Here is a further resource which explains the physics of virtual particle anti-particle pair creation rather well. In particular the Feynman diagram in my post above is explained well in a style that doen't shirk on the physics. No math to follow. There are parenthetical hints to those who have the math.
Virtual Particles: What are they? | Of Particular Significance
It looks like an interesting blog. I came across it when looking for the graph above. A link to getting started as a reader of this blog is here:
New? Start Here | Of Particular Significance