Changes

===Big Crunch===

===Big Crunch===

The Big Crunch theory is a symmetric view of the ultimate fate of the Universe. Just as the Big Bang started a cosmological expansion, this theory assumes that the average density of the universe is enough to stop its expansion and begin contracting. The end result is unknown; a simple estimation would have all the matter and space-time in the universe collapse into a dimensionless singularity, but at these scales unknown quantum effects need to be considered.

The Big Crunch theory is a symmetric view of the ultimate fate of the Universe. Just as the Big Bang started a cosmological expansion, this theory assumes that the average density of the universe is enough to stop its expansion and begin contracting. The end result is unknown; a simple estimation would have all the matter and space-time in the universe collapse into a dimensionless singularity, but at these scales unknown quantum effects need to be considered.

This scenario allows the Big Bang to be immediately after the Big Crunch of a preceding universe. If this occurs repeatedly, we have a cyclic model which is also known as a oscillatory universe. The universe could then consist of an infinite sequence of finite universes, each finite universe ending with a Big Crunch that is also the Big Bang of the next universe. Theoretically, the cyclic universe could not be reconciled with the second law of thermodynamics: entropy would build up from oscillation to oscillation and cause heat death. Other measurements suggested the universe is not closed. These arguments caused cosmologists to abandon the oscillating universe model. A somewhat similar idea is embraced by the cyclic model, but this idea evades heat death, because of an expansion of the branes that dilutes entropy accumulated in the previous cycle. In the big crunch, the universe will end approximately 30 billion years from now.

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===Big Rip===

===Big Rip===

In the special case of phantom dark energy, which has even more negative pressure than a simple cosmological constant, the density of dark energy increases with time, causing the rate of acceleration to increase, leading to a steady increase in the Hubble constant. As a result, all material objects in the universe, starting with galaxies and eventually, all forms, no matter how small, will disintegrate into unbound elementary particles and radiation, ripped apart by the phantom energy force and shooting apart from each other. The end state of the universe is a singularity, as the dark energy density and expansion rate becomes infinite. For a possible timeline based on current physical theories, see 1 E19 s and more. This universe will end approximately 100 billion years from now.

In the special case of phantom dark energy, which has even more negative pressure than a simple cosmological constant, the density of dark energy increases with time, causing the rate of acceleration to increase, leading to a steady increase in the Hubble constant. As a result, all material objects in the universe, starting with galaxies and eventually, all forms, no matter how small, will disintegrate into unbound elementary particles and radiation, ripped apart by the phantom energy force and shooting apart from each other. The end state of the universe is a singularity, as the dark energy density and expansion rate becomes infinite. For a possible timeline based on current physical theories, see 1 E19 s and more. This universe will end approximately 100 billion years from now.