The Big Rip is a cosmological model based on a particular form ofdark energy. It is called phantom energy.
In this model it is assumed that the cosmological constant can in fact vary over time, so that its density will start to increase, despite the fact that the universe is expanding, to reach an infinite value in a finite time. The cosmos will then end its existence in a gravitational singularity in which all structures, from galaxy clusters to atoms, will be destroyed. In a more classical model of dark energy, the expansion remains at a scale higher than that the galaxy clusters and cannot materialise at planet and atom scale, unlike phantom energy. This model was first proposed in 1999 by Robert R. Caldwell, the name Big Rip being coined by himself and his collaborators Marc Kamionkowski and Nevin N. Weinberg in 2003.
The following chronology can be established for the Big Rip:
Depending on whether dark energy is variable in nature, the universe will end in a Big Crunch or continue to expand eternally. This diagram shows the deceleration followed by the accelerated expansion of the universe depending on time. Three possible scenarios for the end of the universe then appear. © NASA/CXC/M. Weiss