Contact

by Carl Sagan

“When a wave of light comes at you—visible light, radio light, any kind of light—it’s vibrating at right angles to your line of sight. If that vibration rotates, the wave is said to be elliptically polarized. If it rotates clockwise, the polarization is called right-handed; counterclockwise, it’s left-handed. I know it’s a dumb designation. Anyway, by varying between the two kinds of polarization, you could transmit information. A little right polarization and that’s a zero; a little left and it’s a one. Follow? It’s perfectly possible. We have amplitude modulation and frequency modulation, but our civilization, by convention, ordinarily just doesn’t do polarization modulation. “Well, the Vega signal looks as if it has polarization modulation. We’re busy checking it out right now. But Dave found that there wasn’t an equal amount of the two sorts of polarization. It wasn’t left polarized as much as it was right polarized. It’s just possible that there’s another message in the polarization that we’ve missed so far. That’s why I’m suspicious about your friend. Kitz isn’t just giving me general gratuitous advice. He knows we may be onto something else.”