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Re: No Hair



Some. The entropy of a black hole depends only on the surface area of
the event horizon which in turn depends on the mass and so is not an
independent property. Nobody has found another independent property
but somebody has found a hole in the chain of theorems purporting to
prove uniqueness. They rest on something called the circularity
assumption which turns out not to be a general property of axially
symmetric spacetimes. Whether or not it is a general property of
black hole solutions in particular is still, to my knowledge, up in
the air (basically, it is the assumption that certain off-diagonal
elements of the metric must vanish -- they don't). There is,
therefore, an outside possibility that you could come up, formally at
least, with something like a toroidal black hole so you could drive
your spaceship through the hole in the middle. That might entail
introducing another hair. Probably a grey one.


I suspect that in the last 25 years lots of work has been done
on this topic, so something made have been added to the list of what
characteristics that define a black hole. I know the entropy of a
black hole is a hot topic. I also recall something that implied that the
hair analogy had split into "short hair" and "long hair" (I think there
was a Physical Review Letter titled " A Black Hole Has No Short Hair"
about 4 years ago).

Thanks
Roger Haar
U of AZ


Paul J. Camp "The Beauty of the Universe
Assistant Professor of Physics consists not only of unity
Coastal Carolina University in variety but also of
Conway, SC 29528 variety in unity.
pjcamp@coastal.edu --Umberto Eco
pjcamp@postoffice.worldnet.att.net The Name of the Rose
(803)349-2227
fax: (803)349-2926