Re: A partial black hole?

Erik Max Francis wrote:
> James Burns wrote:
> 
>> My opinion is very much non-mathematical, though. Is
>> there some theorem that says "once your worldline
>> crosses an event horizon, it won't cross back"?
>>
>> I realize this is more-or-less the /definition/
>> of an event horizon, but I take those definitions
>> to be about simple situations, single blobs, static
>> or spinning or charged, or so on. But how I take it
>> could be different from how it is.
> 
> 
> That is indeed basically the definition, so we're
> dealing with statements that basically have no
> information content.

Then I will try again. Perhaps this time my question
will have information content.

> If you're inside the event horizon of a black hole,
> then you cannot escape for precisely the same reason
> that you cannot travel backward in time; inside the
> event horizon of a black hole, spacetime is distorted
> such that "forward in time" becomes a spatial direction,
> and it leads you closer to the singularity.

Consider a particle inside the event horizon, just as
you describe. /If nothing in the situation changes,/
no message will ever be able to be sent from this particle to
the outside world.

However, a second black hole swoops in at a large fraction
of the speed of light close to the first's event horizon.
Certainly, the event horizons of the first and second
black holes will be affected. I would think that the EH's
would be closer to their respective singularities than
otherwise, because of the gravitational forces canceling
each other to some degree, in between the two, at least.

It may be that certain coordinates that were below the
event horizon before and after the passing of the second
black hole would be above the event horizon during its
passing. I am not asking about that.

Is it possible that a particle that would have stayed
below the event horizon without the second black hole's
intervention would instead be able to communicate to
the outside world -- that is, could it be brought
back up above the event horizon?

Under your definition, the particle was therefore never
below the event horizon, but it seems to me that the
particle would have experienced conditions identical to
below-the-event-horizon conditions. This is probably
as close as we can come, even in theory, to answering
the question, "What is it like below the event horizon?"

Jim Burns