No, Not A Doomsday Device

by Clifford Johnson     Department: Physics & Chemistry

Well, I'd be neglectful if I did not point you to the discussions that have been going on in the press about the unfounded fears about whether the Large Hadron Collider (LHC) at CERN in Europe is somehow going to destroy the earth. (The LHC is a wonderful experiment, the largest scientific enterprise in the history of humankind in terms of the number of people involved and the sheer size of the thing. It fills a tunnel that is 27 Km in circumference. You can get lots more of the  stats at their excellent site.) Over on Asymptotia, I reported on a remarkably wrong-headed lawsuit filed in a Hawaii court to try to affect US involvement in the experiment, on fears that the machine will create dangerous things, among them black holes that might swallow up the earth! You can find links there.

So what's the issue? Well, there are several, but the short version of the story is that no physicist will tell you honestly that there is no way that something can not happen. The issue is more about how likely it is to happen, given what we know. This is science, not religion, so no dogmatic line here, just a discussion of likelihood. Turns out we know a lot upon which to base this assessment of likelihood - for example, Nature does the kind of collisions that are to be done at the LHC all the time in our atmosphere via high energy particles coming in from space. If those dangerous black holes were to be made in the LHC, then they will have been produced a lot already, and the earth is in pretty good shape, considering.

Then there's the whole discussion of black holes in the first place. Where did that come from? Well, this is an actual scientific discussion. If we're hugely lucky, the energy scale of physics where quantum gravity effects (both quantum physics and gravity in play - hitherto not accessible experimentally) could be at about the scale of energy the LHC will probe. This would be hugely more accessible than we'd dreamed in our wildest dreams, since this scale - the "Planck Scale" - is expected to be (assuming there are no new constants of nature, sort of) very many orders of magnitude higher.

But people considered the possibility that maybe we missed something and so what if quantum gravity's physics could be unlocked at the LHC? A hugely long shot, but why not consider it for fun, just in case? If you do, then what we know of that physics suggests that you could create microscopic black holes in the LHC - we would be able to study quantum gravity in the lab! This is the same physics that governed the origins of the universe, and so that would be awfully wonderful! (This is not what the LHC was constructed to study, I hasten to add, and I recommend that you read and follow the links in this post and the companion one, to find out more.... There's some lovely NPR audio too.)

Wait though... the very same physics reasoning that suggests that if we are hugely lucky we could make black holes (maybe, just maybe) also tells you that those black holes will decay away -evaporate harmlessly in the lab- by a process called Hawking radiation. (We'd be studying their decay products, not them directly, as is usual in particle physics when you create exotic things using a particle collider).  So this is yet another reason why the scare-mongering is a bit off the mark. It is cherry-picking the physics, taking the physics that suggests that there could be black holes, and ignoring the conclusion of the same physics that those holes will evaporate.

More reasons why you should not worry? Look at my post on the comments of Frank Wilczek on the whole story (he was interviewed on Science Friday by Ira Flatow on the matter.) For a humourous thought, you can look here... When we switch on the machine will we see micro black holes, or man eating dragons? Sure, both are possible... but how likely? Not very. That's the key point.


-cvj

Tags: black holes, LHC

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