[geordief (OP)]

I appreciate that there is no theory that explains anything before T^-43 secs into the supposed "beginning" of the Universe  but perhaps I can make the possibly unwarranted assumption that it "started" practically infinitely small,broke into 2 asymmetric  parts  and somehow continued interacting with itself and (from our vantage point) got larger and larger.

So ,with that (possibly very wrongly) assumed can I ask whether  it is fairly well understood that this Universe was not expanding "into" anything  but it was just simply expanding "into or out of itself"?

If that is the understanding ,might that imply that (and I know GR does not apply pre T^-43secs)  spacetime curvature was practically infinite in the "beginning" and has flattened progressively ever since (being completely flat now as far as we can tell except in local regions)?

A  kind of add on question I have is whether there could be any regions of the Universe where spacetime curvature could be negative.....?