It is a bit of a `catch-22', however. The idea that `something cannot come from nothing' stems from the Law of Conservation of Mass-Energy. However every conservation law is derived from a symmetry, and in this case it is the fact that physical laws are symmetric in time which provides the Law of Conservation of Mass-Energy.
If time `began' at some point (i.e. the Big Bang), this would clearly be a symmetry breaking event - so the Law of Conservation of Mass-Energy would not hold.
In short: if time (as we measure it) is intrinsic to our universe (and I see no reason why it shouldn't be), then there is no contradiction to the idea that our universe sprung up from nothing.
Now I'm not saying that things necessarily have to be this way, I am merely trying to point out the pit-falls with using logical thinking to describe things outside our universe.
Like I said, it's a catch-22. IF the universe is infinite, then you are right in your analysis of `causation implies infinity'. IF the universe is not infinite, then you might be wrong.
Edited by sepulchrave, 29 October 2009 - 06:29 AM.