Black hole

Discussion in 'Physics' started by Mvjhoda, Jul 30, 2011.

  1. Mvjhoda

    Thread Starter New Member

    Jul 13, 2011
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    What will happen if a ANTI GRAVITY vehicle is driven into a BLACK HOLE?
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Take lots of Gravol before driving.
     
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    You will have the end of a mediocre sci-fi story. :)
     
  4. Wendy

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    Mar 24, 2008
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    The black hole eats what it wants, and throws out the rest.
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Well if a black hole attracts objects using its gravity it would repel the "anti-grav" vehicle? So you can't drive it in.
     
  6. alvinsmith

    New Member

    Sep 15, 2011
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    You can't escape either not even light or else you can go to elsewhere, any dimension maybe possible. The truth, no one knows yet!
     
  7. steveb

    Senior Member

    Jul 3, 2008
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    That's not too different than the simplified explanation of Hawking Radiation. Virtual particles of positive mass get sucked into the black hole, and those of negative mass are radiated away. So, your friends in the regular vehicle are sucked in, and you ride your antigravity vehicle like a surfboard and get ejected right out of the galaxy.
     
  8. DerStrom8

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    Feb 20, 2011
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    I'm surprised no one has mentioned--The vehicle itself may be anti-gravity, but you're not. You'll be sucked right through the miniscule cracks and holes that are in every material.
    Needless to say, you would not survive.
     
  9. steveb

    Senior Member

    Jul 3, 2008
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    As long as you are not sucked in near the black hole (which would need to be beyond the event horizon), this need not happen. The person will feel normal gravity from the black hole, plus the accelleration of the antigravity ship as it is repelled away from the black hole. I guess this would effectively double the gravitational/acceleration force compared to a ship using thrust to remain stationary, because presumably antigravity would create a negative accelleration compared to normal gravity. (assuming the person is much less massive than the ship)

    Of course, at distances moderately close to the black hole, this force may be very strong (multiple g-force) such that it drives you to the floor and might even kill you. The black hole gravity might be comperable to a massive star, and typically that is not strong enough to squash and squeeze people through cracks when outside the event horizon.

    But inside the event horizon getting closer to the center of the black hole, tidal forces are going to stretch and squeeze you into spaggetti, even without the the antigravity ship.
     
    Last edited: Sep 15, 2011
  10. DerStrom8

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    Feb 20, 2011
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    That is a very good point. I was picturing driving INTO the black hole, which would mean you're within the even horizon, but I guess that was never specified.... I suppose this decision is up to the OP :D
     
  11. BillO

    Well-Known Member

    Nov 24, 2008
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    The answer to your question begs a question as to the exact nature of this hypothetical anti-gravity machine. Does it require a gravity field gradient to be active (i.e. does it somehow mirror the field it is in), or does it produce it's own specific (anti-) field gradient (i.e. does it somehow produce a negative gravity of some particular force)?
     
  12. BillO

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    Nov 24, 2008
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    I think the force gradient well outside the event horizon is sufficient to pull a human apart. Due to the inverse square law, the smaller the black hole, the stronger the difference will be over the length of a human body.
     
  13. steveb

    Senior Member

    Jul 3, 2008
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    That's doubtful. Do you have a calculation to show that?

    Consider a black hole with the mass of our Sun. The present radius of the surface of the Sun is "well outside the event horizon" of such a black hole. The force of gravity at the surface of our sun is something like 28 g (28 times Earth's surface gravity). That's not a very large gravitational force to begin with, and might just barely kill a person (consider pilots that survive over 10 g force for short periods). Note that a person in freefall, will not even feel the 28 g, but will feel 0 g, (microgravity). Now, at this distance the gradient of the force (that is, tidal force) will be very small indeed and in no way can be even felt, never mind tear a person apart.

    It's well accepted (EDIT: see correction for small black holes below) that a person passing through the event horizon will have no indication that they just went past the point of no return. There is a good analogy physicists make with water flowing over the waterfall. There is a point where the water begins to move faster than a person can swim. When a person passes this point, they are doomed. However, they would not be aware of this fact right away. Passing the point of no return does no damage in itself, but the crashing on the rocks below is what kills you. Similarly, passing the event horizon feels like nothing, but once nearer the center, the tidal forces grow rapidly ... and then it's spaggetti dinner for the black hole.

    EDIT: I need to modify/correct the above. I did a quick calculation and it seems that at the event horizon, small black black holes do have very strong tidal force that could rip you apart. I also need to write the science channel and complain about the misinformation in their black hole shows. More than one of those physicists have said that passing through the horizon would not be noticable.

    So, well outside the event horizon, or for large black holes, things are fine, but near the event horizon of small black holes will be painful.
     
    Last edited: Sep 16, 2011
  14. Wendy

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    Mar 24, 2008
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    I suspect they were referring to the monsters in the center of our galaxy. There you could wander in and not notice until it was too late.
     
  15. steveb

    Senior Member

    Jul 3, 2008
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    Probably. Certainly those super-massive black holes would have negligible tidal forces at the horizon. I'll be paying more attention to their wording in the future. They keep rerunning those shows and I can't resist watching them. :)
     
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