World Science: Signs of dark matter found?

Treebore said:

I do think we should, when we don't know 99% of what there is to know about black holes. No one has gone out and confirmed the "mass" of a black hole. Its all inferred.

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Dude, listen to me for a moment.

Rule #1: Energy cannot be created nor destroyed. It can be borrowed only for very short times.

Rule #2: E=Mc^2

The theory that leads people to believe that the LHC may create black holes requires that these things be true. The mass of a black hole created in the LHC cannot be greater than what you get from the colliding beams. That energy is well known. That puts an upper limit on the mass of the black hole made there.

Basically, if you question that they're only going to be of small mass, then you question the very thing that tells you they'll be there at all! Please don't tell me you're going to use a theory to suggest a result might happen, but then throw away the theory and keep the result.

Black holes elsewhere can have far greater mass - but they were born of entire stars, not from puny particle beams.

Umbran and LT both make excellent points here, and they're quite correct. I'll just throw in that we actually know quite a bit about black holes. By saying that we've only "inferred" the mass of a black hole, for example, you have to say that we've only inferred the mass of the sun or the earth. Our ability to make some of these measurements in astrophysics may be relatively new (identifying where a black hole is and how much mass it has, for example), but the physics involved in the calculations is centuries old.

Not to mention, just repeating what has been said upthread, the entire LHC experiment has been repeated many times over not only on earth but in stars all around us by cosmic rays. If it were possible for a mini black hole to form and swallow up a planet or star, we'd have seen it happen already.

freyar said:

Not to mention, just repeating what has been said upthread, the entire LHC experiment has been repeated many times over not only on earth but in stars all around us by cosmic rays. If it were possible for a mini black hole to form and swallow up a planet or star, we'd have seen it happen already.

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*nod*. This is an important note. The LHC is not operating in an energy range where we're doing stuff that doesn't already normally happen in the universe around us. Cosmic rays interact at these energies all the time.

The problem is that the detectors necessary to get a good look at the things are huge and immobile. It isn't possible or practical to take them to the events - so, we build the LHC to bring the events to the detectors, so we can watch them.

Here. Discover magazine gives several reasons why this won't happen. The Bad Astronomer also weighs in.

The Bad Astronomer said:

However, studies done by CERN show that the energies generated will be too low to make black holes. Also, due to a weird effect called Hawking radiation, the tiny black holes would evaporate instantly. The two litigants, however, say that Hawking radiation is not an established fact, and therefore we should be more careful. While that’s technically true, they forgot something important: the same rules of quantum physics that make a black hole in a subatomic collision also indicate they would evaporate. So if you’re worried they won’t evaporate, then you shouldn’t be worried they’d be created in the first place.

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Ok, I'll declare immediately my utter ignorance in these matters, which (for good or bad) goes along with great interest. So I'd like to ask for a clarification.
When I briefly studied black holes at high school, what I understood f their nature is that they're born of the gravitational collapse of stars at the end of their "life", which would create an enormous gravitational force sucking in even light.Is this more or less right?
So my understanding was that a Vast amount of matter, translated into gravitational energy, is needed for a black hole to come in existance. How come they can be created by the collision of such a small quantity of matter?

One more comment. I'm not a "fanatic", nor an obscurantist, on the contrary I do study the nature of the world in my own, different, ways, and I am very curious about the new frontiers of science; I also understand there's not a reasonably chance that this experiment in particular will be immediately dangerous; but the fact, acknowledged, that scientists do not wish for the end of the world, does not render certain researches less potentially dangerous. After all, Einstein was a really nice guy, but his researches indirectly led to Atomic bombs, among other useful things.

Atanatotatos said:

Ok, I'll declare immediately my utter ignorance in these matters, which (for good or bad) goes along with great interest. So I'd like to ask for a clarification.
When I briefly studied black holes at high school, what I understood f their nature is that they're born of the gravitational collapse of stars at the end of their "life", which would create an enormous gravitational force sucking in even light.Is this more or less right?

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That's true for astrophysical black holes, ones we find evidence by looking around the sky. There are those born in the gravitational collapse of stars, like you say, which are typically about the same mass as our sun (to maybe a dozen or so times that). There are also supermassive black holes at the centers of galaxies (it's thought pretty much all decent-size galaxies have them, and we have very good evidence that there is indeed one at the center of our Milky Way galaxy) that are millions of solar masses. No one knows precisely how these were formed, but it probably happened in the early universe.

So my understanding was that a Vast amount of matter, translated into gravitational energy, is needed for a black hole to come in existance. How come they can be created by the collision of such a small quantity of matter?

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The question is, when is a certain amount of mass required by gravity to collapse into a point-like object, which is the black hole. The answer is that getting a certain amount of mass within a fixed radius causes collapse; this radius is bigger for bigger mass, and it's the radius of the final black hole. So a more massive black hole is larger in physical size.

So, you can have a black hole with a small mass if you can cram it into a tiny distance. With normal theories of gravity, this distance is incredibly tiny for subatomic particles (and more to the point, the energy/mass scales reached at the LHC). There are some proposed models in which gravity is actually secretly stronger than we thought (though still weaker than all the other forces) at the subatomic level. In that case, the distance needed wouldn't be quite so small, and black holes could be formed at the LHC. But, to put it mildly, these models are a real longshot to be good descriptions of reality.

One more comment. I'm not a "fanatic", nor an obscurantist, on the contrary I do study the nature of the world in my own, different, ways, and I am very curious about the new frontiers of science; I also understand there's not a reasonably chance that this experiment in particular will be immediately dangerous; but the fact, acknowledged, that scientists do not wish for the end of the world, does not render certain researches less potentially dangerous. After all, Einstein was a really nice guy, but his researches indirectly led to Atomic bombs, among other useful things.

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Oh, sure, but the point is that these scientists have made quite sure that this work isn't dangerous. In addition, even if someone had an idea to make LHC-type research dangerous, it would be much harder to do this than, say, make an atomic bomb. For example, building the LHC took a multi-national effort about 20 years to build, and that was built using some pre-existing facilities.

Freyar, thank you very much for you patience in explaining this so clearly.

freyar said:

The answer is that getting a certain amount of mass within a fixed radius causes collapse; this radius is bigger for bigger mass, and it's the radius of the final black hole. So a more massive black hole is larger in physical size.

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To give a bit of perspective on this...

A large star needs to collapse down to something like the size of the Earth (very roughly) in order to become a black hole.

The Earth would have to be compressed down into about the size of a small grape, or maybe a blueberry.

The Moon would have to be compressed down to a radius of less than one millimeter.

So, by extension, a black hole made out of the tiny mass of a few atoms would be very, very tiny indeed.

One more question. As far as I know, black holes are invisible directly (because light can't escape them), and are individuated thanks to the reaction of the nearby (astronomically speaking) matter. Right?
Then, even if a tiny, tiny black hole was created in an experiment like this, would it be observable? Would it be possible to register the reaction of nearby atoms to its existance?

You're right: astronomical black holes can be "observed" due to how they affect stuff around them. The most direct way is that the matter falling into the black hole gets compressed, heats up, and emits light (I believe x-rays for the solar-mass type ones, radio waves for the one at the center of the galaxy --- because that one is so much more massive, light loses more energy escaping the gravitational pull). So we can see the light that's emitted before the stuff falls into the black hole. Also, the black hole at the center of the galaxy has been observed by noticing that some stars around the center of the galaxy are orbiting something that's very heavy and very small very quickly. A black hole is about the only thing that it could be (and radio images make that even more dramatic).

Now, talking about possible micro-black holes: (1) Our best understanding of the quantum nature of black holes is that they have a temperature, and the smaller ones have a higher temperature. So these tiny black holes would emit a lot of stuff just because they're hot, like a fire emits light. But they have a small total amount of energy, so you'd just end up with a spray of particles coming out quickly. (2) If that's actually wrong, the black hole would just go flying out of the detector most likely without doing anything. This is actually a likely scenario for all kinds of discoveries that the LHC could make (including some other dark matter candidates, to get back to the OP). In that case, the detectors would notice the "missing momentum" -- all the energy and momentum of the particles are accounted for carefully, so something missing would be a big sign that something new has happened.