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Actually, if the black hole were to be created, and even if there were no Hawking radiation, then we're still quite safe. After all, the black hole was created in a particle accelerator, so it's moving pretty damn quickly.

Yes, the constituent particles were being collided, and that would soak up a considerable portion of their kinetic energy. But consider the accelerator geometry at the Relativistic Heavy Ion Collider at Brookhaven (the main suspect for creating a potential black hole). The beams cannot meet exactly head-on. Thus, they have significant net momentum that can't be shed without external interaction. Furthermore, the shared component of the two momenta is in a direction tangential to the Earth's surface. Given the angle and typical collider energies, a particularly slow case would have a velocity around 1% of c (note, this example is so slow it is not even the example put forward as a risk).

You might think that in passing out of the chamber the microhole would pick up enough mass to slow down a lot. Probably not. After all, the Schwartzschild radius of this black hole is around 2.5* 10^-54 meters. If we're throwing out Hawking Radiation, then it only interacts via gravity (otherwise 'no Hawking Radiation' is an ad-hoc nonsense rule). Black holes only have additional gravitational power because you can get close to them as a concentrated mass. At a normal interaction radius, they behave normally. So if it is to scoop up matter, it will have to do it by 'direct collision'. Now, quantum particles don't really collide. They just get close enough that the chances of them interacting via a force-carrying boson gets to be reasonable. The problem is that to get scooped up in the black hole, the scoopee has to be within let's say 10^-50 meters (2,500 Schwarzschild radii, an unreasonably generous amount) of the black hole in order for an interaction to be likely. However, protons are normally smeared out over a region 10^35 times as wide (i.e. the nucleus). Considering that Gravity is so weak, the hole would pretty much have to wait for the constituent particles to wander into it by accident, rather than suck them in by attraction. But the black hole isn't sticking around waiting for the probability of the proton having been caught to accrete to a significant amount. Moreover, nuclei themselves have 10^-5 the radius of an atom, which means they have 10^-10 the cross section. Passing through 3 meters of a densely packed solid material would thus provide around two cases of the black hole passing through a nucleus. As established earlier, it would probably (on the order of (1 - 10^-69) probability) zip right through without picking anything up or shedding momentum each time.

The net effect: there is only a vanishingly small chance that the black hole will pick up anything on its way out. If it does, it will probably grab mass-insignificant electrons, or possibly a nucleon, either picking it up or shedding some momentum to shred it and create a particle shower.

Suppose it does pick up a nucleon. Then the momentum of our two-gold-atom microhole will have to be shared among its existing mass and an additional nucleon mass. Whatever, that's like a 1% change in velocity. Now for the sake of paranoia assume that the microhole completely gobbles up every nucleus it touches. Then the first collision will add a heavy-atom mass, effectively dividing its velocity by 3/2. Note that c/150 is around 130 times the escape velocity for the solar system from the surface of the earth. So our intrepid microhole would have to pick up neither one nor two (the expected range given our extremely generous assumption), nor even a few dozen, but two hundred more nuclei to even remain within the solar system. It would have to gather an additional eight hundred to be stuck on the Earth.

Also note that the orientation of the lab is such that these particles will never be aimed at the sun or other planets, but always have a north/south component, heading out of the plane of the system. Yeah, one of those hitting the sun would make us a touch uncomfortable. But they aren't going that way.

So, any black hole the RHIC creates would leave the Terran system and the Sol system at a speed best described as a fraction of the speed of light, never to be seen again. They could have already done so many times, and we would never know.

A few last notes:

  • I have not gotten into the issue of how insanely difficult it is to create a black hole even at those high energies.
  • All that was assuming that Hawking radiation doesn't exist, because if it does, the black hole wouldn't last long enough to get out of the chamber.
  • In the far-future science fiction novel Hyperion, it is ancient history that the Earth was gradually destroyed by an accidentally released artificial black hole.