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My guest today, Jill Tarter, has spent her career on the search for extraterrestrial intelligence, also known as SETI, S-E-T-I. She led programs at NASA and co-founded and led the SETI Institute for 35 years. If you’ve read the book Contact written by Carl Sagan or seen the movie, Jill was the inspiration for the hero, played in the movie by Jodie Foster.

Jill TARTER: It doesn’t matter what I believe. The universe is as it is, the galaxy is, as it is. And it contains, or doesn’t contain, a particular number of technological civilizations.

Welcome to People I (Mostly) Admire, with Steve Levitt.

 Many people are fascinated by the search for intelligent life elsewhere in the universe because they have a deep yearning to know we’re not alone. My own interest in the topic is less romantic and more pragmatic. Many of the problems I work on involve detecting weak signals in noisy data, and nobody faces a harder signal-detection problem than Jill Tarter.

LEVITT: You spent most of your professional life searching for intelligent life beyond earth. And I suspect that’s a pretty polarizing endeavor with some people seeing it as one of the most inspiring questions in science and others may be wondering what the point of it even is. I fear that the audience that listens to this podcast may skew a little bit towards that letter perspective. So, what arguments do you make to skeptics that might convince them they should want to listen to our conversation?

TARTER: Well, I think to know whether there is other intelligent life in the universe is really fundamental to helping us solve our future challenges. We face on this planet, all kinds of challenges that don’t respect national boundaries. And thinking about life beyond earth, thinking about life that isn’t related to us — the idea that, somehow, they managed to survive long enough so that we can be close to them both in space and time in this galaxy that’s 10 billion years old. So, if we could be co-temporal with another technological civilization, it will only happen if, on average, technological civilizations persist for a long time. And that’s long in cosmic timescales, not in human timescales. The idea that we can discover another technology and therefore learn that it is possible to have a long future will, in fact, help us to have a long future. If somebody else made it through their technological adolescence, then we can as well. So, I don’t think they’re going to solve all our problems. I think we’re going to have to do that ourselves, but anything that encourages us to see ourselves as all the same on this planet, all earthlings, when compared to something else somewhere else, I think will trivialize the differences among us and help us solve these large challenges that we face.

LEVITT: So, that’s a very optimistic view of humanity. The idea that we’ll come together over something abstract when we’re having a lot of trouble coming together over something very concrete, like climate change.

TARTER: That’s right. But we don’t know that it will be possible to stabilize our climate. Yet with SETI, if it succeeds, you have an answer. You immediately know that it’s possible to have a long future, and that it’s worthwhile trying to get there. Yes, it’s a very optimistic point of view, but I think, without it, we don’t have a future.

LEVITT: It’s also true that much of what we do in astrophysics has no particular tangible benefit to us. It’s more about inspiration about understanding our place in the world and being driven just by the excitement of discovery.

TARTER: On the other hand, what astrophysics has told us, over some 400 years of observations, is that it actually takes a cosmos to make a human. So, Carl Sagan used to say that “We’re made of stardust.” And we now actually understand that the calcium in our bones and the iron and the hemoglobin in our blood were cooked up inside a distant star that exploded and spread that raw material out for new solar systems and planets to form. So, we have this intimate connection with faraway places and long-ago events.

LEVITT: I actually have a very different rationale for why I think people should be interested, because what intrigues me about your problem is that it is just so unbelievably hard. How do you detect possible signals of an unknown nature coming from lifeforms we may not even be able to imagine sent from across the galaxy and likely to be faint and trying to be drowned out by all the activity on earth? To begin to solve problems like that, it seems to me, it takes incredible ingenuity and creativity and brilliance. And it’s my experience in academics and in life, I guess, that it’s much easier to steal, or maybe I should say borrow, great ideas that other people have come up with and repurpose them then to try to create brilliant ideas from scratch. I think we should be supporting the search for intelligent life, because I suspect there are great ideas in there that might inform my own economic research or the problem of climate change or whatever tough question a particular listener is struggling with. Do you find that logic at all compelling?

TARTER: Oh, I certainly do. And I often tell young people who I’m trying to recruit into this field is that, you don’t wake up in the morning thinking, “Ah, today I’m going to get a signal because you’ll probably go to bed disappointed.” But what you do is you wake up in the morning and say, “I’m going to figure out some way to make the search better than it was yesterday.” And therefore, we’ve seen 14 orders of magnitude improvement with the signal-processing capability that we have today versus when I started. It’s always about doing a better job and you need to do a better job because you’re faced with this enormous phase space. It’s at least nine dimensional. And I’m not very good at imagining nine dimensional volumes, but I have a thought experiment, which is to say, let’s take all of that volume that we might have to search through in order to be successful. And I’ll set that volume equal to the volume of all the world’s oceans. And then when SETI turned 50, I did a calculation and I said, “Okay, how much of the ocean have we searched?” And it turned out that it was one glass of water out of all the Earth’s oceans. And then 10 years later? Well, now it’s more like a small swimming pool because our computing is getting so much better and faster. But a swimming pool is still not much of the world’s oceans. So, there is a vast challenge out there and I’m really eager to recruit the best and the brightest to help us find new ways of searching more.

LEVITT: Can I go back to the nine-dimensional space? I didn’t understand that. What’d you mean by that?

TARTER: So, if we’re right about searching for electromagnetic signals, then what do we have to do? There are three dimensions of space that we have to look through, we have to look through a dimension of time. We have two senses of polarization for an electromagnetic signal. We have a kind of modulation scheme. If there’s any information on that signal, we have to build receivers that are sensitive to that kind of modulation. And then lastly, we don’t know how sensitive our equipment needs to be. We don’t know how strong a transmitter out there might be, and how far away it is. So, that sensitivity is another dimension, and all of those dimensions have a range. Do we look for frequency? Do we look in the optical? Do we look in the infrared? Do we look in the radio? And for spatial dimensions, do we look in the directions of stars like our own, or do we look at the most numerous and closest stars, which are tiny little red dwarfs? There are all of these different parameters that we need to search through.

LEVITT: So, I know very little about this topic, but I have heard about what’s called the Drake equation and I think that’s actually a really good example of a thought experiment that deserves to be widely copied. Could you briefly describe the Drake equation?

TARTER: Sure. And I actually hate the fact that it’s called an equation, because in fact there are so many uncertainties, you can’t calculate a darn thing with it. Instead, it’s a wonderful way to organize our ignorance. So, you ask yourself, “How many technological civilizations might be out there?” And you start by saying, “They probably had to evolve around a star. So, what is the rate of star formation in the Milky Way galaxy? And of those stars, how many of them would be good hosts for a technological civilization?” So, not very massive that they use up all of their fuel in a few tens of millions of years, probably not too tiny because they don’t give off much energy. “All right, now of those suitable stars, what fraction of them actually have planets in orbit around them? And of those planetary systems, what’s the average number of planets in the system? And of those planets, how many are not too close to the star to be too hot and not too far away from the star to be too cold? How many of them are reasonable for life and technology to evolve? And of all those good planets, what fraction of them actually produced life? And of all those life lifeforms, what fraction of them produced a technological civilization? And of all those civilizations,” remember we started with the rate of star formation, so we have to end with a length of time to make this a pure number. “So, what is the length of time for which that technological civilization does something in order to make itself visible?” So, that’s the Drake equation. It’s a great way to think about all the things that we don’t know about.

LEVITT: So, essentially, when you say it’s a way of organizing our ignorance, it’s basically a guess-timation technique that divides up a really big problem — how many intelligent civilizations might we find, into a series of conditional probabilities. And so, each of those individual probabilities we can think about tackling and then we multiply them together. And that gives us the guesstimate of how many potential civilizations we might find out there. Is that a good summary?

TARTER: That’s a very good summary. And the important thing is that if any of those factors, any of those probabilities are completely unconstrained, that is you haven’t got a clue what the answer is, or that all of the guesses that various scientists make vary by huge factors, then you really can’t calculate anything. Probably the two terms that are least understood and least constrained in that string of numbers that we multiply together, is the fraction of suitable planets where life actually begins, this abiogenesis term. And then the last term, what is the longevity of a technological civilization? And that’s why I don’t like it to be called an equation.

LEVITT: So, going back to the early 1960s, when it was developed, what was the range of estimates that people in the field thought might be the answer to how many detectable civilizations are out there? And this is, in our galaxy, right? Our galaxy is tiny relative to the universe.

TARTER: Well, Frank Drake’s initial estimate was about 10,000. But again, it’s nothing but a guess, and you may be comfortable with guesstimates, but I’m less so. And I think that if I told you an answer to that equation, if I told you a number, it would be more like religion than science. I think that the best summary of where we stand in SETI actually turns out to be the last sentence of a 1959 paper written by Philip Morrison and Giuseppe Cocconi. And the last sentence says, “The probability of success in SETI is difficult to estimate, but if we never search, the chance of success is zero.” I think that’s where we are.

LEVITT: So, that makes sense. But I think what is actually surprising to an outsider is if you take the current again, it’s just a guess but the current kind of ranges that researchers suggest for how many civilizations might be find-able, what’s surprising to me is, obviously, it is a big range, but on the high end, we’re talking hundreds of millions, like really a lot. We’re not talking about four or seven or even 10,000. Don’t you believe there’re actually a lot of them out there?

TARTER: Yeah, but “believe” is the wrong verb here. Believe? It doesn’t matter what I believe. The universe is as it is. The galaxy is as it is. And it contains, or doesn’t contain, a particular number of technological civilizations.

LEVITT: Let me put another way. So, the current state of knowledge in science, as I understand it, is that if you take those individual pieces of the equation, that most of them, we think we have a pretty good handle on. They’re estimated with some degree of reliability. And if you take all of the pieces except for the last one, which is how long did the civilizations last, that some people in your field think those all multiplied out to about one. And so, it all comes down to: do civilizations last for a long time or not very long? Is that a fair assessment of what people think?

TARTER: Yes. For a long time, we would write a short form of the Drake equation as, n is approximately equal to L. So, the number of civilizations is approximately equal to the technological longevity in years. And of course, since I started in this business, we’ve gotten much better at understanding the first terms in the equation. There have been two phenomenal game changers that appear to make the universe more biofriendly. And those two changers are the exoplanets. We can now say with statistical certainty that probably every star has at least one planet. There are more planets in the Milky Way than there are stars. And extremophiles. We know about forms of life that can thrive in conditions that you and I couldn’t possibly tolerate. And which we used to say, with great certainty, “There will be no life there.”

LEVITT: This is like the vents at the bottom of the ocean?

TARTER: Exactly. And that certainly makes it appear that the universe might be more biofriendly than we once thought, but we have to prove it.

LEVITT: Is the current scientific belief that life has to be carbon- and water-based or are there models that suggest that some completely different formation might be possible?

TARTER: Well, life as we know it is carbon-based. And some very clever science fiction writers think about maybe a silicon alternative to carbon. The energetics don’t seem to favor it, but then we’re exploring that in terms of the environment, in which we find ourselves. Maybe under other environmental conditions, it wouldn’t be disfavored, and you could find, silicon-based or some other way of making life. And that’s what’s so exciting about this century. In 2005, there was a statement about, the previous century had been the century of physics and we’d had all of these fantastic successes. And this century was going to be the century of biology and Craig Venter was talking about genomics and proteomics and all of that very bold statement. But I think it wasn’t bold enough. I think this is the century of biology on earth and beyond. I would be really excited to be a young scientist in these times with the opportunity to go looking for life beyond earth, physically in reality with rovers and possibly even people within our own solar system. And then all of these spectacular telescopes that we’re building in the coming decade on the ground and in space. I think this is really going to be an eye-opening century.

LEVITT: So, could you go back to the beginning of the search for extraterrestrial life and what was the initial strategy used to look for that life back in the 1960s, which I imagine was limited by the fact that both there was a new question being asked, and so there wasn’t a lot of thought on it, but also relatively crude technologies?

TARTER: That’s correct. So, Morrison and Cocconi in 1959, suggested that we should use radio telescopes, which were being developed after the end of the second World War. And we should use them at a frequency of 21 centimeters, because this was the first natural emission that we had seen from the cosmos. This is the frequency at which neutral hydrogen emits a signal. And that was the only atom that we knew about back then. And so, clearly for them, this was the obvious signpost. Everybody in the cosmos would know about this neutral hydrogen. Of course, as time went on, we had reason on this planet to try and keep people from transmitting at that frequency so that we could keep it quiet so that astronomers could do their work. But this was the first idea that was proposed.

LEVITT: So, we started out looking for that one frequency of radio wavelength, and how much better have we gotten in that same technology than we were in 1959?

 TARTER: That was a single frequency. And, of course, you have to search in a small range around that frequency to allow for the fact that the transmitter might be moving away from or towards you. And there’s a Doppler shift. So, early on we searched perhaps a few hundred hertz cycles per second. And today our systems are swallowing 10 gigahertz. So, 10 billion hertz, compared to a hundred Hertz. And, of course, the thing is we always reserve the right to get smarter. And we also admit that we may be doing a brilliant job at exactly the wrong thing. Maybe we shouldn’t be looking for light waves or radio waves. We should be looking for zeta rays. But we don’t know what a zeta ray is. We haven’t discovered it yet. And until we do, you’re stuck with the technology and the knowledge that you have at your disposal.

You’re listening to People I (Mostly) Admire with Steve Levitt and his conversation with astronomer Jill Tarter. After this short break, they’ll return to talk about Jill’s role in Carl Sagan’s story Contact.

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Morgan LEVEY: Hey, Steve.

LEVITT: Hey, Morgan.

LEVEY: So, a couple weeks ago we had David Keith on, talking about solar geoengineering.

LEVITT: Yeah. And it was amazing because it is the first time that I’ve talked about climate change without being inundated by angry emails. Now, the first time I talked about it, everyone was mad because I wasn’t green enough because I had too many kids and I wasn’t respectful of the planet. And then the next time when I talked about high gas prices and how that was great because that’s actually doing what a carbon tax would do. Everyone was mad at me for being too green. So, I expected to be deluged with angry emails, because that’s what happened when we talked about solar geoengineering back in SuperFreakonomics. But amazingly, I don’t think we got a single angry email from that episode, which is very unusual.

LEVEY: It was very surprising. But instead, we got some actually really interesting questions from listeners. Just covering some of the basics of solar geoengineering and how it would actually work, which were some of the details that we skipped over a little bit in the interview, because we did focus on more of a high-level concept of its viability.

LEVITT: Yeah, I think I really made a mistake, honestly. A lot of the times when I do these interviews, I don’t know very much about it. And so, I ask the questions that people who don’t know anything would ask. I know enough about solar geoengineering, that I just forgot to ask David about some of the basics. And when the listeners wrote in and said, “Hey, what about this?” I just kicked myself and said, “Oops. Yeah. Why didn’t I ask that question?”

LEVEY: And what we actually did was take some of those questions that listeners sent in, and we sent them to David Keith. So, I’ll ask the questions and Steve, you will answer as David Keith did.

LEVITT: Yeah, I’ll be the mouthpiece of David Keith.

LEVEY: So, to start, one question that we got from several people was: If we use solar geoengineering to partially block the sun, will it lower solar energy capture for solar plants and panels?

LEVITT: So, I thought that was such a great question because I had just never thought about it. And once the listeners brought it up, it seems kind of obvious. So, it turns out the good news is that yes, indeed, when you block out some of the sun, it will make solar panels less effective, but David said only about 1 percent less effective for the kind of geoengineering he has in mind. So, this decrease in sunlight will increase the cost of getting electricity out of solar panels by about 1 percent. But just to put into perspective, over the last decade, the cost of solar energy has fallen by a factor of four — by 400 percent. So, we’re really talking trivial differences around the edges.

LEVEY: Also, the assumption is that the cost of solar is going to continue to drop in the future and it’s going to become way more efficient.

LEVITT: Absolutely.

LEVEY: Okay. So, another question we got was if we injected sulfur into the stratosphere to form stratospheric, sulfate aerosols — which would block the sun — would sulfur rain down on humans?

LEVITT: So, of course it is true that if you put sulfate aerosols into the atmosphere, they will eventually come down. But what’s interesting is that the geo-engineering approach puts these sulfates way up into the stratosphere and it turns out they stay airborne much longer than most human emissions of sulfur. Okay. So, it doesn’t take much to do this geoengineering, only 1 to 2 million tons of sulfur per year. Now that sounds like a lot, but indeed right now, humanity — through industry — is putting about 50 million tons of sulfur into the air. So, David Keith’s program would only be an increase of 2 to 4 percent on what we’re currently doing. So, all in all, this would be some impact, but again, a relatively trivial increase over what we’re already doing.

LEVEY: Here’s another question — and I’m curious about this one: What will happen to sunsets?

LEVITT: It turns out that whenever these big volcanoes have erupted, the sunsets have been extremely vivid, more vivid than we’re used to. The painting, The Scream, if you’ve ever seen that — in the background has his red sky.  It turns out that red sky wasn’t just his imagination. That’s what sunsets looked like at the time because of an enormous volcanic eruption that had happened the previous year. So, I said to David Keith, “Oh, that’s great. Sunsets will be better.” And he actually got prickly and he said, “No, I’m an environmentalist. The best sunset is the one that existed before humankind started messing with it.” So, you can take your choice: Are vivid sunsets better or worse? But they would be more vivid.

LEVEY: That’s great. Well, thank you to everyone who wrote in with questions. We hope this answers them. Thanks for listening to our episode with David Keith. If you have a question for us, our email is That’s It’s an acronym for our show. We read every email that’s sent, and we look forward to reading yours.

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So, I want to keep the conversation going by asking Jill about other strategies besides radio waves that are now being used in the hunt for intelligent life. And then maybe to ask the most fundamental question: Are we really so sure we want to find other intelligent life? Is there any reason to think they’ll be friendly?

LEVITT: To me the most interesting part of the story is how the search has become so multifaceted that it began looking at particular radio frequencies. But now it seems like there’s an entire array of strategies that have developed with the discovery of the exoplanets and with the extremophiles. That there’re really great diversity of strategies now for trying to find evidence.

TARTER: That’s correct. And we’re trying to emphasize that by using the term techno-signature or techno-search, rather than SETI, which has this history of radio and optical searches for signals. And we’re simply trying to ask ourselves, “With the new tools that we’re building, primarily for astronomy to explore the cosmos in different ways, what is it that we might detect that would say to us, ‘That’s someone’s astro-engineering?’” We are building both on the ground and in space, larger and larger optical telescopes, and infrared telescopes. And so, these instruments will be the first time that we actually get to try and image individual exoplanets, except for the less than a handful of systems that are really close by. So, I like to think about the Trappist One System. A tiny, small red star, and seven earth-sized planets around it. And indeed, they’re all at different distances from their host star. So, you would expect them to be at different temperatures, right? The ones that are farther away are colder and the ones that are closer are hotter. But suppose someday, we actually take a telescope and point it at that system and make images of those seven planets. What if it turns out that two or three or four of them are in fact all the same? They shouldn’t be, because there are different distances from their star. But if some technological civilization evolved on one of those worlds and saw all the other worlds in their night sky, maybe they decided they’d like a little more habitable real estate. So, they went over to the next planet and geoengineered it to be whatever conditions they happen to prefer. And then we come along sometime and look at those and say, “Huh, nature shouldn’t do that.” So, that might be a techno-signature for someone to find in the future.

LEVITT: So, I also seem to remember reading about scientists who were looking for oxygen because oxygen is a sign of life? Is that true?

TARTER: Yes. You’re thinking about biosignatures now, not techno-signatures. So, the question is, we’re going to have the ability, eventually, to image distant exoplanets, lots of them. And indeed, if you can collect enough photons from that planetary image, you can make a spectra and you can see what kind of absorption features you have in the spectra. And what are you looking at? You’re looking at starlight, which has passed through the atmosphere of a planet, assuming the planet has an atmosphere, bounced off the surface of the planet and come back out through the atmosphere. And in the process, trace gasses in the atmosphere have an opportunity to absorb some of the starlight at specific frequencies. You can think of it as imprinting a set of fingerprints on your spectra. Places where you’re missing light because it’s been absorbed by a gas in the planetary atmosphere. And so, if you look at a spectrum of the Earth’s atmosphere and the way you do that is by looking at earthshine, the moon — when you see a full moon or you see a partial moon, and you see a lighted and a dark side, that light is reflected sunlight that’s bounced off the earth. And you can analyze it to see what our atmospheric spectrum would look like. And you’ll find that we have a lot of disequilibrium chemistry going on in our atmosphere. We have such strong biological source functions on the surface of the planet that keep pumping in oxygen from photosynthesis, from trees, and plants, and methane from bovine flatulence, from cow fart, and from other sources, that you see this disequilibrium. And it’s very indicative of biology on this planet. And when you compare it to the atmospheres of all the other bodies in our solar system, they don’t have this disequilibrium chemistry. And so, these biosignatures are something that we would like to look for to try and understand whether a potentially habitable planet is actually inhabited. And closer to home there has been the report of the detection of phosphine gas in the clouds of Venus. And that’s very interesting because, on earth, every production mechanism that we know of, for phosphine, actually involves biology. And so, you know, big question. First of all, it was only a single line detection. So, did we actually see phosphine or was it another molecule? And second, is there a way to produce phosphine without biological interaction? And we just haven’t figured that one out yet. We got a lot of really young, excited and smart astrobiologists asking these questions. And the thing that I love about it is that astrobiology is such a new field that it wasn’t all stuffed up at the top with old white males, right? All these dudes that don’t allow for any upward movement by young scientists. But now, the young scientists are just flocking to this field and, pleasantly — in my mind, anyway — some of the best and the brightest are young women. And I love to see that.

LEVITT: So, it’s clear in the way you talk that you have a deep fear of false positives, and I suppose that’s driven by the thought that if you cry wolf a few times it could discredit the entire endeavor.

TARTER: That’s part of it. But the other is that when I first started in this, I had to spend so much time trying to make a distinction between SETI and U.F.O.’s. I think that we have now gotten beyond the “little green men, ha ha ha,” kind of a reaction from the public, but it took a great deal of time to gain that credibility. And so, that’s what I fear losing by not being critical enough within the community of what we announce and how we do our science. Indeed, we’ve even created something that we call the Rio Scale to try and help the media and the public understand both the credibility and the importance of any announcement of the detection of a signal. So, the public’s very comfortable with the Richter Scale. An event that has a Richter Scale of seven is a lot more powerful than five. So, we’ve developed the scale over the years. I think I first introduced it in 2000 in the city of Rio de Janeiro at a meeting, hence the name Rio Scale. You can go on the web and Rio 2.0 calculator, you can take a reported detection, or you can take a science fiction movie, where aliens are detected, and you can go ahead and figure out what its Rio scale might be. And the real important number on that scale is zero because zero indicates a hoax. And once an announcement gets made, the media are endlessly interested in this.  And we benefit from that. But, you know, a hoax gets picked up and it’s really hard to quiet it down. And so, you end up spending a lot of time trying to talk to the media and explaining why this indeed is not a legitimate detection. So, that zero is important. And as soon as you can, label this detection as a deliberate hoax, then you can get the media to die down more quickly. So, yeah, guilty as charged. That’s a hobby horse for me. Credibility is all important.

LEVITT: Let me ask you some more personal questions. You entered the Cornell engineering program as an undergraduate in 1961. And engineering must have been such a male-dominated field at that time.

TARTER: I was the only woman in an entering class of 300.

LEVITT: Of 300. So, you must have been very special for Cornell to admit you, and also very special to have wanted to go.

TARTER: You know, I had decided at age eight that I was going to be an engineer and I told my dad, and he died shortly after that. And damnit, I’m doing it. So, I did it.

LEVITT: So, back in the 1970s, the famous astronomer Carl Sagan wrote a novel called Contact in which the heroine was essentially a fictionalized version of you. Did you pitch the idea to him or vice versa?

TARTER: No, I didn’t at all. Carl sent me a pre-publication copy of the book and I read it and I said, “What? Wait, wait. Carl, doesn’t know this about me. How did he know that? How did he know this?” And then I realized that there had been a meeting sponsored by American Women in Science, in D.C. And the backdrop to that meeting was that Teddy Kennedy was introducing legislation to provide funding for women in the STEM fields who had dropped out to raise their family, and now wanted to come back. But of course, needed to reeducate themselves. And they brought together 80 young female Ph.D.s in all kinds of fields of science and in engineering. It was a life-changing event for me to walk into a room full of smart women. As we sat around, discussing our personal histories, it was interesting that an enormously disproportionate number of us had grown up with our dads being the center of our universe, and then having our dads die when we were young. And we decided that we all learned in a very painful, and a very early way, this concept of carpe diem. If you’ve got a question, ask it now, because you may not be able to ask it tomorrow. And I had mentioned this to Carl, and given him a copy of that report, many years before he wrote Contact. And it turns out that I’m pretty prototypical of the female profile that came out of that report. And so, I think that’s what really — yes, Carl knew me. We were colleagues, we’d worked together, but I think probably more than just knowing me, he was aware of what women who succeeded in male-dominated fields were usually like.

LEVITT: And that book was made into the blockbuster movie Contact starring Jodie Foster, playing you. Were you heavily involved in the movie?

TARTER: I wasn’t heavily involved. I was involved. It was really a great privilege to be able to talk with Jodie. She’s just a wonderful actor and a very kind person, as it turns out. And so, Jodie, when they came to film at Arecibo, I was there. Unfortunately, I left one day too early, because the day after I left, they filmed the scene that has that horrible innumeracy in it. This is Matthew McConaughey and Jodie Foster sitting and looking up at the superstructure, and she says, “Look, there are a hundred billion stars up there. And if only one in a million of those stars had planets. And if only one in a million of those planets had life. And if only one in a million of those life forms were transmitting to us, there would be millions of signals to find.” So, she’s taken a hundred million — 10 to the eighth, and multiplied it by 10 to the minus 18, and come up with 10 to the sixth? No, no 13 orders of magnitude wrong. It was so infuriating because Carl died while that film was still being cut, and Carl had been working on that script and apparently he caught this, and couldn’t get it changed. And we had a memorial service for him down at J.P.L. and they showed that piece to a room full of scientists and engineers at J.P.L. who collectively went, “Hhhh…”  And it just drives me crazy every time I see that.

LEVITT: I imagine the movie Contact opened up all sorts of avenues for you.

TARTER: Yes, I liked doing it. And here’s the thing I like most: is now, 20 years on, a young person, particularly a young woman in graduate school will come up to me and say, “It’s my favorite movie. That’s what turned me into a scientist.” And that’s really gratifying to have somebody say that movie inspired me.

LEVITT: So, Stephen Hawking was extremely hostile towards efforts to communicate with other civilizations, arguing that we had no reason to believe they would have friendly intentions. And certainly, in human history, the Aztecs and Africans who were colonized or enslaved would have wished they had never been discovered. And I suspect most non-human species like the bison and the dodo bird probably feel the same. But you must believe that the possibility of something bad happening is incredibly small.

TARTER: Okay. We’re back to that verb “belief.” It doesn’t matter what Stephen Hawking thought or what I think. Yeah, Stephen did the old quote, “Didn’t work out very well for the natives when Columbus showed up on their shores.” So, the thing that other people are worried about is they’re going to show up on the lawn of the White House and eat us for breakfast. So, the fear is engendered by the fact that they can get here, right? We can’t get there, but they can get here. And that means that their technology is more advanced than ours. And how do you have a more advanced technology? Well, I think you stay around as a technological civilization until you get older and manage to create that more advanced technology. So, if they can get here, we’re talking about an older technological civilization. How do you get to be an older technological civilization? I think that after biological evolution, you get the onset of cultural evolution. And if you’re going to be old and technological and stable, you have to lose the aggressive tendencies that probably helped you get intelligent. And in my mind, there is a possibility that an old technological civilization will, in fact, not be aggressive. The cultural evolution will have changed that tide of biological evolution. And they will be, as Steven Pinker says kinder and gentler than we are now, than we’ve ever been before. And I think, technology well in advance of ours and much older than ours will also be kinder and gentler. But that’s a think. I don’t know that, and neither does Stephen. It’s simply another possibility.

So, what do you think? Are you with Stephen Hawking or Jill Tarter on the question of whether we should be looking for intelligent life or trying to hide ourselves from the universe? Well, the real answer is probably, it doesn’t matter much either way. The likely time horizons are so distant that it isn’t worth worrying about. Putting that aside, though, I would have agreed with Hawking before talking to Jill Tarter. But I actually found her argument surprisingly persuasive. I know I’ve picked a good guest when she changes my mind on something. One more thing unrelated to the topics in this podcast. In July, I’m moving with my family to Germany for a year. My wife is from Germany and we want the kids to experience life there. In anticipation of the inevitable disruptions associated with a move, especially a move to a country where I speak the language so poorly, starting in a few weeks, we’re going to temporarily shift to releasing new episodes every other week. If you’re a loyal enough listener that might be disappointing news. And if you want to express that disappointment or any other emotions or insights or questions, you know how to reach us. The email is That’s Thanks for listening and we’ll see you next week.

People I (Mostly) Admire is part of the Freakonomics Radio Network, which also includes Freakonomics Radio, No Stupid Questions, and Freakonomics M.D. All our shows are produced by Stitcher and Renbud Radio. Morgan Levey is our producer and Jasmin Klinger is our engineer. Our staff also includes Neal Carruth, Gabriel Roth, Greg Rippin, Alina Kulman, Rebecca Lee Douglas, Zack Lapinski, Julie Kanfer, Eleanor Osborne, Ryan Kelley, Emma Tyrrell, Lyric Bowditch, Jacob Clemente, and Stephen Dubner. Our theme music was composed by Luis Guerra. To listen ad-free, subscribe to Stitcher Premium. We can be reached at, that’s Thanks for listening.

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TARTER:  Are you hearing that car alarm that’s going off somewhere outside?

LEVITT: That’s the human noise that interferes with finding the signals you care about.

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  • Jill Tarter, astronomer and emeritus chair for SETI research at the SETI Institute. 



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