How do you get something from nothing?

How do you get a universe (space-time, mass/momentum & laws of physics) - or a multiverse - out of nothing? Lawrence Krauss, in "A Universe From Nothing: why there is something rather than nothing" [Free Press 2011] argues that both the very existence and the accelerating expansion of the universe is most likely powered by "nothing".

 http://www.newscientist.com/article/mg21328472.000-trying-to-make-the-cosmos-out-of-nothing.html