On Thu, 15 May 2008 22:12:09 -0700, "N:dlzc D:aol T:com \(dlzc\)"
wrote:

Dear Eric Baird:

Eric Baird wrote in message
.. .
...
Perhaps Hawking radiation might be expected under
//someone else's// general theory, but I don't see
how the effect can appear classically in a model
that's supposed to reduce to the SR equations of
motion, as Einstein's was.

How fortuitous...
http://groups.google.com/group/sci.a...c52e34b1d93586
... just posted on sci.astro.

Oh, that's really cool!

I shall bookmark it and examine it at leisure!



See the approximations that reduce GR to SR involve the patching
technique to connect little bits of spacetime for forming a
"solution space". GR allows curvature (the patches can be
slightly skew), and SR does not.

Yeah, I understand the idea that a curved model has to reduce to
effectively-flat regions if you zoom in on it far enough ... what I'd
take issue with is whether that geometrical reduction has to
correspond to a reduction to the //physics// of special relativity.


One could make the case that if all energy is associated with
curvature, and if lightspeed is regulated between particles by
gravitomagnetic effects, then all physics would be curvature-based,
and there wouldn't be any such thing as "the physics of flat
spacetime" left for SR to describe.

SR might still be a decent first approximation in some ways, but if
you zoomed in far enough to get flatness, you'd then have zoomed in so
far that your region wouldn't contain any particles moving with
significant relative velocities (or any particles at all!).

In that scenario, you could certainly zoom in and get your little flat
"facets" or "patches", but the physics of moving bodies wouldn't then
be described by the internal geometry of any of those facets, it'd be
described by the cumulative mismatches between facets that'd produce
the curvature effects associated with the particles and the distortion
fields between them.

In that hypothetical situation, we'd still be able to have a general
theory of relativity based on the idea of spacetime curvature, but it
wouldn't seem to reduce to the flat-spacetime-generated relationships
of special relativity.



The connection to Hawking radiation is that whle acoustic metrics seem
to be happy to generate indirect radiation through a horizon,
Einstein's implementation of a general theory doesn't seem to want to
cooperate.
Hence the black hole information paradox, and the last few decades
that Thorne, Hawking, Wheeler and the others have spent trying and
failing to find some way to reconcile QM with GR1915.


We'd seem to be able to resolve the black hole information paradox,
and allow GR to tackle classical indirect radiation by allowing it to
reduce to an acoustic metric rather than to a Minkowski metric, but if
we swap out the Minkowski metric, we lose our original justification
for believing that some of the relationships of special relativity are
correct.

If we then wanted to continue using SR as foundation theory, we'd have
to find a new way to derive it without falling back on the idea of a
reduction to flat spacetime, and that seems to be rather difficult.

I don't personally think that a proper solution to the information
paradox is likely to be achievable without deleting special relativity
out from under GR, and I think that it's physicists' reluctance to
contenance that final option that has been holding them back for the
last thirty years and preventing them from solving this thing.

I think that it's great that the "quantum gravity" guys are now
steaming ahead at such a rate, with their work on acoustic metrics ...
they can get away with this because everyone knows that the rules for
quantum gravity aren't quite settled yet, so if the QG guys are
exploring ideas that don't seem to be SR-compatible //yet//, the SR
community don't cry foul ... they expect that, at the last moment, the
final implementation of QG will pull some masterstroke and magically
become compatible with both SR/GR1915 and QM.

I think that when the QG guys get to the logical conclusion of their
current work, the SR guys (and some of the GR guys) are liable to get
a horrible shock.


Not entirely as mysterious as
you imagine...

Oh, I don't regard the situation as mysterious at all!



=Erk= (Eric Baird) www.relativitybook.com
: " Why should I care about Posterity? What's Posterity
: ever done for me? "
: -- Groucho Marx