Re: A partial black hole?

On 2008-03-01, Crown-Horned Snorkack <chornedsnorkack@[EMAIL PROTECTED]
> wrote:
> None of the signals emitted by A after crossing singularity are
> observed outside event horizon - all light emitted by A eventually
> reaches singularity. But can B, while on its way down to
> singularity, observe signals emitted by A?

If B follows close enough behind, yes.  For a stellar black hole, a
millisecond behind is far too late.


>> The singularity pretty much by definition is a place where all
>> timelike and lightlike paths end.

A singularity is anywhere the model breaks down, usually by having
infinite quantities or anything else for which the model behaviour is
mathematically undefined.

Your description matches a spacelike curvature singularity, which does
describe the singularity at the center of a Schwarzschild black hole.
In a Kerr black hole the ring singularity is a timelike curvature
singularity.  Both lightlike and timelike paths emerge from it.

The event horizon of the the Schwarzschild metric is a coordinate
singularity, where some coordinates go to infinity.  However,
coordinates do not describe anything phyical, and other models of the
same space do not have a singularity there.


>>  Once a worldline hits the singularity, nothing more can happen.

Actually it means we don't know what will happen.  In the case of a
spacelike curvature singularity it seems very likely that nothing more
can happen that affects anything outside the singularity, but (like
any singularity) it almost certainly means that our model isn't good
enough to describe it.

General relativity is an approximation.  We just don't have a better
approximation yet.


- Tim