It is not clear that that question has an answer that is meaningful in terms of our world here inside the big bang.

You say that there was nothing before the big bang? But we don't know that. We accept that we have no logical basis to require that the concept of "before" or of "matter or existence before" should have constructive meaning, but so far no one has demonstrated that it does or does not. Speculation on such matters is rife and often ingenious, but not yet materially cogent. Some for example speculate that our universe comprises the effluvia of a black hole in some other "universe" not otherwise observable from where we are.

By way of analogy, imagine you were on our planet's equator; how far could you go east? After due experiment and cogitation you discover that there is no obvious limit in principle to how far you could go east as long as you don't mind treading a furrow into the equator. So, obviously, there should be no corresponding limit to how far you could go south, even less no doubt, since that would be all downhill.

And yet, you know very well that you would finally reach a point beyond which it does not make sense to speak of going further south, not even if you brought a ladder with you. The concepts of east and south differ in important respects. Similarly, the concept of conservation of space, energy and matter might not be applicable to the point beyond (or "before") the big bang.

If that question has an answer in terms that we could be comfortable with, it also is not clear that that answer is accessible to us, much as it does not follow that we can see into a black hole beyond its event horizon, even though any object within that horizon can in principle receive information from outside.

So you can, I hope, see why I am pretty comfortable in saying not only that I do not know, but also that I suspect that I, and you, cannot know.

But then, tomorrow I might suddenly achieve or be presented with a sudden insight...

Where might that come from...?

Cheers,

Jon

The material components of the universe were formed from the huge energy of the big bang (E=mc^2, hence m=E/c^2).  So the real question is where all that energy came from, and then condensed into matter just after the initial formation of the universe. 

It is a question of what is the ultimate substrate of the universe on which it exists.  For example, there is something about the essential fabric of spacetime that--quantum mechanically speaking--permits a pair of particles to spontaneously come into existance for a brief time, then disappear again.  These are called virtual particles and their existance is experimentally proven; in fact many of the measured properties of the fundamental particles are affected by the "cloud" of virtual particles around them.  So the big bang has the possibility of having come from "nothing"--except whatever substrate to reality hosts the physical laws that permit the spontaneous creation of such virtual particles.