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What is singularity?

  1. Jun 18, 2006 #1
    What is singularity?

    How come of it?
     
  2. jcsd
  3. Jun 18, 2006 #2

    DM

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    Quoting Stephen Hawkin's definition:

    "A point in space-time at which the space-time curvature becomes infinite."

    Nonetheless I'd like to read a more extended version of this definition from more knowledgeable people.
     
  4. Jun 18, 2006 #3

    Hawkin's difinition is amusing... But it may be not exact?

    Althought the difinition is right...
     
  5. Jun 18, 2006 #4

    George Jones

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    I am not sure that there is a completely accepted technical definition.

    Roughly, a spacetime is singular if there is a timelike curve having bounded acceleration (i.e, a worldline an observer could follow) that ends after a finite amount of proper time. Singular spacetimes have "edges".

    By the Penrose-Hawking singularity theorems, any "reasonable" classical spacetime must be singular. Very roughly, in any "reasonable" classical spacetime, gravity is so stong that the fabric of spacetime gets ripped, thus creating an "edge".
     
  6. Jun 18, 2006 #5
    Is it Singularities are a unlimited dense point without any volume?
     
  7. Jun 18, 2006 #6
    If we observed the Universe as a whole in 11 dimensions would the strength of Gravity increase. Is it possible that the whole 11th Dimensional Gravity of the Universe is just leaking into all the other dimensions of the Universe within our 4D known Space in singlular points causing matter and or virtual particals to get trapped in its 11th dimensional singularity horizon making matter appear to clump together around it in a horizonal orbit?

    Just a question, nothing more.
     
  8. Jun 19, 2006 #7
    Last edited: Jun 19, 2006
  9. Jun 21, 2006 #8

    DM

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    Besides super duper definitions of singularities like Wikipedias', is there anyone else in this forum with sufficient knowledge on this matter that is confidently capable of stating, in the simplest possible terms, what this phenomenon is all about?
     
  10. Jun 24, 2006 #9

    There's nothing "super duper" about Wikipedia's definition; in fact, it's a pretty loose definition IMO. If you want a simple definition of a spacetime singularity, try this one on for size:

    A spacetime singularity is a point in spacetime at which the (intrinsic) curvature of the spacetime is infinite.

    That's the simplest explanation I can think of, but it doesn't really do the concept justice. In particular, one can have a more exact definition of a singularity by saying that the singular points of a spacetime are those which cannot be included in the maximal analytic extension of the spacetime, but I guess that's a bit more than you want.

    To use the more usual notion (i.e., from popularizations of science such as Hawking's books), a singularity is a point where the predictable nature of physics breaks down because the curvature predicted by general relativity at that point is infinite.
     
  11. Jun 25, 2006 #10
    Would it be natural to say that a Singularity is a condensed infinite continuum point where all Dimensions could be experienced through observation all at once because of the infinite curvature?
     
  12. Jun 25, 2006 #11
    No. That sentence doesn't actually make much sense, quite apart from it being the wrong interpretation.
     
  13. Jun 26, 2006 #12

    George Jones

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    The Edge of Infinity: Beyond the Black Hole, by Paul Davies, has a very-good popular-level treatment of singularities. This book gives a tremendous (and quite accurate) explanation of Penrose's first singularity theorem. I even recommend it as a complement to Wald and Hawking and Ellis for physics types encountering for the first time the technical details of singularity theorems.
     
  14. Jun 27, 2006 #13

    DM

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    Thanks George.
     
  15. Jul 4, 2006 #14
    Hmmm, well people who are perhaps more knowledgable than me can correct me, but a singularity is only a singularity from another frame of reference, am I right? In the frame itself there is no singularity right? Hence no breakdown of laws right?

    Would be funny if laws in nature would break down, for why would they be defined as laws? :)
     
  16. Jul 4, 2006 #15

    Garth

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    Wrong actually, a singularity in one frame of reference would be a singularity in any frame of reference.
    My definition of a singularity is "a point in space where any of the properties of matter or space-time become singular - i.e. infinite or zero. Thus in the limit density, pressure and space-time curvature become infinite and volume becomes zero.

    You can argue whether they actually exist, whether the limit is actually reached, or whether the concept is merely an artifact of an incomplete knowledge of what happens in the extreme conditions as that limit is approached.

    Garth
     
  17. Jul 4, 2006 #16
    Really? So is that described by some kind of theorem or so?

    It appears counterintuitive to me.

    What could be an infinity to an outside frame of reference does not have to be one locally right?

    Take for instance a measurement of an object from an outside frame of reference that becomes a singularity. Time grinds to a halt and volume becomes zero right? But inside, does time stop as well and does voume become zero as well?

    Seems that I am missing something here with regards to your assertion that a singularity is frame of reference independent.
     
  18. Jul 4, 2006 #17

    Garth

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    Are you confusing the singularity itself with the event horizon around that singularity?

    At the event horizon around a Schwarzschild BH the coordinate system becomes singular, but that can be transformed away - just as the Lat. and Long. system of coordinates on the Earth's surface becomes singular at the N. & S. Poles. However you cannot transform away the physical singularity at the centre.

    At the genuine singularity at the centre there is no time - it doesn't 'grind to a halt', there is no way of measuring it at all, it has become singular.

    Garth
     
    Last edited: Jul 4, 2006
  19. Jul 4, 2006 #18
    Sorry, but I am still not getting it. :blushing:

    Let's assume some very small object getting caught by a black hole. At one point it passes the event horizon and after that it gets drawn closer to the center.
    Now I understand that for any outside frame of reference (both inside and outside the event horizon) is appears as if the object is going towards a singularity. But for the object itself? How could it become a singularity?

    It seems to me, and I suppose I am wrong about it, that a singularity is a singularity for all outside frames of references but that the space-time of an infinitessimal small size regarded as the singularity for the outside frames of references is not.
     
  20. Jul 4, 2006 #19

    Garth

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    It gets squashed until in the limit its density and temperature become infinite and its volume zero.
    I'm not sure I understand that statement. :confused: The singularity, at the centre of the event horizon, is a - well - singularity.

    Garth
     
  21. Jul 4, 2006 #20
    Ok then let me reword it.

    In GR the measurement of space and time of a particular region depend on the frame of reference right? So a measurement from any frame of reference, which has to be from inside the black whole since from outside one cannot even make a measurement, of the center of a black hole will result in measuring a singularity. No disagreement here. But the area that is the singularity itself, the infinitesimal small region itself, if we place the frame of reference there, then how do you conclude that even there there is a singularity, that is what I don't understand.
     
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