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Warp escreveu:
> If quantum teleportation exists, I wonder if it would be theoretically
> possible to teleport a particle out of a black hole.
Bah, it all becomes easy when you know we live in a hologram: just look
at it from a different angle... ;)
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nemesis <nam### [at] gmail com> wrote:
> I think it has something to do with the last photons coming out of the
> object entering the EH are severely slowed down by the massive gravity
> and only reach you after much more time than normal has passed.
Photons don't slow down. The speed of light in vacuum is a universal
constant and doesn't change.
What photons do is that they redshift.
--
- Warp
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Darren New <dne### [at] sanrrcom> wrote:
> Warp wrote:
> > If quantum teleportation exists, I wonder if it would be theoretically
> > possible to teleport a particle out of a black hole.
> And therein lies the clash of QED and GR. :-)
Thinking about it, unless I'm completely mistaken, quantum mechanics
doesn't disagree with the notion that *information* cannot be transported
at superluminal speeds (even if quantum effects can).
Transporting a particle out of a black hole, which in practice would be
getting information out of the black hole, would require superluminal speed,
so it would violate this basic principle.
--
- Warp
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nemesis wrote:
> object entering the EH are severely slowed down by the massive gravity
As Warp said. My "have to think about it" would be the "if the occupant of
the spaceship never experiences the crossing, and people outside can never
see/measure it actually happen, does it ever actually happen?"
Kind of a "tree falls in the woods" question if anything.
--
Darren New, San Diego CA, USA (PST)
"Ouch ouch ouch!"
"What's wrong? Noodles too hot?"
"No, I have Chopstick Tunnel Syndrome."
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Warp wrote:
> Thinking about it, unless I'm completely mistaken, quantum mechanics
> doesn't disagree with the notion that *information* cannot be transported
> at superluminal speeds (even if quantum effects can).
QM doesn't show that particles cannot be transported at superluminal speeds.
Indeed, you have to take superluminal speeds into account when you're doing
the infinite sums in order to make them come out.
GR says information cannot be transported at superluminal speeds, which is
why Bell's Inequality is of interest.
--
Darren New, San Diego CA, USA (PST)
"Ouch ouch ouch!"
"What's wrong? Noodles too hot?"
"No, I have Chopstick Tunnel Syndrome."
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Darren New <dne### [at] sanrrcom> wrote:
> Warp wrote:
> > Thinking about it, unless I'm completely mistaken, quantum mechanics
> > doesn't disagree with the notion that *information* cannot be transported
> > at superluminal speeds (even if quantum effects can).
> QM doesn't show that particles cannot be transported at superluminal speeds.
> Indeed, you have to take superluminal speeds into account when you're doing
> the infinite sums in order to make them come out.
Unless I'm mistaken (hmm, I'm using that expression a lot), it's a bit
more complicated than that.
Just because, according to quantum mechanics, a particle can interact
over great distances with no delay doesn't mean that *information* can
be transferred over that distance without the delay (it's one of those QM
weirdnesses that I have no hope of fully understanding). I have the
impression that quantum mechanics doesn't disagree with GR about this
subject.
For example it was specifically noted in the relatively recent test
result of quantum teleportation that although the particles were (at least
apparently) teleported at superluminal speeds, the technique could still
not be used to transfer information from one place to another at superluminal
speeds. Thus there was no contradiction with GR.
GR itself doesn't forbid the distance between two points in space growing
faster than c. This is actually what is currently mostly accepted as
happening in the universe, and the cause for the so-called cosmological
horizon (the farthest parts of the Universe are receding from us faster
than c, which means we can *never* get any information about those parts
by any possible means, which in turn means that there's a "horizon" which
effectively completely conceals the rest of the Universe from us). This is
accepted because it actually doesn't break GR equations.
However, even in this circumstance *information* cannot be transferred at
superluminal speeds between two points in space. In other words, even if
we invented a machine which would create new space between two points so
fast that the two points recede from each other faster than c, this could
not be used to transport anything between the points faster than c.
> GR says information cannot be transported at superluminal speeds, which is
> why Bell's Inequality is of interest.
I think that the first sentence in the related wikipedia page is the
best summarization of QM I have seen:
"Bell's theorem is a theorem that shows that the predictions of
quantum mechanics (QM) are not intuitive, and touches upon several
fundamental philosophical issues related to modern physics."
--
- Warp
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Warp wrote:
> Just because, according to quantum mechanics, a particle can interact
> over great distances with no delay doesn't mean that *information* can
> be transferred over that distance without the delay
I think you're right. Indeed, most recent tests on Bell's Inequality seem to
indicate that the non-local variables indeed do not exist. I didn't at first
understand what you were saying.
But we weren't talking about information. My comment was in response to you
saying that particles can't be transported out of a black hole. That is
essentially what Hawking radiation is. However, since Hawking radiation is
random, information is not leaving the black hole.
In other words, I think we're agreeing with each other.
--
Darren New, San Diego CA, USA (PST)
"Ouch ouch ouch!"
"What's wrong? Noodles too hot?"
"No, I have Chopstick Tunnel Syndrome."
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Darren New <dne### [at] sanrrcom> wrote:
> And at what distance do you start slowing down?
>
> If you take the Earth and condense it down to a black hole, then stop a
> particle in orbit 100 miles above where the surface used to be, the particle
> will accelerate towards the black hole, right? But to avoid crossing the
> event horizon, it must logically decelerate, as seen from the POV of someone
> in orbit (say). You wouldn't stop at the original altitude of the surface,
> but you would stop before you get to the event horizon, so in this case,
> gravity must be causing you to decelerate. Yes?
Here's a couple plots to show the scales involved in your question. For the
earth, the Schwarzschild radius is about 9mm. If you start from 1m, I've
attached plots showing what an external observer sees and what the dead guy
sees. (The units of time are meters, so you need to divide that by c to get
time.) I'm not sure it's correct to think of it as deceleration since that's
really a notion we have from flat space-time. For this case, space-time is
infinitely warped, so even though it may appear that you decelerate to an
outside observer, in fact you accelerate all the way to the center. You can
also see here that the event horizon means nothing to the guy passing through
it.
- Ricky
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Attachments:
Download 'rel1.png' (15 KB)
Preview of image 'rel1.png'
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Sorry. Web viewer. Here's the second plot.
- Ricky
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Attachments:
Download 'rel2.png' (15 KB)
Preview of image 'rel2.png'
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Warp <war### [at] tagpovrayorg> wrote:
> > 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. The closer you get to
> it, the more warped it is. If you were to look out of your spacecraft as
> it's falling, the universe would look really weird. The closer you are
> to the event horizon, the weirder.
>
> And after you cross the event horizon... Who knows. But you certainly
> would *not* see the universe in any normal way, if at all. You probably
> wouldn't be able to measure anything of the universe at all (because,
> if the GR equations are right, *all* geodesics inside the event horizon
> point directly towards the center).
Hm... I never thought about this in detail. I always imagined the event horizon
as nothing more than a theoretical construct, still a good deal away from the
singularity at its center - the distance beyond which a "fixed" outside
observer cannot see anything anymore. I also imagined that a non-fixed observer
in free fall towards the black hole would percieve the event horizon to be a bit
closer to the singularity, because after all light would only have to reach him,
not be able to zoom off to infinity...
.... but then again, if the light from inside the event horizon could still reach
a free-falling observer outside it, then what would stop the light from zooming
off from *there* to infinity?
So from this, and hearing that it would actually take an eternity (as seen from
an outside observer) to *reach* the event horizon, it sounds logical to me that
in fact the event horizon *is* the singularity...
.... whoa! so we have infinitely small spots the size of planets or larger... now
*that* is what I call weird...
.... and it makes me imagine that it is actually impossible to fall *into* a
black hole: If you'd take that trip, you'd experience it as being torn to
pieces by tidal forces, and in the next moment evaporating as hawking radiation
- seeing that the rest of the universe has aged some few gazillions of years...
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