Posted on 03/09/2006 8:34:42 PM PST by snarks_when_bored
DARK energy and dark matter, two of the greatest mysteries confronting physicists, may be two sides of the same coin. A new and as yet undiscovered kind of star could explain both phenomena and, in turn, remove black holes from the lexicon of cosmology.
The audacious idea comes from George Chapline, a physicist at Lawrence Livermore National Laboratory in California, and Nobel laureate Robert Laughlin of Stanford University and their colleagues. Last week at the 22nd Pacific Coast Gravity Meeting in Santa Barbara, California, Chapline suggested that the objects that till now have been thought of as black holes could in fact be dead stars that form as a result of an obscure quantum phenomenon. These stars could explain both dark energy and dark matter.
This radical suggestion would get round some fundamental problems posed by the existence of black holes. One such problem arises from the idea that once matter crosses a black hole's event horizon - the point beyond which not even light can escape - it will be destroyed by the space-time "singularity" at the centre of the black hole. Because information about the matter is lost forever, this conflicts with the laws of quantum mechanics, which state that information can never disappear from the universe.
Another problem is that light from an object falling into a black hole is stretched so dramatically by the immense gravity there that observers outside will see time freeze: the object will appear to sit at the event horizon for ever. This freezing of time also violates quantum mechanics. "People have been vaguely uncomfortable about these problems for a while, but they figured they'd get solved someday," says Chapline. "But that hasn't happened and I'm sure when historians look back, they'll wonder why people didn't question these contradictions."
While looking for ways to avoid these physical paradoxes, Chapline and Laughlin found some answers in an unrelated phenomenon: the bizarre behaviour of superconducting crystals as they go through something called "quantum critical phase transition" (New Scientist, 28 January, p 40). During this transition, the spin of the electrons in the crystals is predicted to fluctuate wildly, but this prediction is not borne out by observation. Instead, the fluctuations appear to slow down, and even become still, as if time itself has slowed down.
"That was when we had our epiphany," Chapline says. He and Laughlin realised that if a quantum critical phase transition happened on the surface of a star, it would slow down time and the surface would behave just like a black hole's event horizon. Quantum mechanics would not be violated because in this scenario time would never freeze entirely. "We start with effects actually seen in the lab, which I think gives it more credibility than black holes," says Chapline.
With this idea in mind, they - along with Emil Mottola at the Los Alamos National Laboratory in New Mexico, Pawel Mazur of the University of South Carolina in Columbia and colleagues - analysed the collapse of massive stars in a way that did not allow any violation of quantum mechanics. Sure enough, in place of black holes their analysis predicts a phase transition that creates a thin quantum critical shell. The size of this shell is determined by the star's mass and, crucially, does not contain a space-time singularity. Instead, the shell contains a vacuum, just like the energy-containing vacuum of free space. As the star's mass collapses through the shell, it is converted to energy that contributes to the energy of the vacuum.
The team's calculations show that the vacuum energy inside the shell has a powerful anti-gravity effect, just like the dark energy that appears to be causing the expansion of the universe to accelerate. Chapline has dubbed the objects produced this way "dark energy stars".
Though this anti-gravity effect might be expected to blow the star's shell apart, calculations by Francisco Lobo of the University of Lisbon in Portugal have shown that stable dark energy stars can exist for a number of different models of vacuum energy. What's more, these stable stars would have shells that lie near the region where a black hole's event horizon would form (Classical Quantum Gravity, vol 23, p 1525).
"Dark energy stars and black holes would have identical external geometries, so it will be very difficult to tell them apart," Lobo says. "All observations used as evidence for black holes - their gravitational pull on objects and the formation of accretion discs of matter around them - could also work as evidence for dark energy stars."
That does not mean they are completely indistinguishable. While black holes supposedly swallow anything that gets past the event horizon, quantum critical shells are a two-way street, Chapline says. Matter crossing the shell decays, and the anti-gravity should spit some of the remnants back out again. Also, quark particles crossing the shell should decay by releasing positrons and gamma rays, which would pop out of the surface. This could explain the excess positrons that are seen at the centre of our galaxy, around the region that was hitherto thought to harbour a massive black hole. Conventional models cannot adequately explain these positrons, Chapline says.
He and his colleagues have also calculated the energy spectrum of the released gamma rays. "It is very similar to the spectrum observed in gamma-ray bursts," says Chapline. The team also predicts that matter falling into a dark energy star will heat up the star, causing it to emit infrared radiation. "As telescopes improve over the next decade, we'll be able to search for this light," says Chapline. "This is a theory that should be proved one way or the other in five to ten years."
Black hole expert Marek Abramowicz at Gothenburg University in Sweden agrees that the idea of dark energy stars is worth pursuing. "We really don't have proof that black holes exist," he says. "This is a very interesting alternative."
The most intriguing fallout from this idea has to do with the strength of the vacuum energy inside the dark energy star. This energy is related to the star's size, and for a star as big as our universe the calculated vacuum energy inside its shell matches the value of dark energy seen in the universe today. "It's like we are living inside a giant dark energy star," Chapline says. There is, of course, no explanation yet for how a universe-sized star could come into being.
At the other end of the size scale, small versions of these stars could explain dark matter. "The big bang would have created zillions of tiny dark energy stars out of the vacuum," says Chapline, who worked on this idea with Mazur. "Our universe is pervaded by dark energy, with tiny dark energy stars peppered across it." These small dark energy stars would behave just like dark matter particles: their gravity would tug on the matter around them, but they would otherwise be invisible.
Abramowicz says we know too little about dark energy and dark matter to judge Chapline and Laughlin's idea, but he is not dismissing it out of hand. "At the very least we can say the idea isn't impossible."
very interesting stuff!
ping
I though Hawking said black HOES . . .
DOH!
Whenever you think that you are facing a contradiction, check your premises. You will find that one of them is wrong.
-- Francisco d'Anconia
That's how science advances. After the Michelson-Morley experiments, Einstein questioned long-accepted premises about the universal constancy of time and the Euclidean geometry of space, resulting in the theories of special and general relativity.
-ccm
It sounds to me that they're not actually *replacing* the idea of black holes with something else that's not a black hole, what they're really saying is that the physics of black holes might be different than previously thought, especially "inside" the black hole.
His second statement isn't quite fair -- as shown by his first statement, people *have* questioned the contradictions, but there's not much you can do about them until you manage to come up with a good way to resolve them. And often it can take a long time for the right "aha!" insight to arrive.
It sounds to me that they're not actually *replacing* the idea of black holes with something else that's not a black hole, what they're really saying is that the physics of black holes might be different than previously thought, especially "inside" the black hole.
Well, as the passage you quoted states, at the heart of a black hole (should such there be) there's a spacetime singularity. That would not be the case for the Chapline dark energy star, inside of which there is vacuum but no singularity. Also, the event horizon of a black hole isn't made of any sort of 'stuff', while the quantum critical shell of a Chapline star would be. These are significant differences and would likely be enough to force a name change, don't you think?
And it is becomer "gianter"!!
mer = ming
"Because information about the matter is lost forever, this conflicts with the laws of quantum mechanics, which state that information can never disappear from the universe."
Holey moley... Where in the heck did this guy study astrophysics? He needs to get a refund on his education. The matter isn't lost. It still exists in the universe. It is simply sucked down to the bottom of a gravity well (black hole) and in fact creates that very same gravity well. If there was no matter tucked away inside of a black hole, it wouldn't have such a strong gravity well.
"Because information about the matter is lost forever, this conflicts with the laws of quantum mechanics, which state that information can never disappear from the universe."Holey moley... Where in the heck did this guy study astrophysics? He needs to get a refund on his education. The matter isn't lost. It still exists in the universe.
Ummm, the writer says that information about the matter is lost, not the matter itself.
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Three cosmic enemas? We don't allow that kinky stuff on FR! Callimg all Moderators!
The team's calculations show that the vacuum energy inside the shell has a powerful anti-gravity effect, just like the dark energy that appears to be causing the expansion of the universe to accelerate. Chapline has dubbed the objects produced this way "dark energy stars".
Sweet. Now question is begged, where did all OUR vacuum energy come from? Bye bye multiverse. (Specualtion on my part.)
As for this stuff, I'm not expert enough to critique it, but my physics sense isn't getting the warm fuzzies. A black hole is a dead-simple geometric effect that pops out of General Relativity. It's really difficult to avoid having them, in fact. And while it's true that quantum mechanics isn't exactly comfortable with them, there's no way we'll know the correct reconciliation until we have a theory of quantum gravity in hand. Without that theory, I don't see how these gentlemen could have stumbled across the correct explanation.
And since they say that if we could study one close-up, the difference between a black hole and a "dark energy star" would be very subtle, I think I'm better off sticking with the simple, well-studied model instead of this abstruse one. (That's not to say they're wrong; just that their idea doesn't seem useful right now.)
Ah, the little-known Hawkins Theory of Pimpin'.
Yes, I take your point (follow the link to Motl's amusing critique of Chapline's work). I do think, though, that there's something to be said for encouraging a variety of approaches to fundamental questions. Just on principle.
This is very interesting stuff. I do like how someone is trying to incorporate quantum mechanics into the description of black holes. That is a very important, and fundamental, description. Perhaps this is an small, incremental step to reconcilling quantum mechanics with relativity. I suppose it won't be a clear reconcilliation until we can probe events at the Plack scale and maybe, detect and deduce any quantum nature of space. Personally, I am more comfortable with this explanation than envoking a singularity and not fully accounting for quantum properties of matter. Anyone know if the Large Hadreon Collider will be able to probe events in these energy scales? I thought I heard it could create mini black holes. If so, there is room for experiments in this area.
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