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Escaping from a black hole

  1. Mar 17, 2009 #1


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    What's wrong with the following method of seeing what life is like inside a black hole and escaping? I can't see anything obvious. We'll assume that time scales and tidal forces aren't an issue (it's obviously impractical -- but is it impossible)?

    1. Get a spaceship which can travel at c (well, as close to c as you can imagine).
    2. Fall into the black hole. Just below the event horizon, inside the hole, fire your rocket engine as fast as you can. This will slow your descent to an arbitrarily slow speed, though not stop it (and certainly not escape). In effect, you will be able to "hover" there as long as you want.
    3. The black hole emits Hawking radiation and starts to lose mass. This causes the event horizon to retreat inward.
    4. The retrating event horizon passes over your hovering ship. Your ship is now outside the event horizon.
    5. You escape.

  2. jcsd
  3. Mar 17, 2009 #2


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    Step 2 won't work - gravity will overcome your rocket. Meanwhile it will tear you and the rocket apart.
    Step 3 takes essentially forever for anything other than microscopic black holes.
  4. Mar 17, 2009 #3
    First, lets assume for one insane minute that it is possible to find a black hole and get to it. Next, you enter the black hole, as you do, intense graitatinal force rips your
    rocket apart. But lets say that you found a way around that part, and got inside the singuarty of the black hole. This is what will happen, you will continue to hover there untill the black hole destablilizes and closes in on you. (This will turn you into a very thin pankake.) That is why your method of escape has no chance of sucsess.
  5. Mar 18, 2009 #4


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    Hi ACG! :smile:

    No it won't.

    You can't hover inside an event horizon.

    Once you're in, you inevitably reach the singularity, and there is a finite (and very short! :wink:) maximum proper time in which you do so.
  6. Mar 18, 2009 #5
    Probably a meaningless question, but once you cross the event horizon, how fast would you accelerate toward the singularity? Would you ever reach anything close to c before encountering the singularity? Again, probably meaningless, but inquiring minds want to know.
  7. Mar 18, 2009 #6


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    In Schwarzschild coordinates, you cross the event horizon at the same speed as light, and once inside you go faster than light (in other words, inside an event horizon, the speed of light is a minimum instead of a maximum).
  8. Mar 18, 2009 #7

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    Just to add to the problems, any black hole bigger than about a millimeter across accretes rather than evaporates.
  9. Mar 18, 2009 #8
    Well, event horizon is a relative thing, it is observer-dependent.
    For freely falling observer there is NO event horizon hence no Hawking radiation
  10. Mar 18, 2009 #9
    I have a different opinion. The falling astronaut can still observe, in principle, event horizon, like no light escape from event horizon. So event horizon exists independent of observers.
  11. Mar 18, 2009 #10

    I agree. The gravity would be so immense, it would be like a 350lb fisherman reeling in a 5oz fish. the fish (in this case the spaceship) would have no chance of escaping. Once you near the singularity, the "cone" shape of the "tail" of the hole would start to compress the ship, much like it compress light waves, or at this point, photon clusters.

    It would be impossible to counter the pull of the gravity, unless you have and Star Wars/I] masivse "Gravity Repulsor Engine" You would inevitably be sucked inwith no escape.

    Attached Files:

  12. Mar 19, 2009 #11
    Even just by accelerating you can create your own event horizon: http://en.wikipedia.org/wiki/Event_horizon#Event_horizon_of_an_accelerated_particle

    And again, horizon location is a relative thing. From the same article:

  13. May 12, 2009 #12
    Even if you are just under c, you will still be unable to escape (the escape velocity of a black hole is c+).

    Hover there as long as you want, but you will still slowly be hovering toward the black hole. Even if you slow down the time it takes to get to the singularity, you'd still reach it someday in your space ship.
  14. May 13, 2009 #13
    You probably would be able to view the singularity for a short second before you are flattened (as was said before and assuming that you can get around the shredding and ripping). Before you are flattened yoou should engage the (warp drive if you have it) and escape
  15. May 13, 2009 #14
    No, in non-rotating BH singularity is always veiled by the apparent horizon.
    In the rotating BH yes, you can see it.
  16. May 13, 2009 #15
    Some day? :)
    In stellar-size BH you reach it in microseconds!

    Also remember that in non-rotating BH the singularity is spacelike (in the future). And pseudoeuclidean space has a very contre-intuitive property, so, the harder you try to avoid the singularity the sooner you fall into it. The maximize your proper time before you hit it you should relax in a freefall trajectory.
  17. May 13, 2009 #16


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    Yea, I was gonna mention that inside the EH all geodesics lead toward the singularity, so no matter which way you accelerate, it's always toward the singularity...o_O

    (I could be wrong, this is what I've heard. I haven't studied GR myself)
  18. May 13, 2009 #17
    I remember reading that somewhere, you're right. Sorry for misinforming :blushing:
  19. May 13, 2009 #18
    Star Trek 2: Escape from BH-6542.D?
  20. May 14, 2009 #19
    I should have guessed
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