Am I misunderstanding, missing a joke, or did the overwhelming majority here consider the probability that the LHC could destroy the world non-negligible? After reading this article, I wound up looking up articles on collider safety just to make sure I wasn't crazy. My understanding of physics told me that all the talk of LHC-related doomsday scenarios was just some sort of science fiction meme. I was under the impression that artificial black holes would take levels of energy comparable to the big bang, and a micro black hole would be pretty low risk even then. (Reading the wikipedia article further, I see that FHI was involved in the raising of concerns over the LHC, which is the closest thing to an explanation for this discussion I've found so far.)
I'm actually kinda concerned about this, since if the discussion on this page is taking LHC risk seriously, then either I or LW had serious problems modeling reality. This wouldn't be in the category of "weird local culture"; cryonics involves a lot of unknowns and most LWers notice this, and UFAI actually makes much more sense as existential risk, since an unfriendly transhuman intelligence would actually be dangerous... but there were plenty of knowns that could be used to predict the LHC's risk, and they all pointed toward the risk being infinitecimal.
If, on the other hand, this was some bit of humor playing on pop-sci memes, used to play with the anthropic principal and quantum suicide, then oops.
The idea is that the risk is infinitesimal but you want to put an approximate number on that using a method of imaginary updates - how much imaginary evidence would it take to change your mind?
Recently the Large Hadron Collider was damaged by a mechanical failure. This requires the collider to be warmed up, repaired, and then cooled down again, so we're looking at a two-month delay.
Inevitably, many commenters said, "Anthropic principle! If the LHC had worked, it would have produced a black hole or strangelet or vacuum failure, and we wouldn't be here!"
This remark may be somewhat premature, since I don't think we're yet at the point in time when the LHC would have started producing collisions if not for this malfunction. However, a few weeks(?) from now, the "Anthropic!" hypothesis will start to make sense, assuming it can make sense at all. (Does this mean we can foresee executing a future probability update, but can't go ahead and update now?)
As you know, I don't spend much time worrying about the Large Hadron Collider when I've got much larger existential-risk-fish to fry. However, there's an exercise in probability theory (which I first picked up from E.T. Jaynes) along the lines of, "How many times does a coin have to come up heads before you believe the coin is fixed?" This tells you how low your prior probability is for the hypothesis. If a coin comes up heads only twice, that's definitely not a good reason to believe it's fixed, unless you already suspected from the beginning. But if it comes up heads 100 times, it's taking you too long to notice.
So - taking into account the previous cancellation of the Superconducting Supercollider (SSC) - how many times does the LHC have to fail before you'll start considering an anthropic explanation? 10? 20? 50?
After observing empirically that the LHC had failed 100 times in a row, would you endorse a policy of keeping the LHC powered up, but trying to fire it again only in the event of, say, nuclear terrorism or a global economic crash?