As part of my article about the search for extraterrestrial life, I interviewed Seth Shostak, a senior astronomer at the SETI Institute in Mountain View, California, about when we'll find ET, why intelligent beings will be artificial, not biological, and why arms and legs make more sense than wheels. Here's the fascinating transcript of what he had to say.
Jennifer Abbasi: How soon do you think we'll find extraterrestrial life?
Seth Shostak: I've said that we'll do it within 20 years, because it's a three-way horserace. Each of these horses has about an equal chance of crossing the finish line first and doing so within two decades.
First, we might just find it within the solar system. There are claims that there are plumes of methane gas leaching out of the rocks on Mars. And that's very strange, because if you release methane on Mars, within 300 or 400 years the sunlight will destroy the methane. So if you're finding methane today, that means something is making it, at least within the past couple hundred years. Some people dispute those measurements, and other people say it can be explained by geology and has nothing to do with life. But there are lots of reasons to think that if you could send a robot to Mars and drill down a couple hundred feet that you might hit a liquid aquifer. You might also find life. When are we going to do that experiment? In the course of the next 20 years, it just might happen. There are other places in the solar system that might have liquid water. To find it requires mounting a big mission with rockets and robots and going to look. The timescale for that is 10, 20, 30 years, depending on the funding.
The second possibility is the Terrestrial Planet Finder (TPF) telescope, which will look for and analyze extrasolar planets. It ran out of funding, which is why it's not being built now, but in the next 20 years, presumably, it will be.
The third way is SETI, looking for intelligent life. The technology would allow you in the next 20 years to examine a million star systems, which is a big number-and I think the right number to have some chance of success.
With these three different approaches, it seems to me likely we'll know within 20 years if there's life beyond Earth. If not, either we didn't spend the money or we're lonelier than we thought we were.
JA: If we ever find extraterrestrial animals, what do you think they could look like?
SS: Nobody really knows, but the facts are that if you just go to your local zoo, you'll find that there are lots of different shapes and designs that work even here on Earth. Most of the things at the zoo don't look like us. We're one design that works. Our chimp pals sort of look like us, so that's a different take on the same basic design. But fish don't look like us, and giraffes don't. They look a little like us, but not too much. And insects certainly don't look like us, and they work just fine.
Life adapts to its environment. This is a planet where the average temperatures are usually above freezing and below boiling. And you've got a thick atmosphere and you've got gravity, and all life here is adapted to that. If you have another planet that's sort of like Earth, a cousin of the Earth, where these sorts of things also exist, then I imagine that a lot of the designs would be familiar to you. Fish look fairly streamlined, particularly fish that have to hunt other fish, like barracudas, or even mammals that live in the ocean, like dolphins. They have to hunt, so they all look like torpedoes. It's because eventually evolution figures out that you can make animals speedier in water if you shape them like a torpedo than if you shape them like, say, a bicycle.
JA: How big could they get?
SS: Animals have been bigger than today in the past, but not much bigger. The whale is probably as big as anything ever got. There's a limit to how big you can make an animal, because their strength goes up as the square of their size but their weight goes up as the cube. So that means if you make things too big, they become kind of incapable of being very nimble; they can't move around. If you were to make something the size of 10 elephants, it wouldn't work anymore because its bones just couldn't be strong enough to support it. It couldn't move around, it would just collapse. So the fact that animals have never been a whole lot bigger than they are today just reflects a basic engineering problem that will be the case on any planet.
JA: And is the same true if you go in the other direction? Could extraterrestrial bacteria be a million times as small as ours?
SS: Well, the answer to that is probably no, because if you make it a whole lot smaller, then there isn't enough volume inside microbes to do the chemistry that is life. You just don't have enough molecules in there. So there are limits anywhere, I would think.
JA: In terms of land animals, what are the characteristics that we tend to have in common that could show up on another planet? Appendages or heads, for example?
SS: Heads are a good deal, and I think they would be a common feature. It's hard to think of species that don't have heads, although there are some. It's good to have a head because it puts some of the sensory organs-eyes, ears, whiskers or whatever-next to the CPU, the brain. And that's a good deal because to get the information from your eyes to your brain, for example, you don't want that to take a whole lot of time, because then you can't react quickly enough, and you get wiped out. So you want your brain to be close to your eyes. Having them up high is usually an advantage because you get a better view and you can see predators or prey, depending on what your interest is. So all of those things point to animals having a head where the sensory organs are.
Having appendages is the result of the fact that we live on a planet that didn't come prepaved. The Earth wasn't born with railroads or roads everywhere; it just had this rough topography. And so if you had animals with wheels, for example, they'd have a hard time getting around. Appendages are much better for that. You can scamper around the ground, climb into the vegetation. And then it turns out that they're also good for wielding screwdrivers and soldering irons. So eventually appendages are useful for technology, too.
We have two arms and two legs, and that's because we came from some four-lobed fish way back. But what if we'd been a six-lobed fish? Then you could play piano duets because you'd have four arms instead of just two. Most of the animals on Earth have six legs, not four. They're called insects. Six works. Probably if you had 106, that wouldn't work so well because it takes too much brain to coordinate it all. So a lot of it just depends on the happenstance of evolution.
JA: What about plants? Are they likely to exist elsewhere?
SS: Plants on Earth managed to pull off a really nifty trick, and that was how to turn nothing more than gases they could find in the atmosphere, a little bit of water that falls on them occasionally on the ground, and sunlight into food. That was a great trick, and of course we call it photosynthesis. Photosynthesis is a great way to convert the environment into food. You would think that that would eventually appear on any planet because it's just an opportunity that's so advantageous-if you could do it, eventually it would happen.
JA: So what will intelligent life look like?
SS: Does it matter how we picture what ET looks like, as long as they can build a radio transmitter that we can pick up?
The problem is that we tend to picture ET as looking something like us. And I think a lot of that has to do with movies that always portray the aliens as looking very much like us, variations on us that are very anthropomorphic. Hollywood does that not just because they're naive about this, but I think because they know that the audience needs to be able to read the intentions of the aliens. "Wow, he looks hungry." Or, "Oh, he looks friendly." You know how to read the faces of humanlike creatures. You can read the intentions of chimps at the zoo but not insects when you look at them up close, because they're so different-looking.
There actually is at least one scientist, Simon Conway Morris, who thinks that we're a good design for an intelligent creature and, consequently, if there are intelligent beings out there they will look something like us. I don't buy that. I don't know why we are the best design. That sounds so self-congratulatory.
From the standpoint of SETI, the important argument is that we invented radio around 100 years ago. In less than a century after the invention of radio, we invented computers, and today computers are very commonplace and they're getting faster. Following Moore's Law, they're doubling in speed every 18 months. By 2020, most home computers will have the computing power of a human brain. That doesn't mean that they are brains, but it means that in terms of raw processing, they can process bits as fast as a brain can. So the question is, how far behind that is the development of a machine that's as smart as we are? A machine that can take over your job and write articles for Popular Science. We're talking about artificial intelligence. Maybe that will take 10 years, maybe 50, 100 or 200 years. There are some people who say we'll never be able to do it. I don't believe those people. Whether it takes 20 years or 200 years, the point is that you invent radio and then, within a few centuries, you've invented machine intelligence.
Most of the intelligence out there must be artificial intelligence. We keep looking for critters like us living on a planet like ours, where in fact the majority of the intelligence out there is not biological. That would be my argument. The timescale to go from being technological so we have some hope of finding you, to going to an artificial-based intelligence is very short.
JA: So what is the definition of the type of artificial intelligence that you're talking about?
SS: From the standpoint of SETI, we consider something intelligent if it can make a signal we can pick up. Can it build a radio transmitter? Can it build a big laser? If it can, we might be able to find it. Of course, that doesn't say anything about whether they have art or music, if they're peaceable or non-peaceable, or whether they're little, soft, squishy gray guys-billions of them on a planet running around doing their thing-or whether they're thinking machines hanging in space or special places in the galaxy.
JA: When do you think we'll find intelligent life, or it will find us?
SS: Finding us is actually harder, because how could they find us? You could conceivably pick up our television, our radar, our FM radio, but you have to be close enough for the signals to have gotten to you within, say, 70 light-years. The number of stars within 70 light-years is maybe a few tens of thousands, but it's not a very big number. I don't know that they're going to find us until we've been on the air for a lot longer. But for us to find them is maybe not such a problem because, after all, the universe has been around three times as long as the Earth has. There has been plenty of time for other intelligence to get way beyond us, so they might have been sending signals for a long, long time, literally millions or even billions of years. There could be signals washing across our planet all the time that we just haven't found because we haven't done the right experiment.
JA: Is there any way to estimate how long it will be before we come across something?
SS: In a paper I wrote a couple years ago, I looked at the increase in speed of our SETI experiment, and I took some reasonable, or what I thought were reasonable, estimates of how many societies are out there broadcasting. I took the range of estimates from 10,000 to a million. Ten thousand is what Frank Drake, the founder of SETI, usually says, and a million is what Carl Sagan said, and those are both guesses. But if those guesses encompass the right number, then you can combine that with the speed of SETI searches as they will increase in the future. I estimated that it was two dozen years until we detected a signal. Within two dozen years we'll be able to look at a million star systems. As of today, we've looked at maybe 1,000 carefully in the radio [wavelength]. That was the basis of the argument. But the point of the number was not two dozen years, so much as it was to say that this is an experiment that, if SETI has any merit, will work relatively soon, within a generation, rather than something that might take 1,000 years.
There have been 10,000 generations of humans before us, 10,000 generations of Homo sapiens before you were born. I think that you're the first generation that will learn whether what's happened on Earth is a miracle or something that's happened many, many times.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.