Re: thunderbolt (was Re: Doomsday vs Diaspora)

From: Anders Sandberg (asa@nada.kth.se)
Date: Sat Apr 26 2003 - 12:15:39 MDT

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    On Sat, Apr 26, 2003 at 09:56:58AM -0700, Damien Sullivan wrote:
    >
    > (Is there any evidence for black holes with singularity at center, as
    > oppposed to just some mass with a superliminal -- or even barely subliminal --
    > escape velocity?)

    The GR equations seems to be pretty firm on that there has to be a
    singularity inside the event horizon - no matter may remain at
    rest (just as no matter outside can avoid moving forward in time),
    so the configuration gets denser and denser in finite proper time.
    In addition you get increasingly blueshifted photons from the rest
    of the universe and they also reach infinite blueshift in finite
    time. So unless there are "materials" in GR that cannot be
    compressed to the extreme extent that they can bend spacetime
    backwards to prevent it (and then they would likely make great
    time machines), GR seems to be fairly conclusive that something
    awful happens at the center. It is not just huge compression
    forces, but curvature itself which is the problem.

    Quantum gravity is far more iffy, and I have seen xxx-archive
    papers showing both that singularities does not happen, that they
    must happen or that something else happens (one of the IMHO
    neatest is the creation of baby universes) - assuming different
    quantum gravity models. Nobody knows.

    > (I remember _Frozen Stars_ suggesting that proper GR black holes
    > never form in the reference frame of an outside observer, since
    > the time dilation of the infalling mass keeps increasing and you
    > never get to see it cross the event horizon.)

    Yes, but this is just the outside view. Someone on or in the star
    will see later phases of the contraction which will never be
    revealed to the outside.

    -- 
    -----------------------------------------------------------------------
    Anders Sandberg                                      Towards Ascension!
    asa@nada.kth.se                            http://www.nada.kth.se/~asa/
    GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y
    


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