Perhaps you’ve seen James Cameron’s recent blockbuster Space Pocahontas, er Avatar. You sat in a theatre packed with makeshift Buddy Hollies as nude extraterrestrials darted among trees. Floating islands and pterodactyls popped out of the screen in glorious 3D, and then our decendents came to pillage the land with fire and obtain its unobtainium (they should have known better). It was fun, wasn’t it?

For all the fanfare though, three-dimensional cinema is nothing new. The idea of showing each eye a slightly different image to generate the illusion of depth has been around for well over a century, and almost every moviegoer has donned a pair of migraine-inducing red and blue shades at some point. But the technology behind this most recent wave of 3D enthusiasm is new, and I was surprised to learn how it worked. The secret is a novel use of polarization.

Light, such as that emitted by a film’s projector, travels as a wave. As it moves along a straight path, it shakes an electric field back and forth, a bit like a tiny snake slithering its way through space. But unlike actual snakes, which must slither along the ground’s surface, the light wave can shake its electric field up and down, side to side, or at any angle. Most sources emit its light waves randomly, so that the electric fields end up shaking in every direction. This is non-polarized light.

In certain circumstances, however, light can be polarized—it can be altered so that only electric fields vibrating in a particular direction remain. Polarized light comes scattering in off interstellar dust clouds and streaming out of magnetic storms on the sun. The light reflecting off a lake’s surface or an icy roadway is also polarized, and so is some of the blue light bouncing down from air molecules in the sky. Interactions between light and the objects it encounters can redirect or block photons based on the direction of their vibration.

As the technology-driven, unobtainium-hungry humans that we are, we’ve even come up with some polarizing materials of our own. Linearly polarizing filters are thin sheets of plastic made of molecules that are stretched out in long parallel chains. A common misconception here is to think of these chains as prison bars with narrow slits between them, allowing only the light waves that slither in alignment with the openings to get through. But light is a strange beast—the opposite is true. It’s the waves that slither perpendicular to the openings that make it out again. As the light waves work their way into polarizing material, the electric fields they shake push on electrons that stick to the molecular chains. It’s like fighting through a thick mud; the electrons slide back and forth along the chains, absorbing energy until our photonic snakes can slither no farther. But the electrons, bound to their stiff molecules, can’t really move anywhere to catch light waves that slither perpendicular to the chains. With no electron movement, there’s no mud, so those waves continue out the other side of the polarizer unscathed, wiggling in directional unison.

It’s this phenomenon that allows anglers to look beneath the surface of a lake. They’ll wear polarizing sunglasses (with horizontal molecular chains) to block out the horizontally polarized light reflecting off the water. If they tilt their heads, however, or lie down sideways on a dock, their glasses will effectively be useless. The same goes for drivers. As a motorist, you can up your odds of survival on icy roadways by using polarized glasses to cut down on glare from the road’s surface. And if you roll your car in spite of this, rest assured, you will be treated to some mildly interesting visual effects as the bright glare of the slick pavement blinks on and off twice per rotation.

Initially I assumed my 3D glasses for Avatar must be operating in a similar fashion, with vertically polarized light reaching one eye and horizontally polarized light reaching the other to produce two separate images. Easy. But at some point, maybe around hour 2.7 or so, I tilted my head 45 degrees to rest it on my hand. With linear filters, this should have let just as many vertically polarized light waves as horizontal through each lens, which would ruin the 3D effect. It didn’t.

Enter the sidewinder.

In biology, if you put two snakes together you get a fight, or you get a lot more snakes later on. In physics, you get a whole different breed. By polarizing light in two directions instead of just one, it’s possible to make a snake that spirals towards its destination. Such a snake can rotate clockwise or counterclockwise, depending on how the electromagnetic waves within it are aligned. This is circular polarization, and as it turns out it’s very useful for showing 3D films. Tilt your head as you run for a clockwise-spinning football, and it will still spin clockwise. Lean your head in towards your date’s at the movies, and a clockwise beam of circularly polarized light will remain clockwise, whether or not you’re paying any more attention to the screen. The two lenses of the Buddy Holly shades filter clockwise and counterclockwise light separately, so the image remains 3D however you look at it.

This is very clever, I’ll admit, and it does a nice job of complementing what I took to be Avatar’s underlying message: that we need to keep up with this kind of cleverness, this rampant innovation, so that when we do encounter alien life sitting on valuable mineralization, we’ll know how to overrun it completely. Space pterodactyls or not, we won’t be beat! Think of the resources! We could rename it obtainium!