Alex,
"Popping out and vanish" is possible because of Heisenberg's uncertainty principle.
Virtual particle may "pop" into existence for very brief time period and then vanish again.. The product: (mass * delta-time) will be smaller than P2*pi() *Planck constant. In this case, the energy preservation principle is not violated. Because charge etc also has to be preserved, particles pop out in pairs (like electron and antielecton, for example).
More on this subject can be found here:
http://en.wikipedia.org/wiki/Virtual_particles