Playing Around, in All Seriousness, With Light

I like browsing in those corners of science that lend themselves to serious play. OK, even outright silliness. Especially when those same phenomena turn out to have practical--even exotic--purposes.

That is certainly true of polarization--something familiar to anyone who has ever squinted into sunlight glaring off water, or tried to stop the glare with Polaroid glasses.

With ordinary Polaroid sunglasses, in fact, you can reveal hidden rainbows in the stressed plastic of airplane windows, turn clear cellophane into a brightly colored kaleidoscope and even--as I discovered one day--”turn off” a friend.

At the same time, polarization is all the rage these days among cosmologists studying the Big Bang. It even sheds precision light on certain oddities of subatomic particles.

Nature at her multi-tasking best.

Polarized light is light that has been, in effect, filtered so that it vibrates in a single plane. Light travels as a wave that vibrates at right angles to the direction of travel: If it’s coming at you, it will vibrate up and down, side to side, and at all angles in between. Polarized light, however, vibrates only up and down or side to side.

Think of it as trying to shake hands through prison bars: The vertical bars “polarize” a handshake so that you can shake only up and down. Horizontal bars, conversely, would allow you to shake only side to side. And two sets of crossed bars allow no motion at all.

In this sense, horizontally and vertically polarized light are literally polar opposites--like right-wing (or left-wing) ideologues. Crossed polarizers let no light (or productive discussion) through. Polaroid filters are like prison bars for light--except the bars are long, stretched molecules.

Normally, only part of light is polarized, and since human eyes can’t tell horizontally vibrating light from its vertical counterpart, the polarization remains a kind of secret signal until something comes along to decode it.

Take those sunglasses. Reflections are naturally polarized. As sunlight hits water, for example, horizontally vibrating light skids off the surface at you like a skipped stone, while vertically vibrating light gets absorbed. Polaroid sunglasses sit on your nose like prison bars, shutting out the horizontally vibrating light--the glare. You can still see because all the other light in the sky vibrates this way and that, so plenty gets through.

In the same way, vertical surfaces polarize reflected light vertically. So if you catch a reflection of a friend in a vertical window (or any shiny surface), you can simply turn those sunglasses on their side and, presto, the friend is gone (or at least, her reflection).

To see colors, you need two polarizers at right angles (popping one lens out of the sunglasses and flipping it 90 degrees should do fine). Crinkle up a bit of cellophane in between the two lenses, and you should see shards of color where before there was dark.

The colors appear because cellophane twists the plane of polarization, so some light can sneak through even these crossed “bars.” Each color, however, gets rotated through a slightly different angle. The result is that the cellophane spreads white light into a spectrum, same as a prism. The crinkles in the cellophane produce the stained-glass effect, each surface twisting the light in a different direction--another facet of your gem.

Not all is fun and games. Polarized light is a navigational beacon for bees, which can distinguish planes of polarization even without sunglasses. (Sunlight scattered off air is polarized most strongly at 90 degrees from the sun’s rays.) And a physicist friend once figured out how to use polarization in wartime to send coded messages from a light atop a hospital. The signals were encoded in the polarization pattern, so even though they were in plain view, the enemy couldn’t read them.

(I’d tell you who it was, but it’s secret.)

As for the universe at large, astronomers recently used polarization patterns to “see” that at least some exploding stars don’t blow up in neat, symmetrical spheres as many had thought, but rather in elongated shapes--like exploding cigars--as if something was pushing them off center.

And it turns out that a tiny portion of the radiation sloshing about in the very early universe may have gotten polarized by ripples in space-time spreading out from the Big Bang. If astronomers can decode these faint signals, they’ll be able to see beyond even the veil of the Big Bang’s afterglow to mere seconds after the universe was born.

There’s much more: Spinning subatomic particles can be polarized, too, allowing physicists to more cleanly probe the innards of atoms. And you can use those crossed polarized filters to find colors in clear Karo syrup.

So it’s just as I said. Science and play. Not poles apart.