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Black hole question

  1. Jan 30, 2009 #1
    I was wondering about a question that popped into my mind recently -Let's say, theoretically, a device existed that could reverse the force of gravity somehow, to the point were it created antigravity. Since black holes are held together by their own gravity, pushing molecules closer than their magnetic fields would normally allow, if you launched this device into the singularity of a black hole, wouldn't the black hole, with no gravity to hold it together, fling itself apart due to it's now-unmatched magnetic force? In fact, wouldn't this work for other dense stellar objects too?
  2. jcsd
  3. Feb 11, 2009 #2
    That's a little crazy of a scenario. Instead, how about just: "what would happen if gravity in a black hole switched off?"

    I would say that it would blow itself apart. With nothing left to counter all that electro-magnetic force / degenerate electron pressure, yea, I'd say that'd be one hell of a bang. Considering the enormous amount of mass it takes to form a black hole, that would be a lot of stuff, to say the least.

    Really, this would work for any mass that's gravity forces particles closer together than they want to be. The more massive, the more gravity, the further back the "sling shot" is pulled.

    Not that gravity is going to switch off any time soon.
  4. Feb 12, 2009 #3
    A antigravity mechanism struck me as the simplest way to introduce the idea at the time.
  5. Feb 12, 2009 #4
    It's all good!

    I follow.
  6. Feb 12, 2009 #5
    I think what you are talking about theoretically is what is known as the theoretical white hole. This is the opposite of a black hole in that it is spitting out matter. Theoretically, a white hole and a black hole are attached by a wormhole. However, this only exists theoretically for now.
  7. Feb 12, 2009 #6


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    This isn't theoretical; this is fantasy. You might as well ask what unicorns would do if dropped into a black hole.
  8. Feb 12, 2009 #7
    I'm pretty sure Einstein's equations do not rule out the theoretical possibility of a wormhole.
  9. Feb 13, 2009 #8
    is a black hole 2D or 3D?

    say it was 2D and as a disk. looking from the top down is where matter is being sucked in, and then underneath it would there be nothing or some kind of vortex that you can see like when you pull the plug out of the bath tub?

    if it was 3D that would mean that matter disappears into some point in space as it gets sucked in.

    actually the 3D one sounds more correct. am i right?
  10. Feb 13, 2009 #9
    A non-rotating black hole would be spherical, like a ball, and you can fall in from any direction.
  11. Feb 14, 2009 #10
    At the geometric point of view of a star would be 3D but mathematically a whole different question since involves variables other than space like time. Although in many movies and cartoons is portrayed as a 2D portal to a different world.
  12. Feb 14, 2009 #11
    Well people have looked at the idea of a varying gravitational constant in the context of general relativity, so one could then postulate that the gravitational constant could be altered by some device and possibly set to zero or made negative. However, I think the black hole would still win. Your antigravity field would be limited to travelling at light speed, and so would not be able to catch up with infalling matter before it had become incorporated into the black hole, and after that whatever happens there is no way that it can affect what is outside the black hole. It might be informative (if somewhat difficult) to do the calculation though.
  13. Mar 8, 2009 #12
    So what if it's fantasy, You have to start somewhere.
  14. Mar 8, 2009 #13
    FOR THE LAST TIME.........WHITE HOLES DO NOT EXIST, THEY NEVER DID,NOT NOW, NOT EVER!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! See why in my post: why white holes do not exist in the astrophysics section. Srry, got carried away.......(:
    Last edited: Mar 8, 2009
  15. Mar 8, 2009 #14
  16. Mar 9, 2009 #15
    Umm... All I asked waswhat would happen if you turned off gravity in a black hole, there was no white holes or wormholes involved. I think Archosaur answered the question the best.
  17. Mar 9, 2009 #16
    errrrrrrrrrr...................thats ok though. I enjoy answering other people's questions. Check mine out though it's intersting. (:
  18. Mar 10, 2009 #17


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    Perhaps, but it doesn't belong on this board.
  19. Mar 12, 2009 #18
    Question: is it even theoreticly possible to swich off a black hole's gravity?
  20. Mar 12, 2009 #19
    No. No no no it's not. I'm not saying it really happens, or is possible. I'm just thinking from a bare bare bones point of view. Assume the cow is a sphere, y'know.

    Just mathematically speaking, say you had a bunch of particles that attracted each other with force A to the point where they completely overrode the repulsive force B, crushing them to a singularity. If force A were to suddenly vanish, what would happen to the particles?

    It is not possible to switch off a black hole's gravity. I just said that so I could skip all that "force A/ force B" stuff, but since I couldn't get away with even the slightest degree of implication, there you go.
  21. Mar 12, 2009 #20


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    It's not that we're simply being pedantic about the point, it's that there's no way, even in principle, to separate out the cause for the disappearance of gravity from the effect.

    It's similar yet even more pronounced than the classic thought experiment "what would happen to the Earth if the Sun instantly disappeared?"

    The sun cannot disappear in a way that violates physics. If you wanted to violate phyiscs to make it happen, then the answer you would get (such as, for example, superluminal cause and effect) is meaningless.
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