If you're an inveterate tube-o-phile, you may remember the episode of "Cheers" in which Cliff, the postman who's stayed by neither snow, nor rain, nor gloom of night from his appointed rounds of beer, exclaims to Norm that he's found a potato that looks like Richard Nixon's head.
This could be an astonishing attempt by taters to express their political views, but Norm is unimpressed. Finding evidence of complexity (the Nixon physiognomy) in a natural setting (the spud), and inferring some deliberate, magical mechanism behind it all, would be a leap from the doubtful to the divine, and in this case, Norm feels, unwarranted.
Cliff, however, would have some sympathizers among the proponents of Intelligent Design (ID), whose efforts to influence school science curricula continue to swill large quantities of newspaper ink. As just about everyone is aware, these folks use similar logic to infer a "designer" behind such biological constructions as DNA or the human eye. The apparent complexity of the product is offered as proof of deliberate blueprinting by an unknown creator--conscious action, presumably from outside the universe itself.
What many readers will not know is that SETI research has been offered up in support of Intelligent Design.
The way this happens is as follows. When ID advocates posit that DNA--which is a complicated, molecular blueprint--is solid evidence for a designer, most scientists are unconvinced. They counter that the structure of this biological building block is the result of self-organization via evolution, and not a proof of deliberate engineering. DNA, the researchers will protest, is no more a consciously constructed system than Jupiter's Great Red Spot. Organized complexity, in other words, is not enough to infer design.
But the adherents of Intelligent Design protest the protest. They point to SETI and say, "upon receiving a complex radio signal from space, SETI researchers will claim it as proof that intelligent life resides in the neighborhood of a distant star. Thus, isn't their search completely analogous to our own line of reasoning--a clear case of complexity implying intelligence and deliberate design?" And SETI, they would note, enjoys widespread scientific acceptance.
If we as SETI researchers admit this is so, it sounds as if we're guilty of promoting a logical double standard. If the ID folks aren't allowed to claim intelligent design when pointing to DNA, how can we hope to claim intelligent design on the basis of a complex radio signal? It's true that SETI is well regarded by the scientific community, but is that simply because we don't suggest that the voice behind the microphone could be God?
In fact, the signals actually sought by today's SETI searches are not complex, as the ID advocates assume. We're not looking for intricately coded messages, mathematical series, or even the aliens' version of "I Love Lucy." Our instruments are largely insensitive to the modulation--or message--that might be conveyed by an extraterrestrial broadcast. A SETI radio signal of the type we could actually find would be a persistent, narrow-band whistle. Such a simple phenomenon appears to lack just about any degree of structure, although if it originates on a planet, we should see periodic Doppler effects as the world bearing the transmitter rotates and orbits.
And yet we still advertise that, were we to find such a signal, we could reasonably conclude that there was intelligence behind it. It sounds as if this strengthens the argument made by the ID proponents. Our sought-after signal is hardly complex, and yet we're still going to say that we've found extraterrestrials. If we can get away with that, why can't they?
Well, it's because the credibility of the evidence is not predicated on its complexity. If SETI were to announce that we're not alone because it had detected a signal, it would be on the basis of artificiality. An endless, sinusoidal signal - a dead simple tone - is not complex; it's artificial. Such a tone just doesn't seem to be generated by natural astrophysical processes. In addition, and unlike other radio emissions produced by the cosmos, such a signal is devoid of the appendages and inefficiencies nature always seems to add - for example, DNA's junk and redundancy.
Consider pulsars - stellar objects that flash light and radio waves into space with impressive regularity. Pulsars were briefly tagged with the moniker LGM (Little Green Men) upon their discovery in 1967. Of course, these little men didn't have much to say. Regular pulses don't convey any information--no more than the ticking of a clock. But the real kicker is something else: inefficiency. Pulsars flash over the entire spectrum. No matter where you tune your radio telescope, the pulsar can be heard. That's bad design, because if the pulses were intended to convey some sort of message, it would be enormously more efficient (in terms of energy costs) to confine the signal to a very narrow band. Even the most efficient natural radio emitters, interstellar clouds of gas known as masers, are profligate. Their steady signals splash over hundreds of times more radio band than the type of transmissions sought by SETI.
Imagine bright reflections of the Sun flashing off Lake Victoria, and seen from great distance. These would be similar to pulsar signals: highly regular (once ever 24 hours), and visible in preferred directions, but occupying a wide chunk of the optical spectrum. It's not a very good hailing-signal or communications device. Lightning bolts are another example. They produce pulses of both light and radio, but the broadcast extends over just about the whole electromagnetic spectrum. That sort of bad engineering is easily recognized and laid at nature's door. Nature, for its part, seems unoffended.
Junk, redundancy, and inefficiency characterize astrophysical signals. It seems they characterize cells and sea lions, too. These biological constructions have lots of superfluous and redundant parts, and are a long way from being optimally built or operated. They also resemble lots of other things that may be either contemporaries or historical precedents.
So that's one point: the signals SETI seeks are really not like other examples drawn from the bestiary of complex astrophysical phenomena. That speaks to their artificiality.
The Importance of Setting
There's another hallmark of artificiality we consider in SETI, and it's context. Where is the signal found? Our searches often concentrate on nearby Sun-like star systems - the very type of astronomical locale we believe most likely to harbor Earth-size planets awash in liquid water. That's where we hope to find a signal. The physics of solar systems is that of hot plasmas (stars), cool hydrocarbon gasses (big planets), and cold rock (small planets). These do not produce, so far as we can either theorize or observe, monochromatic radio signals belched into space with powers of ten billion watts or more--the type of signal we look for in SETI experiments. It's hard to imagine how they would do this, and observations confirm that it just doesn't seem to be their thing.
Context is important, crucially important. Imagine that we should espy a giant, green square in one of these neighboring solar systems. That would surely meet our criteria for artificiality. But a square is not overly complex. Only in the context of finding it in someone's solar system does its minimum complexity become indicative of intelligence.
In archaeology, context is the basis of many discoveries that are imputed to the deliberate workings of intelligence. If I find a rock chipped in such a way as to give it a sharp edge, and the discovery is made in a cave, I am seduced into ascribing this to tool use by distant, fetid and furry ancestors. It is the context of the cave that makes this assumption far more likely then an alternative scenario in which I assume that the random grinding and splitting of rock has resulted in this useful geometry.
In short, the champions of Intelligent Design make two mistakes when they claim that the SETI enterprise is logically similar to their own: First, they assume that we are looking for messages, and judging our discovery on the basis of message content, whether understood or not. In fact, we're on the lookout for very simple signals. That's mostly a technical misunderstanding. But their second assumption, derived from the first, that complexity would imply intelligence, is also wrong. We seek artificiality, which is an organized and optimized signal coming from an astronomical environment from which neither it nor anything like it is either expected or observed: Very modest complexity, found out of context. This is clearly nothing like looking at DNA's chemical makeup and deducing the work of a supernatural biochemist.
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Seth Shostak is an astronomer at the SETI (Search for Extraterrestrial Intelligence) Institute in Mountain View, California, who places a high priority on communicating science to the public. In addition to his many academic papers, Seth has published hundreds of popular science articles, and not just for Space.com; he makes regular contributions to NBC News MACH, for example. Seth has also co-authored a college textbook on astrobiology and written three popular science books on SETI, including "Confessions of an Alien Hunter" (National Geographic, 2009). In addition, Seth ahosts the SETI Institute's weekly radio show, "Big Picture Science."