forever or not
• Entropy (arrow of time)– Use of the second law of thermodynamics to distinguish past from future
• False vacuum decay– Hypothetical vacuum, less stable than true vacuumPages displaying short descriptions of redirect targets
• Heat death of the universe– Possible fate of the universe
• "Last Contact"– A short story describing what Big Rip would be like from an everyday perspective

External links

• Overbye, Dennis (17 February 2004)."From Space, A New View Of Doomsday".The New York Times.
• Devlin, Hannah (3 July 2015)."This is the way the world ends: not with a bang, but with a Big Rip".The Guardian.
• Mastin, Luke (2009)."The Big Crunch, the Big Freeze and the Big Rip".Physics of the Universe.