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Can naked singularity actually move the space craft in PAST?

  1. Apr 15, 2007 #1
    Can naked singularity actually move the space craft in PAST???

    A singularity is a place where the laws of physics break down. So if singularities can interact with the outside Universe, then anything is possible. For instance, it would be possible to send a spacecraft round such a naked singularity on a trajectory that takes it into the past, achieving genuine time travel.
    the text in bold ..... can u explain me??????
    Singularity if not so hidden so can become the strong and extraordinary source of energy... so it is possible that matter will through with great intensity if near to the Naked singularity so by the above sentence in bold what may i understand that it is possible that this ebergy source will move my space craft not actually in forward direction of the cone of space time?so it is possible to go in PAST anyway? .... my threads are not answered basically thats why i am explaining briefly what my problem is...
     
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  3. Apr 15, 2007 #2

    Wallace

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    You got this much right :smile: Because of this discussing what would happen if you 'fell into' a singularity is beyond the reach of current science. In the centre of a black hole GR 'blows up' and things go to infinity. We strongly suspect that this points to an inadequacy of GR rather than this point truly having mystical powers!

    One of the things that a successful quantum theory of gravity should do is explain what happens at r=0 in a black hole. We don't currently have a completer quantum gravity theory however.

    On your point about time travel, there is nothing in GR that allows you to use a black hole (whether the singularity is naked or not) to travel backwards in time.
     
  4. Apr 15, 2007 #3
    Stop right there. There are very, very good reasons for believing that naked singularities do not and can not exist in nature. These reasons render the rest of your question moot.
     
  5. Apr 16, 2007 #4
    I don't think that's right- Schwarzchild black holes have no angular momentem or charge- making them almost certainly unphysical- as a nonrotating mass would have to undergo a perfectly symmetrical collapse in order to form a BH with no rotation-

    since every physical BH likey does have rotation naked singualrities ARE possible considering the Kerr metric for instance- through the mutual negation of the Inner [Cauchy] and Outer event horizons you get a naked singularity-

    because we get naked singularities when considering actual physical conditions that should obtain in a real BH the idea of naked singularities is actually vastly closer to what should exist in Nature than Schwarzchild BHs are
     
    Last edited: Apr 16, 2007
  6. Apr 16, 2007 #5
    A singularity is a place where our theories break down.
     
    Last edited: Apr 17, 2007
  7. Apr 16, 2007 #6
    This isn't correct. I'm travelling at the moment so don't have time to go into this in detail, but there have been plenty of, for example, numerical studies of linear perturbations of the Kerr solution which suggest that bounded linear perturbations always lead to a black hole rather than a naked singularity.

    Furthermore, there's a famous paper by Schoen & Yau called "The Existence of a Black Hole due to Condensation of Matter" (CMP, 1982-ish) that proves in a physically acceptable manner that when one has a sufficiently high matter density black hole formation will occur. Surprisingly, this result does not rely on the assumption of even small perturbations away from spherical symmetry.

    I can't make sense of this, particularly given that it contradicts what I've said above. Care to elaborate?

    As I said before, there are persuasive reasons for why it is believed that naked singularities don't exist. This has led, for example, to the proposal of several cosmic censorship hypotheses of various strength.
     
  8. Apr 16, 2007 #7
    The bottom line is that nobody has proven that GR excludes naked singularities.

    That GR would be in big trouble if naked singularities were to exist is of course true but this is obviously not a credible argument against naked singularities.

    Actually, a black hole has no center.
     
    Last edited: Apr 16, 2007
  9. Apr 16, 2007 #8
    For anyone:
    Does gravity at the center of the earth goto infinity?
     
  10. Apr 17, 2007 #9
    This is all I needed to explain to me, that extremely ****ed up wikipedia page on Naked Singularites and CCH.
     
  11. Apr 17, 2007 #10

    Wallace

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    Oh come on, you know what I meant by 'centre', which is of course where r=0. In some sense you can say this is not a centre in the way a circle has a centre but in the context this was used it was perfectly clear what was being meant. There is no need to be so argumentative :frown:

    On the other hand I must commend you for pointing out that it is indeed our theories, rather than physics, that blows up at the central singularity. This is a somewhat subtle but enormously important distinction that is at times forgotten :smile:
     
  12. Apr 17, 2007 #11
    Yes you are right, a bit of a nitpick from my side.
    Sorry!

    Indeed. While I am a great admirer of the theory of general relativity it certainly has its problems. :smile:
     
  13. Apr 17, 2007 #12
    black hole centers?

    Originally Posted by Wallace
    "In the centre of a black hole GR 'blows up' and things go to infinity.
    One of the things that a successful quantum theory of gravity should do is explain what happens at r=0 in a black hole. We don't currently have a completer quantum gravity theory however."

    Does gravity at the center of the earth goto infinity?
    The question was asked to motivate Wallace (or anyone else)
    to reason on it and any any applications it might have regarding black holes.

    If a hole passed through the earth, through its center,
    and an observer could free fall through it from some distance d above the surface, they would experience the standard inverse square law acceleration until they reached the surface.
    While moving toward the center, the mass behind them would decelerate
    the motion. At the center the hemishpere ahead would cancel the hemishere
    behind giving a net acceleration of zero.
    Therefore you would be weightless at the center.
    The curve plotted for the acceleration would not be the typical funnel.
    The principle overlooked here is extent. Excluding the questionable
    singularities, mass/matter has extent and is not a point.
    Therefore would a black hole also have zero gravity at its center?
     
  14. Apr 17, 2007 #13

    Wallace

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    No and No are the short answers!

    We only get a singularity in GR if the Schwarzchild radius for a body (such as the Earth) is greater than the size of the body. For an object the mass of the Earth the Schwarschild radius is maybe a few kilometres (correct me as to the correct value here anyone), but in any case much smaller than the earth. You only get the singularity issues if you have a very small very massive body, not just a very massive body.

    We can't answer the second question because the normal ways we have to say what the potential and hence direction of acceleration due to gravity is blow up for r=0 in a black hole.
     
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