On Tuesday, January 24, 2017 at 2:18:03 PM UTC-7, Martin Brown wrote:

On 23/01/2017 03:50, wrote:

But the Big Bang doesn't posit what existed outside of that
singularity. There could have been an entire universe around a
black hole that breached confinement for all we know.

There doesn't need to be anything outside though. You are imagining a
spacetime with nothing in it apart from a dense proto universe. The
mathematics of GR permits a solution where at the singularity there is
nothing - no space *OR* time and no "before" either. This is in the
realm of metaphysics since there is no way we could test it. Quantum
effects means that this is almost certainly wrong for sizes less than
the Planck length

Or the cube root of the number of elementary particles in the universe
times the Planck length. But that's still very small.

but we have no testable theories for that era.

I am entrigued by the cyclic possibilities of the Steinhardt-Turok
ekpyrotic (sp?) model of the universe which might yet be validated by
observations and would circumvent the need for Guth's inflation.

I'm intrigued by their model also; however, there does appear to be
inflation in the universe today (dark energy). And I don't think
Steinhardt goes far enough. He posits a second brane that collides with
our brane, but if there are two branes, why not three, or four, or
millions or ....

It could make sense to suppose that our own Universe is the only one
that can exist or does exist. Once, however, evidence arises that
there is a second Universe as well, then it becomes absolutely
ridiculous to suppose that there are two and only two Universes. If a
second Universe can exist, then an infinite number can.
Isaac Asimov

Steinhardt's ekpyrotic model assumes a collapse, but dark energy would
seem to imply expansion will go on forever. And brane-banging, being a
recurring phenomenon, means that a new genesis will happen (may have
already happened) and there may be matter from previous brane-bangs out
there somewhere.

Gary