Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: HellsMascot on 23/04/2013 04:37:51
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I saw this query on a YouTube video comments section and thought it had some validity:
"If a graviton exists, and all force-carrier particles move at the speed of light, and a black hole is massive enough to bend space-time to a point where a particle must move faster than c to convey its force to an outside observer... then how can a graviton escape the event horizon to convey the gravity of that black hole to objects outside the event horizon? Does this not break causality and entropy?"
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I saw this query on a YouTube video comments section and thought it had some validity:
"If a graviton exists, and all force-carrier particles move at the speed of light, and a black hole is massive enough to bend space-time to a point where a particle must move faster than c to convey its force to an outside observer... then how can a graviton escape the event horizon to convey the gravity of that black hole to objects outside the event horizon? Does this not break causality and entropy?"
See http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_gravity.html
When you start speaking of quantum mechanical objects in a classical theory like GR you're going to run into problems. There is no quantum theory of gravity as of yet.
However it seems reasonable to assume that the gravitons from the singularity could be virtual particles, which can go faster than the speed of light. When they come out of the event horizon they'd turn into real gravitons and slow down. Same thing with a charged black hole and virtual photons.
Recall that near the event horizon of a black hole there are virtual particle pairs being created. One goes inside the event horizon and the otherone escapes. The ones that escape become real and the ones that are swallowed by the black hole contribute negative energy to the mass so that the mass decreases.
Pretty slick, huh? That and $1.50 will get you a good cup of coffee. :D
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Recall that near the event horizon of a black hole there are virtual particle pairs being created. One goes inside the event horizon and the other one escapes. The ones that escape become real and the ones that are swallowed by the black hole contribute negative energy to the mass so that the mass decreases.
Your proposed explanation to this hypothetical paradox is rather what I was thinking as well, but I did not know about this virtual particle pair creation. Thank you!
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Write this up with a lot of complex mathematics and I can see a Nobel prize looming
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Write this up with a lot of complex mathematics and I can see a Nobel prize looming
Nobel prizes have never been awarded for solving problems like this.
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I saw this query on a YouTube video comments section and thought it had some validity:
"If a graviton exists, and all force-carrier particles move at the speed of light, and a black hole is massive enough to bend space-time to a point where a particle must move faster than c to convey its force to an outside observer... then how can a graviton escape the event horizon to convey the gravity of that black hole to objects outside the event horizon? Does this not break causality and entropy?"
There is no need of gravitons escaping the horizont event: there already is warped spacetime outside of it.
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I saw this query on a YouTube video comments section and thought it had some validity:
"If a graviton exists, and all force-carrier particles move at the speed of light, and a black hole is massive enough to bend space-time to a point where a particle must move faster than c to convey its force to an outside observer... then how can a graviton escape the event horizon to convey the gravity of that black hole to objects outside the event horizon? Does this not break causality and entropy?"
There is no need of gravitons escaping the horizont event: there already is warped spacetime outside of it.
The idea behind gravitons is that its they which cause objects near the source to accelerate and in some sense do the "warping." Therefore its wrong to say that they aren't needed.
However one can look at a black hole as a collapsed star whose matter never makes it into the event horizon because it gets frozen just at or outside the event horizon, as the link I providewd above suggests.
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But aren't gravitons (in whatever theory you use) just a way of quantizing the gravitational field. And isn't the gravitational field described by the curvature of space-time? Therefore, shouldn't gravitons appear wherever space-time is curved, so they'd appear outside a black hole? I imagine they should be emitted from the event horizon in this case, not from the singularity...
Gravitons seem to be a bit of a side issue. This question seems like it could be rephrased, "How does a black hole curve space-time outside of the event horizon, when there is no way for information about 'how to curve' to be transmitted from the singularity to outside the event horizon?"
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The idea behind gravitons is that its they which cause objects near the source to accelerate and in some sense do the "warping."
? It wasn't mass to warp spacetime? As JP says, gravitons should (if I have understood it) act for the grav field as photons act for the EM field: it's charges who generate the fields, not photons.Therefore its wrong to say that they aren't needed.
But even if they are needed, what I wrote is not that "they aren't needed", but that "there is no need that they come out of the BH".
Do you agree?
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It's true that gravity seems to ignore our definitions of singularities. If one imagine it a 'force' then we need a explanation for it, although, could it just be a geometry connected to mass. Or if one like strings and branes http://www.ams.org/notices/200502/what-is.pdf
I liked Einsteins definition of it, as the 'metric of SpaceTime', defining it. As some sort of topology. If it is you might consider it two ways, either from a closed universe, with some sort of boundary enclosing it, even if 'infinite'. Or you might wonder why we expect those boundaries, instead questioning what it would be if there was none, more than described from constants.
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However one can look at a black hole as a collapsed star whose matter never makes it into the event horizon because it gets frozen just at or outside the event horizon, as the link I providewd above suggests.
If we are allowed to say the collapsed star never makes it to the event horizon, then for the same reason, are we allowed to say that future infalling matter from the end point of the spiral inflow will never leave that end point near the horizon and so cannot be distributed about the hole, but results in a non-symmetrical black hole shape?
Perhaps checking-out the silhouette of a black hole against a starry background will show this odd shape??
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I'm still wondering about this one lean bean. http://news.sciencemag.org/sciencenow/2010/11/physicists-create-black-hole-light.html .Not sure how close a analogue it is, but if it are we might be able to 'probe' a black holes configuration from it. This is a thing I hope JP to give us a better answer on.
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The best thing would be if we could find a way to 'bend light' by itself. But that doesn't seem to be possible? Although we have the 'invincibility cloak' created from light, at a small scale that is? I don't know, but I find it very interesting
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Yes,very interesting. Whatever happened to that idea of naked singularities?
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I'm still wondering about this one lean bean. http://news.sciencemag.org/sciencenow/2010/11/physicists-create-black-hole-light.html .Not sure how close a analogue it is, but if it are we might be able to 'probe' a black holes configuration from it. This is a thing I hope JP to give us a better answer on.
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The best thing would be if we could find a way to 'bend light' by itself. But that doesn't seem to be possible? Although we have the 'invincibility cloak' created from light, at a small scale that is? I don't know, but I find it very interesting
You have to be careful about reading too much into the optical analogue. What's done is to use the idea that light rays passing from, for example, air to glass gets bent. One can design structures that bend light in more interesting ways, including bending it in ways similar to a black hole. The problem is that it's just an analogue--there's an approximation going on to make light bend similarly to how it does in a real black hole. As the critic in that article points out, in theory light bends perfectly like it does in a black hole, but in practice, you can't design these structures with infinite precision, so there is some scattering of light and it doesn't quite perfectly match a black hole. Another big issue is that you can't model the singularity at the center of a black hole this way. That would require infinitely small features in the designed "optical black hole," which is impossible. What you'd get is a lot of light in a small region, and you'd also have to figure out a way to remove it or the device would melt from overheating.
If you can't tell from this, I'm very skeptical about the claim that these devices can accurately model black holes.
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Why is it required that the matter beyond the event horizon be compressed to a quasi infinite extent would the event horizon not still be there if the density was say three times that of a neutron star.
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what is it they say?
"if it sounds too good to be true then it probably isn't"
I see your point there JP :)
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Just for fun, and apropos cloaking devices, or 'invisibility cloak' as I should have called it, missing that my spell correcter happily translated it into 'invincibility', as I first checked my spelling? :)
Any which way: http://skullsinthestars.com/2013/04/25/physics-demonstrations-cloaking-device/
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According to Einstein, nothing can fall to a black hole's event horizon, so they never form. This doesn't necessarily answer the question but I think people should realize there is no reason to think event horizons (or singularities) can form.
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Where did you get that from Android, whoever wrote it is wrong. Einstein and Rosen created the Rosen Einstein bridge to define electrons as examples of a warped/distorted space treaded by EM radiation. In their definition they also made it a possibility of such a tunnel joining different universes, that as the second thermodynamic law won't allow this solution. But relativity doesn't speak about it the same way as thermodynamics and entropy. A black hole joined to a white hole, traveling backwards in time, as defined by us becomes a abomination thermodynamically, if both exist in our universe. But if you define the 'white hole' to another universe then it may make sense. Einstein wanted things to make sense, and what troubled him wasn't the idea of time going one way or another, that as GR is a time symmetric solution, but the idea of a singularity's center in where all known physic breaks down.
Now, that's not my way of thinking of a arrow, but as Einstein saw it time was a illusion.
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It wasn't mass to warp spacetime?
I don't understand this question. Can you please rephrase if for me? Thanks LA.
As JP says, gravitons should (if I have understood it) act for the grav field as photons act for the EM field...
That's my understanding of the situation.
.. it's charges who generate the fields, not photons.
That is not my understanding of it. Charges are the source of the field. The photons mediate the interaction giving rise to the electric field. However this is all quantum field theory stuff and that's a subject I haven't learned ... yet! Soon though! :)
But even if they are needed, what I wrote is not that "they aren't needed", but that "there is no need that they come out of the BH".
Do you agree?
I don't understand quantum gravity so if I either agree or disagree it would be out of ignorance. All I know is classical GR and in classical GR there are no gravitons.
I posted a link in my first post in this thread. It's worth reading.
If[/b] we are allowed to say the collapsed star never makes it to the event horizon, then for the same reason, are we allowed to say that future infalling matter from the end point of the spiral inflow will never leave that end point near the horizon and so cannot be distributed about the hole, but results in a non-symmetrical black hole shape?
I'm sorry but I don't understand what you wrote here. Please rephrase for clarification for me. Thank you.
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I'm sorry but I don't understand what you wrote here. Please rephrase for clarification for me. Thank you.
Maybe I was taking your wording too literally…
Pmb However one can look at a black hole as a collapsed star whose matter never makes it into the event horizon because it gets frozen just at or outside the event horizon, as the link I providewd above suggests.
Assuming a rotating black hole has an accretion disk from which matter spirals down, 'spiral inflow,’ to the horizon, my question…
If your saying matter never makes it into the event horizon and is ‘frozen’ at/outside the event horizon, then are we allowed to think any future or later matter that spirals down from the accretion disk will never be seen to reach the horizon but is accumulating at the end point of the spiral inflow near the horizon?
Thus, I suggested wouldn’t this make the shape of the black hole non-symmetrical?
But yes, I know in an in-faller’s frame he crosses the horizon without noticing anything special. It is only the distant observer who never ’sees’ the in-faller/matter reaching the horizon. It was a flippant question. :)
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Assuming a rotating black hole has an accretion disk from which matter spirals down, 'spiral inflow, to the horizon, my question…
If your saying matter never makes it into the event horizon and is ‘frozen’ at/outside the event horizon, then are we allowed to think any future or later matter that spirals down from the accretion disk will never be seen to reach the horizon but is accumulating at the end point of the spiral inflow near the horizon?
I’m not 100% certain of what ...end point of the spiral inflow near the horizon..
is but if it’s what I think it is then the answer to your question is yes.
Thus, I suggested wouldn’t this make the shape of the black hole non-symmetrical?
I’m not 100% certain about this either but I think the answer is no. I think that information like that gets lost when it falls into a black hole.
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Wonder how infalling matter is seen from a event horizon?
Assuming light to blueshift everything outside the event horizon should speed up, locally measured from the Event Horizon, and infalling mass should then seem to arrive, as good as, instantly. That is if it speed up, locally defined? You can also imagine yourself accelerating, to get that effect, which then close to light speed would mean, what? Just think of some other frames trajectory or geodesic, then accelerate, if now your local clock slows down relative a universe, will those geodesics mass move faster, as defined by you? It's also a question of your motion relative theirs naturally, but what I'm wondering about is how a local clock will define other frames motion, when close to 'c'.
If you think it will, is there a point where that trajectory or geodesic, for you accelerating, will seem to move ftl? It can't be , unless 'c' is wrongly defined. Because we define it locally. We can also assume a uniform motion, after such a 'final' acceleration. Will your clock still 'tick' slower relative other frames of reference, equivalent to your accelerating, or do you expect that local clock to become of one rhythm, same for all uniform (relative) motions?
First of all, there's degrees of hells here :) A relative motion it still must be, but you accelerated first, as close to 'c' as you could. So, what would you expect?
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I don't believe gravity is caused by a stream of particles, such as the hypothesized gravitons, streaming out of a celestial object such as a planet or singularity. In the case of a singularity, they theoretically could not escape from it.
Perhaps gravity is caused by a stream of particles (gravitons) streaming into a celestrial object. In this way they could somehow carry things along with them toward the surface. The problem with this tho is what happens to those particles (gravitons) once they reach the center of the object? They don't seem to just pile up there as that would seem to produce a gravitational field of ever-increasing strength (unless motion of the particles is necessary for gravity). However, I would think some other effect of there piling up there should be noticable (someday). Maybe they pass right through each other at the center, continuing along their path, and are rendered unable to effect anti-gravity while they are passing through a stream of gravitons moving in the opposite direction which are producing gravity.
In the case of a singularity tho, the gravitons may be unable to escape and simply pile up after passing through the center. Again, some effect of their piling up may be noticable (someday). Another possibility is, they may not be affected by gravity in any way and simply continue on their way, thus escaping from the singularity.