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No Naked Black Holes
Science News reports on a paper to be published in Physical Review Letters in which an international team of researchers describes their computer simulation of the most violent collision imaginable: two black holes colliding head-on at nearly light-speed. Even in this extreme scenario, Roger Penrose's weak cosmic censorship hypothesis seems to hold — the resulting black hole (after the gravitational waves have died down) retains its event horizon. "Mathematically, 'naked' singularities, or those without event horizons, can exist, but physicists wouldn't know what to make of them. All known mechanisms for the formation of singularities also create an event horizon, and Penrose conjectured that there must be some physical principle — a 'cosmic censor' — that forbids singularity nakedness ..."
Oh jeez.
Does anyone else get sad at the thought that there are so many weird things in the universe you may not learn the answers to in your lifetime? What if everyone posting here never finds out the reason for the cosmic censor? Sort of depressing.
It's already asking a lot for nerdlings to not snicker at any reference to a "hole".
Adding in nakedness just goes beyond any reasonable expectation of restraint.
'a';DROP TABLE users; SELECT * FROM DATA WHERE name LIKE '%'... if you're reading this, it didn't work.
Penrose conjectured that there must be some physical principle â" a 'cosmic censor' â" that forbids singularity nakedness...
God, is that you?
Seems to me, most people on Slashdot likely *only* experience singularity nakedness.
Slashdot "libertarians": Small government for me, big government for those I disagree with. -1, I disagree with you
...the maximal Cauchy development of generic compact or asymptotically flat initial data is locally inextendible as a regular Lorentzian manifold.
Right?
Lemmings are silly; dinosaurs are extinct.
Heh... I knew who Roger Penrose was long before I heard of Richard Dawkins, and I suspect that I'll forget who Richard Dawkins soon enough. But I'm biased for being a physicist.
And the boom from a black hole is usually in the form of X-rays or gamma rays radiation and, in energetic terms, it's very loud.
Doesn't it make you feel good to know that our freedoms are protected by politicans, lawyers and journalists.
Quantum physics was baffling to me (still is, actually), but I eventually came to see it as a way that nature avoided some inherent paradoxes and contradictions that were present when you took classic physics down to the level of fundamental particles. I have no doubt that, on a larger scale, the same principle applies: Somehow, someway, the laws of physics will always resolve with no singularities, no contradictions, no divide-by-zero-error, no infinities. If our formulas seem to indicate that one will be found, I suspect our understanding is incomplete.
In other words, yo momma's so fat, her Schwarzchild radius is visible to the naked eye?
Which is why the DVDs "Physicists Gone Wild" were never really successful. Although the LHC did turn up as the hottest collider in Europe, so far still no naked singularities.
It must have been something you assimilated. . . .
You had me at naked...
If I'm recalling correctly Hawking addressed that issue in Brief(Briefer?) History of Time. He explained that for small black holes the difference in how strongly gravity is pulling one end of you(feet) compared to the other end(head) would tear you apart before you could reach the event horizon. Large black holes (on the order of millions of stellar masses, like the ones at the center of galaxies) would be a much more gentle ride intially. In fact he said, you could pass right through the event horizon and not notice anything particularly weird happening. You wouldn't even notice. Nevertheless as you get closer to the singularity at the center you'd still get ripped apart.
A few years ago, I might have agreed with you. After all, on a basic level you are correct, if we program what we know into a simulation, the simulation will be based on what we know!
Last semester I took a class in complex system, and it really opened my eyes about what computer simulations can do for us in providing unexpected behavior. Most of this is because we have a pretty good grasp on simple systems, and can take those simple systems and program them into a computer with rules of interaction to see how they will interact without human guidance.
Let me give you an example: Most everyone here at one point of time or another have programed "Life" into a computer. We understand the rules, we understand the program itself, and we understand how everything is going to work, but until you actually run the program, you would never have expected the results! How could you have predicted the formations that would develop? The stable formations, the chaotic formations, the moving formations? Much less how these formations would interact when they collide?
I think in a way this is what was being simulated in the program mentioned above. We think we have a pretty good idea about the simple systems which make up a complex entity like a black hole. But how do these simple systems interact when they encroach upon another black hole? Assuming we really do understand these simple systems, and that they stay constant, I think this simulation gives us a reasonable expectation as to how black holes will react to a collision.
I haven't lost my mind!
It is backed up on disk...somewhere...
...the most violent collision imaginable: two black holes colliding head-on at nearly light-speed.
What about 3 black holes colliding head-on at nearly light-speed?
All the mass of a black hole is compacted into an extremely small region at the centre - possibly infinitely small, but at the very least as small as physics allows matter to get. This is the singularity.
When we speak of the size of a black hole, we're actually referring to the region around that central object from which nothing can escape. As you approach the black hole, the gravitational field gets stronger and stronger, and there's a point of no return at which the escape velocity reaches c, the speed of light. Nothing nearer the hole than this can ever escape. This we call the event horizon - because no events beyond the horizon can ever be observed from outside. The more massive the hole, the further out the event horizon: look up 'Schwarzschild radius' for the equation.
The result of this is that any singularities in the universe are expected to be hidden behind event horizons, and cannot be seen. It's occasionally suggested that a naked singularity might form - for instance, a black hole might be spinning so fast as to counteract the effect of gravity and allow the singularity to be viewed from outside. This could have extremely bizarre results for the universe as a whole, so most physicists expect there to be some kind of 'cosmic censorship' principle that ensures that this does not happen. What we're looking at here is one way in which that might happen.
Real Daleks don't climb stairs - they level the building.
Anything based on a computer simulation is based on our arbitrarily incomplete knowledge. To base even the least significant conclusions upon it seems laughably irresponsible and unscientific.
We eagerly await your analytical solution to the n-body-problem. I mean, it's really simple stuff, right?
Until you're finished, we'll have to calculate all those spacecraft trajectories with computer simulations.
But if time is moving infinitely slow, then how does matter ever get to the center? Shouldn't all the matter be concentrated at the event horizon?
Remarkably well said.
A black hole isn't some mystical thing unrelated to the other cosmological objects. Black holes are just stars that have consumed most of their fuel through fusion over billions of years, then collapsed. But consumed doesn't mean the mass is all 'burned up' and gone, but converted from hydrogen and helium into heavier elements that are harder to participate in further fusion reactions, resulting in decreasing internal pressure from energy being released by the star. If the conditions are right, the compacting force of gravity from all the 'star stuff' that's left exceeds the declining expansive pressure provided by the fizzling nuclear reactions inside the star, and it ultimately collapses into an incredibly small size. If the size is less than the Schwarzschild radius, it will become a black hole.
But it's still just a lump of star stuff with mass like what the star had, but in a dramatically smaller package. It doesn't suddenly go on a cosmic rampage, marauding around and sucking up everything in sight. If something external has sufficient distance and velocity that it would have flown by or orbited the former star, then it will fly by or orbit the hole, as these parameters are solely determined by the masses of the star/hole and the external thing. If something would have fallen into the star, it will fall into the hole as well. Whether it falls into a black hole or a star, it's not coming back out.
Astronomers infer the properties of black holes from what they can observe about the objects that are influenced by them, and from what they observe about the progression of stars throughout their lifetimes. Just because we can't see into black holes doesn't mean they are totally mysterious.
Against stupidity, the Gods themselves contend in vain. --Friederich Schiller
A photon is not subjected to the flow of time at all since it travels at the speed of light, and thus has a time dilation factor of infinity compared with any other frame of reference.
So pity not the photon, for even an eternity is less than a moment to it.