"I know of a few different versions to answer this question.
1. The most widely accepted one is that the big bang came from a quantum fluctuation that inflated. The expansion converted gravitational energy into particle energy. So in this case it all came from nothing. No cosmic egg. The energy balance in the universe is still zero. BTW- most of the matter in the universe is invisible. The matter that makes up what we see is a very small fraction of the total.
2. The one I like the best however is Smolin's hypothesis that universes are born in black holes of sufficient mass. I like this one because it correlates quite well with the story in the Sri Bagavatum where Vishnu sits in the Cosmic Egg on a serpent and new universes emanate from his nose.
3. The latest one is a two-brane string theory cosmology where we sit on one brane and the two branes periodically come together to produce a big bang. So matter is always there. But the release of energy can always produce more matter
The COBE type data, with additional sensitivity available from a new detector in space, will be able to distinguish between 1 & 3. Even Smolin does not promote #2 so it is out of vogue.
So matter comes from energy. There is experimental evidence for this. We can create an electron and a positron at a point in space with enough focussed energy. We understand theoretically how it could have happened in the aftermath of the Big Bang."
Ok, but where did gravitational energy come from?
Where did the black holes come from? Where did the two-brane string come from? Where did the energy come from? Ok, forget all those questions.
Just answer these. Is there a chronilogical begining on the evolutionary timescale? If there was, what started it? Has the universe been around forever? What I'm saying is was there a begining? KC2GWX 73's