At the science blog of the NewScientist, I came across an article that, even though probably meant as a humouristic piece, I found nevertheless interesting enough to think about a bit more. In it Joe Marchant, the article’s author, began with this:
How do you get rid of a black hole that’s threatening to gobble the Earth? It could be as simple as popping it in a box and shooting it into space.
A handful of doomsayers have argued that the Large Hadron Collider particle accelerator at CERN near Geneva, currently gearing up to start smashing protons together this autumn, could produce Earth-destroying black holes.
Now, this is a strange concept. Strange enough for me to dig a bit deeper.
First, the author writes loosely about black holes. The one’s in question here however are not the massive black holes that have been proved to exist, but hypothetical micro black holes (mbH). If they indeed exist, they would be very tiny.
The smallest mBH, i.e. the one that requires the least energy to create would have the dimension of the Planck length lp (dimension of 10-35 m) and the Planck mass mp(dimension of 10-8 kg or 1016 TeV/c2). To create the mBH, the Planck mass would have to be crammed into a region of the size of the Planck length. As a comparison, the LHC will be colliding protons at an energy of 7 TeV, or around 7/10,000,000,000,000,000 of what is needed to create such an mbh.
If the usual theories hold, it is simply not going to happen. However, there are theories, most notably some string theories, that would lower the energy required to a the GeV range and then it could happen. So let’s assume that it does happen. What now?
Chances are that it would not even be noticed, because it would evaporate, i.e. give off all its energy, due to Hawking radiation in a very short amount of time in the range of 10-97 s. So why are we so certain, that such mbhs are not being created and are not decaying all around us all the time? We may just not be able to see them, because they disappear quickly after having been created. In fact, that behavior would be consistent with the quantum foam or with the zero-point field behavior. Such mbhs with the above properties are also called Planck particles.
Great, but what if, due to some little understood interaction with the zero-point field the mbh does not evaporate or could be prevented from evaporation? Which are the properties such a thing would have, could it be controlled and could it be used to generate energy out of nowhere?
If there is such a thing as a stable charged micro black hole then it surely is possible to cage it into an electromagnetic field, as the author proposes. This is because the gravitational pull of the mBH would be small as compared to the electromagnetic forces. But there may also be a problem here. Since the electromagnetic field is just another form of energy or matter, wouldn’t that feed the mBH and lead to its growth?
The keeping-it-from-growing part might be the tricky part in such a scenario. It turns out that even in this scenario, the growth rate, or accretion rate as scientists call it, would be extremly slow, i.e. in the billions of years.
Thankfully, scientist have come up with their own assesments of the likelihood and the impact of such mBH creation scenarios at low TeV scales. One treatise is here.