I'll be short here. In each cm3 of vacuum there is more energy than there is in all the universe. When folks were developing equations in the late '20s that took into account the wave nature of matter, negative energy solutions came out as answers. They were particles of negative energy, the same charge, moving backwards in time. Most rejected them as sports. Dirac was the first to point out that these would be noticed as positive energy particles, of opposite charge, moving forward in time. These particles are called antiparticles. Dirac envisioned the vacuum as a sea of these, "holes", filled with regular particles. His first calculations were with electrons and positrons, later it would be shown that hadrons and leptons exist as pairs. When they are paired, there is nothing observable, except the properties of the vacuum.
The early considerations were with single particles. Later fields were quantized, to look at systems of particles. The particles arrise out of the fields, in this case the electromagnetic field. Feynman did(1949) that and calculated the the fine structure of spectrum of the hydrogen atom exactly, by including terms, called the self energy, that included the electrons interaction with the vacuum. That's what confirmed the correctness of QED, quantum electrodynamics.
That interaction occurs, because the vacuum is not silent. According to the law of conservation of energy, energy can neither be created, or destroyed. The uncertainty principle says that the energy of a particle can only be known to a certain precision. That's expressed as hbar ~ E*t, where t is the time of the observation. If the time is short enough and your looking at the vacuum, (actually it's a particle looking at the vacuum) particles of E ~ hbar/t will be seen. Yukawa explain the weak force in this way back in ~1930. His particle was a pi meson. It is echanged between protons and neutrons, that convert back and forth between each other according to which one holds the meson. There's a probability one of them will drop the ball, a neutron will decay and the nucleus decays. Outside the nucleus the neutron only has a 1/2 life of ~12secs.
There's an experiment that was done around ~1950, but I can't remember the guys name. To metal plates are positioned very close to each other. Since all those particles are popping in and out of the vacuum and observer should be able to measure a force. They do, it's called the (?C... effect, sorry CRS). The force and energy are useless though to do work in this universe.
THe interaction with the vacuum is also what gives black holes their black body radiation. That's radiation that emits from anything with a temperature. There's still not a net gain in E from the vacuum though, because when this happens the antiparticles are decreasing the black holes size. It is essentially boiling off. I'll be gone for some time, maybe someone else could add.