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Man-Made Black Holes Looming?
camusflage writes: "The New York Times has a story that some physicists think it might be possible to make black holes at the under construction Large Hadron Collider at CERN, slated to come online in 2006. Trying to allay concerns about a man-made black hole blipping us out of existence, they say "The same calculations ... predict that around 100 such black holes a year are `organically' and apparently safely produced in the earth's atmosphere in cosmic ray collisions." As long as we can keep critters from building nests in the singularity, we should be okay."
As everyone knows, gravity is the weakest of all the fundamental forces by a very very long way, something like 40 orders of magnitude weaker than the weakest of the nuclear forces. I remember reading an article here long ago (can't find it and put a link to it because Slashdot search is down...grr) that talked about some speculation that gravity is so weak because the universe has more dimensions than the four that we see (this is also a prediction of superstring theory), and while the other three forces are only capable of propagating there, gravity is able to propagate through these extra dimensions, making it seem weaker. These dimensions are supposed to be curled up small so we don't normally notice them, so one of the implications of this theory is that the value of the universal gravitational "constant" should shoot up dramatically when you try to measure it at smaller scales; the smallest scale at which gravity has been measured so far is on the order of centimeters only. Another implication is that it should be possible to create low mass black holes with less energy than the weakness of gravity as we know it predicts. So if these scientists are successful in making such small black holes, it could go a long way to validating this theory.
Qu'on me donne six lignes écrites de la main du plus honnête homme, j'y trouverai de quoi le faire pendre.
Black holes have a reputation for being mass-gobbling irreversible singularities, and they are. But this doesn't mean a black hole where the Sun is would swallow the Earth. I'm not an expert so someone can correct me if they know it better or more accurately.
Any amount of mass can be turned into a black hole - you just have to crush it into a small enough space. This is because every bit of matter has an event horizon, including the Sun (or the Earth for that matter). The difference with the Sun and most things is that the event horizon for the amount of matter in the sun is smaller than the Sun. If you crushed all of Sun's matter into a sufficiently tiny space that it was all inside, then everything else that moved inside would collapse and not return.
What most people don't realise is that if the Sun spontaneously turned into a black hole, we wouldn't die from being sucked in. We'd die from lack of solar energy. Because the Sun-black-hole would have the same mass, everything orbiting it would continue to orbit it the same way it is at the moment. The only big difference would be when something happened to wander inside the event horizon at which point it wouldn't leave, if you ignore all the wierd relativity things that go on at that point at least.
So I guess the point is that just because someone says they might be able to make a black hole, it doesn't mean you'll be instantly sucked in tommorrow without any warning.
Fast forward a few years, scientists make a black hole. Why doesnt it destroy the earth?
1) The black hole weighs no more than the particles slammed together to make it. It has essentially zero pull on anything. A grain of salt would make an incredibly more effective attractor.
So you say, yes, but the black hole will persist and continue to grow in mass by swallowing more and more particles.
But the scientists in the Times article say the black hole will "evaporate".
The following paragraph, from this page, states it well:
Since the 1970s, it has been known that black holes are not completely black. In fact, they emit very low-energy radiation called Hawking radiation. The lower the mass of a black hole, the higher the energy of the emitted Hawking radiation. As a black hole radiates, its mass decreases, and it starts emitting more and more radiation, causing it to evaporate more and more rapidly. Eventually, it shrinks to around the Planck mass, the point at which its DeBroglie wavelength is equal to the Schwarzschild radius. At this point, we no longer know what happens, since to describe physics at the Planck scale requires a theory of quantum gravity.
From the article: We've been trying for a century, and we still don't fully understand black holes," said Dr. Andrew Strominger. And then he goes on to conclude that we need to make some.
If they're going to do something which at least sounds dangerous, I would really like it if they could say, "Nothing can possibly go wrong", not, "Our understanding is incomplete."
Actually, there's a pretty ironclad argument for this being safe - the same one that comes up every time the press starts fearmongering about more powerful accelerators:
Cosmic rays with energies far higher than will be produced by any accelerator any time soon have been striking the earth and the moon for billions of years. If high-energy collisioins could cause catastrophy, they would have already, because they've been happening in our neighbourhood for quite a while.
The fact that nothing around here has been sucked into a black hole yet leads us to conclude that if micro-black-holes can be formed, they don't do much.
Our current models of black holes suggest that micro-holes would evapourate in a burst of Hawking radiation almost as soon as they're formed. The smaller the hole, the more intense the Hawking radiation (and so the faster it loses mass).