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Black Holes Disputed
JScarpace writes: "Researchers at the Los Alamos National Laboratory in New Mexico and at the University of South Carolina in Columbia have proposed the existence of "gravastars" which are bubbles of superdense matter. If they are correct, the idea of a black hole with a singularity at the center may be just a fantasy."
Where do all my left socks go from the dryer?
From the outside, these objetcs would look exactly the same as the black holes that most astrophysicists currently believe in. The only difference is that there's no actual hole in the center, just a very dense lump of matter. If you got sucked into one, you'd be spread out over its surface, not stretched into a long string.
If this turns out to be true, the discovery will also cast a shadow of doubt over the big bang theory which also features a singularity.
So when did Alex Chiu get hired at Los Alamos? What with his revolutionary understanding of gravity, energy and the universe.
"I would say that 99 per cent of what my father has written about his own life is false." - L. Ron Hubbard Jr.
4 pages in your choice of formats here.
And I thought traditional black holes were wacky enough. According to this, it's possible that our entire universe is contained within one of these gravastars.
I've never heard of this site, but I must admit that was an extremely well-written article; they shoved a lot of physics in it but maintained a really high level of clarity (though it seems to based on a New Scientist article, so they may have just lifted passages from there).
A "singularity" is a point at which the gravitational force is infinite. This logically doesn't even make sense, so it's no wonder that it's disputed.
Cryptnotic
My other first post is car post.
New Theories Dispute the Existence of Black Holes
January 17, 2002 08:00 CDT
Two U.S. scientists have questioned the existence of black holes and suggested, in their place, the existence of an exotic bubble of superdense matter, an object they call a gravastar. The two are pointing out that physicists have swept some "humiliating" problems with black holes under the carpet. By confronting these problems, they claim to have found an alternative fate for a collapsing star.
Emil Mottola of the Los Alamos National Laboratory in New Mexico and Pawel Mazur of the University of South Carolina in Columbia think gravastars are cold, dense shells supported by a springy, weird space inside. They'd look like black holes, lit only by the material raining down onto them from outside. In fact, they seem to fit all the observational evidence for the existence of black holes.
So far, however, physicists have mixed feelings about the idea of gravastars. Their verdicts range from "outstandingly brilliant" to "unlikely." What's certain is that gravastars will rekindle a great debate of the early 20th century: are black holes fact or fantasy?
The idea of black holes dates back to the First World War, when German astronomer Karl Schwarzschild solved the equations of Einstein's newborn theory of gravity while serving on the Russian front. He showed that space-time around any massive star would be curved. Squeeze a large enough star into a tiny enough space and its density would become infinite and the curvature of space-time would spiral out of control. The gravity near one of these objects would be so strong that nothing -- not even photons -- could escape its grasp.
Einstein shared the view of most physicists of that time that such objects, later dubbed black holes, were too outrageous to exist. He argued that it was all academic anyway, since stars never shrink this small. But scientists gradually became convinced that they do. If a star is very massive, it will blast apart in a supernova explosion at the end of its life; and if a core twice as heavy as the Sun remains, no known force can prevent gravity squeezing it to a point.
The result is a "singularity" with infinite density, where the known laws of physics break down. The singularity's gravity would be so powerful it would be cloaked in an "event horizon", a boundary beyond which matter or light couldn't escape.
The dramatic idea of a black hole, which would rip to shreds anyone caught inside it, fired the imaginations of scientists, artists and writers alike. But no one has ever rooted the drama in fact.
"So far, there is no direct observational evidence to show that any of the things astronomers call black holes have event horizons or central singularities," says Neil Cornish, an astrophysicist at the University of Montana in Bozeman.
We know there are compact objects millions of times as heavy as the Sun that hog the centers of galaxies. These black hole candidates give themselves away because hot stars, gas and dust spiraling toward them emit bright X-rays. But that doesn't mean there's a cataclysmic black hole in the vicinity; it could simply be a very massive object. The debate petered out decades ago but there's still no ironclad proof that black holes exist.
There are enough problems in black-hole theory itself to make their existence seem implausible to say the least. These problems stem from the fact that our Universe is actually very different from the one that Schwarzschild considered. If we're to produce a proper description of the Universe we live in, Einstein's classical theories need to be meshed together with what we know about the quantum laws governing the behavior of fundamental particles and fields.
Mazur and Mottola have been thinking about quantum gravity for nearly a decade. They began by examining the nature of "quantum fluctuations" in space, time and even in energy fields. Empty space, for example, is never really empty.
On the tiniest scales, little particles are popping in and out of existence all the time, creating a seething, fluctuating fluid. "Like a fish in a calm pond, who is not aware of all the incessant jiggling of the water molecules, we are usually not aware of the quantum medium we are immersed in," Mottola said.
And they have found that quantum fluctuations in the electromagnetic fields that describe tiny things like photons can influence gravitational phenomena on the large scale-such as black holes. So, they reasoned, when early black hole theorists ignored quantum effects they were creating an unreal space-time.
This traditional approach to black holes has produced strange anomalies anyway, and these have remained unresolved, Mazur and Mottola claim. There are problems, for instance, with a black hole's entropy -- a measure of the amount of information it holds. An object that contains many possible states has high entropy, in the same way that a computer with more bits of memory can store more information.
When a star forms a black hole, all the unique information about the star -- its chemical composition, for instance -- appears to be squashed out of existence. Yet current theory suggests black holes have enormous entropy -- a billion, billion times that of the star that formed them. No one can fathom where all this extra entropy comes from or where it resides. "Where are all these zillions of states hiding in a black hole?" says Mottola. "It is quite literally incomprehensible."
Another seemingly impossible feature is that photons falling into a black hole would gain an infinite amount of energy by the time they reach the event horizon. But the gravitational effects of this enormous energy are ignored in the classical theory. Mottola says these problems have forced physicists to dream up far-fetched excuses. They say, for example, that some of the black hole's entropy might be hidden in other universes.
Mottola doesn't buy these "esoteric assumptions" and concludes that black holes are a bag of contradictions that don't make a good case for their own existence at all.
But is there an alternative? Could it be that when a star collapses, something happens to prevent a black hole forming? Mazur and Mottola think so. They have shown that quantum effects can make space-time change into a new and curious state that would lead to the formation of a strange new object.
That change is a phase transition, like liquid water turning into a solid block of ice. They believe that in the extreme conditions of a collapsing star, space-time undergoes a quantum version of a phase transition. The phenomenon is nothing new. The Nobel Prize for Physics in 2001 was awarded for the observation of just such an event in the lab: the transformation of a cloud of atoms into one huge "super-atom," a Bose-Einstein Condensate (BEC). This clump of atoms, which all share the same quantum state, forms at temperatures within a whisker of absolute zero.
When an event horizon is about to form around a collapsing star, Mazur and Mottola believe that the huge gravitational field distorts the quantum fluctuations in space-time. These fluctuations would become so huge they would trigger a radical change in space-time, very similar to the formation of a BEC.
This would create a condensate bubble. It would be surrounded by a thin spherical shell composed of gravitational energy, a kind of stationary shock wave in space-time sitting exactly where the event horizon of a black hole would traditionally be. The formation of this condensate would radically alter the space-time inside the shell.
According to Mazur and Mottola's calculations, it would exert an outward pressure. Because of this, infalling matter inside the shell would do a U-turn and head back out to the shell, while matter outside the shell would still rain down on it.
In a paper submitted to Physical Review Letters, Mazur and Mottola have shown that, like classical black holes, gravastars are a stable solution of Einstein's equations. What's exciting, they say, is that gravastars don't suffer any of the mathematical ailments of black holes.
There's no riotous singularity where the laws of physics break down. There's no event horizon to imprison light and matter. And the entropy of a gravastar would be much lower than that of any star that might collapse to form it, dodging the problem of excessive entropy that plagues black holes.
Take a gravastar with a mass 50 times that of the Sun, for example. Like the event horizon of a black hole with the same mass, the shell would be roughly 300 kilometers in diameter. But it would be around just 10-35 meters thick. Just a teaspoonful of the material would weigh about 100 million tons. But Mazur and Mottola have shown it would have a temperature of only about 10 billionths of a degree above absolute zero. And it wouldn't emit any radiation, making it as black as any black hole would be.
Gravastars would be just as much fun for sci-fi buffs -- in fact, they'd be even more ruthless. Imagine a black hole of a million solar masses, like the one thought to sit in the center of our Galaxy. You could cross its event horizon without feeling a thing: it's only as you approached the singularity that you'd be torn apart by the huge gravity gradient. But if you were drifting toward a gravastar of the same size, you'd never get anywhere near its center. As soon as you hit the shell you'd explode into pure gravitational energy.
Marek Abramowicz, an expert on black holes at Gothenburg University in Sweden, calls the idea of gravastars "outstandingly brilliant. Their unique and remarkable properties could explain several high-energy astrophysical phenomena that now are puzzling." He thinks they might explain gamma-ray bursts -- ultra-intense flashes of gamma radiation from a distant source that appear somewhere in the sky about once a day.
Astronomers aren't certain what causes gamma-ray bursts. It might be the formation of a black hole in a supernova explosion, but this process would struggle to muster enough energy. The birth of a gravastar, on the other hand, would be extraordinarily violent and might shed enough energy to account for gamma-ray bursts.
Mottola points to another possible connection between gravastars and astronomical observations. Three years ago, data from distant stellar explosions suggested that the expansion of the Universe is getting faster all the time (New Scientist, 11 April 1998, p 26). Many physicists ascribe this acceleration to a mysterious "dark energy" that gives space an outward pressure.
Mottola says that if you scale the size of a gravastar up to around the size of the visible Universe, the pressure of the vacuum inside roughly matches the pressure that seems to be accelerating the expansion of the Universe. So our Universe might be one big cosmic gravastar: a giant shell trapping the Milky Way and all the other galaxies we see. "We might be able to entertain the really radical notion that we -- and everything we see in the Universe -- could be inside such an object," Mottola speculates.
It's a bold claim, and he and Mazur are still working out whether it's justifiable. Unlike their hypothetical gravastar, the Universe contains copious ordinary matter and its visible edge is always ballooning outward. But they're keen to see what happens when they modify their gravastar model to include these complications. "It is certainly premature at this point, but the seeds of a possible new cosmological model are contained in the gravastar solution," says Mottola.
In the meantime, they are trying to figure out how they could tell ordinary-sized black holes and gravastars apart. The differences might be subtle -- after all, in isolation, they're both dark and the gravitational fields outside a black hole event horizon and the gravastar shell would be the same. But a good guess would be that gravastars would shine more brightly, since matter falling onto one would be turned into radiation. Black holes would gobble all the matter, but a gravastar would let its energy escape.
The next step is to identify the telltale signs of a gravastar, Mottola said. "It is the only way to convince the skeptical-including ourselves-that nature really behaves this way." Yet physicists aren't even sure what black holes look like.
In October last year, they reported seeing what appeared to be a heavyweight black hole, but material falling onto it is emitting far brighter X-rays than theories predict. The excess energy is roughly equivalent to the output of 10 billion Suns. If it is a black hole, it's not clear why it's so bright.
The object may be whirling round and dragging magnetic fields at the event horizon with it, and these could generate the extra energy by whipping up and heating nearby gases. But Mazur thinks there's a better explanation for that extra energy. The "black hole" could be a gravastar, he says. Stars, gas and dust raining down onto its shell would violently dissolve into pure gravitational energy that might emerge as bright X-rays.
To try to resolve this issue, Mazur is working out what a rotating gravastar might look like. Like every other compact object in the Universe, a gravastar would almost certainly be spinning rapidly.
Not all astronomers are as enthusiastic about gravastars. Cornish questions whether an exploding star could really lose enough entropy to form a gravastar, given that the second law of thermodynamics says that the entropy of an isolated object will always tend to increase.
"In other words, a cup can break into a thousand pieces, but it is highly unlikely that a thousand shards of pottery will spontaneously come together to form a cup," says Cornish. "Mazur and Mottola talk about a star shedding entropy in some way to make the formation of a gravastar possible, but I don't think that is a likely scenario." But Mottola points out that when exploding stars form other remnants, such as neutron stars, they do shed entropy.
And although Cornish admits that black hole singularities are mathematically troublesome, he also believes that a satisfactory quantum theory of gravity will cure this problem. Then there'll be no need for gravastars, he says. Robert Wald of Chicago University adds that Mottola and Mazur have put forward no arguments about how gravastars could form in the devastating collapse of a massive star.
Even if they did form, how would they survive the onslaught of matter raining down on them? "What happens if a gravastar has accreting matter showered upon it? Won't it collapse to a black hole?" he says.
"The gravastar is stable," counters Mottola. He says that matter falling onto the shell could make it wiggle and radiate away energy, but because the gravitational pull of the shell balances the force of the springy vacuum inside, it couldn't actually collapse. Any matter that fell onto the shell would simply become part of it, he says.
All the same, Mottola and Mazur admit there are still unsolved issues with the formation of gravastars. "We must have a better idea of how this phase transition actually occurs in the gravitational collapse process," says Mottola.
The exact nature of the exotic stuff inside the gravastar shell is still open to debate, and they hope to find out whether gravastars can really form in the mayhem of a star's violent death -- and whether gravastars could merge to form the heavyweight objects that sit at the center of galaxies. They are encouraging others to join the investigation. "There are many unanswered questions and we are really just opening a new direction for future research," says Mottola.
But if gravastars can weather the controversy, then maybe there'll no longer be any need for black holes -- maybe they really are pure fantasy. It wouldn't be the first time that Einstein's dazzling intuition has been proved correct.
Source: New Scientist
Cosmiverse Staff Writer
What I do find interesting is that this gravastar model, like the black hole model, implies that the universe and black holes/gravastars are similar in nature: that they belong to the same class of objects. It is a wonderful puzzle to look into a black hole wondering "what's IN there", when the answer might be something that has qualities similar to the life-cycle of our own cosmos.
Until we get some solid predictions about ways to differentiate one from the other, this is going to be a purely theoretical debate. Hopefully someone can advance the debate into the experimental realm soon. Maybe the new gravitational observatories can "shed some light" on this shadowy subject. ;)
I've got a bad attitude and karma to burn. Go ahead. Mod me down.
And now every single Linux user on the planet will chime in with their own expert opinion on this topic
/., because that is what you will get alot of. For better or worse people are free to post here even if they aren't an expert.
But isn't that the point of slashdot?
I mean, this is a discussion forum, and most people here want to read and post.
Perhaps if that bugs you, you shouldn't read
Michael
There is no cryptographic solution to the problem where the intended receiver and the attacker are the same entity.
Fine, I shall rename them.
From now on they will be referred to as Doom Spheres.
I'm glad to see that the anti-MS sentiment is applicable to the science of astronomy. I'd be so disappointed if this kind of thinking was only relevant in the limited context of the software industry.
The state is the great fiction by which everyone tries to live at the expense of everybody else. ~F. Bastiat
Of course, to observe that this accounts for much of the traffic on Slashdot is itself not terribly insightful.
Two U.S. scientists have questioned the existence of black holes both seem to be superdense not that this matters. The theroy is currently only supported by a springy, weird space the pair cannot explain. So far, however, physicists have mixed feelings about the idea of gravastars. Their verdicts range from "outstandingly brilliant" to "unlikely." as we can see this 'outstandingly brilliant' is obviously 'unlikely' due to the fact that The gravity near one of these objects would be so strong that nothing -- not even photons [light] -- could escape its grasp. However, The exact nature of the exotic stuff inside the gravastar shell is still open to debate, as any man and his dog's guess can be supported maybe there'll no longer be any need for black holes -- maybe they really are pure fantasy. To the dismay of Sci Fi writers arround the globe.
Source: Old Scientist
Escape velocity not only depends on the mass, but also on the distance from the center. In a black hole, escape velocity only exceeds the speed of light if you get closer than the event horizon.
Now, if for some reason the necessary mass would not fit into the event horizon, no black hole could occur. This new theory stipulates that if you have such a huge mass, it will actually form a hollow sphere where much of the mass is actually concentrated outside of the event horizon. Now, a hollow sphere has the following "interesting" properties (or would have, in classical mechanics):
- outside the spere it is the same as for a point mass: mM/r^2
- within the shell it would be approximately linear in r: mM*(r-r_inner)/r_outer^2/(r_outer-r_inner)
- inside, it would be zero
Probably this is not 100% exact, as we're in a relativistic context here, rather than a classical one, but we can still presume that gravity inside the sphere would be much weaker than outside.(approximative formula, for "thin" shells)
This would basically mean that you would not have an escape velocity exceeding the speed of light anywhere:
Say no to software patents.
Ok, my physics is a little rusty but.. this doesn't make sense.
As the article mentions - you just CANT go around violating the second law of thermodynamics like they do (i.e. for a gravstar to form it must 'lose' entropy).
According to these guys the spherical outer shell (a standing gravitational wave) would balance out with the incoming matter. Now waiiit just a minute. Eventually the matter on the shell would exceed the force of the inner substance supporting it - then what do you have? They say that it would cause the sphere to wiggle and radiate away energy - well every struture has it's limits, what would happen when, say, a more massive gravstar impacts a less massive gravstar? Or two gravstars of equal mass impact each other?
Just b/c our understanding of physics breaks down at the singularity doesn't mean it does not exist (remember we can't describe in physical terms just what the first few picoseconds of the big bang where like - the physics just can't cope with the amount of matter/energy involved).
Now, we can *never* actually observe a black hole (God Abhors a Naked Singularity) which doesn't mean they don't exist.
"infalling matter inside the shell would do a U-turn and head back out to the shell, while matter outside the shell would still rain down on it." TO do so the matter woudl have to exceed the speed of light. Right.
Occam's Razor -- These guys say that there are a lot of discrepancies in the Black Hole theory that are unanswered, and provide alternate explanations. There are some problems with their own theory --
...whether an exploding star could really lose enough entropy to form a gravastar, given that the second law of thermodynamics says that the entropy of an isolated object will always tend to increase.
That point in itself would be against the gravistar theory. Because, they themselves have admitted that there have been mathematical shortcomings. The implication of this is that quantum behaviour _can_ stabilise, in which case, we would have had BEC occuring naturally, which is not the case.
"The gravastar is stable," counters Mottola. He says that matter falling onto the shell could make it wiggle and radiate away energy, but because the gravitational pull of the shell balances the force of the springy vacuum inside, it couldn't actually collapse. Any matter that fell onto the shell would simply become part of it, he says.
It is easier to accept the Black Hole theory. Just consider the Chandrashekar limit for example - if you are withing range, you are absorbed, else you are pulled closer. And since photons themselves have been proved to be absorbed by these, there is evidence of even horizon. But in this, we would be having an evergrowing event horizon. Given the age of the universe, if the horizon _does_ grow, just imagine for a moment what this means. Heck, there would absolutely no chance of survival for giant stars, which is not the case. Agreed, could be anamolies, but nevertheless worth a thought, right?
IMHO, as someone with experience in particle physics (I've worked on SQUIDS), I feel that this theory has a lot of points which need to be ironed out.
SEATTLE - Bill Gates, richest man in the world, announced late Friday evening, that in keeping with his company's new policy of "Discover Your World" he would be putting 30 billion dollars into funding a trip to the far reaches of outer space to finally put an answer to the question, " What is a black hole?"
"We must strive to stretch our horizons" Mr. Gates said while unveiling a mock up spacecraft. "The Qube is singularly revolutionary - it is controlled via neural networks which interface between the ship with these nifty lasers that go over one eye."
However skeptics maintain that information will not be able to travel back from the ship even if it does collect scientific data about the nature of black holes. Microsoft, however, seems unfazed; "We realize at the current time, that issue may cause us problems, though we aren't worried - we work best under deadlines - take our release of windows 97 . . . well that's a bad example, umm. . . Microsoft has a great team that helps us get out of tight situations - take the DOJ trials - no one expected us to come out of that scot-free."
Top Enron executives also expressed interest in coming along for the trip, and plan on funding their portion selling Enron Ethics Handbooks on Ebay , with a source close to the vice president mentioning that "Anyplace would be better than here when our employees find us." - a view shared by Garth Wayne Johnson, Ken Lay's future cellmate in New York's "Ban Gurahz" prison, "Ah no dat da eron beetches ah gonna be ah hoes, so dey nee' packtis an' shit!"
The universe is expanding yes? What is it expanding into?
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These problems stem from the fact that our Universe is actually very different from the one that Schwarzschild considered. If we're to produce a proper description of the Universe we live in, Einstein's classical theories need to be meshed together with what we know about the quantum laws governing the behavior of fundamental particles and fields.
Ofcourse. And that is what the Unified Field Theory is all about. In fact, if only gravitons could be proved to exist, then there is a very high probability of the existence of the UFT. In fact, there are just 6 universal constants which need to be meshed in with their corresponding DEs to get the UFT up and running. Which, I'd say, seems simpler than what these guys may have to offer. Are these guys trying imply that UFT does not exist?
They believe that in the extreme conditions of a collapsing star, space-time undergoes a quantum version of a phase transition. The phenomenon is nothing new. The Nobel Prize for Physics in 2001 was awarded for the observation of just such an event in the lab: the transformation of a cloud of atoms into one huge "super-atom," a Bose-Einstein Condensate (BEC). This clump of atoms, which all share the same quantum state, forms at temperatures within a whisker of absolute zero.
In this context, are these people trying to say that the gravistar behaves as a BEC? That makes it a hell lot more complex because you will need really low temperatures, and adding more particles rushing to you at the speed of light increases the temperature and the entropy, both of which their theory goes against. Also Bosons (which are carrier particles, having an integer spin measured in the units of h-bar) would all possess exactly the same quantum state. So considering the existence of identical entities elsewhere, we could jump to any of these thingys just like that. Or any matter trapped in even one of these, could be spread across multiple copies of these entities.
The implications are really wierd, I somehow feel that Black Hole theories were a lot more plausible.
The reason wasn't that I'm particulary skeptical about black hole theory, but that I figured I really didn't need to assume anything about it, as long as all the other assumptions I make hold (which they won't, but that's an entirely different matter :-) ). The central engine of quasars can be whatever it likes... :-)
My knee-jerk reaction to the article posted was that it seems like the gravastar isn't allowed to grow, and it has to grow, right? However, skimming the researcher's preprint, it seems like they are addressing the issue, so it is probably just something I've missed. Besides, there'll be enough knee-jerk postings here... :-)
Employee of Inrupt, Project Release Manager and Community Manager for Solid
I know this is modded down, but it actually is something to think about.
Maybe that 'light' people see is your 'soul'[?] escaping from the gravastar or what-not.
Although, I've seen plenty of reports that say that the 'light' and euphoria is nothing more than a LSD trip your brain makes up to mask the horrible pain of dying.
Get your Unix fortune now!
It's not as if it needs another one, is it? (-:
On a more serious note, the theory will simply get re-engineered and tweaked and plastered over until a new unproveable conjecture happens along. But it must be one which doesn't smack of Young Earth Creationism, or otherwise - as Richard Lewontin wrote - ``allow a Divine Foot in the door''.
My guess is: when the time comes to admit that the new idea is much sexier (it does have a springy foundation, after all), the small differences between a Cosmic Egg and a First Cosmic Balloon won't get anyone but theorists too excited.
If it involves balloons, though, MacDonalds will want it attributed to Ronald.
Got time? Spend some of it coding or testing
>Anyone see the problem with that? The first
>problem is that no reason is given for the
>airstream over the top to have to meet up
>with the airstreem under the bottom. Why
>can't it just flow straight back?
See here for one of many explanations of the Kutta condition, one of the foundational principles of aerodynamics. This has nothing to do with an explanation for the layman. Basically, it states that the air MUST meet smoothly at the back of the wing.
Logically, if you spend some time thinking about the flow, you cannot possibly construct a situation where the air above the wing somehow slips past the air below. Remember that a jet moves so fast that its wing is only passing through a portion of the air for fractions of a second - it's simply not possible to make the air move fast enough to slip like this.
This principle has been demonstrated NUMEROUS times. You can demonstrate it very easily with a line of smoke through which a wing passes, among a zillion other simple experiments.
--Brandon / Split Infinity Music
Some of the serious expose material should be more than side-splitting enough by itself, however...
I think there'd have to be a Balderdash edition as well, where people put in realistic-sounding explanations that are either total and deliberate frauds and/or proposed by people who really have no idea (like my ex-wide, who asked me (and this is a literal quote) ``I've always wondered, how do they get the batteries into battery chickens?'').
Dawkin's weasel would have to feature in the Balderdash book, together with Haeckel's ontogeny recapitulating phylogeny and that wonderful theory of electricity involving different coloured electricity for the different colours of traffic lights and so on.
Got time? Spend some of it coding or testing
"...gravastars are cold, dense shells supported by a springy, weird space inside."
Black holes are really Moon Pies?
No, I actually meant LSD.
I saw a HUGE thing long ago about near death experiences, and some scientists said the brain goes through a LSD trip. While there is no LSD [of course] there is the 'trip'.
Get your Unix fortune now!
Hey, it even says so, in bold: Stating that the fluid flowing above the airfoil is accelerated with respect to the fluid flowing below it ``because it must travel for a longer route in the same time'' is then definitely wrong. Betrayed but your own reference texts, eh?
As harlows_monkey says, in order to understand why the streams do meet if there is a correct angle of attack, you do need deeper insight into aerodynamics than is spelled out in the simple "lay-man's" explanation.
Say no to software patents.
"That doesn't make sense."
Nobody ever said quantum mechanics made sense, either (and if they did, they're lying). But not making sense doesn't mean it's not right.
Having studied basic fluid mechanics, I think the two explanations, via vortices and speed differences, are essentially equivalent. A vortex flow around the wing is equivalent to the velocity difference that is the usual explanation. If you compute the force either via the vortex effect, or via the pressure difference, you should get the same answer. The vortex approach is more sophisticated, so it is almost always the other explanation that is given to laymen.
--
The Cap is nigh. Time to get a fresh new account.
How does the recent observation of quantum gravity effects change the model of either singularities or "gravistars?"
Not LSD, ketamine. Obviously in the typical NDE there is no ketamine. but there are several other mechanisms in the brain that may produce the effect.
Tom Swiss | the infamous tms | my blog
You cannot wash away blood with blood
A famous former surgeon general discovered the first of these monsters a few years ago, and named it drkoop.com (the .com designation is often used to help identify black holes). Then there was altavista.com, webvan.com, and many others.
The escape velocity exceeds the speed of VC money. Since nothing can go faster than VC money...
Enron, by the way, is not a black hole. It's a pulsar -- a dead star that regularly flashes us with reminders that it's dead ("Enron doesn't have any money," "Enron doesn't have any money," Enron doesn't have any money," etc.).
So the stae of matter below the horizon has NOTHING to do with properties of the such a compact object above it. This is because of causality - there is no information flow from behind the horizon..
<^>_<(ô ô)>_<^>
Modern physics is anything but "voodoo". In fact, the whole point of it is that it is open to independent verification. You don't HAVE to be a "priest" to weigh in. What you DO have to do is put in the intellectual effort to understand what has already been done; learn some math, learn some physics, and nuclear chemistry - then you can examine the evidence for yourself.
Big Bang: take a simple spectrograph and a telescope (e.g. the Mt. Wilson 100-inch, which you can rent time on). Look at a sample of distant galaxies. Measure the wavelength of the hydrogen emission line (which is doppler shifted according to the relative velocity between the telescope and the galaxy); you'll see that the more distant the galaxy is, the faster it is receeding from you. Think about what that implies about the past. Certainly the simplest (if not the only) answer is that in the past the galaxies were closer to each other than they are now - ultimately at some point they would have to come from a single point.
It goes on and on - but the point I'm trying to make is that you shouln't treat modern physics as some kind of revealed religion. Instead, understand the evidence for and against the various theories - but also give the honest effort to learn the tools of modern science (above all math, but also physics, chemistry & astronomy).
If you don't then you're just spouting an uninformed opinion - and there are too many of those on /. already!
Human genome = 3 billion base pairs = 6 GBit. Windows + Office = 20 Gbit. Which is more impressive?
It's not just your theory, Occam's Razor, when applied to Black Holes, fails too.
:-P
From their paper -
Further, when a massless field such as that of the pho-ton is quantized in the fixed Schwarzschild background, one finds that the black hole radiates these quanta witha thermal spectrum at the asymptotic Hawking temperature TH = _h/8*kBGM [1]. The inverse dependence of TH on M implies that a black hole in thermal equilibriumwith its own Hawking radiation has negative specific heat.
In fact, that point in itself is a strong OR against BHs. But anyways, coming back....
Well, I reasoned Occam's Razor for the following reasons -
From the paper:
Energy conservation plus a thermal radiation spec-
trum imply that the black hole has an enormous entropy, S 10 77 k (M=M ) 2 [3]
Laws of thermodynamics clearly define that Entropy is on the rise. Given the amount of matter in a BH, this is acceptable (although theories on where these are a little wierd).
The novel assumption required for this solution to exist is that low energy gravity can undergo a vacuum rearrangement phase transition in the vicinity of r = RS, in which the energy density and eq. of state change.
Occam's Razor. Now just imagine a handful of dark matter in the vicinity, it no longer is _low_ gravity. I'd like to argue more technically, but I'd prefer it over e-mail than here.
Hence essentially all the mass of the
object comes from the energy density of the vacuum con-densate in the interior, even though the shell is responsi-ble for all of its entropy.
Different entropy concentrations? It's as wierd as BH causing Hawking Radiation and a high entropy of S ~10^77 k (M=M )^2
Since theentropy of these objects is some 20 orders of magnitude smaller than that of a typical stellar progenitor, a violentprocess of entropy shedding, as in a supernova, is needed to produce a cold gravastar remnant.Explosive bursts in which a finite fraction of atoms are ejected have been observed in attractive BEC's in the laboratory
A laboratory is one thing, a naturally occuring phenomenon is another. I do not mean to be derisive, but I find entropy shedding a little too hard to believe.
Agreed, BECs can be formed at high density too, besides low temperatures, but just apply Occam's Razor here and you will see that this means.
These are presumably characterized by a finite density of vortices of normal phasepenetrating the condensate core. Such rotating gravitational vacuum condensate stars, dark `grava(c)stars' arecandidates for the stable remnants of stellar evolution for stars exceeding the Chandrasekhar limit.
....
The remnants are left in an excited oscillatory state afterwards.
Have these been observed outside the lab? There is evidence of what seem to be black holes. Occam's Razor.
Let's hope their paper doesn't include words like "zillions." Also:
But if gravastars can weather the controversy, then maybe there'll no longer be any need for black holes -- maybe they really are pure fantasy. It wouldn't be the first time that Einstein's dazzling intuition has been proved correct.
It also wouldn't be the first time his dazzling intuition has been proved wrong. Remember, Einstein didn't believe quantum mechanics was possible (at first, anyway).
-Legion
According to the article (in gr-qc/0109035, not the horrible thing linked from the /. article above), we essentially have a phase transition that results in an inflationary subspace inside this thin shell! I grant that, for some odd assumptions, this might be a stable solution, but I kind of doubt it. It has been proposed before that the collapse to a singularity triggers internal inflation, which is plausible but still gives a black hole, not a "gravstar".
Anyway, and I quote from their own article, "Here we forgo any discussion of the details of the quantum phase transition and present only the solution of Einstein's eqs." Mazur and Mottola have no clue how to make such a beast, either. If nothing else, the energy density wouldn't approach that needed for a phase transition until long after the entire assemblage was well within its own event horizon, again giving -- you guessed it! -- a Schwartzchild black hole. Recall, when a solid mass reaches the density required to fall within its own event horizon, the total density isn't much above nuclear densitites. During big bang baryosynthesis, densities are easily this large and inflation obviously didn't occur then (or else we'd have no protons in the universe).
Quantum mechanics: the dreams that stuff is made of.
So did I understand correctly that an attempt to fly through one of those would result in a severe case of indigestion? Of-course, with me every mission is a suicide mission, but still... Or will my body simply end its normal existence and would be transformed instantly into some amount of gravitational energy and some X-Rays? Then you can call me the X-Ray man!
You can't handle the truth.
How about Sinistar?
Hah! Well-picked... but actually, she's skinnier (and always has been) than her less-broken more-honest replacement.
Got time? Spend some of it coding or testing
Probably this is not 100% exact, as we're in a relativistic context here, rather than a classical one, but we can still presume that gravity inside the sphere would be much weaker than outside.
:) ). Now, if the mass of the object is gravitationally bound into the shape of a shell, how does the shell remain in a stable orbit? It seems to me that this is an unstable sort of object, and is doomed to collapse into a black hole.
:)
Yep. But this is a sketchy line of reasoning. Even outside of the event horizons of Schwarzchild black holes, there is a region where stable orbits cannot exist. So, if this thing has mass equal to that of a Schwarzchild hole smeared into a thin shell, it will act like a point mass to someone outside (neglecting tidal effects, which are also non-neglible around a black hole
Of course, I don't know all that much about meshing GR with QM (not that anyone does...), so I could be totally wrong
In Soviet Russia, sig types you!
>What this demonstrates: you don't need to reach escape velocity to get out of a gravity well.
:P
Well, of course not, if you assume infinite energy, which you have done by "Keep supplying enough force to keep the object moving away from earth at 10 miles/hour". In that sentence, you are really saying "provide enough power to counter gravity, whatever the hell it may be".
Escape velocity refers to a ballistic track, that is, one that doesn't have any acceleration other than the initial one. If you want to stop being ballistic, fine. Let's try it without assuming infinite energy, shall we?
A object cannot pass the speed of light because as it gets close to that speed, it takes more and more energy to do the pushing. Look, mass is energy, right? Well, when you accelerate an object, you pump a lot of energy into it. Therefore when you try to accelerate it some more, you're pushing not just the mass, but that energy you've pumped into it as well. This gives an obvious upper limit on how fast you can push it without having infinite energy. Do the math, and you get C in a vaccum. Thus, if we don't assume infinite energy, then we can't go any faster than light in a vaccum. And here's a neat trick: an upper limit on acceleration _also_ exists, because if we get it to a point where we can't push it any faster due to lack of power, then we're not really accelerating it, now are we?
Now, escape velocity of a black hole is higher than the speed of light. Since we don't have infinite energy, we ain't gonna get out ballistically. We also can't provide acceleration to counter gravity forever due to lack of infinite power to do so once we're inside the event horizon. Thus, you're stuck. QED.
In point of fact, you can't provide enough power to counter gravity at all, once you're below the event horizon. Gravity now has a pull that's higher than you can counter without infinite energy. Acceleration has an upper limit too, remember. So you can't even go away from the singularity, much less out. The only possible direction you can move becomes "towards the singularity". In some solutions, this is expressed by eventually solving out as -radius = +time. That is, forward in time becomes equivalent to going towards the singularity. It's a weird solution, but this is a natural consequence of not assuming the impossible.
- Give a man a fire and he's warm for a day, but set him on fire and he's warm for the rest of his life.
If I had moderator points today, I'd moderate you insightful just for spite. :)
What about QM doesn't make sense? Makes sense to me.
-- SIGFPE