CERN - Large Hadron Collider and the Very Early Universe

Hi DevilsAdvocate. I'm not much of a poster these days, but I feel the need to speak up about this one. I agree that this guy is being very deceptive, but things are not as simple as your post makes it sound either. The cosmic ray analogy is a powerful one, but there are a number of possibly relevant differences between cosmic rays and the collisions at the LHC that prevent it from being perfectly reassuring. Yes. Those are some of the most powerful rays ever measured, but this comparison is a bit unfair. What is more fair is to look at it from the perspective of one of the protons in the LHC collision. From the proton's perspective it is at rest, and the beam striking it is enormously higher in energy than when it is considered in the lab frame. If you do the proper transformation your factor of 1 million is really closer to a factor of 100.Secondly, you can argue that the cosmic rays are not a good model for the heavy ions that the LHC will occasionally collide. These collisions of clusters of hundreds of particles, each individual one of which is at a lower energy, could conceivably lead to something dangerous that cosmic rays and proton collisions do not produce.Thirdly, and perhaps importantly, what if dangerous particles (black holes or whatever) are produced in super-high energy cosmic rays all the time. They would be traveling at the speed of light relative to the earth. It's crazy to think about, but what if their cross section for interaction with the earth becomes tiny at these high speeds, and they pass through it just like a neutrino. For an electrically neutral stable black hole, this seems quite likely. In contrast, a similar black hole (or whatever) produced at the LHC could conceivably be produced with less than escape velocity, and so it would be caught by the earth's gravity, perhaps in an orbit that is inside of the earth itself. This could possibly provide it with time to behave dangerously.In the end, we can't rely on experiments or observations to be 100% sure this is safe. We have to trust the calculations and theory at some level, which I for one, am not trained to understand. I have been informed that it is theoretically impossible to conceive of stable mini black holes. And that even if black holes are stable, the cosmic rays would produce them, there would be some which are charged, and they would have already been captured by the earth and destroyed it. Indeed, the latest safety reports suggest that if there were a black hole trapped in the earth, and we assume that they consume material at a rate slow enough for astronomical bodies to have the observed lifetimes, then there is no way it could take less than billions of years to grow large enough to become dangerous.Well, I hope the theorists have done their homework properly ... and about strangelets as well as black holes. As an experimentalist who does not have a year+ available to go out and learn quantum gravity, etc, I will just have to take their word that the LHC is safe. Or maybe I don't ... I'm fine with taking a tiny risk of catastrophe in the name of big science. I could imagine others might disagree though.

Hi Rahvin -I agree that mini black holes are supposed to disintegrate immediately according to theory. But this is something that can only be theoretically understood until we find a way to study some real black holes up close. So some of the good folks at CERN have done some theoretical studies where they assume that black holes are stable and see what happens. I think the fear would be that such a stable black hole that's inside the earth might be capable of occasionally consuming a particle every once in a while and growing. Any scenario where the LHC is capable of producing mini black holes is also one where gravity blows up and becomes very powerful on small distance scales. Your argument that it is too weak to break atomic bonds seems reasonable in a hand wavy sort of way, but it sounds like there are some models where the black hole would absorb matter in a dense environment (this really is beyond my field of expertise). So I'm glad that they've made these studies and determined that if any rate of consumption would be high enough to be dangerous, it would also be high enough that some of the dense stars that we see would have been consumed long ago. The relevant paper can be found here.I'm willing to take the author's word that this is safe, at least in the case of black holes. I'm simply pointing out that you can't say "cosmic rays", wave your hands, and prove that the LHC is safe beyond all doubt. That's pretty convincing, but you have to also dig into the meat of some very complicated physics models to approach certainty. I wouldn't even bring this up if the fate of the world weren't possibly involved. . But I'm certainly not losing any sleep over it.

Hi Devil's Advocate,I agree with you on just about everything here, I'm just arguing the details. I want to see the LHC go ahead ... hell, I'll be looking for a job if it doesn't. I just am not willing to tell the public that this won't destroy the planet unless I really am *sure* of it. All I can say is, a doomsday scenario seems very unlikely to me based off of what I do know of cosmic rays (these are reassuring because the are *similar*, but they are not the *same*) and past colliders, the theorists have done calculations showing that it's safe, and I don't think they'd say that unless they really were sure. You Lorentz Transformed to the rest frame of the cosmic rays, I Lorentz Transformed to the rest frame of one of the protons in the collider. Either way you become about a factor of about 10^4 closer, so the most powerful cosmic rays are really only effectively about 10^2 more powerful than the LHC. I think we are in agreement on this. That certainly makes the collider seem safe (though if anyone builds a super-LHC that reaches >100 TeV this argument breaks down) ... it's only the possibility of cosmic rays being artificially safe because of their boost or LHC collisions being dangerous in the heavy ion case that someone could legitimately worry. I agree with the quote completely. ALICE and CMS will study these, and yes, those are what I was referring to. It is conceivable that heavy ions may have some dangerous property in high energy collision that does not exist for proton collisions, or in cosmic rays which tend to have low atomic number. But yes, RHIC was safe at lower energies. As an agnostic, I would prefer not to speculate on what will happen when we study the new conditions created at the LHC. There is no reason to think anything dangerous would happen, and cosmic rays do give some reassurance, along with the calculations of the theorists. Absolutely! (Though I would rather not to speculate on the probability). There is a tiny chance that something devastating will happen despite how safe past colliders were, despite how safe similar cosmic ray collisions are, and despite everything the theorists can come up with. But if we're going to consider highly unlikely scenarios, there is probably a much more likely tiny chance that something truly wonderful and revolutionary will come out of this like warp drive technology. Research into the unknown is always potentially dangerous, but it has worked out well for us throughout all of human history. I prefer not to operate in a state of fear of the unknown, but I would rather be honest that the risk is not zero and let the public decide. Steve Giddings goes ice climbing for fun. He's brilliant and I trust what he says, but I think his standard for what is safe is a little bit different than mine. Well, I think that all adds up to at least a nickel for me.