Big Rip

The Big Rip is a cosmological hypothesis first published in 2003, about the ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, is progressively torn apart by the expansion of the universe at a certain time in the future. Theoretically, the scale factor of the universe becomes infinite at a finite time in the future.

The hypothesis relies crucially on the type of dark energy in the universe. The key value is the equation of state parameter w, the ratio between the dark energy pressure and its energy density. At w < −1, the universe will eventually be pulled apart. Such energy is called phantom energy, an extreme form of quintessence.

In a phantom-energy dominated universe, the universe expands 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 gets ever closer. When the size of the observable universe is smaller than any particular structure, then no interaction between the farthest parts of the structure can occur, neither gravitational nor electromagnetic (nor weak or strong), and when they can no longer interact with each other in any way they will be "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 Caldwell of Dartmouth College, calculate the time from now to the end of the universe as we know it for this form of energy to be

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

where $w$ is a measure of the repulsive force of Dark Energy , H₀ is Hubble's constant and Ω_m is the present-day value of the density of all the matter in the universe.

In their paper they consider an example with w = -1.5, H₀ = 70 km/s/MPsec and Ω_m = 0.3, in which case the end of the universe is approximately 22 billion years from now. This is not considered as a prediction, but as a hypothetical example. The authors note that evidence indicates w is very close to -1 in our universe, which makes $\Omega$ the dominating term in the equation. The closer (1 + $w$) is to zero, the closer the denominator is to zero and the more distant (in time) is the Big Rip. If $w$ were exactly equal to -1 then the Big Rip could not happen, regardless of the values of H₀ or Ω_m.

In their scenario for w = -1.5, the galaxies would first be separated from each other. About 60 million years before the end, gravity would be too weak to hold the Milky Way and other individual galaxies together. Approximately three months before the end, the solar system would be gravitationally unbound. In the last minutes, stars and planets would be torn apart, and an instant before the end, atoms would be destroyed.

Experimental data

Current experiment points against a big rip, since the dark energy does not seem to be increasing in the way that it would need to for the rip to occur.

See also

• List of astronomical topics
• Heat-death of the Universe
• Big Crunch
• Big Bounce
• Accelerating universe
• Ultimate fate of the Universe
• Phantom energy
• Cyclic Model
• Dark energy

External links

• Daily Kos: Science Friday: Long Live the Big Rip!
• The Big Rip: New Theory Ends Universe by Shredding Everything