What Do You Say to An Extraterrestrial?

December 2, 2004
by Seth Shostak - Senior Astronomer

I once thought that worrying about what we should broadcast to extraterrestrials made as much sense as fretting over the small talk I’d venture with King Carl XVI Gustaf if I won the Nobel Prize. I reckoned there was no need to dwell on the problem, as it was both hypothetical and irrelevant.

Well, I’ve changed my mind. Not about the chances for a Nobel Prize, but about the value in devoting some cerebral CPU cycles to the matter of interstellar messaging. Part of this shift is due to my colleague at the SETI Institute, Doug Vakoch, who has penned a number of erudite articles on the problem. A few of his insights have managed to percolate through the walls that separate our offices. In addition, new telescopes being built for SETI will soon speed up our search by factors of a hundred and more. So it’s entirely possible, in my view, that we could retrieve a message from another world within just a few decades. Suddenly, the idea of “talking back” would become more than just a wry, dry academic straw man.

There’s also the enticement that pondering what to say and how to say it might help snag that extraterrestrial signal in the first place. It could give us a clue as to what we’re looking for.

Fact is, we’ve occasionally sent deliberate messages to the stars. For example, there was the plaque on the Pioneer 10 and 11 spacecraft, with an engraving featuring a friendly couple in nature’s garb and a map of our location in the Galaxy. The Pioneers’ interplanetary successors, the Voyagers, carried a crude videodisk, with music, voices, and a small selection of inoffensive photos that could be played with a 16-2/3 rpm turntable and a mechanical needle. Thirty years ago, a radio message was broadcast by the Arecibo radio telescope to a star cluster in the constellation of Hercules. It was a spartan graphic, amounting to a mere 210 bytes of data.

All our messages have been, like Igor, short and simple. This has led us, I think, to imagine that future cosmic broadcasts would also have to be compact and easily intelligible to beings who (unlike those on TV) will not have mastered colloquial English. Messages based on imagery or the regularities of music and mathematics have all been proposed.

But I suggest that we may have been too limited in our thinking. When Samuel Morse tapped out the first intercity telegraph message in 1844, it consisted of a paltry four words (“What hath God wrought?”) Well, no surprise: the bandwidth of the telegraph was low, as was the patience of the crowd.

The bandwidth for interstellar messaging does not have to be low, however. At microwave radio frequencies, you could easily send a megabyte a second. At infrared wavelengths, you could up the bit rate to a gigabyte per second over long distances, and a hundred times more over shorter spans (say less than 1,000 light-years). These transmission speeds are largely set by the dispersive effects of the hot gas that fills interstellar space, and they vary a bit depending on direction and wavelength. But the point is, there’s no need to skimp on the information you transmit to cosmic listeners. The data pipe is fat.

At a recent International Astronautics Congress, I presented these calculations and a few suggestions regarding their implications. For example, a society outfitted with an infrared laser of sufficient power could send the equivalent of the Encyclopedia Britannica to a million solar system targets in a day. In this way, an inquisitive civilization could “ping” large numbers of worlds, thereby raising its chances for successfully signaling a planet inhabited by thinking beings.

So here’s my take on message construction: Forget about sending mathematical relationships, the value of pi, or the Fibonacci series. Rid your brain of the thought (no doubt borrowed from “Close Encounters of the Third Kind”) that aliens are best addressed with musical arpeggios. No, if we want to broadcast a message from Earth, I propose that we just feed the Google servers into the transmitter. Send the aliens the World Wide Web. It would take half a year or less to transmit this in the microwave; using infrared lasers shortens the broadcast time to no more than two days.

Sure, the Web contains a lot of redundant information (and a lot of unsavory material, too, but after all, that’s part of the human condition). And yes, it’s largely in English, which even their universal translators might not know. But the point is, with so much redundant information, clever beings will have sufficient data for decipherment. When Jean Francois Champollion decoded the Egyptian hieroglyphics in the 19 th century, he benefited greatly from access to the Rosetta Stone. But even without that rocky document, someone would have puzzled out the hieroglyphics eventually, simply because there are so gosh-darn many of them. They cover wall upon wall in ancient Egyptian edifices. Same with the Web: there’s just lots of data, and the redundancy (and perhaps the pictures) would help any translator.

The difference between Samuel Morse’s first, terse telegraph message and the bit stream spewed by a modern telecommunications satellite is enormous. Keep that in mind when you think of contacting other societies with something akin to the Pioneer plaque. Sure, that gold-plated greeting card was a great start, but if we’re really thinking about interstellar messages, we should think big.