# Big Rip

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 (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.

The possibility of sudden rip singularity occurs only for hypothetical matter (phantom energy) with implausible physical properties.[1]

## Overview

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. If the dark energy in the universe increases without limit, it could overcome all forces that hold the universe together. The key value[why?] is the equation of state parameter w, the ratio between the dark energy pressure and its energy density. If w < −1, this dynamical vacuum energy is known as phantom energy, an extreme[how?] form of quintessence.

### Expansion

A universe dominated by phantom energy is an accelerating universe, expanding at an ever-increasing rate. However, this implies that the size of the observable universe is continually shrinking; the distance to the edge of the observable universe which is moving away at the speed of light from any point moves ever closer. When the size of the observable universe becomes smaller than any particular structure, no interaction by any of the fundamental forces can occur between the most remote parts of the structure. When these interactions become impossible, the structure is "ripped apart". The model implies that after a finite time there will be a final singularity, called the "Big Rip", in which 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 end of the universe as we know it for this form of energy to be

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

where w is defined above, H0 is Hubble's constant and Ωm is the present value of the density of all the matter in the universe.

## Authors' example

In their paper, the authors consider a hypothetical example with w = −1.5, H0 = 70 km/s/Mpc, and Ωm = 0.3, in which case the Big Rip would happen approximately 22 billion years from the present.

For w = −1.5, the galaxies would first be separated from each other. About 60 million years before the Big Rip, gravity would be too weak to hold the Milky Way and other individual galaxies together. Galaxies would be destroyed as stars separate from the main black hole. Approximately three months before the Big Rip, the Solar System (or systems similar to our own at this distant time, as the survival of our Solar System 22 billion years in the future is a questionable assumption) would be gravitationally unbound. Planets would be detached from the star's orbit. In the last minutes, stars and planets would be torn apart, and 10-19 seconds before the Big Rip, atoms would be destroyed. At the time the Big Rip occurs, even spacetime itself would be ripped apart and the scale factor would be infinity.[2]

## 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 that 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 equal to −1, the Big Rip could not happen, regardless of the values of H0 or Ωm.

According to the latest cosmological data available, the uncertainties are still too large to discriminate among the three cases w < −1, w = −1, and w > −1.[3][4]

• Big Bounce – A hypothetical cosmological model for the origin of the known universe
• Big Crunch – Theoretical scenario for the ultimate fate of the universe
• Big Chill – Future scenario assuming that the expansion of the universe will continue forever
• Entropy (arrow of time)
• False vacuum – A hypothetical vacuum, less stable than true vacuum
• Heat death of the universe – A possible end of the universe
• Last Contact - A short story describing what Big Rip would be like from an everyday perspective

## References

1. ^ Ellis, George F. R.; Maartens, Roy & MacCallum, Malcolm A. H. (2012). Relativistic Cosmology. Cambridge, UK: Cambridge University Press. pp. 146–147. ISBN 978-0-52138-115-4.
2. ^ Caldwell, Robert R.; Kamionkowski, Marc; Weinberg, Nevin N. (2003). "Phantom Energy and Cosmic Doomsday". Physical Review Letters. 91 (7): 071301. arXiv:astro-ph/0302506. Bibcode:2003PhRvL..91g1301C. doi:10.1103/PhysRevLett.91.071301. PMID 12935004.
3. ^ "WMAP 9 Year Mission Results". wmap.gsfc.nasa.gov. Retrieved 22 September 2017.
4. ^ Allen, S. W.; Rapetti, D. A.; Schmidt, R. W.; Ebeling, H.; Morris, R. G.; Fabian, A. C. (2008). "Improved constraints on dark energy from Chandra X-ray observations of the largest relaxed galaxy clusters". Monthly Notices of the Royal Astronomical Society. 383 (3): 879. arXiv:0706.0033. Bibcode:2008MNRAS.383..879A. doi:10.1111/j.1365-2966.2007.12610.x.