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clipka wrote:
> Talk about atoms - the ancient greeks "invented" them.
Yes, and they also didn't believe in irrational numbers even after they were
proved to exist. So I don't think you can pick one success out of history
and call it a "prediction".
I mean, there's really only two or three possibilities: Stuff is atoms,
stuff is continuous, stuff is a mixture. :-)
The greeks had no evidence of atoms, as far as I know. It was just a guess.
It wasn't until Mendeleev (or the work that lead up to the periodic table)
or so that people actually had evidence that atoms were the right answer.
--
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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clipka <nomail@nomail> wrote:
> Warp <war### [at] tag povrayorg> wrote:
> > With this taken into account, can you just go from Earth to the nearest
> > black hole, get an enormous speedup and come back at 100x the speed and
> > slam onto Earth at that speed? From a gravity assist only, I don't think so.
> > I think it would be against conservation of energy. If you were travelling
> > from Earth to another star system, then maybe, but I don't think it works
> > in the closed case.
> It does.
> The trick is that the slingshot affects both bodies: That Huge Planet Over There
> and yout Teeny Weeny Space Machiney.
> Guess which one *seems* to be affected most...
> So if you use a black hole to slingshot you around back home, at the same time
> you sort of slingshot the black hole around your spacecraft into the opposite
> direction... it's just that the black hole won't bother *much*, being the fat
> lazy sucker it is.
Actually it would work if the black hole was moving towards us. Then
the spacecraft could go there and rob part of this momentum and get a
speed boost back towards Earth.
If the black hole was moving away from us then it would certainly not
work.
Think about it as an elastic collision. It's a pretty accurate way of
thinking about it.
> > - If you go so close to a black hole that it will give you a stronger
> > slingshot effect than a regular star would, the tidal forces would
> > probably rip you apart. Not very practical.
> Nah, I don't think so. Would tidal forces rip you apart at the surface of the
> sun? I doubt.
Remember: When the Shoemaker-Levy was on collision course against Jupiter,
tidal forces broke it in 9 parts well before it reached the surface. And
Jupiter is a lot less massive than the Sun.
Ok, maybe if your spacecraft is sturdy enough, it might survive a
slingshot from the Sun. However, we are talking about black holes here,
and black holes have several times the mass of the Sun (because stars
as small as the Sun cannot collapse to black holes), and getting very
close to the event horizon (for it to make a difference compared to a
regular star).
> > - The humongous amounts of radiation around a black hole would probably
> > be enough to fry you to ashes in a fraction of a second, no matter what
> > kind of shielding you use, especially if you go so close that you would
> > get a larger speed boost than from a regular star.
> Again, only if there's an accretion disk. Remember: Black holes don't emit
> anything - only their surroundings may ;)
They don't emit anything, but by their nature as being really massive
objects they surely tend to aggregate lots of nasty stuff orbiting around
them, and this stuff often emits large amounts of radiation by several
means.
For example one concern about sending probes to orbit Jupiter is the
large amount of radiation there (which could break electronics if not
shielded properly). Jupiter, as a very massive object, gathers tons of it.
And Jupiter is a lot less massive than a normal black hole.
> However, maybe you also want to check the magnetic field of the black hole - I'm
> not sure about the orders of magnitude, but I wouldn't want all my electrons go
> spinning off to the left while the protons go off to the right - not to speak
> of the resulting synchroton radiation ;)
Yeah, that too.
--
- Warp
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Warp wrote:
> The major objections against singularities are more or less philosophical,
> rather than based on hard science. It's "hard to believe" that mass could
> be compressed into a point of zero volume.
I think that maybe used to be the case, but I think the objections are also
that it's in conflict with QM right now.
> If someone objects to the notion of a singularity, he would have to show
> some evidence that GR doesn't work as predicted in this case.
I thought that's why it's called a singularity? :-)
> There must be
> some property of the Universe which makes GR not work in this situation,
> something which actually stops the singularity from forming. What could this
> phenomenon be? Has anyone ever measured such phenomenon to exist?
QM uncertainty, and symmetry rules that indicate you can't lose information
about individual particles. You *can't* compress something down to zero size
and not know both where it is and how fast it's moving, for example. QM also
says you can't have two fermions in the same quantum state in the same
place. (More precisely, the probability that it happens is zero, once you
add up all the possible virtual paths.) Hence, you can't collapse an entire
star into a single point.
I don't think the objects are just "it's hard to believe". It's just that
nobody knows how to resolve the problem, since the incompatible theories
both satisfy all the experimental evidence gathered so far.
> The thing is, if GR equations are right, and there is a lot of evidence
> suggesting that they are,
... at the macroscopic level ...
But a singularity is, by definition, microscopic. :-)
> There's no known way for matter/energy to stop going towards this center.
You wouldn't think a single electron could be larger than a house, either,
but they've done that in a laboratory.
I think the real answer is that people just don't know yet. GR says one
thing, and every experimental investigation we can do matches GR. QM says
another thing, and every experimental investigation we can do matches QM.
However, we don't have the capability (yet) of doing any experiment that
would encompass both GR and QM in the same experiment that would give
different answers in the area where they conflict.
Now, what would be fascinating would be for someone to come up with an
experiment that proves you can't measure things in a way that would make QM
and GR conflict. :-)
--
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:
> You'd wind up changing the course of the black hole much less than you'd
> change the course of your spaceship, is all.
The black hole would have to be moving towards the general direction
of Earth, in that case.
> I also think the black hole would be better, because you can get closer and
> get a bigger time dilation from the gravity also.
But you get tons of other problems, as I described in my post. :P
> > - The humongous amounts of radiation around a black hole would probably
> > be enough to fry you to ashes in a fraction of a second,
> FWIW, it's the accretion disk that generates the radiation, so you could
> kill two birds with one stone by finding one without.
As very massive objects, and ones usually formed from collapsing stars
(the collapse leaving behind tons of stuff), I think it would be rather
difficult to find "naked" black holes, without the accompanying stuff.
--
- Warp
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Warp wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>> You give one particle that is constantly emitting photons in all directions
>> a push due south towards the singularity. You have an observer due north of
>> the singularity looking south. The observer due north will continue to see
>> photons coming off the particle indefinitely?
>
> You can distribute a finite amount of photons over an infinite amount
> of time with a simple 1/x formula.
And therefore, yes, you would see photons coming off the particle
indefinitely. :-) That's kind of what I was asking. If you see photons
coming off forever, then you know that shortly before the most recently
observed photon, the object still hasn't crossed the EH.
So since the person falling in will never see himself cross the EH (because
his time slows), and the person outside will never see him cross, then stuff
falling into a black hole does *not* fall into the singularity. Nothing
crosses the EH, so nothing gets compressed into the singularity, yes?
(Discounting the black holes that have paths to the singularity that don't
cross an EH, of course.)
--
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:
> QM also
> says you can't have two fermions in the same quantum state in the same
> place.
At least not in normal, almost-cartesian space, with extremely weak
gravity.
How about inside space which is so curved that it forms an event
horizon because of a practically infinite gravity?-)
Gravity is such a weak force in normal situations that you usually don't
have to even take it into account when making QM calculations. However,
inside a black hole gravity, rather obviously, overwhelms all other
forces and becomes absolutely dominant. What happens to eg. fermions
when gravity is immensely stronger than eg. the strong nuclear force?
Under such pressures matter degenerates. Do fermions even stay as
fermions, or do they degenerate to something more elemental? Something
which might not be bound to QM laws?
> > The thing is, if GR equations are right, and there is a lot of evidence
> > suggesting that they are,
> ... at the macroscopic level ...
> But a singularity is, by definition, microscopic. :-)
Gravity is in effect also at subatomic levels, even though it's often
ignored because it's so weak in normal circumstances.
> > There's no known way for matter/energy to stop going towards this center.
> You wouldn't think a single electron could be larger than a house, either,
> but they've done that in a laboratory.
"You wouldn't think" is different from "there's no known way". The
former is something related to my intuition. The latter is related to
current scientifical global knowledge.
(Well, always with a big "AFAIK". I'm *not* a scientist.)
--
- Warp
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clipka escreveu:
> "nemesis" <nam### [at] gmailcom> wrote:
> Interestingly though, the real-existing phenomenon of "black holes" was
> originally a purely hypothetical prediction of GR - not some already known
> effect that needed to be explained. And it did predict their properties quite
> well as it seems. So this is strong evidence that the GR is a very good tool to
> make predictions.
It is, no doubt. A very solid model, which QM enthusiasts are still
plotting to supplant. :)
Evidence was found of objects with imense gravitational fields occupying
relatively tiny areas in space and this matches with GR's predictions.
But there's as of yet no evidence that singularities physically exist or
that matter entering a blackhole is forever lost, except as a somewhat
vague Hawking radiation...
So, the QM guys thought it would be a good idea to imagine an alternate
model to explain such objects without relying on singularities and lost
information. And it's testable in lab, right here on Earth. Of course,
they are trying to somehow fit the lab effect to the observable
phenomena, but without explaining why such effect would occur in the
surface of stars...
> So in order to show that *their* theory is at least an equally good tool, they
> would actually have to demonstrate how their own theory explains not only the
> same *phenomenons* as GR, but *postulates GR itself* - or demonstrate how their
> theory is just a different way of looking at GR.
QM so far has made good predictions is the small, very small. :)
> BTW, speaking of it: When falling into a black hole I guess it may be best not
> to try to fight the inevitable... suppose you manage to stay at a fixed
> distance from the center - with all the blueshift of the photons falling in,
> you're gonna get your daily maximum dose of gamma rays in a few split
> seconds... so better fall in to experience the same blue shift (effectively
> leaving the shift unchanged from your perspective) and hope that the
> singularity is just a transition to a better life somewhere - um, I mean
> someWHEN - else...
a very good suggestion too. :)
Perhaps it's like passing through a corridor in flames: you should run
towards the end of it... :P
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Darren New <dne### [at] sanrrcom> wrote:
> So since the person falling in will never see himself cross the EH
I'm not sure where you are getting this one. I have not heard of it.
The only thing I have heard is that an *external* observer never sees
anything "touch" the event horizon.
Time for an observer itself is always the same, regardless of where
he is.
--
- Warp
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Warp escreveu:
> point towards the center. There's no known way for matter/energy to stop
> going towards this center. Just advancing in time makes it advance towards
> this center.
I like how Hawking puts it: "The singularity is the future: as you
advance towards it, you also moves towards the future" or something to
that effect...
> The only possible conclusion is that all the matter and energy compresses
> into a point of zero volume. If the singularity does not form in reality,
> then something must explain why. Something more than philosophical objections.
Well, if it was like that in the beginning, why couldn't it be possible
now, huh? Which also begs the philosophical question of whether passing
through the EH leads to a whole new universe beginning from yet another
big bang...
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nemesis <nam### [at] gmailcom> wrote:
> Which also begs the philosophical question of whether passing
> through the EH leads to a whole new universe beginning from yet another
> big bang...
I don't think the spacetime geometry inside the event horizon of a
black hole would allow for a universe to exist in there.
--
- Warp
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