In his excellent recent book The Particle at the End of the Universe, Sean Carroll cited an episode from The Daily Show I missed when it first played on TV in 2009. Correspondent John Oliver traveled to CERN in Switzerland to visit the Large Hadron Collider (LHC) to see the detectors and talk to scientists. Since the Daily Show is a comedy program, though, Oliver’s not just there to learn about physics: he’s there to accuse the physicists of trying to blow up the world.

The key part of the above clip starts around 2 minutes in. After beardly CERN physicist John Ellis strongly states there is no chance of the LHC destroying Earth, a man named Walter Wagner asserts that the probability of destruction is 50%: either it will happen or it won’t. (Wagner went so far as to file a lawsuit to shut the LHC down, which was dismissed before trial.) Even for the sake of humor, Oliver can’t go along with that idea.

While it’s certainly true that either the LHC will destroy Earth or it won’t, that hardly makes the possibilities equivalent. The truth—which has been pointed out by many physicists over the years—is that if there were truly any danger, Earth would have been gone a long time ago. The energies we produce in our most powerful particle colliders are insignificant compared to the power of the Force the energies of some cosmic rays, particles bombarding Earth from violent cosmic phenomena. Case in point: the “oh my god particle”, a cosmic-ray proton detected in 1991, which possessed about 40 million times the energy of the LHC; since then, many other cosmic rays with comparable energies have been observed. If  particles of that sort didn’t trigger catastrophe, there’s no way the LHC could either.

All chances, great and small

Consider this: I walk nearly every day to my local library to write (I’m typing these words there now, in fact). While walking, I could be struck and killed by a truck running a stop sign; it happens to people all the time. It’ll happen or it won’t. However, the specific chance of it happening to me on a given day isn’t anywhere close to 50%. If it was, I would be dead by now, or extraordinarily lucky.

Or consider this: if you and your partner decide to have a child via natural child birth, then the probability of the baby being born a girl is pretty close to 50%. (I’m oversimplifying: the chromosomal situation is more complicated than that, but bear with me for the sake of the example.) That probability holds true each time you make the attempt, which is why it’s not a good idea to keep having kids for the sake of ending up with (for example) a boy, or having an equal number of children of each gender. You can see why this example is different than me walking to the library: if my chances of death were 50% each time I went out, then it would be wisest to stay home in my second-floor apartment. And even then I wouldn’t be safe, because there would still be a 50% chance of a meteorite coming through my roof and fatally bonking me on the noggin.

Wagner may be an extreme case, but he’s hardly alone in misunderstanding the odds involved. In fact, while few of us are intuitive about judging chances, the human brain seems particularly challenged by low probabilities. Upon being told that something is 99.9% effective, it’s like our minds automatically focus on that 0.1% chance of failure. (That’s a likely a reason why the anti-contraception fanatics focus on [oft inflated] failure rates for contraception methods, but that’s a story for another day.) However, understanding small probabilities is important, and misunderstanding them has real-world consequences beyond frivolous lawsuits against the LHC.

That topic is the subject of one of my ScienceOnline sessions, coming up in two weeks: “Never Tell Me the Odds!”, with my friend Cedar Reiner. After the conference I’ll do a follow-up post (as Cedar probably will too), but for now, I’ll leave the topic, to avoid spoilers of my particular talking points for those who want to attend. Suffice to say: there will be asteroids!

[The post title comes from a song by The Flaming Lips.]