Many astrophysicists speculate that everything came from nothing. How can something come from nothing? The above speculation would break the law of conservation. Either something has always been here or what we call something is actually made of nothing (nonmaterial.) Please give me your prospective. Thank you, Awareness1963

My perspective: Even if matter hasn't always existed, something or other has always existed (which is compatible with the claim that our Big Bang occurred finitely long ago). For the perspective of someone much better-informed about this issue than I am, see this link.

I'm not quite as happy with Prof. Kraus's way of putting things. I'd suggest having a look at this review by philosopher/physicist David Albert:

http://www.nytimes.com/2012/03/25/books/review/a-universe-from-nothing-b...

As for whether something has always existed, Prof. Maitzen and I may well agree, but there's some ambiguity here that's worth thinking about.

If we say that something has always existed, the most plausible way to understand that is that there has never been a time when nothing existed. If there's no time before the Big Bang, then we can say that something or other has always existed.

Suppose, however, that there are times earlier than the Big Bang. One possibility is that what there was is an earlier cycle in an oscillating universe. In that case, the "something" was the sort of thing that's around in this phase of cosmic history.

Another possibility is that what was around was the vacuum of quantum field theory. The vacuum, indeed, is not matter, but it's also not nothing. Indeed, it's the sort of thing that can produce familiar matter and energy. That's the point that Albert is at pains to emphasize in his review of Kraus. In this case, once again, there's no difficulty with the idea that there was always something, even if it wasn't palpable matter.

But leave the quantum vacuum aside, and forget about the Big Bang. What about the possibility that space and time (or space-time) stretches back into an infinite past, but that matter/energy doesn't? What I'm imagining is that before, say, 20 billion years ago there was nothing except empty space, stretching back infinitely in time. But beginning 20 billion years ago, there was matter and energy.

This would indeed violate conservation laws. But conservation laws aren't true as a matter of math or logic; they're true because the world happens to be structured in a certain way. It's at least possible in the broad sense of "possible" that conservation laws don't hold always and everywhere.

Also: the scenario that I described doesn't mean that something came from nothing. That is, it doesn't mean that nothingness was a source that produced matter or whatnot. It would just mean that at one time there was no matter/energy and at another, later time there was. But...

Would this mean that there was a time when there was nothing? Not necessarily. There's a longstanding philosophical dispute about space and time. On one side are substantivalists, who think that space-time) isn't just nothing. On this view, space-time is real in its own right, even if it's empty. Newton held a version of this view. On the other side are relationalists. They hold that talk of space and time is a disguised way of talking about relations among more familiar physical things. Leibniz held this view, and argued for it at length in his correspondence with Newton's supporter Samuel Clarke.

If the substantivalists are right, then there was something in that empty stretch: space-time, which is in modern terms a kind of a field with its own properties. (What properties? Ones, for example, that have to do with whether the space is Euclidean or not.)

If the relationalists are right, then it doesn't make any clear sense to say that space-time stretches back into an infinite stretch containing no matter/energy. And if that, in turn, is right, then we still don't have an example of a time when there was nothing at all.

For the record, I'm far from happy with Krauss's way of putting things, which is why in my response I linked not to Krauss's book but to Albert's (scathing) review of it, the same review later linked to by Professor Stairs.

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