Darren New <dne### [at] sanrrcom> wrote:
> >   From a timescale point of view, an observer falling to a black hole
> > would not see any change in timescales for himself. How he sees the
> > rest of the universe, however, is another story.

> I think that's what I was saying. I don't understand why anyone inside *or* 
> outside would think it takes infinite time to fall in.

  Things get weird on the extremes with relativity.

  For example a photon might travel billions of years from a star and
collide on Earth. However, from the point of view of the photon itself,
what is the distance it has travelled and how long it took for it to
travel it?

> > For example if the falling object had a clock (and let's
> > forget those tidal forces ripping it apart) and the external observer
> > would look at this clock with a telescope, the clock would slow down
> > indefinitely. Well, until no photons arrive anymore from the object and
> > it could not be observed anymore.

> But inside, he'd still be falling. And outside, he'd still be falling, yes? 
> He'd just look stopped yet still falling to those outside.

  Not stopped. Asymptotically slowing down.

  (But as I said in my original post, I don't think it would be possible to
observe the object indefinitely from the outside. It just stops sending
photons at some point.)

> >   Does QM say that space is not continuous?

> I believe that's correct. Or that gravity at least is not continuous 
> (because nothing is continuous).

  Unless I'm mistaken, the "graviton" is one of those particles invented
by quantum mechanics for the simple reason that "because everything seems
to consist of particles, then there must exist a particle for every
phenomenon we can see, including gravity".

  In other words, it feels more a question of principle than a result of
measurements or predictions of some theory. Gravitons must exist. Why?
Because.

  I really can't understand why quantum mechanists have such a problem
in thinking about gravity as timespace geometry rather than as the exchange
of some exotic particles which cannot be detected. I don't understand
what would be the problem. Why do we *need* a gravity particle? What
would it explain that gravity-as-timespace-geometry doesn't?

  Timespace curvature *is* something which can be (and has been) measured.
A graviton isn't.

>  I don't really understand it, but my 
> layman understanding is that GR's math only works if "forces" are 
> continuous, and QM says that "forces" are not.

  How is, for example, momentum quantized? What is the particle which is
the smallest unit of momentum? Or kinetic energy? Or inertia?

  Must everything be quantized?

> >   Assuming Hawking radiation indeed exists...

> If it doesn't, you've still lost the information. :-)

  If you add two pieces of information together, has some information been
lost?

> >> With a big enough black hole, you'll never know when you cross the event 
> >> horizon.
> > 
> >   I have heard this, I have a very hard time understanding how it would be
> > possible.
> > 
> >   Space is *really* warped near the event horizon.

> Not necessarily. It's almost really warped just outside, and it's just a 
> little bit more warped inside. So while the slope is steep, the second 
> derivative isn't.  At least, that's how I understand it. :-)

  Well, given that the event horizon is, by definition, the area of space
were the curvature of space is so large that even photons have no way out,
and that this curvature of space increases as you approach the event
horizon, I have hard time believing you wouldn't notice anything when you
approach and cross the event horizon.

  When you start approaching the event horizon light starts visibly bending
because of the curvature of space. Any light which traverses closer to the
event horizon gets "sqeezed", and thus everything seems to flatten.

  Wikipedia has a good image about this: Assuming GR is right, what a
"bare" black hole (ie. one with no accretion disc or other stuff orbiting
around) would look like against a starry background, from a relatively
close distance:

http://en.wikipedia.org/wiki/File:Black_Hole_Milkyway.jpg

  I suppose the size of the black hole only affects the rate at which
the change happens as you get closer to the event horizon, rather than
the strength of the visual effect.

  (Btw, that image might not be totally correct, as it seems to lack
red-shifting of the light closer to the event horizon...)

-- 
                                                          - Warp

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