Phantom energy is a hypothetical form of dark energy that is even more potent than the cosmological constant at increasing the expansion of the universe (i.e., it satisfies the equation of state with ). If it exists, it could cause the expansion of the universe to accelerate so quickly that a scenario known as the Big Rip would occur. If this is true, the expansion of the universe reaches an infinite degree in finite time, causing expansion to accelerate without bounds. This acceleration will pass the speed of light (since it involves expansion of the universe itself, not particles moving within it), causing the observable universe to shrink, as light and information emitted from distant stars cannot "catch up" with the expansion. As the observable universe contracts, objects will be unable to interact with each other via fundamental forces, and eventually the expansion will prevent any action of forces between any particles, even within atoms, "ripping apart" the universe. This characterizes the Big Rip as a possible end to the universe.
One application of phantom energy in 2007 was to a cyclic model of the universe.