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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
If photonst have weight, they can be effected by gravity, and a black hole can form around any object with sufficient mass to trap light. That's all there is to it. There is no magical singularity where the laws of physics break down. There doesn't need to be.
...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.
That's heavy, Doc.
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...
This means that not only are we living in a simulation, but we're being run on a digital computer.
You appear to have no idea what's going on here. Okay, first of all, the Cosmic Censorship Hypothesis in question (short version): All singularities other than the one from the Big Bang are hidden behind event horizons.
The equations of relativity, which were used to run the simulation, say nothing about cosmic censorship. The C.S.H. wasn't formulated until 50-odd years after general relativity because of a problem - relativity actually readily admits (physically-implausible) solutions that do have naked singularities, hence the censorship. Apparently, something always conspires to hide them.
This simulation confirmed the hypothesis' prediction: Even in the most violent circumstances physically realizable, the singularity ended up behind an event horizon.
Frankly, it's time we admitted it... the only way we're going to find a naked singularity is to go for a joyride in the direction of the Great Attractor in a sycamore-seed-shaped ship.
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?
Time appears slow to the outside observer, for the object crossing the horizon it's business as usual, super fast acceleration, stretched out and sucked into oblivion. Lovely :)
But black holes exist within the universe. If time inside a black hole is stopped relative to the rest of the universe, then shouldn't a black hole take infinitely long to form?
As a corollary, shouldn't you be able to look behind you and watch the end of the universe?
I'll take the second point first. And believe me I'm no expert, I mearly take an interest in Astronomy and I've read quite a lot on the subject.
If you 'look' behind you as you enter a black hole you see the light that was entering immediately behind you so you see the static universe as you normally would. But as with a lot of complicated maths and physics, human language and common experience can't really serve as a metaphor for what is going on. It's an unfortunate answer to a great many questions.
Your first question I'm not too sure about, it is a very insightful question. After a black hole is formed then yeah, time slows down to a crawl *if* there was any way to look in (past the event horizon). But I don't really know how to explain the fact that as it creates a sigularity time should slow down. I think an important concept to understand is that there is no universal clock. Imagine everyone in different gravity wells running along different percieved time-scales and you be along the right tracks. Really I'm in over my head though!
Try here for an excellent podcast on black holes and the notes page has a ton of links. This is were I get most of my Astronomy info. The podcast really will stretch your immagination!
http://www.astronomycast.com/black-holes/episode-18-black-holes-big-and-small/
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.
Perhaps someone could educate me here but how accurate is this because surely we've never done any study into the effects of gravity at the speed of light. Doesn't gravity act differently at this speed?