What I’ve Learned:
“Uncertainty principle: you’ll never be a know-it-all; you can only be a know-it-half.”
The uncertainty principle is an important tenet of quantum mechanics, first stated by Werner Heisenberg in 1927. And, like most concepts in quantum mechanics, it’s best explained with an analogy to a scene in Cool Hand Luke.
(No, seriously. I’m pretty sure ninety percent of Richard Feynman’s lectures involved stories about eating fifty hard-boiled eggs. You can look it up.)
In a nutshell, what the uncertainty principle says is this: at the quantum level, there are certain pairs of properties of a particle — like position and momentum, for instance — that cannot be accurately determined at the same time. The more precisely one property in such a pair is determined, the less certain one can be about the other.
That’s a fairly textbook definition of the uncertainty principle, which means any of us who ever took a class with an intro to quantum mechanics once slept through a very similar paragraph, probably drooling on our desks. Therefore: Cool Hand Luke.
Say you’re out there in the prison yard like Luke, wearing leg irons — double irons, to be precise — and the guards have decided to break you. Boss Position says you got a bunch of your dirt in his ditch, and you’d better get it out. So you go to work, and you dig it out.
Then Boss Momentum comes up, and asks what the hell you’re doing. Get your dirt out of his yard, he says. So you shovel your dirt back into the ditch. At which point, Boss Position comes back and yells at you to get your dirt out of the ditch, and somebody smacks you with a walking stick and you get your mind right for a while until you and George Kennedy ride off in a dump truck together.
Okay, some of that bit has nothing to do with physics. It’s just a really good movie.
The point is, you’ve got a ditchful of dirt, which stands for your ability to measure. You can put all your dirt in the ditch and measure position to a T — but then you’ve got no dirt left over to measure momentum. Or you can dump all your dirt in the yard and nail down momentum, but then position is a mystery. Or you can split the dirt, half-ass an estimate for both, and then nobody’s happy. It’s your choice. But there’s no more dirt to work with.
Also, the man with no eyes will probably shoot you in the end, either way. Because in quantum physics, nobody gets their mind right for very long.
One last important thing about the uncertainty principle: it’s not solely a result of the way you do your measuring. Some people — including Heisenberg — explained the uncertainty principle in a way that made it seem the ambiguity came from the act of measuring.
(Probably because Cool Hand Luke hadn’t been made yet in 1927. I think we can all agree that would have saved everyone a lot of time.)
And while it’s true that measurement will often alter the properties of a particle under study — a photon from a microscope changing a particle’s path is a classic thought experiment example — that’s not the same thing. That’s called the “observer effect”, and beyond any ambiguity that brings to the party, there’s still a fundamental, no-getting-around-it, baked-into-the-universe uncertainty principle lurking underneath. Even in a perfect world, with a measuring device that leaves a particle entirely undisturbed, you still can’t know both the position and momentum (for instance) of a quantum particle with complete certainty.
It’s almost as though what the two properties have is… a failure to communicate. Talkin’ physics over heah, boss.
