31 03 2008

I’ll admit it, I’m highly excited about the impending opening of the Large Hadron Collider at CERN, and especially at the prospect of the Higgs boson finally being discovered — or not, which has the potential to be just as revealing. It appears, however, that some people don’t share my enthusiasm. This isn’t anything new, by the way — the same sort of fretting occurred prior to the opening of the Relativistic Heavy Ion Collider in the US.

Now, concern over the possibility of a doomsday situation is not, I’ll concede, entirely unfounded (although it is quite unnecessary). The two main fears concern the formation of microscopic black holes — mini black holes, as they’re often called — and the production of strangelets, a form of exotic matter which could hypothetically catalyze a chain reaction which would reduce the entire Earth to a lump of hot strange matter. The hazard of the former is pretty much precluded by the laws of physics as we know them (although the black holes could hypothetically be formed), whereas the latter is not really worth discussing, for a wide variety of reasons.

I don’t blame the average person for worrying about the possibility of black holes being formed; after all, don’t black holes simply consuming everything surrounding them? Couldn’t they eat straight through the Earth and start to devour it from the interior outward? Well, no. There’s something called Hawking Radiation, which essentially causes all black holes to evaporate over time. It works something like this: what is generally thought of as empty space is not empty in actuality, it is seething with shortly-lived particle-antiparticle pairs, known as virtual particles. These virtual particles can briefly coalesce out of energy borrowed from the vacuum, which has an classical energy level (to coin a phrase, I believe) of zero. Of course, the particles are not technically allowed to do this — the first law of thermodynamics, correct? — but they do it anyway, which illustrates some very odd phenomena in quantum mechanics. The caveat is that they must immediately make restitution, so to speak, and return the energy in debt to the vacuum. Accordingly, they immediately annihilate one another, at which point the whole messy situation is swept under the proverbial rug.

Except when a black hole is involved. If this is the case, when the pair of virtual particles is formed with sufficient proximity to a black hole, in the infinitesimally brief period of time in which they exist, one can cross the event horizon, at which point it is inexorably sucked towards the singularity of the black hole. This frees the other particle in the opposite direction, towards infinity. Obviously, this poses a problem: under normal circumstances, the particles annihilate each other, leaving us with a lovely, pristine vacuum with its lovely, pristine energy level of zero. However, we now have an issue: an energy debt that is unpaid still exists, and the debtor has gone running off into space. We cannot go creating energy (which equates to mass — E=mc2) — but it appears that this is what has occurred. So what can be done about it? It turns out that the energy debt is filled, and that the energy comes from a convenient source: the black hole that consumed the particle originally. Enough energy from the black hole is released to fulfill the debt, and this phenomenon, occurring over and over again, will, by logical extension, be compounded over time to the eventual evaporation of the black hole. It also turns out that, the smaller the black hole, the more rapid the evaporation. So, hypothetically, mini black holes would evaporate due to the Hawking Radiation before they could cause any significant damage. Bear in mind, however, that this is all strictly theoretical, as the Hawking Radiation has never been actually observed. However, it makes sense, without any significant problems, so it is most likely the way that things are. (Edit: Pol Lambert has informed me, via his comments below, that the waveforms of elementary particles may not fit inside black holes of this size at all, doubly precluding danger. Thanks, Pol.)

Concerning strangelets, no one is actually sure that the catalyzation described would actually occur, and furthermore, if they did indeed behave is such a manner, the probability of a strangelet being produced and becoming issue is minute, in the vicinity of that of winning the major prize in the lottery three weeks in a row.

There is no real cause to be concerned about the LHC, especially as it could produce such monumental gains in our understanding of the Universe. This is not something to be discarded over unfounded, spuriously-based fear, and I sincerely desire that this post will have allayed any that you possess.




8 responses

31 03 2008

Well written post Linus, quite impressive. The ignorance and fear mongering of some however, astounds me.

1 04 2008
Pol Lambert

Even without the Hawking radiation, mini black holes pose no risk. Black holes only eat stuff in their immediate vicinity. The area from which no escape is possible is bounded by the so-called Schwarzschild radius. The heavier the black hole, the bigger this radius. The radius for a black hole created in a particle accelerator is very small, too small to actually eat stuff. Particles at the quantum level are not pointlike, they also look a little bit like a wave and are therefore bigger than a mathematical point. The point is that every elementary particle is too big to fit in the black hole and therefore can’t be eaten.

Also, wikipedia has a nice entry: http://en.wikipedia.org/wiki/Micro_black_hole

1 04 2008


1 04 2008


Pinto’s: Thanks.

Lambert: I didn’t know that, thanks. I’ll append it to the post.

Anonymous: “MOER”. And I would be horrified, particularly at the debasement of science, if I hadn’t seen the same thing on Slashdot repeatedly.

1 04 2008

Actually, Pol Lambert, I believe that the fear is that they will accumulate in the center of the Earth. Not being a theoretical physicist, I can’t say whether or not your info precludes that… care to expound?

1 04 2008
Pol Lambert

These blakcholes would be very small and only interact with other stuff (including other blakc holes) through gravity, the weakest of the four forces. This means that the black holes almost don’t interact or zip right through everything, including you, me and the center of the earth. So getting them in the center of the earth and letting them stay there is actually almost impossible.Not only that, but you would need to collide the black holes in the center of the earth with each other. Being small and all, compare this aiming 2 golf balls at each other across the solar system, only worse. Now you need to repeat this enough times for your black hole to grow big enough to interact with ordinary matter. I guess this process will take so much time, that we, nor another earthling would need to worry about it.

But seriously, using confirmed phyics, LHC can’t create a black hole (not enough energy) Using unconfirmed physics (string theory, …) it ‘might’ be possible, however this approach also predicts that the black hole is unstable. There is no physics, compatible with existing physics, which predicts small stable black holes and even if this is all wrong, there are still the arguments I’ve given above.

1 04 2008

Cool, thanks.

3 04 2008

Prepare for unexpected consequences … Doctor Free- er, I mean, Linus.

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