Phantom energy

Phantom energy is a hypothetical form of dark energy satisfying the equation of state ${\displaystyle P=w\rho c^{2}}$ with ${\displaystyle w<-1}$. It possesses negative kinetic energy, and predicts expansion of the universe in excess of that predicted by a cosmological constant, which leads to a Big Rip. The idea of phantom energy is often dismissed, as it would suggest that the vacuum is unstable with negative mass particles bursting into existence. The concept is hence tied to emerging theories of a continuously created negative mass dark fluid, in which the cosmological constant can vary as a function of time.