Looking for ET

Using radio telescopes, the SETI Institute has been listening for signals from space that could be a communication from extraterrestrial intelligence. As Seth Shostak says in this interview, it's a challenging undertaking on many fronts, from knowing how and where to look, to discerning a true signal from the noise, to finding funding to carry on the search.

RADIO SIGNALS

NOVA: When did you first become interested in looking for alien intelligence?

Seth Shostak: I have to say that I was interested in the idea from a very young age. I don't think that's particularly remarkable. I'm sure that seven out of every 10 kids would say the same. And, in particular, that interest was stimulated by a lot of cheesy sci-fi films.

But I didn't actually consider doing an experiment until I was a graduate student and I was doing radio astronomy at the Owens Valley Radio Observatory in California. I was reading a new book that the library had just acquired, Intelligent Life in the Universe by I.S. Shklovsky and Carl Sagan. So reading that late at night and using the antennas made me think, you know, gosh, this same technology could be used to hunt for signals.

So fast-forward a few decades. Can you talk about the significance of the announcement earlier this month of the Earth-like planet found in the constellation Vela, as well as more than 50 new exoplanets for SETI?

I think it's significant in three ways. To begin with, it validates the basic assumption in SETI that habitats where life, even intelligent life, could arise, are not extraordinarily rare. And that's something we've been saying for 50 years. But it's one thing to assume that it's true, and it's something else to actually get data. So at least that assumption seems to be validated.

The second thing it does is give you a whole bunch of targets. If they were to find another 50 planets that seem to be in the habitable zone, other worlds that might be small enough to have liquid oceans and maybe atmospheres and stuff, clearly you want to turn your antennas in those directions. And we are doing that.

Point three, however, is slightly more subtle. Just because we find a few hundred Earth-like worlds eventually, that's hardly any guarantee of SETI's success. You could have looked at the Earth for many billions of years without finding any radio signals. So what you need is a sample size that's enormously larger than that.

On the other hand, two things drop out of it. One is that there may be some correlation between having an Earth-like world and the kind of star system you're talking about. Do certain kinds of stars with certain properties—more metal, less metal, whatever—seem to preferentially have those kinds of planets? In that case, that would give you a way to sort out what targets you ought to be looking at a little better.

The other thing it makes you think about is, is this the right approach anyhow? Should we be looking for our planetary siblings? Or is maybe that too provincial an approach? As soon as you invent radio so that you're on the air, within 100 years you've invented your intellectual successor, artificial intelligence.

"The origin of intelligence is still a mystery. We don't know why it happened here."

That means that the majority of the intelligence in the universe, assuming there is some, is synthetic intelligence. It isn't biological, soft, squishy intelligence. Consequently, that might change your SETI search strategy somewhat, because you don't necessarily require an Earth-like world for that. Biological intelligence may be a short-term player.

You could come to that conclusion independent of the findings of exoplanets, right?

You might think that anyway. But SETI proceeds from the most conservative to the somewhat less conservative thoughts. Frank Drake's original SETI experiment was predicated on looking at sun-like stars. Those were the targets. Today we know that sun-like stars aren't the only ones that could host habitats for life.

How many communicating civilizations do you think there are in the universe?

I don't venture guesses on that. I just take the guess of my colleague whose office is right above mine, Frank Drake, who estimates 10,000 in the galaxy. Well, that sounds good.

Would you say that most or even all scientists believe that there is life—not necessarily intelligent life—elsewhere in the universe?

I think you'll find that well over 90 percent of scientists think that there is life beyond Earth. Because otherwise you're asking them to believe in an extraordinarily unusual situation, and they're conditioned by history to be suspicious of any such things. There is plenty of precedent for showing that if you think you're a miracle, there's good reason to think that's probably not true.

INTELLIGENT LIFE

Do you think there's any kind of scientific consensus around the question of whether there's intelligent life besides us in the universe?

If you ask a thousand scientists do they think there's intelligent life beyond Earth, I don't think it is going to be more than 90 percent. It'll still be the majority, I'm quite sure, but it won't be quite as high as saying life. Because the origin of intelligence is still a mystery. We don't know why it happened here.

Some scientists argue that the evolution of Homo sapiens was the result of happenstance and contingency and so forth. They could name 10 different things in the evolution of life on this planet that, if they had gone the other way, we wouldn't be having this conversation. There'd be dinosaurs in downtown Somerville.

But that's very difficult to say, because we don't know whether the circumstances that resulted in intelligence here on Earth really were all that special.

"If you can build a radio transmitter, then you're intelligent."

Does intelligence have enough value that, sooner or later, it will spring up on a lot of these worlds that have life? It only has to spring up on some fraction of them that's not zero, and then you might have a target for SETI. It's true that intelligence engenders more debate than just saying life in space.

What do you think is the best way to define intelligence for the purposes of this question?

For this question we just have an operational definition: If you can build a radio transmitter, then you're intelligent. That's it. It's real simple. And, you know, it doesn't mean that you're very good at composing rock 'n' roll, for example. But it does mean that we can hear you. And then, suddenly, we define you as intelligent.

If there were some other way to search, would the operational definition of intelligence be different?

Yeah, because for the people who do optical SETI the definition of intelligence is that you can build a powerful laser. But that's hardly any different. They're more or less at the same level of knowledge and technology. There are no low-tech ways to get in touch across many light-years of distance.

THE DRAKE EQUATION

In the Drake Equation, what are the factors that we can assign values to with the greatest confidence? And what are the factors that are hardest? [The Drake Equation is used to estimate the number of detectable extraterrestrial civilizations in the Milky Way.]

That hasn't changed since 1961, when Frank Drake cooked up the equation. We know the first couple of terms. We know the rate of star formation, you know, within a factor of two or three or something like that. And that's good enough.

The next term, which is the fraction of suitable stars that have planets, they estimated that to be 10 percent. The real answer may be 50 percent or 80 percent or something like that. Research has sort of validated the optimism of the early estimates.

"If I gave you a million worlds that are covered with liquid oceans and thick atmospheres, quite a few of them would produce life."

What fraction of these might have planets somewhat similar to Earth where intelligence could arise? That we still don't know. But Kepler [a NASA satellite searching for planets that lie within the habitable zones of their solar system] is quickly going to fill that number in, maybe within the next six months, next year, whatever. And it's looking like it'll be a number between 1 and 10 percent, which again validates the early optimism. This is the remarkable thing about the new research—it's looking good.

So those three terms, you know something, but after that the fraction of planets that are habitable on which life will arise—we don't have any data there. So all the other terms are still speculative. There's been a little bit of movement in some of them. You can say that we have found extremophiles. We have some theories about how life got started on Earth.

If I gave you a million worlds that are covered with liquid oceans and thick atmospheres, quite a few of them would produce life. That's not proven, but it doesn't seem so unreasonable anymore. The fact that life got started very early on Earth is sometimes used as an argument to say it's not so hard.

In terms of the rise of intelligence, it's just basically Darwinian evolution that pushes some species in the direction of higher intelligence. But we're still, fundamentally, stuck with the astronomical terms. Those are the ones we've really had data for.

It's hard to have only one data point, only us here on Earth.

Indeed it is. It's so hard. Everything you say is slightly inconclusive.

WHAT'S NEXT FOR SETI?

Can you imagine a new finding that would significantly change the odds, short of actually hearing from an extraterrestrial intelligence? A game-changer?

From my point of view there's a three-way race to do that. SETI is only one of those horses in the race. The other two are trying to find life in the solar system by direct exploration, or trying to find oxygen or methane or something like that in the atmosphere of another planet using a telescope.

All those are experiments that could be going on. Most of them are not, for lack of money. In fact, all three horses are hobbled by lack of hay. But you could do the experiment with sufficient funds. I think that within 20 years the funds will come to do these sorts of things.

To my mind the horse that's more likely to cross the finish line is to find some evidence of life on Mars or Europa or Titan or any of the seven worlds in our solar system that might have liquids on them or underneath the icy crusts. And that would tell you right away that life is not a miracle, that biology is going to be around. I don't know if it's a game-changer, but it would validate the optimistic assumption that we have lots of cosmic company.

What do you think is the strongest argument for the existence of extraterrestrial intelligence? Is it the sheer numbers of stars and galaxies?

The numbers, certainly, because the numbers are very, very big. You don't have to have a very high success rate to still have lots and lots of company. So that's probably the strongest argument. The other argument is to say that although we still don't understand how we got smart, it's just not clear that there was some miracle involved. We don't have any evidence that we're different from everybody else.

You've said that intelligence is going to evolve very quickly into synthetic intelligence. How would that change the way you search?

It changes things in two regards. One is that artificial intelligence isn't condemned to a planet like ours. It doesn't have to be a habitable world. It needs matter and energy, but it doesn't need oceans, or moderate temperatures, or anything like that.

That means it could spread out; it could go places where we couldn't survive. They could actually undertake trips between the stars; we might or might not ever go to the stars. So the first consequence is that it might be in different locations than you would expect biological intelligence to be.

The second thing is that they're freed of Darwinian evolution. Darwinian evolution has done okay. It's produced the squirrels outside my window here. But it's bottom-up, and it's very slow. It took four billion years to make us, right? That's a long time, whereas if you're talking about artificial intelligence that can manufacture stuff, then you're designing things. So suddenly evolution is extremely fast compared to biology. And that means you're in a completely different league.

Speaking of machinery, what's the status of the Allen Telescope Array that was being used for SETI? I understand it went into hibernation. Is there any hope of it coming back online?

We're going to turn it back on probably mid-to-late October, though I'm not sure exactly when. But it's going to happen, because there is enough money to put it back online for a while. We hope that we'll be able to establish more secure funding for it on a long-term basis. It will be back pointing the antennas at the sky, rather than at the horizon, within a month.

"I regard SETI more as exploration than conventional science."

The British Science Council recently spent a year working out this definition of science: Science is the pursuit of knowledge and understanding of the natural and social world following a systematic methodology based on evidence. Do you think that's a good definition? And how does the search for alien intelligence fit into that?

I think it's as good a definition as I've heard recently. You might not need a great definition in order to pursue SETI. Nobody has a very good definition of what it means to be alive. What is life? You would think that there would be a good definition for that, but there isn't.

You can always find exceptions to any definition. High school biology textbooks say anything alive has metabolism and reproduction and all that stuff. But I can think of a lot of other things that are clearly not alive that have all those properties, too. So there is no good definition of life, and yet there are plenty of biologists. So in a sense maybe it doesn't matter.

I regard SETI more as exploration than conventional science. Usually in science you set up a hypothesis, and then you concoct an experiment and try to falsify the hypothesis. Well, you can't falsify the hypothesis that there is intelligent life in space. No way to do that. All you can do is hope to find something. You can prove that it's true, but you can't prove that it's not true. So it's a little different than conventional science. It's a scientific exploration.

Do you anticipate something useful technologically to come from looking, even if we never find anything?

There have been developments in digital receiver technologies. I can't say that I've seen anything that has set the world on fire in terms of technology. Sometimes you just don't know what the technology you've developed will be useful for 10 years down the road.

But I never advocate that as a reason for doing SETI. I think that you have to weigh it on its own merits. I think it's a very interesting question that anybody you ask would have some opinion on.

It's a question that people were asking a thousand years ago, but there was nothing they could do about it. We can do something about it. We can actually mount an experiment that looks good on paper. How crazy would it be not to at least try?