May 22, 2012 12:00 PM Text Size: A . A . A 
SETI started out as radio searches, and today we do both radio searches and optical searches. We're looking in both cases for engineered signals: In the radio, we're looking for frequency compressionâ€"signals that occur at only one wavelength, because we can do that with technology and nature can't. And in the optical, we're looking for time compressionâ€"bright optical flashes that last only a billionth of a second. Again, we can do that with technology, like lasers, and Mother Nature can't. We want to do more: Take optical into the infrared, take our search for radio signals and begin looking for broader-band, information-rich signals that can still be distinguished from astrophysics.
But the real thing that's changed recently is where we point o ur telescopes, because now we have this huge wonderful repertoire of exoplanets. In the past, we only knew about stars, and we picked stars that were old enough and had enough metals around that they could maybe have rocky planets. Now we're looking at where we know there are planetary systems.
That's a great project to be working on. It's kind of stalled right now. In some sense, we need to wait until Kepler weighs in with information about how frequently planets of a particular size occur around stars of a particular spectral typeâ€"that will tell us how big we need to build the telescope to look for biosignatures. If, in fact, there are rocky planets in the habitable zone of almost every star, then you can build a smaller telescope because you don't need to interrogate so many stars to find a planet that might have life. If, on the other hand, it turns out that the habitable planets are few and far between, then you're going to have to build a bigger telescope.
But we ought to be working on what constitutes a smoking gun biosignature because that's hard. It's hard to come up with something that cannot be produced abiologically in any other fashion.
The story that it's telling us is the amount of habitable real estate out there might be a lot greater than we once thought. When we were saying, for there to be life, temperature has to be between the boiling and freezing points of water, it has to have a neutral Ph, the radiation environment has to be benign, and there has to be one gravity, we were making a list of requirements that really did reflect where humans were comfortable. Now we're finally giving microbes the respect they deserve. We've known for a while that we're just one small twig on an evolutionary tree, but our ego hasn't really allowed us to integrate that. Now, with our understanding of how adaptable life really is, we're beginning to have a broader appreciation of what life could be on other worlds. And I suspect that in reality, biology on another planet given different conditions, might be even more extraordinary than what we've experienced here on this planet.
No, I think nature's got a better imagination. Our science fiction writers have been doing this for a century or more; they've come up with some very interesting ideas. One of my favorites is
Fred Hoyle's black cloud. Can we, in fact, have a dispersed plasma intelligence? We'll see. That's one of the problems in this area of science: We're working from what we know. And we don't always realize the biases that we're internalizing.
That's one of the nice things about the way we're now doing SETI. When you point a radio telescope in a particular direction, you see the whole planetary system. You're not just pointing at the one or two planets that Kepler or one of the ground-based systems has found. If, indeed, technological life exists on something other than a rocky planet in the habitable zone, we'll have an opportunity to find it.
11:15 AM
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