p6 wrote [reordered]:

[...]

We are mostly familiar with Big Bang where the
entire universe before inflation is just planck size.

The currently visible portion of the Universe, but that
need not be the entire Universe.

What's more likely. A Big Bang where everything starts from
a singularity or M-theory Big Splat (ekpyrotic scenerio)
where two higher dimensional colliding branes produced
the matter and energy in our universe??

Try a web search on "black hole", "cauchy horizon", and
especially "mass inflation".

To keep Uncle Al off my case, here is a link to what is
generally regarded as the seminal paper on mass inflation
in black holes (and a couple of other miscellaneous links):

http://prola.aps.org/abstract/PRD/v41/i6/p1796_1

"Internal structure of black holes"
by Eric Poisson and Werner Israel

http://www.cap.ca/awards/press/2005-Poisson.html

Herzberg medal awarded to Eric Poisson in 2005
for his work on black holes and the Cauchy horizon

http://www.phys.unm.edu/~finley/P570...ackCauchy.html

Interiors of Black Holes and their Cauchy Horizons (1999)

In the right circumstances (currently an active area of
research), when mass or radiation, even a modest amount,
falls into black hole which is rotating and charged
(as all physical black holes almost certainly are)
the result is a colossal amplification of the energy
inside the black hole at a region called the Cauchy
horizon.

It's hard to believe, but the resulting mass/energy can
be that of our entire universe outside the black hole.
None of this is discernable to an outside observer, as
the interior of the hole is "causally disconnected"
(i.e. no information can escape).

Currently, what goes on "beneath" the Cauchy horizon is
largely a closed book, except that I gather the radial
time-like coordinate between the event horizon and the
Cauchy horizon can, beyond the latter, flip back to
being a space-like coordinate (as it is to us outside
the event horizon).

So, getting to the point finally, it seems quite plausible
that the Big Bang, and hence our Universe, is none other
than a continuation, or dynamic evolution in some sense,
of the Cauchy horizon nearer the centre of a Black Hole,
most likely a common or garden galactic one, in some
universe just like ours (perhaps our Universe itself?!
Nah, now I'm freaking even myself out ;-)

Assuming our universe itself contains black holes, to
model this mathematically, one would presumably have
to start with a set of general relativity equations
for the outer black hole, and find some endomorphic
structure to these, i.e. express them in coordinates
which can be parametrized by other coordinates that
themselves in certain ranges satisfy the original
equations (or at least equations consistent with GR).

An obstacle to this is that at the Cauchy horizon
spacetime crumples up to a curvature comparable with
the Planck scale.

One closing thought (almost certainly not original,
and probably quite commonplace by now among the
experts, but you never know): In theory the Cauchy
horizon packs all the mass/energy that enters the
black hole from our Universe during all future times,
from a standpoint outside the hole.

(Some experts worry about this, as it seems to require
an infinite energy density there; but if the Universe
is expanding and that expansion will accelerate, this
doesn't apear to be an issue, and indeed practically
proves in itself that the expansion _will_ accelerate.)

Thus, in some sense and at some rudimentary level, the
energy at the Cauchy horizon is correlated with the
mass/energy outside the hole, and if that persists
into the interior, then by our assumption it carries
over into the new universe inside.

So who knows, if Everett's "many universes" hypothesis
has any bearing on reality, maybe Nature has chosen to
implement it not as "side by side" universes but as an
inconceivably vast labyrinth of one-way interconnected
black holes!


Cheers

John R Ramsden