Zero-point energy
If you look at the way physics is going, there are atoms, then there are subatomic particles making up atoms (e.g. electrons, protons, neutrons), then further subatomic particles making up those subatomic particles (e.g. quarks, gluons), and now there is string theory. String theory says that those smallest subatomic particles are made of vibrating strings of energy, and that those strings have practically no actual width whatsoever. So all the matter of the universe could be compressed into an extremely small space, hence the Big Bang theory. If this is the case, the large energy interpretation of zero-point energy seems likely.