It’s been a week with an exoplanet focus, what with the interesting Kepler results yesterday and the five, or perhaps seven, planets found around the same star by the HARPS instrument. But I can’t close the week without recourse to Seth Shostak’s recent comments on biological versus machine intelligence. Paul Davies took much the same tack in his recent book The Eerie Silence (Houghton Mifflin Harcourt, 2010), arguing that any civilization we encounter will likely be composed of intelligent machines. Shostak thinks SETI should take that seriously.
Searching for Doppelgängers
Right now we’re searching for what Shostak calls ‘doppelgängers of humans’ — i.e., SETI has focused on places that could support life forms that do more or less what we do, which includes not only using radio to communicate, but much broader traits like living for finite lifetimes, following basic biochemical dictates and being subject to evolution. That biases the search toward places that could sustain life as we know it, a reasonable bias in my opinion, but one that may not take our own development into consideration. After all, we may be living in the short window between developing radio and building true artificial intelligence.
Suppose, Shostak asks in this BBC story (with accompanying audio interview), we develop true AI by the end of this century. What would happen next? This is where things get interesting. Shostak:
At some point they may just pick up and leave, at least some of them, maybe most of them… If you’re a machine, you’re interested in only two things I can think of. And that is matter and energy, because those facilitate whatever it is you’re doing. And matter and energy are not in particularly great supply here.
The result: AI lifeforms go to places more suited for their kind of existence, which could include the galactic core or, perhaps, the neighborhood of a hot, young star. Shostak is arguing that we should allocate a small percentage of our observing time — perhaps up to ten percent — for searching in places AI is more likely to call home. Thus far we’ve searched fewer than a thousand star systems intensively, and our all-sky search is of necessity unable to linger on a target. We’re new at the game, in other words, but let’s tune up our target list.
Is Biology the Issue?
The problem with SETI is that we’re forced to make assumptions about how aliens would operate, an issue that continues to bedevil the field today. Recently we’ve looked at the Benford brothers’ call for a different kind of search, one homing in on the kind of interstellar beacons an alien culture would be likely to create. The discipline is rife with new ideas as we try to figure out the basic parameters that any intelligent species would have to possess in our galaxy. But getting into an alien mind, much less an artificial one, is tricky business. The best we can do is build on our knowledge of physics and extrapolate a line of rational behavior.
The Benfords extrapolate from both physics and economics to argue that an interstellar beacon will likely use short, powerful bursts rather than continuous broadcasts. But SETI has lacked the ‘long stare’ needed to find such a signal. To me, the issue is less AI vs. biology than it is continuous survey vs. pinpoint search. The SETI League’s Project Argus, discussed in these pages recently, is an attempt to set up 5000 amateur receiving stations to implement the ‘long stare.’ It would be a low sensitivity survey, but as the cost of equipment drops and its power increases, it should become possible to implement at the amateur level, and it could be a powerful adjunct to more sophisticated (and focused) searches.
Methods like these could detect an alien beacon, whether built by machine or biological beings, out to several hundred light years, with the sphere of detection growing as we replace older stations with newer technology. They’re a great complement to higher-powered instruments. If we’re looking for beacons, a continuous, high-sensitivity stare along the galactic plane is a sensible way to proceed. But there’s a place for minimal assumptions and broad coverage too, and the advantage of an all-sky survey is that it takes what it finds, which might involve the kind of surprises SETI is made for.