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Re: Black Holes And Spaceships

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Posted by David Tate/">David Tate on January 31, 1998 03:11:43 UTC

: : : : : Or to put it another way, as long as I can counteract the effect of gravity and maintain a forward velocity, no matter how small, I can eventually escape. I do not need to attain escape velocity if I have an engine that will keep burning long enough. : : : No, inside the event horizon all light rays curve : : : into the singularity. That is part of the proof : : : that there must be a singularity inside. It may : : : be a long, gentle curve, but eventually it must : : : lead into the singularity. For a truly gigantic : : : black hole where the gravity at the event horizon : : : is at or about 1g, your spaceship can cross the : : : event horizon without noticing anything unusual. : : : But once inside the event horizon, you must follow : : : the path that light rays take, and that will lead : : : your ship into the singularity. And as you approach : : : the singularity, tidal forces will become a problem : : : before actually reaching it. : : : I would agree , if we are talking about a : singularity, but I am not. I am just talking : about sufficient mass to create a large black : hole. Not a small one, with a singularity in it. Also the tidal forces in such a large black hole would not be particularly bad.( Well, I would choose a black hole large enough to avoid such forces.). Anyway, even with a singularity in the centre, I am talking in terms of seriously big. Sufficiently big so that the g force at the event horizon is relatively small, and under such circumstances it is by no means inevitable that I MUST follow the path of a photon. Consider a comet, travelling at 20Kmps, it can not escape the sun. But I could, at far less velocity, as long as I avoid tidal forces and as long as I don't go too close to the sun and as long as my fuel lasts. The shuttle is boosted to near escape velocity only because it is more efficient to accelerate to escape velocity that to travel all the way at 10Kmph. Fact is, it could make it to any place in the universe at 10kmph, if only it had enough fuel - and time.

: This has become a very interesting discussion.

: Any mass sufficient to create a black hole (within : a certain sphere), will collapse to a singularity : surrounded by an event horizon. That's because the : forces that are responsible for keep atomic particles : distinct from one another are overwhelmed by the : force of gravity and at that point there is nothing : to stop the matter within the EH from compressing : to a mathematical point (i.e. singularity)

: I agree that a massive black hole could have any g force at its : event horizon, and thus it's conceivable that a : spaceship could cross the EH of a super massive : black hole without noticing any unusual tidal : forces and such.

: However, let's suppose your spaceship is a photon. : It travels at the speed of light always. It never : slows down. However once inside the EH all light : rays bend around into the singularity. So this : spaceship/photon is doomed to end up colliding with : the singularity.

: Space is in effect defined by light rays. Wherever : light rays travel, that can be considered space. : Inside the EH light and in effect space converges : into the singularity.

Sorry to but in on as very interesting conversation, but I thought the EH was defined as the point where the escape velicity was that of the speed of light and it was the strength of the gravitional pull, it the G force that determined the escape velicity? If this is the case then the G force at the EH must always be the same?

If this is true then in order to escape the EH you must travel greater than the speed of light, not 10KPH.

Sorry if I am changing the subject I would be happy to start another discussion topic?

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