You don't believe that anything comes from nothing Naomi?
That sounds like a religious position not that far removed from someone's belief in God.
Virtual particles *do* come in and out of existance - this has been demonstrated in the Casimir effect
http://en.wikipedia.org/wiki/Casimir_effect
You may or may not choose to believe it, but it is the case.
I haven't had time to watch it all I might do later but there is a fundamental question to the Universe that even Professor Hawking doesn't have a good answer to.
This is why the Universe is so finely tuned for life. There are many constants in physics like the strength of Gravity, the charge on an electron, the mass of a proton etc.
We have no idea why they are set to the values they are - this is important because change some of them by even a bit and you get a Universe with no matter, let alone no life.
Many, and I thing Stephen Hawking is amoung them will say that there must be many Universes each with different values.
This is an answer but not a good one. It has been directly derived to answer this problem and there is no evidence for it, no any prospect of testing it.
It has simply been invented much like the concept of the Trinity to solve a doctrinal issue.
That's not to say that I think God set the constants but I do think sometimes people of making light of the weak areas in their argument. Yes I know religonists do it all the time but rationalists should be better than that