Big Rip

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The Big Rip is a cosmological hypothesis about the ultimate fate of the Universe, in which the elements of the universe, from galaxies to atoms, are progressively torn apart by the expansion of the universe.

The hypothesis relies crucially on the type of dark energy in the universe. The key value is the equation of state 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, a more extreme form of quintessence.

In a phantom energy-dominated universe the "fabric" of 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 furthest parts of the structure can occur, neither gravitational nor electromagnetic (nor weak or strong), and they will be, for all intents and purposes, "ripped" apart. Once universal expansion has ripped apart structures even at Planck length, no interaction at all is possible, the entropy of the universe is at maximum, and time therefore effectively ends.

If the hypothesis holds, the first structures to be separated from each other would be the galaxies. Arguably, this is what is happening right now, with galaxies moving outside the observable universe at about 13.7 billion light years away. Individual galaxies such as the Milky Way would be gravitationally unbound about 60 million years before the end; the Solar system, approximately three months before it; stars and planets, in the last minutes. The authors of the hypothesis calculate that this end would lie at approximately 35 billion years after the Big Bang, or 20 billion years from now.