[AGarvin]

Existing space would be an absolute frame of reference for the Universe.

Fom the viewpoint of General Relativity and BB theory, this statement is correct.

GR is a theory of geometry, and within that geometry you choose a set of coordinates (generally comoving coordinates). As the universe expands with the Hubble flow, these coodinates, including "Cosmic" time, move with it. So even though the distance between two points increases with cosmic expansion, a point in space remains the same with respect to another, providing an absolute frame of reference. Of course ALL objects also have local peculiar motion through space, and Special Relativity comes into play.

No one knows how big was the original object that caused Big Bang, or what was the velocity of the matter expelled by it.

Steven has commented on this but just to clarify. What he is saying is that matter didn't expand at all in the BB, the universe did. Matter is inside the expanding universe. Matter only has local peculiar motion. This is why objects can receed from us greater than c....they are moving with the Hubble flow which has no speed of light restriction. It's the local peculiar motion through space, governed by Special Relativity, that has the c restriction.

Anrdew.