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Anti black hole

  1. Oct 16, 2006 #1

    taylaron

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    "anti" black hole

    hey,
    is there evedince that leads to the idea that there is a "formation" of an anti-black-hole. i dont know how to explain it because it has no name. anyways, what if there was a star or some phenominon that insted of having "stupendious" gravity (black hole) had stupendis anti-gravity. it repells everything. including light. now, if it repells light, you might see it as a very bright light. mebe mistaking it for a star. i dont know. i may be totally wrong. thats why im posting this. :confused:
    this is described in the diagram that i drew below...
     

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  2. jcsd
  3. Oct 16, 2006 #2
    Perhaps you are talking about so-called "phantom energy"?
     
  4. Oct 16, 2006 #3

    taylaron

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    i also heard that you can get light to travel "backwards" which apparently is faster

    HUH????
     
  5. Oct 17, 2006 #4
    What you're likely referring to has nothing to do with cosmology, and is barely interesting at all. One method uses dispersive fibre optics (doped with erbium I think). You can construct media that will amplify the first front part of an extended light pulse (same as a laser gain medium) but only scatter the rest of the pulse. Thus, the peak of the emerging signal occurs before the peak of the initial pulse would have arrived. No signal arrives any earlier than you could theoretically have detected it in the first place.
     
  6. Oct 17, 2006 #5

    LURCH

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    Try looking for topics on "White Holes".
     
  7. Oct 17, 2006 #6
    Last edited: Oct 17, 2006
  8. Oct 17, 2006 #7

    pervect

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    There isn't any evidence that such a thing exists, but the idea (or a similar one) has been talked about before in physics literature, for instance Hermann Bondi, "Negative Mass in General Relativity", Reviews of Modern Physics 29, 423 (1957).

    One can replace the mass M in the Schwarzschild metric with a negative number, and find that an object with negative mass gravitationally repels nearby objects, and that objects nearer the negative-mass black hole age faster rather than slower.

    It's worth noting that such an object doesn't have an event horizon, so it's not really a black hole.

    The Bondi article may be hard to get a hold of (I don't have a copy myself) - there is a reasonably good popular discussion in http://www.npl.washington.edu/AV/altvw14.html however.
     
  9. Oct 17, 2006 #8
    Yes but instead it has a barrier, nothing can enter it from the outside, not even light. :smile:
     
  10. Oct 17, 2006 #9

    pervect

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    If one posutlates a point negative gravitational mass, an effective potential analysis (such as the one at http://www.fourmilab.ch/gravitation/orbits/)
    shows that it would require infinite energy to reach r=0. One could come as close to the central point mass as desired, but never reach it with a finite "energy at infinity".

    But if one postualtes a distributed, rather than a point, mass, this issue goes away. A distributed negative gravitational mass would have a metric that was well-behavied everywhere, and one could reach the center of it without any special problems.

    So there wouldn't be any event horizon, nor would there be any singularity, or any difficulty reaching r=0, with a finite negative mass of nonzero volume.

    Negative mass has a lot of other problems though. Thermodynamically, for instance, it's a real mess. One would expect particles with negative mass to gain negative energy from their surroundings, for instance, heating up the surroundings while the negative mass particles gain "negative energy".
     
  11. Sep 3, 2010 #10
    Re: "anti" black hole

    Here's a thought:
    For a 'white hole' to display 'anti-gravity' properties to emit/disperse 'stuff', it has to have received 'stuff' from somewhere.

    I came up with 3 possibilities:

    1. A 'black hole' changes to 'white hole' after reaching it's 'threshold of attraction/gravity' (whereby nothing can escape it's gravitational pull).

    2. An existence of a 'parallel universe' in which exists a corresponding 'black hole' which supplies the 'white hole' with 'stuff'.

    3. A 'white hole' attracts 'anti-matter' and repels 'matter' (converts anti-matter to matter). (Opposite to a 'black hole' attracting 'matter').


    Cheers,
     
  12. Sep 3, 2010 #11

    JesseM

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    Re: "anti" black hole

    White holes wouldn't have anti-gravity, you'd fall towards them just like black holes, it's just that nothing could ever reach the horizon from the outside. White holes are just the time-reverse of black holes, so just as anything falling through the event horizon of a black hole must hit the singularity at the center, anything that comes out of the event horizon of a white hole must have been emitted by the white hole singularity.

    Incidentally, it's better to start a new thread rather than revive one that no one's posted on for years!
     
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