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Doubting the Existence of Black Holes
The Good Reverend writes: "It seems that there's a growing movement that doubts the existence of black holes, going against most of the rest of astrophysics. They suggest the existence of gravastars, "star-size agglomerations of "wavelike" substance" (space-time fabric, if you will). Different scientists claim to have created the "wavelike substance" in a lab, called Bose-Einstein condensates." I understand gravastars taste terrific with cream cheese and red onion.
Would that be rather like neutron stars? My understanding is that current orthodox astrophysics models meutron stars as either a Bose-Einstein state, or as (in effect) a single, very big, neutron. (Or, er, are those the same things?) C'mon astrophysicists, enquiring idiots want to know! ;)
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Man, I thought I read this article on a Slashdot link a few weeks ago, but I guess I read it somewhere else.
No, it's not just semantics. There's actually a huge difference between gravastars and black holes. The key difference is that a black hole contains a singularity. A point at which our physics break down. This is commonly described as the point where the physics are "undefined". A gravastar doesn't have this. Physics contiue to make sense within a gravastar. I haven't studied it in detail, but that's the claim.
No alternate universes, no place to go, except a big fat heap of particle soup to go crashing into. Okay, more like a big particle rock, than a soup.
Of course, the biggest difference is that gravastar is just a much cooler name.
I think these people are going to run up against the principle Metatheorem of Quantum Gravity: All theories of quantum gravity are wrong.
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...whether a theory, unifying the gravitational force with the other three fundamental forces, would be at odds with the existence of black holes?
:)) how a quantum view of gravity would affect theories on black holes and the birth of the universe. Basically my question is: If gravitational attraction is carried by a particle (the graviton) as is conjectured by many scientists, then how can one of these escape from a black hole any more than another particle?
:)
I have often wondered (but never had the time, inclination or intelligence to go find out
I guess that either:
a) It can't, ergo black holes don't exist;
b) It can, and Einstein was wrong somewhere;
c) There is some effect similar to the X-ray "emissions" from black holes, whereby the particles appear to come from the black hole but actually never cross its event horizon.
Which just goes to show that a little knowledge is a dangerous thing.
These sigs are more interesting tha
Black Holes Disputed
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"Claim" is hardly the correct word, since it is not disputed (to my knowledge). Last years Nobel Prize in physics was awarded to the first experimenters who created this sixth (depending on how you count) state of matter. The existence of Bose-Einstein condensate is not in itself any challenge to black holes.
The article states: Calculations show that a black hole would contain astoundingly more "entropy" than the matter that fell into it
If the article was less sensationalist, they would have mentioned that there are also calculations based on Hawking radiation that show the entropy of a black hole to work out perfectly. Some say the entropy is wrong, others don't. Also, referring to singularities as "paradoxes" seems strange. One would rather not deal with them, of course, but paradoxial? Nah. Since they are always hidden and cannot be reached in finite time, the philosophical question is whether they even can be said to exist in the same way as other things exist.
The article also does not increase in credibility, when it refers to the uncertainty principle as "eerie" and to black holes as "spooky" and "scary".
What about gravastars then, are they for real? Dunno... Most theories are at the fringe for a good reason, though.
Opinions stated are mine and do not reflect those of the Illuminati
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Whether or not the matter condensed into some kind of Bose-Einstein condensate or collapsed to a point is entirely academic because whatever it is would still be within the event horizon, and would act the exact same way in either case.
-- Give me ambiguity or give me something else!
My first opinion of this hypothesis is that it is a big stretch. First, a little background.
A very massive star has a very massive gravitational field. Through its lifespan the star does not collapse under its own weight due to the ongoing fusion reaction which powers all stars. When the nuclear fuel finally runs out, the star begins to collapse inward. (For those of an astronomical bent, yes I am skipping over some details as to the various stages of fusion that grant temporary repreives to the collapse).
As a star collapses, the atoms that make up the star are packed more and more tightly together. If the star is massive enough, the electrons and protons are finally merged together to form neutrons. The neutrons then pack together more and more tightly until the repulsive force between the neutrons prevents further collapse (for stars not quite massive enough to become black holes) or the neutrons themselves crush in upon each other into even more degenerate states of matter. As far as we know, once you pass this point there is NO OTHER REPULSIVE FORCE available to keep the collapse in check. The star collapses all the way down to a single mathmatical point.
The second bit of background we need is an explanation of Bose-Einstein Condensates. First, you need to know that all particles can be described as waves. In the macroscopic world in which we live our daily lives, the waves are such tiny little packets that we don't perceive them as anything more than particles. However, on the microscopic level, particles begin to really demonstrate just how wave-like they can be. When a group of atoms is collectively cooled down to very close to absolute zero, the behavior of the individual atoms become linked together and they begin to act a single atom. (The wave functions describing the individual particles merge). It is a funky-cool state of matter that is regularly used now in a range of physics experiments.
The hypothesis in the article on black holes is that spacetime itself can undergo a "phase change" not unlike the way that matter can go from solid to liquid to gas -- or even (in labs) to a Bose-Einstein condensate.
The important thing to note here is that
(a) no one has ever seen a phase change in the fabric of spacetime (I'm not sure the concept even makes sense, personally).
(b) The authors are NOT saying that the black hole's stellar material BECOMES a Bose-Einstein condensate -- they are saying the the fabric of spacetime itself becomes the "spacetime-equivalent" of a Bose-Einstein condensate (whatever that would be!).
My feeling is that while it *could* be the case, basically they are trying to dream up a totally hypothetical new phenomenon (phase changes for spacetime) to find some way to get rid of black holes in physical theory. I don't see that the new phenomenon has any grounding in theory or observation -- it's strictly hypothesized for the end result -- and is therefore very unlikely to be true.
Now, that's NOT to say it CAN'T be true. However, I expect their may be dozens to hundreds of other such hypothetical creations designed to counter the infinite collapse that supposedly occurs in black holes -- the concept of a black hole is "offensive" in physics because you end up with a big "divide by zero" error in the universe. We do, however, have good evidence for the existence of black holes, so no matter how much physicists hate what they do to the math, we may have to simply accept them.
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First we faked moon landings, now we've faked black holes! Is there even really any stars at all up there or is it just a bunch of lights in a big dome?
As a rock-in-roll Physicist once said, No matter where you go, there you are.
A black hole is a term for a mass that is compact enough that it lies within an event horizon. Heuristically speaking, light cannot escape because the escape velocity from the object is faster than the speed of light, so it appears dark.
In General Relativity, given a sufficiently large mass (say, a 10 solar mass star), there is no source of rigidity strong enough to withstand gravitational collapse, so black holes will eventually form.
Big stars exist, so avoiding black holes requires either a new theory of space time (or gravitation), or a new type of matter.
These guys have opted for a new type of matter,_analogous_ to a Bose-Einstein condensate. The existance of Bose-Einstein condensates in the lab for regular matter (routine, now), says nothing about whether this exotic matter exists out there.
This is still pretty wide open from a theory vs experiment sense. Most claims for black holes are really observations of dense collections of matter. Some would be black holes for sure in General Relativity, but this is no proof.
The best source of proof for black holes will probably come from detection of Gravitational waves from their formation, which should come in the next few years from experiments such as LIGO or LISA .
I would like to point out that posting an article before the team concerned has published their paper is very bad news for the team.
What often happens is that the team becomes doubted initially because they haven't published the paper, or because the article writer doesn't know what he/she is writing about. Sometimes it blows up in their face, ala Cold Fusion.
I would also like to note that the technical quality of the article is poor and shows a lack of understanding of the subject matter.
For example:
"The location of a particle constantly varies according to a statistical pattern -- one moment it's here, another moment it's there"
This shows a complete lack of understanding of the uncertainty principle! The particle has no 'position', and as such it can't be here one moment and there the next. Its position-space wavefunction is the best we can get.
There are also quite a lot of claims made in the article that really deserve a reference - hence the problem if the only reference is unpublished - in particular I would like to see an argument for why spacetime undergoes a phase transition inside the black hole. What theory predicted this? Certainly not General Relativity, which is what predicted black holes in the first place. What modifications must be made? How is quantum mechanics used in this setting?
Note that quantum gravity is still an unsolved problem, so I'd be surprised if this prediction turns out to be spot-on. But I can't tell for sure since the paper is unpublished =(
" Rather, this substance would be the underlying "space-time" fabric of the universe, which, as Einstein showed long ago, "curves""
...
Aaaaaargh. This article reads like BBC2's _Horizon_ programme. All "these people discovered some random idea, aren't they wonderful?" BS explaining why "blue" is a colour to the clueless population never mind concentrating on the idea to hand at all - apparently Bose-Einsten condensate is somehow the "fabric of the universe"?
I said way back at Uni, and will say it again: I don't want to know whether Einsten *liked* a particular idea, I want to know the *idea* and I'll make up my own mind. Give me equations, keep the pop-psych AWAY.
~Tim
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And what Bose-Einstein condensates have to do with it is murky at best. Like a BEC but made of space-time rather than atoms? What the fuck is that mealy mouthed shit supposed to mean?
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I believe that it was not Einstein who first noticed that the GR equations yield solutions which have spacetime singularities, i.e. blackholes. This was first found by Schwartzchild.
Einstein's equations do not predict blackholes. Blackholes are simply compatable with his equations.
This does not mean that blackholes may be incompatable with other physical laws, notably those of quantum mechanics/field theory and those of thermodynamics, which is why it is theoretically interesting to try to derive the quantum and thermo properties of blackholes to find either a contradiction or an interesting property which one might try to observe from earth.
Someone who says they do not believe in black holes either
1) does not believe Einstein's equations, of which they are solutions.
2) believes that other physical laws prevent the occurrence of these solutions.
The first paper on this Bose-Einstein condensate stuff poses another solution of the GR equations in which the point singularity is replaced with a different structure, the BEC. The math seemed all on the up and up.
(BTW the Schwartzchild solution doesn't really have a singularity. The singularity is an artifact of the coordinate system used, just like the singularity of latitude and longitude of the earth -- and we do believe in the north and south poles here, right? Kruskal exhibited coordinate systems in which there is no singularity.)
So what we have is a new analytic solution to the GR equations (and there are not many, so this will undoubtedly make it into graduate texts in the next decade).
The bad news is that the geometry around a gravastar is identicle to that around a blackhole. It is just different when close to the phenomenon, so all that business about terrible cosmic death at the hands of a gravitational giant is still there.
This story first hit /. several weeks ago. I am glad to see the astrophysics community taking it onward and upward. Me no like blackie-holes. There is that ugly problem of infinities, entropy imbalances, loss of information, and so forth - none of which appear in the gravastar model...with the added bonus that a gravastar in every other way behaves exactly like a "black hole" (gravitationally).
Cosmology DOES contain ideas of phase changes occurring during the development of the universe after the big bang, so gravastars with space-time phase changes fits in there too.
It still permits sci-fi some cool material too, so the loss of classic black holes would be no biggie on that front.
Bring REASON back and eliminate "black holes". Silly, impossible buggers they are.
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This "Gravastar" might be indistinguishable from a black hole. The article says that the star collapses to the point that the material undergoes some kind of phase transition to become a single waveform of space-time, analogous to a Bose-Einstein Condensate.
If this happens when the object is less than a Schwarzschild radius in size, it would look and behave exactly like a black hole to an outside observer.
(The Schwarzschild radius is the distance inside of which not even light can escape from the object. It doesn't make a difference how the matter is distributed inside the Schwarzschild radius)
I'd also be interested to know how gravastars scale with mass. The article mentioned only stellar-mass black holes, but our greatest evidence for BHs is the supermassive black holes that are thought to exist at the centers of most massive galaxies. These have masses of millions of solar masses; can a gravastar hold up that much mass?
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This discusses the possibility of tiny black holes created by high-energy collisions (discussed in a previous Slashdot), which the researches hypothesize happens regularly in our upper atmosphere (bit of a stretch). It also discusses a novel theory as to why gravity is so significantly weaker than other local forces -- That unlike other forces, gravity acts through all the 'extra' dimensions hypothesized in super-string theory.
One of the more interesting things about the article is that it shows that with recent developments (the new Large Hadron Collider, etc.) scientists are beginning to reach a point where they can start to prove or disprove parts of super-string theory... Interesting stuff indeed!
A black hole would swallow clouds of stars like a whale gulping down plankton. Black holes would literally be points of no return; fall into one, and you'd be trapped forever. If Earth bumped into a black hole, it would be goodbye Earth.
This part right here tells me the author doesn't know much about Black Holes! First of all, they are not that big. In fact the largest, and abnormally, sized Black Hole that we can observe is about 14 magnitudes greater than our own Sun. Add to that the actual size even then is perhaps the size of the moon, or less!
So when a black hole travels though space-time, it gets near another object, the process that starts takes years to finish. IT does not gobble up handful's of stars at one sitting.
We can detect Black Holes by observing the siphoning of the starts gas from a long distance. It looks like the star grows a very thin and long tendril that extends away from the star main sphere. The tendril of star stuff isn't directly consumed by the black hole. The Tendril actually forms a swirl of gas around the black hole. As the black hole closer to the star, the tendril changes form to a more amorphous shape. At that point the black hole would be totally shielded behind a torrent of star-stuff that would totally block it out any direct observation. The Star, and the black hole would begin to revolve around one-another in a dance that would end with the black hole assuming the mass of the star.
If you can imagine what I just wrote, that is what astronomers have observed.
Not only that, the author also appears to have a gross inability to describe the Bose-Einstein Condensate. The reality is that a condensate cloud could probably never exist in nature, and to call it the actual space-time stuff is absurd. The condensate cloud is more like the 5th state of matter (solid, liquid, gas, plasma, and Condensate cloud). Think of a Condensate cloud as the extreme opposite of plasma. Where one is really hot, the other only exist at supper cold temperatures. In fact, the Bose-Einstein cloud is the coldest thing we have ever created I think. At such a cold state of matter, time almost seems to stop. A really bizarre occurrence is when photons are shot into the cloud, and they appear to slow down while in the cloud, then speed up as they exit.
This same topic was publicly introduced in the Scientific American magazine a few months ago. The article was interesting, but at the end had this part about how the universe could actually be surrounded by a giant condensate cloud. The idea sounded really good until that part.
What this seems like to me is we humans have recently discovered this cosmic snaik-oil, the cold condensate cloud, and are now looking for a place to make it fit in the universe, no matter how sensational.
It isn't a lie if you belive it.
Not as far as any external observations go. What is comes down to is philosophy of science.
The definition of a black hole = singularity is a modern one. The idea that things might be so massive that light cannot escape predate Einstein by a couple of centuries. Hawking has the paper in the back of one of his books, the one that starts 'Consider a Hausdorfian Manifold of Lipschit signature...' clearly one of his pop-science efforts.
There being no observable difference from outside the black hole the issue of what happens inside is irrelevant (except to omnipotent beings). Conventional physics might as well go hang when it tries to predict what happens since the area beyond the event horizon is out of bounds.
There is a similar debate in QM (which Einstein was also on the losing side of), does God really play dice? The apparently random interactions of QM can be explained deterministically if one posits the existence of hidden variables. However a theory based on variables that cannot be observed is not empirically verifiable, let alone falsifiable and thus lies in theology rather than science.
What underlies the whole debate is the question of whether physics is a model of the universe or THE TRUTH. Theoretical physicists often fall into the belief that they are discovering the truth about everything rather than merely a theory that is consistent with empirical observations. This is what is really behind the Sokal attack on Literary criticism, he takes offense at the insistence of Derrida and others that science is a set of working assumptions rather than an absolute. Ironically Sokal appears to be enlisting Popper in his cause which is strange because Popper's entire point was that absolutist ideas were bad and that the term 'science' was being abused by the pseudo-science of Marxists and Freudiam Psychoanalysis. Later discussions between Popper and his critics (notably Khune) makes it very clear that Popper was quite consciously raising the bar of 'scientific method' above the standards science itself applies.
So the fact that the standard model and relativity fall apart in the inside of black holes does not worry me much. We know that they are both wrong since they are (currently) incompatible.
Black holes and the QM hidden variables appear to me to satisfy Broomfondle's demand for 'rigidly defined areas of doubt and uncertainty'.
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The folks at Los Alamos (Mottola et al.) who dreamt this up were trying to devise a scheme in which gravitational collapse led to an object similar to, but without what some perceive to be the inconsistencies of, a Black Hole. While they get points for trying, there are a lot of problems with their proposed model.
First, it requires that under extreme situations gravity undergoes a "phase change", which for all intents and purposes means that the region inside the gravastar posseses a positive cosmological constant, effectively a non-zero energy density inherent to space itself. The notion of a cosmological constant has been troubling relativists and particle theorists for over 70 years and we still don't understand whether there is such a thing and where it might come from. Current astronomical observations suggest that there may in fact be a very small CC, but no one knows a mechanism for how this might be "produced" inside a gravastar. The earlier work of the Los Alamos crew makes some suggestions for how this might come about, but is itself based on a field theoretic treatment of gravity, a pretty shaky proposal whose predictions are hard to identify and must be taken with a grain of salt.
Second, they propose an interface layer between their "gravitational BEC" and the world outside the gravastar, made up of "ultra-stiff fluid". In GR we often resort to desribing distributions of gravitating energy and matter as a perfect fluid with an equation of state that relates how much energy density there is to how hard it pushes out, or its pressure. There is a "stiffest possible" equation of state consistent with causality (the speed of sound of disturbances in the fluid is equal to the speed of light). This is what they use to make their interface. Such a fluid has fascinating properties and is the subject of a lot of attention right now, but no one really knows of any such substance or what its microscopic physics might be. Therefore a lot of guesswork goes into any numerical estimates they might suggest.
Third, their gravastars are extremely cold and don't seem as if they would be useful for the types of processes that astrophysicists typically invoke Black Holes to explain. Black Holes are conjectured to be responsible for a wide array of highly energetic processes that we see in the Universe, and these gravastars just don't seem as if they would even be stable in such situations.
Last, if you go to http://arXiv.org and search for this paper, you will see that it has been revised five times since it was originally submitted. It isn't unusual for papers to be revised, even that many times, but I know that some of the revisions are due to calculational errors.
The paper is entertaining and has some neat ideas, but is in all likelihood not the way things are. There is a movement among some condensed matter physicists who claim that the principles of CM physics are actually fundamental and should form the basis for any consistent model of gravity and particle physics. This paper is a nod in that direction. While some ideas from CM might find fruitful application in high energy physics, it doesn't seem likely that phenomena at the Planck scale (where quantum gravitational effects become important) will benefit from them.