system
Given the following post, respond as if you're commenting on Reddit:
human
If half of the matter falling in to a black hole during Hawking Radiation emission are anti particles and half are their particle counterparts, why does it cause the black hole to shrink?

Why aren't the effects of particles and anti particles netted out?
gpt
There is a variety of misleading information in this thread.

To begin with, you are correct: the absorption of particles or antiparticles would increase the mass of a black hole.

Next: this whole description you are referencing is a description of one way of calculating the existence of Hawking radiation, but you should not take the description of the calculation to be a physical description of what happens (and, in fact, there are other ways of doing the calculation).

To expand: There are physical particles in nature -- things we are familiar with, like electrons and photons and so on.  In certain approaches to particle theory calculations, there are separate entities called virtual particles.  Virtual particles are NOT physical particles; there is no way to observe them.  One way we know they are not physical is that there are ways of doing particle physics that do not use virtual particles at all!

Hawking radiation occurs because quantum mechanics allows for states that start out as just a black hole and end up as a slightly smaller black hole plus an outgoing particle.  The way Hawking first showed this is with the creation of a real particle/virtual particle pair near the event horizon, with the virtual particle getting absorbed, and the black hole decreasing its mass.  You can also show this without virtual particles but using tunneling (à la Parikh and Wilczek).

Trying to think too literally about the virtual particle calculation is problematic because you can wind up trying to reason about non-physical objects as if they are physical.