From: Anders Sandberg (asa@nada.kth.se)
Date: Fri Jul 11 2003 - 18:06:29 MDT
On Fri, Jul 11, 2003 at 04:01:56PM -0700, Mike Lorrey wrote:
> On a different note, keep in mind that phenomena like
> supernova would not form black holes as they do if gravity did not
> travel in wave fronts at a finite velocity. If gravity propagated
> instantaneously, then massive stars would just magically turn into
> black holes without all the messy explosive effects.
Huh? I think you are getting confused here - the stability of massive
stars is not dependent on the speed of gravity since it is a static
property (some complications for truly massive stars where relativistic
instability forces them to oscillate). When a star collapses to a black
hole it does so when the mass concentration inside a region becomes
larger than the Schwarzschild criterion; you could compress it or add
mass very slowly and still get a quick "schlurp" once the last atom
broke spacetime's back.
(event horizons, being somewhat virtual and arbitrary things, can "move"
faster than light, such as when a non-axisymmetric black hole relaxes.
But they are about the same class of objects as light reflected on a
remote wall - it is possible to move them faster than light but they
don't transmit information)
In general it seems that the speed of gravity disturbances is very close
to the speed of light. It might be interesting to imagine a universe
where this was not true. What about a world where gravity was as slow as
the speed of sound?
-- ----------------------------------------------------------------------- Anders Sandberg Towards Ascension! asa@nada.kth.se http://www.nada.kth.se/~asa/ GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y
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