Darren New <dne### [at] sanrrcom> wrote:
> I thought Warp might like seeing this, since he has talked about relativity 
> and warped space time and (I think) dark matter here before.

>
http://www.newscientist.com/article/mg18925423.600-three-cosmic-enigmas-one-audacious-answer.html

"One such problem arises from the idea that once matter crosses a
black hole's event horizon - the point beyond which not even light can
escape - it will be destroyed by the space-time "singularity" at the
centre of the black hole. Because information about the matter is lost
forever, this conflicts with the laws of quantum mechanics, which
state that information can never disappear from the universe."

  General relativity predicts one thing, quantum mechanics another. Why
must GR be wrong and QM right? Why couldn't it be the other way around?

"Another problem is that light from an object falling into a black
hole is stretched so dramatically by the immense gravity there that
observers outside will see time freeze: the object will appear to sit
at the event horizon for ever."

  I'm not sure that's exactly correct. From the point of view of an external
observer, when an object approaches the event horizon of a black hole the
frequency of the light coming from that object decreases. If the frequency
of the light decreases to zero, it's basically not emitting any light at
all and thus cannot be observed.

  While from the outside point of view the object never actually reaches
the event horizon, and consequently the frequency of the emitted light
never reaches true zero, there's probably a limit to how low the frequency
can be for it to be observed (as there are such limits in almost everything
related to quantum particles).

  After all, the object cannot (and does not) emit photons forever. It stops
at some point (ie. when it crosses the event horizon), so no infinite amount
of photons can reach the external observer. The external observer sees the
photons coming less and less frequently, until the frequency becomes so low
that it's practically nonexistent.

"The team's calculations show that the vacuum energy inside the shell
has a powerful anti-gravity effect, just like the dark energy that
appears to be causing the expansion of the universe to accelerate. [...]
All observations used as evidence for black holes - their
gravitational pull on objects and the formation of accretion discs of
matter around them - could also work as evidence for dark energy
stars."

  I don't really understand how the same object can both repel (with
antigravity) and attract (with gravity) at the same time. Isn't that
a bit contradictory? Which is it?

"Dark energy stars and black holes would have identical external
geometries, so it will be very difficult to tell them apart,"

  If that is so, then wouldn't it behave in the same "problematic" way
with regard to an external observer watching an object fall towards this
star? What would be the difference?

  The article doesn't claim that time dilation near massive objects doesn't
happen. It just says that time dilation near the event horizon of a black
hole causes problems with respect to quantum mechanics. If these dark stars
behave externally so much like black holes that they would be very hard to
distinguish from them, how does it solve any such "problem"? The time
dilation would still be there due to the mass of the former star being
accumulated close to the Schwarzschild radius.

-- 
                                                          - Warp

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