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Thought experiment(escape from black holes)

  1. Feb 20, 2004 #1
    How to get out of a black hole....?

    The event horizon is when the escape velocity equals the speed of light, right?

    Do you really need to reach a bodies escape velocity to into orbit, yes, however you don't need to reach the escape velocity to simply leave the suface. Saying the event horizon prevents everything from escaping says you must to exert all of the force you have in a single instant like a shell out of a canon. But is it not also true that you can also spread that force out?

    In normal cases this would take more energy, but I am thinking it would take less in a black hole, for it would be less then infinity since it doesn't need go at the speed of light.

    I do not know if it is possible for something to exert a constant pressure on something in a black hole but if it was, I would think it would be possible for something to escape a black hole without hawking radition.

    Would appreciate any feedback, positive or negative.
  2. jcsd
  3. Feb 21, 2004 #2
    Someone who has fallen into a black hole is in serious trouble. I don't know how to get them out. It may be impossible.

    Speculation - Suppose that wormholes exist. Send the mouth of one end of a wormhole into the black hole and let the other end remain far away from the hole. The observer inside the event horizon can travel through the wormhole to the outside. I.e. he can "worm his way out" of the trouble he has gotten himself into! :-D
  4. Feb 21, 2004 #3


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    Deeviant, there is another issue you're not dealing with: time dilation. How do you go anywhere if you no longer experience time?
  5. Feb 21, 2004 #4
    A person falling into a black hole will experience time as usual. I.e. the only thing that will be different than if he was in flat spacetime in the absense of gravity is that he'll experience tidal forces. But for him time will run as normal. I.e. he will observer is wristwatch to run normally.
  6. Feb 21, 2004 #5


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    I agree with the initial premise, that escape velocity is not required in order to move away from the center of gravity. Escape velocity is only necessary for objects "coasting" away from the center. Given a continuous trust, speed becomes irrelevant. Indeed, this is the entire idea the proposed "space elevator".

    However, I think the real problem of escape from a black hole is not simply the fact that escape velocity exceeds lightspeed. Rather, the real problem is the curvature of space that causes escape velocity to exceed lightspeed. This curvature appears to redirect any energy expended so that it becomes a force propelling an object toward the center. I think the only escape would have to be pmb's wormhole idea, or some other method that removes one from normal space-time.
    Last edited: Feb 21, 2004
  7. Feb 21, 2004 #6
    That is a interesting idea lurch.

    I was just thinking that since a black hole's very exsistance is afforded to it by its event horizon which is calculated by the Schwarzschild radius. And the only thing the sch. radius says the escape velocity has met the speed of light.

    It could be the space is curved so greatly that force somehow gets inverted. But I don't think I've seen any data to that fact. It would seem, going by the current theories, it would take a large but non-fininite amount of power to escape a black whole if it is applied evenly rather then all at once.
  8. Feb 22, 2004 #7
    Re: Re: thought experiment(escape from black holes)

    I thought there was no air/oxygen in a black hole? wouldn't the guy die. Anyway u don't no how long it would take for him to get out the wormhole thing.
  9. Feb 22, 2004 #8


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    True, but what he percieves as normal time is infinite to an outside observer. I think the way that would manifest itself for our intrepid astronaut is once inside the black hole, he'd turn around and see an infinite distance behind him to get out.
  10. Feb 23, 2004 #9


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    As he enters the blackhole, if he were to look back he would see the universe age at an increasing speed due to time dilaiton. so even if he were to try this idea of escape he would probably think its not worth it as he would see the universe end in what ever way this may happen.
  11. Feb 23, 2004 #10
    You're all wrong, he wouldn't see anything at all. He'd be dead. :wink: Ok, that's been said, now we can move on from considering whether there's oxygen or whether he'd want to leave, and continue on a purely theoretical level. I do think it's an interesting comparison that if he passed the event horizon and looked back, there would appear to be an infinite distance to return. While this seems correct at first, light and such are still being absorbed by the black hole, and so shouldn't he be able to observe things even though he cannot escape? Would all the light that entered after him be between him and the event horizon? It seems to me that if light has no mass, yet is still affected by the gravity of a black hole, perhaps spacetime itself is being sucked into the black hole and therefore you WOULD have to exceed the speed of light to escape. Travelling the same distance through a more dense spacetime would mean travelling at an increased speed.

    P.S. - Personally, I think he would leave once he got hungry.
  12. Feb 23, 2004 #11
    Ok how about this..

    An extremely powerful particle beam is shot into a back hole. It could possibly drive into it and create a constant pressure on the other side thereby driving matter out of it.

    edit: Spelling
  13. Feb 24, 2004 #12
    Lets leave Humans at a far away location from a Black Hole and do the experiment using a innocent bird flying/falling into the BH instead?

    Ok you are the far away observer looking at a Dove that is flapping its wings (instincively!), it is falling towards a Black Hole Horizon. The closer it gets to the BH the less it moves and the less movement you observe from your far away location.

    As it enters the outer horizon of the Black Hole (think of concentric shells ) it is reduce dimensional from a 3-D object to a 2-D object (spagettifacation?). But you still see its last image frozen at the last 3-D location, the Dove has ceased flapping its wings, and its image is eternal, as long as you(far away observer) are in direct line of site that is.

    Now there is the interesting property of Black Holes and Entropy.

    Let me say just a little on the regions around Black Holes, that is 'collapsing regions' or dimensional reduction and Dimensional Projection, this is known formally as the Holographic Principle.

    The basis of this principle is that information fits into Area's in certain units, and certain paramiters like Time, Direction and Observation become entangled?

    Ok I am sure you all know the basic Holographic Principle for general Spacetime regions..fi not do a search and there is a wealth of pre-print papers available ie: G T Hooft, R Bousso, Bekenstein and Jacobson....and so.

    Back to our little Dove WHO IS FROZEN IN TIME as far as we..the observer is concerned. Now if we move a little to the left, (it would have to be minute as we are far away and any small deviation for us would be greatly enhanced for our Dove), but anyway, what do we see?

    Let actually get a glimpse, who want to see the basic idea?

    Those who want to SEE what I am relaying, then take you bankcard/creditcard or anything that has a hologram image impregnated onto it, some lucky ones will actually have an image of our Dove!

    Now if you keep the card still, and look from directly above, you see the image frozen, move the card ever so slightly and you see a totaly different image, depending where you are depends on what youo see!

    Now the Holographic Principle has area's in around the BH as being area's of Projection, for the far off observer you see the time of the Dove at a single instant (call it a TIME-SINGULAR-UNIT) if only to give a picture in you mind(actually a picture is a good analogy!).

    The really amazing thing is, if you were inside the horizon before the dove approached and was looking at Dove's direction, the whole projected image would be reversed, I will leave it to your imagination of what you could see, for it would certainly be not just the Dove!
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