Small regions of empty space will see large energies…

““Small regions of empty space will see large energies appear in the form of these fluctuations. they may be energetic electromagnetic waves. They may even appear as particle-antiparticle pairs-supposing, of course, that the energy of the fluctuation rises above the rest mass of these particles. There is no a priori carrier for the fluctuating energy in empty space, in contrast, to say, the crystal. Rather, the appearance of such a carrier is another consequence of the energy fluctuations implied by the uncertainty relation. Their short-lived existence keeps us from noticing such fluctuations in our everyday existence. The shorter their lifetime, the larger they get-this is another formulation of the uncertainty principle: It relates energy to time in the same way that it relates location to velocity. Lifetime, range, and magnitude of an energy fluctuation in a vacuum are always related such that the energy uncertainty includes the smallest possible energy value. It is large for short lifetimes and small volumes, smaller when the lifetimes are longer and the volumes larger. Energy fluctuations cannot be larger than what is needed to have them reach the zero level by means of the uncertainty relation; conversely, there must be fluctuations within this range. The principle mandates the existence of energetic fluctuations of short lifetimes as well as that of lower-energy ones with longer lifetimes. Electromagnetic excitation of the vacuum, such as light, may have very little energy; that makes these fluctuations carriers of long-lived energy fluctuations. Once the energy is, by dint of Einstein's mass-energy relation, sufficient to create electron-positron pairs, virtual particles may, and must, appear for very brief times as part of the energy fluctuation. Since the fluctuations, like every process in nature, don't change the total electric charge, electrons and positrons can be created (and destroyed!) only in pairs.””

— Henning Genz