Dr. Craig is a liar.

[Mister Agenda]

I don't know.  I'm not a quantum physicist.

You can read up on the Copenhagen interpretation.

I've never seen anyone giving a reason for this.... Usually just general hand waving, and appeal to very small things or vague references.   Thought maybe by the way you where talking, you knew something that I didn't.

I'll take a stab. The Heisenberg Uncertainty Principle states that we cannot simultaneously know the position and velocity of a particle. A nonexistent particle would have a position and velocity of (0,0). We can't even know that, so when we use our instruments to detect the effect of an absence of particles on an incredibly tiny scale, we find effects that can be explained by particle pairs 'popping into existence' and immediately annihilating each other. It's like someone squeezed on zero and made it divide into +1 and -1 for a nanosecond. A variety of 'forces' seem to be mediated by virtual particles.

I am not a physicist, I hope one comes along and gives a better explanation and shows where I'm wrong.