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.^[1] 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.^[2][3]