It's common for religious theists to ask "how can something come from nothing?" This question is typically part of an argument designed to show that "something" can only come from "something" and therefore a Big Bang without a God is impossible. This argument, however, depends upon faulty understandings of what "nothing" really is.
Fortunately, science already has better information for us -- it's just up to these religious theists to pay attention.
"There is no barrier between nothing and a rich universe full of matter," [Frank Wilczek of the Massachusetts Institute of Technology] says. Perhaps the big bang was just nothingness doing what comes naturally. This, of course, raises the question of what came before the big bang, and how long it lasted. Unfortunately at this point basic ideas begin to fail us; the concept "before" becomes meaningless. In the words of Stephen Hawking, it's like asking what is north of the north pole.
Even so, there is an even more mind-blowing consequence of the idea that something can come from nothing: perhaps nothingness itself cannot exist.
Here's why. Quantum uncertainty allows a trade-off between time and energy, so something that lasts a long time must have little energy. To explain how our universe has lasted for the billions of years that it has taken galaxies to form, solar systems to coalesce and life to evolve into bipeds who ask how something came from nothing, its total energy must be extraordinarily low.
That fits with the generally accepted view of the universe's early moments, which sees space-time undergoing a brief burst of expansion immediately after the big bang. This heady period, known as inflation, flooded the universe with energy. But according to Einstein's general theory of relativity, more space-time also means more gravity. Gravity's attractive pull represents negative energy that can cancel out inflation's positive energy - essentially constructing a cosmos for nothing.
"I like to say that the universe is the ultimate free lunch," says Alan Guth, a cosmologist at MIT who came up with the inflation theory 30 years ago.
Source: New Scientist, July 23, 2011
It probably seems counter-intuitive to think of something coming from nothing, but it shouldn't. After all, what basis do you have to form any reliable intuition about what "nothing" is really like and whether it can produce "something" or not? None. We don't have direct, personal experience with a true quantum vacuum that would allow us to be certain what such a "nothing" should or should not be like.
True, we do have experiences with states that seem like "nothing" -- like an empty room, for example, or the emptiness of space. But those are not the true, absolute "nothing" of a quantum vacuum. So why shouldn't something be able to arise naturally out of nothing? What is there, exactly, that would prevent something arising out of nothing?
You'll find lots of theists who simply assume and take for granted that something can't come from nothing, but they'll never be able to explain how or why that's the case. They don't have a shred of evidence that it's true. So don't let them use it as an unchallenged premise in an argument.