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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.
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.
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
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.
Life is short: void the warranty.
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 .
As I understand it the current best guess at the theory of everything is called M-theory
m en s.html)
(http://www.fortunecity.com/emachines/e11/86/di
which talks about the universe being a single membrane, of which all matter (and energy and everything else) in the universe is part. This exists in 11 dimensional space.
M-theory is an evolution of string theory
The theory goes that gravity is seepage from another universe a small distance away (like a few mm) in 11 dimensional space.
They believe that in essence gravity is the same strength as the strong nuclear force but what we feel is the translation of that into just 3 dimensions and acting at a short distance. This would then imply that the limit on gravitational forces would be of the same order and would occur when two such universes where very close.
Incidentally M-theory also can explain the big bang as a collision of two membrane universes.
You can't win Darth. If you mod me down, I shall become more powerful than you could possibly imagine
Actually, since neutrons have a spin of 1/2 they are in fact fermions and not bosons. Thus, a neutron star is in fact modelled as a degenerate Fermi gas. Fermi gases exert pressure as a result of the exclusion principle (even at T=0). This pressure is what prevents further collapse of not too massive stars. However, if the gravitational pressure is larger than the Fermi pressure (because of a large mass), then the star collapses further, eventually giving a singularity.
It's also a spelling mistake.
It's gravistars, not gravastars.
There are a lot of things possbily wrong with the theory, but then Black Holes have some problems with them as well.
New Scientist had about three weeks ago something on this, which is fairly simple to digest.
Good news is that there is a way ot tell the two phenomena apart. So it's at least disprovable.
I have often wondered (but never had the time, inclination or intelligence to go find out :)) 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?
The latest theory of quantum gravity under discussion is the 11 dimensional m-theory, which models the universe as a four dimensional spacetime embedded in 10 space and 1 time dimensions. In this theory, gravity, and therefore gravitons, are the interaction between two closely seperated membranes, one of which is our universe. gravitons propagate in all 11 dimensions of the theory, and can therefore propagate out of the 4-d black holes 3-d event horizon by taking a trip through the higher dimensions.
It's not that Einstein was wrong, as his field equations still produce the correct results for large scale gravity in m theory, but just that he didn't go far enough towards a quantum theory of gravity, for which the mathematical tools just weren't available.
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?
Insanity is the last line of defence for the master diplomat. But you have to lay the groundwork early.
So far no Black Hole was made in labs.
/. posts about that.
They are just building the new accelerator for trying to do so. Micro Black Holes, just made from two atoms. They hope that they get the Hawkins radiation detected to see that it is a black hole.
The implication to have made a black hole would be that we have several further dimensions in the scale of a millimeter(besides the standard 3 dimensions we all *see*).
There are several
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angel'o'sphere
Cost free eBook I read (by iBook/Kobo/Amazon/ObookO/Gutenberg etc.): "The Green Odyssey" by Philip Jose Farmer.
"The event horizon is nothing more than the distance at which escape velocity is the speed of light"
/. about it.
Since escape velocity is the speed of light and because relativity prevents you from accelerating to the speed of light, if you fall inside the event horizon then according to relativity you can't get back outside.
This does not mean that you will die as you pass the event horizon but it does mean that as far as the outside world is concerned the only measures that you ever existed are the changes in the mass, angular momentium, and charge of the hole which you caused.
Hawkings, using quantum theory, showed that you will eventualy make it out of the hole via the emmision of one part of a particle/anti-particle pair(Hawking radiation). But the only information about you that will be conserved will be again be your mass, angular momentium and charge, so your not coming out the way you went in.
But besides all that those of us who find ourselves trapped inside a massive event horizon can still live happy and productive lives, we just can't post on
Hawkings, using quantum theory, showed that you will eventualy make it out of the hole via the emmision of one part of a particle/anti-particle pair(Hawking radiation). But the only information about you that will be conserved will be again be your mass, angular momentium and charge, so your not coming out the way you went in.
This is something that I hear ALL the time: that Hawking radiation lets some matter escape from a black hole. In actuallity, the particle/antiparticle pair are created (via the QM fluxuations of empty space) OUTSIDE the event horizon. One of the pair goes past the event horizon and the other (just barely) escapes. This is Hawking Radiation.
I couldn't tell if you were experimenting with poor-man's cryogenics or looking for the orange sherbet.
The paper was originally published on 9/11/01 and revised 4 times thereafter, the most recent being about a month ago.
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.
False Dilemma
Besides that, the existance of black holes have nothing to do with creationism. Creationism usually does not dispute the current laws of physics, because that would be silly.
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
As I understand it everything would pile up just outside the Schwarzschild radius, and would look almost the same to an outside observer. This avoids the the problem of crossing the Schwarzschild radius, it never happens.
I'd also be interested to know how gravastars scale with mass... millions of solar masses; can a gravastar hold up that much mass?
The condensate would expand the same way as the Schwarzschild radius would. I believe the forces go down as the square of the radius. The "holding up mass" effect would then be a constant.
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