Just curious. Do we even know what we could learn or is it just something that sounds amazingly cool?
Well, for starters, physics as we now know it says that we can’t, under any realistic circumstances. So if we actually did, we’d learn that there’s something wrong with the physics we know, and the exact circumstances under which we accomplished the feat would tell us something about just what was wrong.
Plus, from the hole itself, we’d probably learn something about quantum gravity. At any mass where we could even plausibly create a black hole, quantum gravity effects would have to become relevant, either in the characteristics of the Hawking radiation, or in its lack. According to current theory, the typical energies of Hawking-radiated particles should be inversely proportional to the mass of the hole, but this implies a cross-over point (roughly at the Planck mass) where the emitted particles would each have more energy than the hole they came from. This is absurd, so clearly the current theory must break down at some point well short of that extreme extrapolation… But as of yet, we don’t know how it breaks down. Observing an actual tiny black hole should shed some light on that.
If we were lucky enough to find a micro-black hole somewhere in our solar system, it would be the most extreme test of General Relativity possible. It would be carefully observed and the observations measured against the predictions of GR. And if it was small enough to actually emit detectable Hawking radiation, then measurements of it would constrain possible theories of Quantum Gravity.
Maybe I’m mis-remembering the debate about the LHC, but I thought that we could create black holes. It’s just that they wouldn’t be produced very often and that such small black holes wouldn’t be particularly dangerous. (For example, this article here.) What am I missing?
Um…
So to speak I guess..
Some models did predict that the LHC could produce black holes, but those models were never mainstream, and were largely the result of what amounts to wishful thinking. It really would have been great if they had worked out, and the potential payoff was enough to justify a fair bit of investment of physicists’ time, but alas, they didn’t.
This article suggests you need energy levels 3,00,000 billion (three hundred thousand billion) times more than the LHC creates in order to theoretically create a mini black hole.
Well, we’d get to know what a black hole feels like…
As Chronos points out, creating a micro-BH would finally tell us that we’re wrong about something, which is probably the thing that every physicist is yearning for the most right now. So far, what the LHC’s told us is that our current ‘best’ model has been depressingly, boringly, even worryingly right about just everything—even the Higgs boson seems to have just the predicted properties, and nothing more.
So, finding a micro-BH would be hugely exciting for that reason alone, as it means new physics, of whatever kind. And if we’re lucky, the analysis of such a BH might even give us a hint as to where, precisely, we’re wrong, even more so since these objects live in a region where we’re pretty sure something must be wrong about our current understanding, namely the region where gravity and the quantum world clash, and our best theories give predictions that seem inconsistent with one another.
One theory, for example, which such black holes could yield evidence for is that of ‘large’ extra dimensions. As Chronos mentions, normally, creation of black holes is ludicrously beyond our current capacities—that is, beyond the energy levels we are capable of attaining. But, if there are extra dimensions, then the force of gravity might be much stronger on short distances—strong enough, perhaps, to create a black hole even with the modest energies we are able to achieve. So this would be one thing we could learn from black hole production: whether out universe has, besides the usual three, additional spacetime dimensions.
How would the creation/appearance/brief “stability” of a micro black hole (MBH) manifest itself?
Particles in the neighborhood would be moved, I assume, and that would be noticed.
In the hypothetical, or in the theoretical of the physicists who thought (still think?) an MBH might show up: with the current observational technology and mathematics, what might we find that would be mind-blowing? (Including the immediately observable grist for new mathematics which later on might reveal more mind-blowing stuff.)
I now see the last graf in my preceding post is basically the OP, just addressed more to what those physicists who are hung-ho on achieving the phenomenon.
Oh, OK… so the black hole scare was based on both 1) non-mainstream ideas about creating black holes and 2) non-mainstream ideas about how dangerous they’d be?
I guess I should have expected that. The real question, then, is why the Mayans didn’t warn us about all those black holes. 
If you mean “moved by the gravity of the black hole”, then no. A black hole has the same amount of gravity as any other object with the same mass and distance. The only sense in which a black hole has higher gravity is that you can get closer to a black hole than you can to any other mass. But you can get pretty darned close to any fundamental particle, so that’s not very relevant here.
But there would be definite signs. Many physicists say that one signature of a black hole event would be that the decay products would have a thermal distribution. Me, I don’t necessarily buy that: Hawking radiation from normal-sized holes has a thermal distribution, but I don’t think we can justify extrapolating that all the way down to the tiny black holes we’re talking about here.
A more significant sign would be an event which violates conservation of baryon number and/or lepton number. No such violation has ever been observed, nor does current best theory allow for them (though many relatively-plausible unproven models do), but black holes should be completely unconstrained by lepton number and baryon number.
There’s also the matter that black holes can probably have a continuum of masses. There’s some minimum mass to form a black hole, but you should be able to form one of any mass at all greater than that, as opposed to most particles that have discrete values of mass.