A Sea Of Virtual Particles

"'Space is not a passive framework for events to happen in. It is a sea of virtual particles. They constantly go in and out of existence according to the uncertainty principle. The energy density implied is tremendous.'"
-Poul Anderson, Starfarers (New York, 1999), p. 8.

I used to think that the conservation of energy meant that particles could neither begin nor cease to exist. However, apparently, they begin and cease in numbers that preserve the total quantity of energy - except maybe back at the Beginning before the Big Bang? But, if that earliest moment really was the earliest, then no period of non-existence preceded the first moment of existence. There was merely that first moment of existence.

I used to think that contingent existence could be explained only by reference to a necessarily existent being which I identified with the Biblical creator. However, I now believe that logical necessity is a feature of some propositions, not of any being, thus that all existence is contingent. It could have happened that nothing existed. But it seems that being and nothing interact dynamically like heat and cold in the Yawning Chasm or Gaping Void of the Norse creation myth. Virtual particles constantly beginning and ceasing to exist sound like a stage intermediate between something and nothing. Also, physics answers questions that I had thought would forever remain metaphysical.

Addendum, 3 Feb 2017: Of course, matter and anti-matter particle pairs appearing and mutually annihilating emerge from and return to energy, not nothing?