Seth Shostak must love it when people at parties ask him what he does for a living. "What do I do? I search for alien life." Nice conversation starter for Shostak, senior astronomer at the SETI Institute in Mountain View, Calif., which searches telescope data for signals from alien civilizations. In Cosmic Company (Cambridge University Press), a book out this week, Shostak and co-author Alexandra Barnett take a whack at some of the issues surrounding the possibility of extraterrestrial life. I recently E-chatted with Shostak about the book and his views on the chances for life somewhere out there.
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Next News: What in your book would a skeptic find most persuasive in regard to 1) the possible existence of life elsewhere; and 2) the existence of intelligent life elsewhere?
Shostak: There are many recent astronomical discoveries that lean in the direction of a universe chock-a-block with life. For instance, investigations that show that planets are commonplace. Of course, the only planets we can currently find are large, inhospitable worlds, but if there are big planets, the chances are pretty good that small ones exist as well. This could have turned out differently: it could have been the case that planets were very rare. They're not. There may be hundreds of billions of planets, just in our galaxy! So that's one thing. Another recent development (for which we can thank the space program) is uncovering the remarkable fact that some of the moons of Jupiter might have large, hidden oceans of liquid water. There could be life in those dark seas, and it's interesting to note that such moons were never before seriously considered as abodes for life. The point is that the range of celestial habitats has been broadened, and this too bodes well for cosmic biology.
But will much–or indeed any–of the life that might appear on other worlds be intelligent? After all, there's only one truly intelligent species on Earth, and perhaps our emergence was a fluke, not to be repeated elsewhere. That's possible, of course, but there's a greater understanding developing in the research community of how, and how often, "intelligence" evolves. While we are certainly the smartest creatures on this planet, other species (dolphins, whales, some birds, other primates, etc.) have also developed a lot more brain power in the last 50 million years or so. This suggests that intelligence is not an extremely rare characteristic. Given complex animal life, intelligence may be a frequent evolutionary occurrence. We will know if this is true or not only if we find it, of course.
Next News:A study was recently published suggesting that planets might have formed earlier in the existence of the universe than previously thought. Doesn't that make it all the more curious that we have not seen any evidence of life, intelligent or otherwise (save for the disputed Mars microbes)?
Shostak: I don't think the fact that planets may have formed a few billion years earlier than was previously thought possible affects my reaction to the fact that we still haven't found any really good evidence for extraterrestrial life of any kind. Quite frankly, our reconnaissance for life–intelligent or otherwise–has so far been extremely limited. We've nosed around the surface of Mars and examined a few meteorites. That hardly constitutes a thorough search for biology (dead or alive) elsewhere in our solar system. As for SETI and the hunt for sentient life, there, too, we've only scratched the surface. We're looking for a needle in a haystack, and while I'm confident that there are many needles in our galactic stack, we've hardly pawed through much hay. That will change during the course of the next two dozen years, thanks to new telescopes and new instrumentation.
Next News: I understand Fermi's paradox as basically this: The galaxy is billions of years old. Surely an advanced technical civilization should have formed billions of years ago. Even if it had fairly slow interstellar travel, and did not form colonies rapidly, it should have expanded onto every potentially habitable world by now. So where are They?
Shostak: There has actually been a "cottage industry" for those who are interested in resolving Fermi's paradox. There are many possible scenarios in which the galaxy houses many sophisticated societies, and yet Earth would remain uncolonized. To begin with, it's worth noting that on our planet, all colonization efforts eventually run out of steam (the Romans, the British, whatever . . . .). They run out of resources, or simply lose the will. Perhaps this is a general phenomenon. Or maybe the galaxy is colonized, but in a very nonuniform way. Much as North America is "colonized," but you don't find people everywhere . . . . Perhaps we're in a galactic backwater. Finally, it's possible that colonization is not something that you bother to do if you're a truly advanced society. You might decide to stay more or less confined to your home region of the cosmos and learn all you want to know via mammoth telescopic instruments that are quite beyond our current capability and imagination. Bottom line? I don't see any elephants in my backyard. It would be a major logical leap, however, to conclude on this basis that elephants don't exist anywhere.
Next News: What is your take on the idea of the great filter the idea that since we don't see any evidence of massive astroengineering like Dyson spheres we must conclude that the list of steps that lead to advanced intelligence includes one or more events that are extremely unlikely?
Shostak: This is, of course, a variant on the Fermi paradox: We don't see clues to widespread, large-scale engineering, and consequently we must conclude that we're alone. But the possibly flawed assumption here is when we say that highly visible construction projects are an inevitable outcome of intelligence. It could be that it's the engineering of the small, rather than the large, that is inevitable. This follows from the laws of inertia (smaller machines are faster, and require less energy to function) as well as the speed of light (small computers have faster internal communication). It may be–and this is, of course, speculation–that advanced societies are building small technology and have little incentive or need to rearrange the stars in their neighborhoods, for instance. They may prefer to build nanobots instead. It should also be kept in mind that, as Arthur C. Clarke said, truly advanced engineering would look like magic to us–or be unrecognizable altogether. By the way, we've only just begun to search for things like Dyson spheres, so we can't really rule them out.
Next News: What do you think aliens would look like? Do you think it would be more likely that they would be artificially intelligent machines rather than biological beings? And if alien intelligences wanted to explore the universe, wouldn't it be easier for them to just beam their digital consciousness across the universe rather than build metal spaceships?
Shostak: In our book, we speculate a bit on the possible appearance of intelligent extraterrestrials. Obviously, it's impossible to know to what extent they would resemble us; looking at the enormous diversity of life on Earth suggests that many "designs" are feasible. But a few things we can say with some certainty. They will have eyes, and two is probably the right number for animal (and ultimately, intelligent) life, because stereo vision helps you to catch dinner. Intelligent aliens will neither be too large (weight increases faster than strength as you scale an animal up), nor too small (not enough volume to have a clever brain). They will have appendages, of course, not merely for locomotion, but also to be able to build the transmitter that allows us to find them. Despite all these similarities to humans, it's far too naïve to expect them to bear a strong resemblance to us, of course, as they always do in "Star Trek."
But another point that we make in the book is that truly sophisticated societies (including our own) will soon enough invent artificial intelligence. Thinking machines could evolve far more rapidly than biological brains ever could. It may be that if we find a signal from space, it's coming from sentient machinery.
Next News: What are your favorite sci-fi books or films?
Shostak: I don't read much written sci-fi, but am a fan of cheesy cinema science-fiction. There are many that I like–Alien had tremendous style, and was more gripping than locking pliers. But I think my all-time favorite was George Pal's War of the Worlds. And after all, Los Angeles had it coming.
