Slashdot Mirror
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.
" 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
--
Rushing on down to the circle of the turn
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 "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?
Liberal (adj.): Free from bigotry; open to progress; tolerant of others.
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.
I'm not talking about string theories which deal with 10d line objects, of which there are 5, but the parent theory of all 5 string theories and supersymmetry, that deals with membranes in 11-d.
So far no one has produced any strong objections to m-theory, and m-theory has been used to produce a model (the Ekopyrotic model) for the instant of the big bang. The ramifications of this model are currently being worked out, by amoung others, Martin Rees, Steven Hawking and Neil Turok (in Cambridge alone). The current work is to calculate the effect the Ekopyrotic model has on nucleosynthesis, baryon fraction and primordial CMB imprints and structure formation in the early universe. With the advent of CMB anisotropy experiments such as the VSA, CBI, DASI, Planck and MAP, these predictions will be tested in the next decade or so.
M-Theory also has possible implications for results in within the reach of the LHC accelerator at CERN, which should start producing results of searches for supersymmetric particles about a decade from now.
QCD does have problems with renormalisation, and perturbation techniques at low energies, but these vanish as the energy of the particles increases.
I won't comment on you theory above until you have a working mathematical model for the theory.
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'.
Looking for an Information Security student project suggestion?
Try http://dotcrimeManifesto.com/
A brilliant philosophy professor of mine once described the formulation of fantastic theories unsupported by enough empirical evidence as "creating castles in the sky". Black holes, we may one day find, are far more tangible, real, and even observable than a puff of clouds that resembles a drawbridge. When confronted with phenomena that cannot be explained, a select few physicists and astronomers are apparently compelled to come up with the most unlikely explanations, seemingly borrowed from bad sci-fi movies. Witness the dark matter debacle, in which the many interesting (read: ridiculous) theories concerning other universes and dimensions suddenly caved to the harsh fact that dark matter really *is* nothing more than matter that we can't observe for a myriad of reasons, and not matter sitting in some kind of other space-time continuum. Occum's razor, baby--Occum's razor.
OK, let's start with what we know. From the article: "Astronomers are sold on black holes." Yes, they are. Black holes are out there. The question is what's inside.
Nobody can see inside, so it's anybody's calculated guess. The two main problems with the current theory are singularities and entropy.
Personally, I'm not a huge fan of singularities. I think it's a cop-out to say, "at some point, all the known laws of space-time break down, and that's that." Many people seem to be of the same mindset, including the authors of this paper. They suggest that at some point, the collapse of the black hole is balanced by some quantum force. Now, if I recall correctly, didn't Hawking already suggest this himself?
As for entropy, Hawking wrote that black holes emit radiation by sucking up nearby anti-particles. I've never understood why black holes should statistically acquire more anti-particles than particles, but then again, nobody understands the statistical nature of matter vs. antimatter anyway. I'll take his word that the math works.
This paper amounts to little more than a comparison between black holes and Condensate, and considering that condensate is near-absolute COLD and black holes are something akin to absolute HOT, I think it's a pretty immature analogy.
The paper isn't even published. Why are we talking about it?