system
Given the following post, respond as if you're commenting on Reddit:
human
Where does the energy go when particle-antiparticle pairs spontaneously appear and annihilate?

Still trying to wrap my head around Hawking Radiation, but I was wondering about those particle-antiparticle pairs that are spontaneously appearing. 

If they appear and annihilate (elsewhere in space, not related to black holes), wouldn't that release energy? I thought energy could not be created, but wouldn't the annihilation of those particle pairs release energy into the surrounding space, increasing the total energy of the universe? Where does the energy go?
gpt
The energy doesn't go anywhere, because there was zero energy to begin with and zero energy after.

The particle-antiparticle pairs you're referring to are called *virtual particles*. They aren't real particles, and they don't actually exist. They're mathematical tools that are used in calculations, but they fail to have many of the properties of real particles. In particular, *real* particles have a relationship between their mass, energy, and momentum: E^2 = p^2 c^2 + m^2 c^4. In particular, their (mass+kinetic) energy is always positive. That relationship is not true for virtual particles, and one of the pair of virtual particles just has negative energy (so the pair has total energy zero).

But--just to reiterate because this causes so much confusion--virtual particles aren't real. They're just a mathematical tool.