[eastsider]

Each cm3 of vacuum contains more energy than the entire other 1/2 of the universe.

What kind of energy, and what is the source of that energy?

[spunkets]

Same kind of energy that occurs here. In fact everything that occurs and is seen in this universe is composed of the energy that popped out of the vacuum. There is no source for the energy in the vacuum, it always existed.

All the different particles of matter that exist have an antiparticle possibility. The vacuum is composed of the entire spectrum of particles and their antiparticles.

For instance the antiparticle for the electron is the positron. It's a negative energy electron, moving backward in time. In this universe it looks like(behaves like) a positively charged particle of the same mass as the electron, positive energy, moving forward in time.

Particle pairs pop out of the vacuum all the time, but have an extremely short lifetime. Their life is limited to ~<h, Planck's constant, divided by the total energy of the pair. If they stay any longer they would violate the conservation of energy. While they're out they do interact though and experiment shows it.