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SR forbides BHs and GR demands them

  1. May 7, 2007 #1
    I read a statement on another message board the SR forbides BHs and GR demands them.

    Does SR forbide Black Holes, if so, why?
     
  2. jcsd
  3. May 7, 2007 #2

    Chris Hillman

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    Beware of boards!

    Hi, Johnny R,

    Did you ask for clarification from the poster, call him P, in this "other board"?

    The first guess which occurred to me was that P meant that a Lorentzian spacetime conformal to Minkowski spacetime won't admit event horizons. That probably won't make sense :uhh: but never mind, because I think the more important point is this:

    P's remark should be tempered by observing that gravitation is not treated by str, which arises as the relativistic theory of kinematics, i.e. relations between time and distance measurements for observers in different states of motion ("kineo" is a Greek root suggesting "motion"). Early attempts to model the gravitational interaction using various types of force law or classical relativistic fields in Minkowski spacetime failed; this was part of the motivation for Einstein's exploration down the path which eventually led to gtr. It's also important to be aware that str is the foundation for gtr in a precise sense: gtr models spacetime as a Lorentzian manifold, subject to conditions encapsulated in the Einstein field equation (EFE), and the tangent spaces of a Lorentzian manifold have the same geometry/trigonometry used in str, which basically means that kinematics is infinitesimally equivalent in gtr and str, and also that Minkowksi spacetime can be viewed as just a particular vacuum solution of the EFE. Unfortunately, it takes a fair amount of background in physics/math to understand what I just said!

    If you're worried that you might be obtaining contradictory information in different "boards" or from different posters in said "boards", you might see my remarks near the top of http://math.ucr.edu/home/baez/RelWWW/HTML/more.html
    See also the cautionary remarks by myself, Moonbear, ZapperZ, and some others in the PF thread at https://www.physicsforums.com/showthread.php?t=168397&highlight=Google+Wikipedia?
    The discussion there focuses on Wikipedia, but all of these posters seem to agree that the local public library is still your best bet for obtaining reliable information.
     
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