Stephen Baxter’s “Turing’s Apples,” which originally ran in a collection called Eclipse Two (2008), is an intriguing take on SETI and the problem of extracting meaningful information from a signal. It’s a bit reminiscent of Fred Hoyle’s A for Andromeda (1962) in that the SETI signal received on Earth contains instructions for building something that may or may not pose a threat to our species. Sorting out the issue involves discussion of information theory and Shannon entropy analysis.
Say again? Best to handle this by quoting from the story. In this scene, the protagonist’s brother, who is obsessed with the signal his team has received from the direction of the Eagle Nebula and, ultimately, the galactic center, is explaining how information is being extracted from it. Shannon entropy analysis looks for relationships between signal elements. The brother goes on:
“You work out conditional probabilities: Given pairs of elements, how likely is it that you’ll see U following Q? Then you go on to higher-order ‘entropy levels,’ in the jargon, starting with triples: How likely is it to find G following I and N?
“As a comparison, dolphin languages get to third- or fourth-order entropy. We humans get to eighth or ninth.”
“And the Eaglets?”
“The entropy level breaks our assessment routines. We think it’s around thirty…It is information, but much more complex than any human language. It might be like English sentences with a fantastically convoluted structure – triple or quadruple negatives, overlapping clauses, tense changes.” He grinned. “Or triple entendres. Or quadruples.”
“They’re smarter than us.”
And that reminds me of an old friend, an amateur linguist but an extraordinary one, who once at a memorable lunch pulled off a triple pun involving three different languages, one of which was proto-Hebraic! I had to be led through its complexities before I could begin to appreciate it (and that only after I thought about it for the rest of the day). Now that’s high-level entropy…
I had the pleasure of talking about the Baxter story with Claudio Maccone over dinner last weekend in Austin. Claudio was on his way to the SETI Institute to give a lecture on the latest work on his statistical approach to the Drake Equation. The potential encounter with intelligence far greater than our own is what accounts for the fascination of SETI. No one knows whether we are alone in the galaxy or simply outliers amidst a sea of extraterrestrial civilizations, but the engagement with the latter possibility energizes a search that is now fifty years old.
Last week saw global coordination among SETI researchers as a way of marking that 50th anniversary, with astronomers from thirteen countries on six continents observing several nearby stars including the two that started it all, Epsilon Eridani and Tau Ceti. It was in April of 1960 that Frank Drake used the Green Bank instrument in West Virginia to listen in on the latter two stars. Project Ozma drew its name from The Wonderful Wizard of Oz, so the ongoing Project Dorothy picks up the theme by associating itself with that story’s heroine. The Project Dorothy observations involve both radio and laser signals, unlike the radio-only Project Ozma.
But the project is something more than merely commemorative. If one day we do receive a signal that appears to be the real thing, we’ll need to coordinate observations on a global scale. The SETI Institute’s Douglas Vakoch makes the point:
“Astronomers can now do SETI research at observatories from South Africa to the Netherlands, from Argentina to India, from Japan to Italy, as well as from the longstanding American projects at the SETI Institute, the University of California at Berkeley, and Harvard University. The lessons learned through Project Dorothy provide critical preparation for the day we finally detect a signal from another civilization. By learning how to coordinate international SETI observations now, we’ll be better prepared to track a signal continuously, around the world, after first contact.”
This Washington Post story discusses SETI basics and the new international exercise, which includes observatories in Italy, India, Argentina, Australia, France, Germany, the United Kingdom, South Korea, Sweden, the Netherlands, and several in the United States and Japan. Behind the observations is Shin-ya Narusawa (Nishi-Harima Astronomical Observatory, Japan), who notes the value of studying Tau Ceti and Epsilon Eridani in the venture. “They remain the symbol of the project Ozma,” Narusawa said, “and so are two of the target stars for Project Dorothy.”
We have reasons for doubting either of these stars might support an extraterrestrial civilization, but for that matter we have no confirmed rocky planet in the habitable zone of any star (and yes, that includes the hypothetical Gliese 581g, whose existence seems more and more unlikely). If SETI ever does get its breakthrough, it will be because we didn’t narrow the search too drastically based on our own assumptions, but remained open to the possibility of surprise.
Read the Baxter story for one take on SETI and surprise (it’s in the 26th annual Year’s Best Science Fiction volume edited by Gardner Dozois). But if you read no other science fiction on the subject, read James Gunn’s superb The Listeners (1972), as fine a take on the wonder-injecting business of listening to deep space as has ever been penned. It was, among other things, an inspiration for Sagan’s Contact. Gunn on SETI and the human spirit:
“…perhaps it was not just the reality but the imagery, like poetry, that soothed their doubting souls, the bowl held up to catch Donne’s falling star, the ear cocked to hear the shout from the other side of the universe that faded to an indistinguishable murmur by the time it reached them. And one thousand miles above them was the giant, five-mile-in-diameter network, the largest radio telescope ever built, that men had cast into the heavens to catch the stars.”
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Great post,reminded me of ‘Macroscope’ and Anthony some years ago. On the real side Carl Devito at the University of Arizona has done great work on the foundational base of any language a ET might use to communicate ie it will have to be in some form of mathematics ,likely set theory. From this you get math,physics,bio( as a special case of physics) and so on. One can get a very detailed picture of the ‘world’ as a Et sees it but the stuff about intentions,hopes,fears and such ,the guts of human interpersonal communication,well that might be a bit much to expect.Consider the Cetacea whom we share a planet and mediums with,it is clear they have big brains that are doing something,they have a complex communication and feature rich sensory apparatus but even with detailed viewing and interaction we have no insight to their mental life other than the most trivial,hungry,hurt,etc….all else and this pains me as a fan of John Lilly is just projections and wishing. Now extend this to a rationality that had a very different path through natural selection….gulp….just what or where would be the intersecting congruences that might make communication above the mere facts of the world possible? I do not know but it seems we need to have a good think,or in terms of the Bard,’work,work your thoughts’.
ps Frudenthal created Lincos last century to help address some of these questions.
There’s the disturbing possibility that we might receive an apparently information rich signal that’s a super-Trojan, able to take-over all our computer systems and – with a bit of effort – us as well. Vernor Vinge’s “A Fire Upon the Deep” and Ken Macleod’s “The Cassini Division” have variations on that particular nightmare.
OTOH the best medium of exchange between the stars might well be information and ETIs beam soft-ware versions of themselves to study us and do their trading for them – Edward M. Lerner’s ‘InterstellarNet’ stories explore that particular scenario, as well as what happens when the ETs come visiting in person eventually.
We’ve a Galaxy of possibilities Out There, so we might as well look, listen and wonder…
For an alternative view, Lem’s “His Master’s Voice” that suggests that we may never be able to understand a signal.
Try as I might, I don’t see the rationale for alien signals. I’ve listened to the ever more desperate ideas that are discussed to explain where next to look, and these signal types become ever more targeted and transient.
Far more likely that long lived aliens would have sent probes out to target stars to monitor life bearing planets and monitor them. If c is a absolute limit, then the probe will alert them well before the target intelligences ever reply to a signal. Conversely, is c is not an absolute limit, the probe’s signals will be returned at whatever speed they can achieve. A beacon, targeted or otherwise is not going to be as effective as a local observer.
If a probe exists in the solar system, it might be anywhere, any size and possibly stealthy. But no-one has seriously, systematically looked AFAIK.
I think that the best take on this is Ted Chiang’s 1999 novella The Story of Your Life, which richly deserves all the awards and nominations it received. Elegiac hard SF with an absorbing main character — up there with Le Guin and Tiptree.
Why does SETI assume that radio-producing cultures must be concentrated so that they make single planets constantly radio-noisy? Modern research shows that apes are too competitive to willingly teach their knowledge and that cavemen were rare all the time yet spread over large areas. The cavemen thus eradicated the whole contradiction between egoism and altruism, allowing them to evolve extelligence and become human. Alien extelligent life must also have evolved by successfully avoiding competition. Ergo, any extelligent species who invent efficient spacefaring will scatter to avoid congestion, so SETIs criterium that a signal must recur many times excludes mosttechnological species in the universe by assuming single planets to be highly radio-noisy. “The great silence” is probably a misinterpretation.