Zero-point energy is the energy of the vacuum space, the space between the subatomic particles within atoms. There are a few theories about how much energy there is in that space. There is the theory that there is an incredibly small, very near-zero amount, the theory that there is zero energy there, the theory that the amount of energy is indeterminable, and the theory that a cubic centimetre of vacuum has a few levels of magnitude more energy than would be required to create the Big Bang.