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2020 Isaac Asimov Debate: Alien Life 

[150 Years | American Museum of Natural History logo animates out.]

[Text reads, “2020 Isaac Asimov Memorial Debate, Alien Life.”]

[Neil deGrasse Tyson speaks to camera from an office-like setting, with a framed picture of stars behind him.]

Neil deGrasse Tyson (Frederick P. Rose Director of the Hayden Planetarium): Welcome, one and all. I am Neil deGrasse Tyson, your personal astrophysicist. You…if you are seeing me now, you are live streaming our—is it 19^th or 20^th—annual Isaac Asimov Panel Debate from the American Museum of Natural History. And this was started back—when Isaac Asimov died, we wanted some way to remember him. He was local to the upper west side of New York. In fact, many of his more than 600 books were written based on research he conducted at our institutional library.

And so, his family got together, they joined us to figure out a way to remember him. And he had covered so many topics in his novels as well as his books of nonfiction, that we felt that a good way to remember him is to keep a living memorial in his name, the Isaac Asimov Panel Debate. And every year, we take some new topic that’s hot and interesting and unsettled, primarily, and this year’s topic is the search for alien life on earth and in the universe.

By the way, this year, we are celebrating—is it the—celebrating the birthday of Charles Hayden himself. Is it the 100^th anniversary? You know, I should have looked that up, and I didn’t. I’m sorry about that. But anyway, we’re celebrating him, Charles Hayden, who first put out the money to bring the universe to New York City and create what famously became the Hayden Planetarium, where I now serve as director.

I had actually attended there as a kid. That’s my first night sky. You grow up in the city, you don’t know anything about a night sky until you go into a place where there’s an expert, and they can point it out to you on a dome because the buildings are tall, the lights are bright, pollution was rampant at the time. And so, planetariums have a way of influencing us all, I think, especially me when I was a kid. But let’s get straight to this.

The format of this evening is I have five panelists, each a world expert and why we have them on this panel. And you’re going to eavesdrop on us. This is not a formal debate, point/counterpoint. That’s not how we do this. There’ll be topics that’ll be put on the table, and each of us will explore them coming from the point of view of our own expertise, at their own expertise. And you get to hear scientists thinking out loud. And it’s as though you’re eavesdropping on a conversation we’re having at a conference lounge, between talks or at the end of the day. And so, that’s the spirit and the soul of what it is we are bringing to you. 

So let me first introduce the entire panel, just so you can get a look at them. All right? Nathalie Cabrol, from the NASA Astrobiology Institute. Nathalie, welcome to the American Museum of Natural History virtually, and thanks for being on this panel.

[Panelist Nathalie Cabrol appears in a split screen with Tyson. She speaks from an office-like setting with framed pictures and a telescope model in the background.]

Nathalie Cabrol (Director, Carl Sagan Center for Research, SETI Institute): Thank you very much for having me, Neil.

Tyson: Yeah, and we’ll come right back to you in a sec. I just want to get everybody up there. Next, I have Vera Kolb of the University of Wisconsin, and…in the chemistry department. Vera, welcome.

[A box with panelist Vera Kolb appears below Tyson and Cabrol. A circular painting hangs on the wall behind her. It is an abstract image with a sperm-like figure entering a nebula-like form.] 

Vera Kolb (Professor of Chemistry, University of Wisconsin-Parkside): Thank you very much for having me.

Tyson: Excellent. And who else do we have? We have Carol Cleland. Did I say that right, Carol?

[The screen is now split four ways as panelist Carol Cleland joins. She sits in front of a book case.]

Carol Cleland (Director of the Center for the Study of Origins and Professor of Philosophy, University of Colorado): You did.

Tyson: Yes, excellent. And you’re at the University of Colorado. A lot of snow there right now, I think, a little premature snow. And you’re the Department of Philosophy there. All right? No conversation is complete until a philosopher says so.

[LAUGHTER]

Tyson: So…oh, you agree with that. Good to see.

Cleland: Thank you, Neil. 

[Panelist Seth Shostak joins the screen. He wears headphones and an old film projector and other equipment are in the background.]

Tyson: Next we have Seth Shostak, an old friend, Seth, from The SETI Institute. There you go, Seth.

[LAUGHTER]

Seth Shostak (Senior Astronomer & Institute Fellow, SETI Institute): Well, it’s great to be here where, you know, the people are still smiling.

Tyson: The people are still smiling. Yes, yes, because we, you know, the whole world is not—can’t always be about COVID at every moment.

Shostak: Well, California is burning. That’s why I say this.

Tyson: Yeah, California’s burning as well. Yeah. So these are all signs of some apocalypse. I’m not quite sure which. And last on this panel, we have Max Tegmark. Max, from MIT Department of Physics, a long-time friend and colleague. Welcome back to you, Max. This is your third time on an Asimov Panel, I think. Is that right?

[Final panelist Max Tegmark joins the group. Behind him on the wall are framed mathematical equations.]

Max Tegmark (Director of the Foundational Questions Institute and Professor of Physics, MIT): Third time’s a charm.

Tyson: Third time. And, Seth, this might be your second time? Is that right?

Shostak: Yep, that’s correct. Yes. 

Tyson: Excellent. Excellent. So it’s great to have all of you. So let’s go back, and I just want to hear if each of you in, take 30 seconds or so, just to introduce yourself and what your expertise is that you’re bringing to the table. Nathalie, let’s start out with you.

[Cabrol solo on-screen.]

Cabrol: Yeah. I am the Chief Scientist at The SETI Institute. I have a background in planetary geology and astrobiology. And I explore extreme environments, and I’ve been doing some work on Mars as well, with rovers.

[All panelists on-screen.]

Tyson: So you have not been on Mars…

Cabrol: With rovers.

Tyson: With rovers, okay.

[LAUGHTER]

Tyson: Just, you know, I never know about you guys. You know, what you…where you’ve been. You said I work on Mars. No, you don’t. You work on Earth.

Cabrol: I work on Earth, but being a part of Mars missions with Mars Explorers and Rovers, Spirit, in particular.

Tyson: Excellent. And you come to this as a geologist, or as an astronomer?

Cabrol: As an astrobiologist with a background in planetary geology.

Tyson: In planetary geology, okay. Excellent. And let’s go to Vera. Vera, tell us about yourself.

[Kolb solo on-screen.]

Kolb: I’m a Professor of Chemistry at University of Wisconsin-Parkside, and my expertise is in astrobiology. I got my training in astrobiology from Stanley Miller and Leslie Orgel. I would like to take the opportunity to…to say to the audience there is a nice book that everybody, I think, will love. It’s called Astrobiology for a General Reader: A Question and Answer Approach, which I wrote with a coauthor, Benton Clark, who is also my fiancé. And for those people who want to go into depth, I spent two years of my life to edit Handbook of Astrobiology, came out in 2019.

Tyson: Wait, Vera, aren’t handbooks supposed to be little?

[All panelists on-screen.]

[LAUGHTER]

Kolb: Well, you see, I started…

Tyson: It’s supposed to fit in your hand. You’re lugging the thing up with your hands…

[LAUGHTER]

Tyson: So just, you know, and you’re still…you still have your fiancé after you finished the book, so that’s a good sign.

Kolb: No. Actually, he proposed after we finished the book, which was very nice.

Tyson: Okay.

[LAUGHTER]

Tyson: It’s still a good sign, still a good sign. Carol, tell us about yourself.

[Cleland solo on-screen.]

Cleland: I’m Carol Cleland. I’m a professor of philosophy at the University of Colorado Boulder and the Director of the Center for the Study of Origins. My area is philosophy of science. I’m especially interested in philosophy of the natural sciences, especially historical science, the geosciences, reconstructing the past. And I’ve been a member of the NASA Astrobiology Institute, both a coinvestigator on several scientific teams, and also a co…key collaborator on several scientific teams. And I’ve written a book on the quest for the universal theory of life and edited a collection of essays on the nature of life from a philosophic-borne scientific perspective.

[All panelists on-screen.]

Tyson: Excellent. Well, thank you—thank you for that. And just for those who don’t know, the NASA Astrobiology Institute is a virtual institute. You can be a participant in that. There’s grant money to support your research, and you would still be—have…keep your native affiliation, wherever that is. But you collectively participate in this sort of unified search for life in the universe.

Seth, also of The SETI Institute, just like Nathalie. So welcome back. So tell us briefly about yourself.

[Shostak solo on-screen.]

Shostak: Well, it’s not interesting, but I’ll tell you anyhow. I’m…I am the senior astronomer at The SETI Institute, which I think is a reference, mostly, to my age. The project that I’m most interested in is SETI, which is a search for extraterrestrial intelligence. In other words, looking for life out there that’s at least as clever as your next door neighbor. And we do that by, well, just what Jodi Foster did in the movie Contact. We try and eavesdrop on radio signals. There are other strategies that we’re looking at as well. And although I’ve written a couple of books, nobody every proposed to me when they were done.

Tyson: Okay.

[LAUGHTER]

Tyson: And you mentioned Jodi Foster in the film Contact.

Shostak: Yes.

Tyson: She used headphones to listen for aliens. Is that what you’re doing right now, during this session?

[All panelists on-screen.]

Shostak: Well, I personally am not, but in fact, our…the…some of our experiments are running, at least I hope they’re running, if they haven’t burned to the ground.

Tyson: Okay. All right. Max, tell us about yourself.

[Tegmark solo on-screen.]

Tegmark: So I’m here at MIT. I’m a professor in the physics department. I’m also in the Center for Brains, Minds, and Machines, and also part of this brand new center we have on artificial intelligence and fundamental interactions. And I hope to bring two things to this panel. One of them is during my work as a physicist, I’ve spent a lot of time studying our cosmos out there, and mapping it, and thinking about the physics of what limits we actually can place on—on life. 

And the second thing I hope to bring is from my work in artificial intelligence, which is what I’ve been doing mainly at MIT for the last few years, which, I think, can tell us a lot about technological life elsewhere in space, and even, perhaps, what kind of space-faring life we humans might create.

[All panelists on-screen.]

Tyson: So it’ll be fun with you as part of this panel, because you’re the only one with no formal biology expertise at all. So…

[LAUGHTER]

Tegmark: And I do have a claim to fame in that I married an alien, actually, which is a little bit related to the time when I wrote my first book…an illegal alien.

Tyson: Oh, okay, I got you. Undocumented alien, I think, they call them.

Tegmark: Undocumented, yes.

Tyson: So…so, but good to hear sort of the base physics perspective on what is and is not possible in the universe. All right. So let’s—let’s get to our…let’s get to our topics. Just so the public knows, I have a list of questions that I’ll be bringing to the panel. And they’ve seen them all, but they’re not bound to them. They can go wherever they want within them, and I have a steering wheel. I just want to make sure I get through the topics, but they’ll take us wherever…whatever off-ramps the moments require.

So, Carol, let me just…no, no, no. Let’s save that one for…no, hold on. We’ll come back to you, Carol.

[LAUGHTER]

Tyson: Nathalie. 

[LAUGHTER]

Tyson: Yeah. Yeah. We can’t lead with a philosopher. That’ll…that’ll…that’ll…

Cleland: That’s where you should lead.

Tyson: No, no. That’ll confuse everything.

Cabrol: Carol, don’t worry. Don’t worry.

[LAUGHTER]

Cleland: You should end with the philosopher. 

Cabrol: I’ll segue to you. Neil doesn’t know what he’s getting himself into.

Tyson: I don’t know what I’m getting into. That’s maybe a good thing. So, Nathalie, tell us, from your…from your side of the fence, what is life?

Cabrol: Well, you know, the interesting response to that is that we don’t have a definition for life, at least not one definition for life. We don’t really know what life is, and basically, we are still trying to figure out. I think that, you know…and the question I really like is that is there a need for a definition for life?

As somebody who is doing, you know, experiment, I think that we can use some definition for life for a specific purpose. But if you are looking at what astrobiology does right now, it’s looking more at what life does. So, you know, the things we can measure, which is like metabolism, physics, and chemistry, that leads to the metabolic activity of life. But then, does that gives us…does that give us any answer to why life is? And then you go into the nature of life.

And so, either you are dealing with the piping of life, which I call the piping of life, like astrobiology does, and then we become plumbers. We are good plumbers. We are worrying about the pipe, what the pipe is, the interaction of the pipe with the water. But does that tell us anything about the nature and where the water is coming from?

And then today, if you are going to other extremes, there are new theories, and I’m taking one out of my hat here, but information technology or quantum physics are taking us in places where science and philosophy are getting much closer together.

Theories like biocentrism are taking life way back at its most extreme quantum level, where you say everything is energy and information, and information is only energy that is being understood, when you can look at it and understand it.

And if this is really that, then astrobiology is only telling us about life as we can understand it. But these new theories are telling you life is everywhere, and maybe the universe is alive. And so, we don’t define life, but then you just understand its manifestation and diversity. And I think this is beautiful. It’s an incredible spectrum.

Tyson: So it sounded like once you brought in information and energy, I know Max will have something to say about that in a few minutes, but does that mean there could be life out there that would not satisfy that sort of base criterion? I know what life is when I see it. You know, that’s the gut, you know. That’s life. That isn’t. Are you saying there might be some ways that life manifests that doesn’t satisfy that gut understanding of what life should be?

Cabrol: Astrobiologists are still trying to figure out whether life is a transition, or if it’s something that happens abruptly because something, you know, weird happened. But these new theories are telling you life is everywhere. There is no need to define life, because the universe is alive. And basically, what we call life is only what we can recognize as life.

Tyson: Well, that’s scary, because there might be life staring us in the face, and we don’t recognize it as life, that I don’t…I don’t know how that encounter will end.

[LAUGHTER]

Tyson: I worry about that. Vera, what is panspermia?

[Kolb solo on-screen.]

Kolb: Panspermia is an old idea, proposed by an old Greek philosopher, Anaxagoras, who believed that universe is populated with seeds of life, and these seeds fell down upon earth and started life. So, at that time, it was just an idea. And about in 19^th century it to start…started to look like a hypothesis.

And at this time, it is definitely a hypothesis, because we have found out that spores of organisms can survive in space. This was done experimentally at the International Space Station. And also, spores can travel through space inside the rocks which protect them from the radiation, and that is called lithopanspermia, again, from Greek. Panspermia means seeds everywhere. Lithopanspermia means seeds inside the rocks.

And then, finally, this hypothesis was strengthened by the discovery that meteorites can travel between planets, for example, Mars to Earth and vice versa, and between other planets. So all of the sudden, what looked like an old Greek idea, now this idea became a hypothesis. It seems to have enough support to be considered seriously scientifically.

[All panelists on-screen.]

Tyson: And we had a readymade word for it.

Kolb: Yes. Definitely.

[LAUGHTER]

Tyson: Already in the catalog. By the way, that—that painting above your head looks a little [spermic]. What’s going on with that painting?

Kolb: Yes. Well, I’m glad you asked this. This is my favorite painting by an artist Mark Dancey from Detroit. You cannot see all of the details, but there are thousands of little specks of paint, which look like stars. And there’s this red balloon traveling through space. I saw it as a sperm traveling through space, trying to reach another planet in the universe. Although, the artist named this painting The Apathy of the Stars, I call it Panspermia.

[LAUGHTER]

Tyson: Okay. Well, all good art should allow you to interpret it in whatever way your feelings require.

Kolb: Yes.

Tyson: And if it’s not, then what…what’s it good for, right?

Kolb: Exactly. Exactly.

Tyson: So, Carol, coming…you come from a whole other side of the fence here, and you’re trying to blow open people’s understanding of and their definitions of life. Where are you trying to…where are you trying to send things? What fights are you trying to create, really, is what I’m getting at here? 

Cleland: So—so I think one of the biggest mistakes is the whole project of defining life, the scientific project define life, because keep in mind that we only…

Tyson: Sorry. To…to define life or to find life.

[Cleland solo on-screen.]

Cleland: The idea of defining life.

Tyson: Defining life.

Cleland: Yes. There are—I won’t go into—there are these serious logical problems that philosophers are well aware of with the whole idea of defining what are called natural kind turns, which are basically categories that are carved out by nature and not human understanding. But our problem with life is we only have a single example. All life on earth is remarkably similar at the molecular level. We’re all descended from a com…all known life on earth from a unique common ancestor.

And I love what Nathalie said about life as we understand it. If you try to define life, you’re dissecting your current concept of life. You’re presupposing that all life in the universe is like our form of life, and we just don’t know that. We certainly know there are certain conditions that are probably similar, but to—and a certain number of them are going to be similar between our kind of life and other life in the universe, probably complexity and, you know, thermodynamic disequilibrium, extracting energy from the environment in order to maintain order, and through an extended period of time against the, shall I say, ravages…

[All panelists on-screen.]

Tyson: Wait. Just to be clear, when you speak of disequilibrium, if we were in total equilibrium with our environment, we could not function, right?

Cleland: Yep.

Tyson: We have to be something really different to be what it is that we are, right?

Cleland: And we know that life does that, but so do tornadoes and hurricanes, and they last longer than mayflies. So I think that it’s important to keep in mind that, yeah, we do have certain things that are almost certainly universal for life, but a lot of the features that we think of as common to life as we know it, even natural selection in the sense of standard Darwinian evolution, what if you had a world which was, you know…

[Cleland solo on-screen.]

Cleland: Natural selection’s really well designed for a world that is not too stable and not too extreme in its changes, so that organisms have a chance to adapt to the environment and to have the kinds of hereditary changes that provide them with the resources for natural selection to operate.

But what if you had a world which was very slow and didn’t have much in the way of extreme environmental changes? It wouldn’t be particularly adaptive to have mutations, because you’d already be well adapted. Mutations also cause organisms not to be so well adapted.

And so, I—I think that we have to be very careful trying to extrapolate some of the things we think of…which are universal for known life on Earth, to alternative forms of life in the universe. Because it’s going to be very environmentally dependent, even though I think there are certain features…there obviously are certain features that are universal to all life, and our form of life exhibits those, but we don’t know what they are.

[All panelists on-screen.]

Tyson: You make an interesting point. I just never thought about it. If you had a completely stable environment, it might be possible to adapt your way into extinction, because there’s nothing to adapt to, and all of these changes are happening beyond your control. 

Cleland: Or you adapt so that you don’t have much in the way of mutations. That is to say maybe initially there’s a period of time, and you become…and the environment’s very stable, and now it’s maladaptive to engage in too many…too much in the way of mutations.

Tyson: So, okay, so you would mutate in such a way that you wouldn’t mutate so much. That’s what you’re saying.

[LAUGHTER]

Cleland: Well, I don’t know how life starts, but if we assume it starts by, you know, we’re getting gradually adapted to an environment, and then the environment becomes very stable, then I think that the kind of natural selection and evolution that goes on on earth might be maladaptive. I mean, you’d have to…it’s…we are in the sweet point between changes happening in the environment too fast, where extinctions occur, like the, you know, end-Cretaceous extinctions when a meteorite hits, and we almost lost everything, and environments which are very, very stable. So evolution’s very well adapted to our environment, but it’s not clear to me the different environment.

Tyson: I like the idea that evolution adapted to us…

[LAUGHTER]

Tyson: …instead of we adapting to evolution. Seth, you’re—you know, one of the letters in your acronym is an I, SETI. And that stands for intelligence.

Shostak: Right. That’s why I don’t have that letter.

Tyson: So let me pick up a baton from Carol, who she implicitly handed me, and I’m going to ask you, you have defined, presumably, ourselves as intelligent, and using that as a measure of the intelligence of a species you’re looking for. Well, what is intelligence?

[Shostak solo on-screen.]

Shostak: Yeah. Well, I…I…not having any—had any personal experience with it myself, I can’t say too much.

[LAUGHTER]

Shostak: But…but…fortunately, fortunately, when it comes to looking for extraterrestrial intelligence, which is to say, you know, aliens, we don’t have to worry too much about these questions that Carol worries about, like what is life, right? Because we don’t have to find life. We just have to find a signal that intelligence made. 

Now, you might say, well, that’s a, you know, a distinction without a distinction, but it’s not really so. If you pick up a radio signal, and that…it’s coming from the sky, and it moves across the sky as the Earth rotates, you know, and that signal is at one spot on the radio dial, the way WNYC is, for example, at one spot on the radio dial, you can say, well, that’s not a quasar, pulsar, or any of those other kind of r’s. It’s a signal made by a transmitter.

Now, what’s behind the transmitter, yes, maybe it’s a little green guy, you know, who looks sort of like us, and if he moved in next door, you might, you know, invite him over to dinner eventually, but maybe it’s nothing like that at all. I mean, in a…it’s not a very sophisticated idea that I’ve promoted occasionally that, in fact, we’re only here to get the machines going. You know, we—we don’t have machines that are intelligent enough to take over Neil’s job, for example, although they probably could take over mine.

But, you know, 50 years from now, that situation may change, and it may be that human intelligence, as nifty as we think it is, may be a very short lived affair. And if that’s the case, then most of the aliens are likely to be, or at least the ones we’d hear from, are likely to be machines. And in that case, this whole discussion about what is life would be like trilobites sitting around figuring out what the dinosaurs are going to look like. Well, they’re going to be kind of a flat and bilateral, and they’re going to rove around on the bottom of the ocean, and all of that would be wrong.

[LAUGHTER]

[All panelists on-screen.]

Tyson: Okay. Did you just analogize us to trilobites?

Shostak: The better of us, yes.

[LAUGHTER] 

Tyson: Just so that…I just wanted to make a note of that.

[LAUGHTER]

Tyson: Max, you…you, like Carol, are…you’re probably on the same side of the fence as her from everybody else. I want to ask you what is life? And is artificially-created intelligence life, in your definition?

Tegmark: I like to define life simply as a process that can retain its complexity and make copies of itself.

[Tegmark solo on-screen.]

Tegmark: And I like it so much that you’ll even find the definition on…on my t-shirt here. 

[Tegmark tilts camera down to show his t-shirt. It depicts a grid. On the Y-axis, text reads “Can it survive and replicate? Can it design its software? Can it design its hardware?” On the X-axis, text reads, “Life 1.0 (simple biological, Life 2.0 (cultural), Life 3.0 (technobiological).” In each of the nine gridded boxes, different illustrations depict the nine different square intersections.]

[Tegmark tilts the camera back to his face.]

Tegmark: And the reason I like to give such a broad definition of life is because I really hate the two anthropocentric definitions, which I view as as carbon chauvinism. My sons, Phillip and Alexander, I looked at their textbooks from the Winchester Massachusetts school system, and where they defined life as a laundry list of—of criteria, including being made of cells and so on, which it seems so narrow that I’m almost certain that if…if Seth finds life in another solar system, it’s not going to meet, you know, that textbook definition. 

Then you asked about intelligence. There, too, I like to think about it in the terms of a process of information, an information processing process, which is simply…in this—in the case of intelligence, able to not necessarily reproduce, but able to accomplish goals. And the more complex the goals are, all right, the smarter it is.

So it’s very easy to imagine that we could design future robots and other AI systems that also meet the definition of life, but we could also make things that are intelligent, perhaps, without being alive or conscious, so that they could help us with things without us having to feel guilty about switching them off. In summary, I feel that the essence of both life and intelligence should be thought of not in terms of what kind of atoms go into it, you know, but in terms of what it’s actually doing from an—an information process.

[All panelists on-screen.]

Tyson: So was this the foundation of your recent book, life…was it…I’ve lost track, 2.0 or 3.0?

Tegmark: 3.0.

Tyson: Life…so what’s life 1.0?

Tegmark: So life 1.0 is really dumb life, like bacteria, and no offense to trilobites. It—it—it won’t learn anything during its lifetime and has its intelligence basically hard coded in by its DNA. And I call us here life 2.0, because unlike bacteria, we actually learn stuff during our lifetime, right? We can install a module in our brain that speaks a new language or knows a new job skill. So we can install new software in our brains, basically, but we still can’t upgrade our hardware. Life 3.0 can replace not just its software, but also its hardware, and the sort of future technological life that Seth thinks he might find would…would probably be life 3.0. If it decides to be stronger or faster or whatever, it can upgrade its hardware.

Cleland: So can I just respond to Max?

Tyson: Yeah, yeah, please. Go ahead. Jump right in.

Cleland: Yes. So, Max, I—I agree with you that it’s probably a necessary condition for life that it be a phenomenon or a system that’s—that’s complex and maintains itself in a sort of out-of-equilibrium state. But that’s not a definition. The problem is you’ve just given some general conditions, and again, we have tornadoes and hurricanes, which last a remarkably long period of time, as we all know, that do the same thing.

So to get actually at life, unless you’re going to count all kinds of phenomenon as living that we don’t normally, you’re going to have to add some other conditions. And I…that’s—that’s what I don’t think we have a good understanding of, which is why I hate people who talk about…I don’t hate people. I hate definitions of life. Sorry. I like them, but I don’t…

[LAUGHTER]

Tyson: I knew it. I felt it. I felt it.

[LAUGHTER] 

Cleland: But—but I think the whole project of defining life locks you into this box, because definitions give you necessary and sufficient conditions. They tell you what life is, and anything that doesn’t fit into the box is immediately consigned to the nonliving category. So I think the word definition is really problematic in…

Tyson: Wait, wait, Carol, but there’s another…possibly another way to imagine this, that you can define something and, depending on the definition, it could embrace something you’d never imagine it could have embraced before. For example, if you…we agreed in the biology books, metabolism…whose…it was your—your son’s book, Max?

Tegmark: Right.

Tyson: Metabolism, cell, it would have to reproduce itself, you know. And—and if you looked at stars, they reproduce themselves. They have a metabolism. They’re born. They live out their lives, and they die. So there’s definitions of life where stars are alive.

Cleland: Yes, and the great Immanuel Kant, a very famous philosopher in the discovery of the…as an astronomer, I think he discovered the galaxies.

Tyson: Well, he…he…he…the nebular hypothesis was very popular and correct.

Cleland: Yeah, the nebular hypothesis. He…and he and other people, going back to Aristotle, did wonder whether stars were alive, because an Aristotle definition of life, it turned out that the very fact that everything on Earth stops—you push it, and it stops—but of course, we have in the heavens these bodies that continue moving. And so, the view was, he thought, that motion, motility was a defining feature of life, because he thought that the natural state of motion was rest.

Tyson: Well, that’s why we don’t learn our life lessons from Aristotle. 

[LAUGHTER]

Cleland: But that’s also a lesson…

Tyson: Galileo came along.

[LAUGHTER] 

Cleland: We may be a bit like Aristotle in our current state of knowledge.

Tyson: Oh, I see. That’s the analogy.

Cleland: Yes. That’s the [indiscernible].

Tyson: So let me ask you, and I’m just…Nathalie, I’m just trying to understand something. You look for alien life…I call it alien life…exotic life on Earth, because there are places that have been sort of biologically distinct, separated for immense periods of time, right? So you’re—you’re intrigued by places on Earth that has truly exotic life. But if we…if we agree that all life on Earth has common DNA and a common single-celled ancestor, how alien is the life that you’re finding on earth? It’s just less familiar to you. Why is that a useful model for anything you might look for anywhere else that’s not Earth?

Cabrol: I think that’s a fair question, except that I wouldn’t call this alien. I wouldn’t say it’s isolated. Nothing on Earth is isolated. We live in a system, and this is maybe something that people have a hard time, you know, figuring out, especially right now, that everything you put in that system is going to come back at you and bite you some time. 

But let’s say that where we go, we go to places that are what we call extreme environments. And they are producing very good analog environment, which means that they are similar to something. And those something are like the very beginning of Earth history, very different conditions, where you had lots of ultraviolet radiation coming at the surface, because there was no ozone layer. But these condition are also very similar to what Mars was at the time. 

And I won’t go back to those, you know, definition of what habitability is and all of these things, but imagine that you have conditions that are very similar from one planet to the other, very early on, and the stuff that makes us, like carbon, like oxygen, hydrogen, and nitrogen, etc., it’s also very common. And we also have found organic molecule on Mars. We know that they are there. Organic molecules are not life. They are the bricks of life, just like Legos. They are only…

[LAUGHTER]

Cabrol: …Legos when they are put on the table, and then you can put them together, and they may become more or less complex, right?

Tyson: We’ve got to complete the analogy. So early life would have been Duplos, but later complex life would be Legos, right? That’s how it…

[LAUGHTER]

Cabrol: Exactly. No, but the point is that when we go to those places, we can look straight in the eyes, and I don’t know if bacteria have eyes, but we can look at these very, very ancient and primitive organism that are telling us something very profound about what life was early on. And in conditions that are very relevant to what, say, Mars or any other planet, for that matter, we can now extend to [indiscernible] planet, because we have this gallery of new planet, try to figure out what life would respond to extreme environment that are analogous to different planets elsewhere.

Tyson: Okay. I had not fully appreciated that important dimension of that work. I kept thinking of it as it’s an exotic life form, and you don’t find it anywhere else in the world, so you study it. But if that environment matches some other environment we know that’s not on Earth, you…clearly, you will learn things from it.

But let me ask, so Vera, if we go to Mars, and we do find life, of the kind Nathalie is imagining, or that you might even be imagining, might it have DNA? Is there anything that we’ve suspic…could…could DNA be universal in the same way geologists expect the rocks to be similar? Iron oxidizes on Mars just the way iron oxidizes here on Earth. Could there be some…and I’ll bet Carol has something to say about this, too, about a universal understanding of life. But could DNA, as complex as it is to us to think about, could it be a universal thing that biology does?

Kolb: Well, let me answer first this way. The first question is is life on Mars, if we find it, or its remnants, the same as life on—on Earth in terms of DNA? Because you were specifically for…

Tyson: I think she froze.

Tegmark: It’s that Martian environment.

Tyson: Yeah. No, the Martian…the Martian…oh, wait. So, Vera, you’re back. Could you give us that sentence…could you give us that sentence one more time, because you froze up on…right in the middle. We think martinis did it, but okay.

Kolb: So to answer your question directly, if we find life on Mars or its remnants, is DNA going to be the same as DNA on Earth? This is the—your question the way I understood it. And my answer is the following. There are two possibilities…or, well, two main possibilities. Either we will find the same type of DNA as we have on Earth, which could indicate panspermia from Mars to Earth, because there is—there is currently an understanding that life could have started on Mars first, and then it was transferred to Earth via panspermia. Or it could be different.

However, in my opinion, DNA or its functional equivalent, the emphasis is on factual equivalent, must exist as part of any life. Now, let me support this somewhat. When you think about DNA or RNA, which are on—on Earth right now, there are literally millions and millions of years of evolution where this was perfected. DNA was perfected for its function.

And when chemists tried to make DNA lookalikes, thinking maybe DNA lookalikes could be important for extraterrestrial life, they did two specific things. They tried to change the backbone of DNA from phosphates to sulfones, and they found out the whole thing collapsed. It couldn’t make a helix. It just coagulated and collapsed, which means there were some requirements for this backbone had to be repeated to charge. Another thing chemists did, they said… 

Tyson: So, when you said it have to be, maybe they’re just not clever enough. Why—why do you say it has to be…

Kolb: Well, I was going to comment on this in a second, in another attempt, and then I’ll comment on this if they’re clever enough. So another attempt was why do we have to have ribose? We could have other sugars. And Eschenmoser, a very talented chemist, basically, synthesized all different sugar analogs of DNA and found out—by the way, the previous work was done by [Bener] with sulfones—and found out it functions, but not so well. Now, talking about not being smart, with all due respect to my fellow chemists, and I’m one of them, we, I think, are very smart, but you cannot do in lifetime of a chemist what evolution did in billions of years. So chemist against the evolution, chemist lose.

Tyson: Okay.

[LAUGHTER]

Tyson: Carol, the—this problem of a sample of one, it plagues all branches of science, and you’re—you’re a philosopher of science broadly, as well as your specific interests. So how do you as a philosopher think about the—the—the singularity…no, I can’t use that word. No singularities.

Cleland: Please, don’t.

Tyson: Max’ll get on my case. How do you think about this, the problem of a…of a singular genesis for anything? 

Cleland: So, I think…so I think in general, it’s a problem. But we’re in better shape with regard to other areas of science, because we have more than one example. We have no evidence, for example, that water on earth is distinctively a single example, like we have evidence that life on earth comes from a single example. And the—and the evidence for that is just what Vera talked about. I mean, it’s actually narrower than that. It’s nucleic acids, where we know that there are alternative bases that could have our created nucleic acids that would be perfectly functional in the right organismal environments, except they aren’t used by our form of life. Same with proteins.

So we have reason to believe, unlike we do for other phenomena, that we really do have a single example. And the column we’re using from the single example, logically, is just very profound. I mean, if you were an alien, and you came down, and you were interested in coming up with a theory of mammals, and you had only zebras to look at, what would you emphasize? What would you think would be the general features of mammals? It wouldn’t—

Tegmark: All mammals have stripes, of course.

Cleland: Yeah, exactly. It wouldn’t be their mammary glands. Only 50% are going to have them.

[LAUGHTER]

Cleland: So it’s only— 

Tyson: And they’re tasty to lions. Yeah. This would be the total conclusion.

[LAUGHTER]

Cleland: And they’re tasty to lions. But—but it’s really important, I think, to see that biology is in a position that other fields, like chemistry and physics, aren’t, because we have good reason to believe that the central category, life as we know it, is descended from a single example, and we don’t know what the alternative possibilities are. Maybe Vera’s right. Maybe always life uses nucleic acids. But it’s not clear to me that environments very different than earth, such as Titan, [Derk Sherks Mikak], just for example, argued that, you know, most of our laboratory work on silicon as a non-carbon based form of life talks about how it doesn’t—it’s not a very—it doesn’t make very good polymers that have the kind of characteristics that, say, DNA, especially, and proteins have. That under environments on Titan, for example, he argues, there’s some reason to believe low oxygen, very low temperatures, no liquid water, it can form much more complex polymers that would have the capacity to, perhaps, provide us with an informational molecule. I—I just don’t think we know what the—

Tyson: So—so Vera’s point was that if it’s not DNA, it’s got to be something that—that codes information.

Cleland: Yes. That—that I’ll agree.

Tyson: And—and—and, Max, if we’re trying to code information, does it even have to be molecular? I mean, that’s—that’s another kind of bias. That’s a—that’s a—that’s a molecular bias, if you will.

Tegmark: Yeah. Let me…I mean, let me give two answers to that. If we are trying to code information in a way that evolution can evolve from scratch, then it’s going to have…be very limited, the—the range of solutions we can…it has to be made out of a molecule that are abundant in the biological environment. It has to be an organism that can self-assemble, and then we get…and so on. Whereas if we get to design it with our intelligence, now you don’t need any of that. There are so many more possibilities, right? And I…I think, for that reason…

Tyson: Well, to—to Vera’s point, we do invoke our intelligence, and it’s human beings working over several months or years, and we’re not getting it, but nature had a billion years to get it right. So…so what do you mean, let’s use our intelligence, and we can…we can figure it out?

Tegmark: What I mean is, if you…if you zoom out and look at this in a more cosmic perspective, then I think in our universe, life will probably end up being like a one-two punch. First it takes a really long time for—for life at our level to evolve. We’ve been sitting around…Earth has been sit…our universe has been sitting around for 17.8 billion years until, you know, the Asimov lecture series was launched, right?

[LAUGHTER]

Tyson: 13.8 billion.

Tegmark: And then in very short order, we went from—from inventing fire to inventing smart phones to flying into space and so on. And we now realize from the laws of physics that it’s actually pretty easy to build technology that spreads life to other solar systems, and ultimately, even other—other galaxies. It can happen way faster than the 13.8 billion years we’ve been waiting so far.

So I think when we look for advanced life elsewhere in our universe, I agree with Seth, that it’ll be very unlikely that the first life we find is still stuck in stage one, its biological stage. It’s much more likely that we’ll see something which has transitioned to a designed, technological stage. And in that case, they’re not going to be using information storage and DNA. They’re going to be using something much more efficient that they invented.

Cleland: So…so can I just say something here? I agree with Seth, but not necessarily with you, Max.

Tegmark: All right.

Cleland: And this is the sense in which I agree with Seth. I think that when you’re talking about intelligence, that robotic forms of intelligence are likely to be—exist in, you know, maybe wandering the galaxies. I don’t know. But I think that calling it life information, purely informational, nonphysical or nonchemical phenomena like this, calling it life, that’s a different issue. For example, you can imagine a simulation of water and a computer, a very complete, very accurate simulation of water, but do you really want to call it water? Are the chemists going to be very interested in it? So, I think life is more like water than it is like intelligence. And that’s, by the way, it’s philosophically— 

Tyson: [Indiscernible] I’ve got to pause for a second on that.

[LAUGHTER]

Tyson: Life is like water, but it’s like…

[LAUGHTER]

Cleland: It’s wet.

Tyson: Let me get back to that in a second. Nathalie, Carol mentioned Titan several times here, Titan, a moon of Saturn with a very thick atmosphere, and you study exotic environments. Is that environment too exotic for you to imagine life to thrive in, given it’s a very cold temperature?

Cabrol: [Indiscernible], and Titan is really about a different chemistry from what we know. But, you know, it’s always the same debate. We have to start somewhere, so we start with the environment we know. If we take what we know, and we just export it to Titan, then we have a problem. But it might be that Titan came up with something completely different. And again, this is not my area of expertise. I am not a chemist. But what we see in the atmosphere of Titan is the formation of organic molecules, and it’s…they are raining down. They are raining down on an environment that is very exotic to us, like ethane and methane oceans.

We also know that there is a water [indiscernible] ocean underneath, under the surface of Titan. So what…what if those molecules are actually penetrating in the subsurface and reach that ocean? We don’t know. We really don’t know, but it…

Tyson: But you’re still trying to eek life as we know it out of an environment that could be making life as we [indiscernible].

Cabrol: Because it’s the only thing I can do at this point in time. As I’ve said, I am not a chemist. I am not a [mother] and a chemist. Somebody like Vera, who is doing physics and chemistry, might be able to take those molecules that we know and project them into an environment that is exotic. And this is basically what we are trying to do right now when we are going to those extreme environment and trying to understand how life can adapt, how far it can adapt, how can we stretch it?

And obviously, this is life as we know it. But can it adapt to some of this environment we see in the outer solar system? For instance, is life possible on Pluto, right? Like three years ago, four years ago, I would have waved my arm and say, you know, you are nuts. But see what’s happening. Sharon and Pluto, they are pulling on each other. There is energy. There is shelter. There is etc., etc.

Tyson: Sharon and Pluto, Pluto’s moon, Charon.

Cabrol: Yeah. Yeah. Sharon. And—and so, you see those worlds that are we learning about with Kepler and with TESS and soon with [indiscernible]. We have to start somewhere. I think that it’s absolutely right to understand our constraint, but it’s also fair to say that we have to start with something we know and move from there. And I think we are doing pretty good with that. We are starting to stretch, you know, our gallery or our zoo of potential habitable environment, and by no mean in my mind I am constrained or limited to search for life as we know it. But I am certainly more familiar understanding the constraint of such life and trying to expand them somewhere else. That’s all I…

Tyson: Let me ask you, Seth, is there an analog to this problem in the SETI world? Because you’re assuming they’re using radio signals, you know. There’s been a lot of assumptions going on here. Is there someone stepping out of it and saying maybe they’ll try to communicate in a whole other way? Let’s be more inventive than that?

Shostak: Yeah. Well, certainly, a lot of my correspondence speaks to that. By the way, I…I…I…

[LAUGHTER]

[Shostak solo on-screen.]

Shostak: …do feel that I should point out that the namesake for this debate, Isaac Asimov, actually wrote a paper on alternative chemistries for life. And so, he investigated, you know, whether, for example, silicon-based life, which is the choice of nine out of 10 Hollywood screenwriters, you know, under what conditions would that be possible. Anyhow, not to—to take things away. but…

[All panelists on-screen.]

Tyson: But just to clarify, because I…if—if people don’t remember their chemistry, silicon pops into the creativity of screenwriters and storytellers because it sits directly below carbon on the periodic table of elements. And as you might remember, all of the elements in a column make similar families of molecules to each other. So the—the notion that you just swap in a—a silicon atom with a carbon atom and then replicate life, silicon-based life. So I just want to make sure everybody’s on the same page.

Shostak: Yeah, and underneath…underneath the silicon, I believe, is germanium, and underneath that is tin. And we do have an example of tin-based life in The Wizard of Oz.

Tyson: Okay.

[LAUGHTER]

Cabrol: The only thing that is funny with silicon life is that they are actually coughing sand.

Shostak: Yes, they are coughing sand.

Tyson: I’m sorry. They—they are what?

Cabrol: They are coughing sand.

Shostak: Coughing sand. Well, they should get tested. That’s all I’m going to say. But [indiscernible]…I’m sorry.

Tyson: Go on.

Shostak: No, no, no, your question, you better repeat it, because it’s been so long ago…

Tyson: Oh, yeah. No, no, no. I would say—I was headed somewhere else. I just wanted to get—to hear from you how inventive people could be.

Shostak: Oh.

Tyson: Because you’re…you’re…you’re still listening for radio waves. Maybe…

Shostak: Yeah. Okay. Well, well, yes. You’re right, and—and—and there are plenty of people who will say, well, you know, radio, that’s so old school. But of course, it’s not really old school. Radio is a technology. Television is a radio, right? I mean, the Internet is, your Wi-Fi, it’s radio. It’s all the same, from the same [indiscernible].

Tyson: Seth, you sound like an old man on the porch in a rocking chair, saying it’s all the same. These young’uns, what are they doing? 

Shostak: Well, well, that’s right. I find myself doing that more and more often.

[LAUGHTER]

[Shostak solo on-screen.]

Shostak: But one tries to think out of the, you know, the quadrilateral, whatever, because in fact, we’re already looking for, for example, flashing lasers in space. There are several experiments at the University of California Berkeley and SETI Institute to try and find communication that way, and you get more bits per second, you know, with that kind of communication. So maybe the aliens are doing it.

But I would suggest to you that an alternative approach, which I’ve become enamored of recently, is to look for the most advanced societies, because those, if they are societies, at least the most advanced intelligence, because they’re likely to have done the most to make their presence obvious or not obvious, perhaps. And that is to look for artifacts, right? If you have a really advanced society, maybe they’ve just built a giant, what’s called a Dyson sphere, a…you know, a big fleet of solar panels orbiting in their solar system to collect all of the energy they need. Or maybe they’ve built something else, big, something obvious, something that isn’t natural. Maybe they’ve rearranged star systems. Maybe they’re even trying to change…

[All panelists on-screen.]

Tyson: Are you looking for this? There’s a lot of maybes. I don’t hear you saying that you’re looking for it.

Shostak: Well, I, you know, are you old enough to hear this story? Okay. Let—let me say that we haven’t actually…

[LAUGHTER]

Shostak: …that’s really hard to do, actually. Looking for artifacts is a great scheme. That’s the way they found life in the 19^th century, or intelligence. They looked at Mars, and they saw, you know, crisscross-y lines, which they assumed were canals. So it—it has a long history, but it doesn’t…and it’s not prescriptive. It never tells you this is what you should look for, and that’s the problem with it. But all astronomers should pay attention.

Tyson: Vera, what…what…what pre-life chemistry is required to get life as we know it, or maybe as we don’t know it? Because all life, all biology is chemistry manifested at some complex level. So have you…how much attention is given to what the pre-life conditions need to be?

[Kolb solo on-screen.]

Kolb: Pre…prebiotic chemistry, which is chemistry which occurred before life and occurred naturally without any outside investigators, obviously, intervening, this type of prebiotic chemistry has been now part of laboratory experience, and we have made tremendous progress. What was done before, for example, nucleotides and nucleosides, which were very difficult to be prepared directly from nucleobases and sugars, now chemists, notably Sutherland and Powner, found creative ways to make these prebiotic chemicals.

And so, to answer your question, I do not believe that prebiotic chemistry right now is a big problem for our understanding of life. What is the big problem is how the abiotic to biotic transition occurred. So, you can think about the abiotic chemicals. Let’s say they were all made on early Earth or early Mars or other planets. They were made by this chemical path, was depending which type of chemicals they had, but these chemicals were pretty similar.

So now, we have a heap of chemicals, okay, a heap. That is not life. This heap to become a life has to become a system. Now, what is a system, and how does system differ from a heap? In the system, the parts interact among themselves in a complex manner.

So life as we know it has three subsystems, metabolism, information system, and a—a membrane system. And it is a part of a larger system, which is environment and biosphere. So this is the big system of life. And then we have abiotic heap, if I may say that, and we do not know how the transition occurred. So this is the biggest knowledge gap in the theory of life, and we believe that we can possibly solve this there…you know, through some more experiments. There are experiments along the lines of synthetic life, Craig Venter and others. There are also a few… 

Tyson: Just to be clear, synthetic life is people creating life in the laboratory.

[All panelists on-screen.]

Kolb: Well, we haven’t done that yet completely, but you know, you can sort of take a cell, get its DNA out, and put artificially-made DNA into a cell and cell functions. Okay? So we have not made life from scratch, but I would not be surprised, looking at the tremendous progress, think about the fact that DNA was discovered in 1954, okay? And what we have now is tremendous progress. So I think if we make any sort of synthetic life, it may not be the same replica as our life, which is a historical process.

Tyson: But, Vera, didn’t we all see that movie, where they—we made synthetic life? And it didn’t end very well.

[LAUGHTER]

Kolb: You know, I stay away from any science fiction movie, because science is much more mysterious to me than science fiction movies.

Tyson: So, they asked Ray Bradbury why do you write such dystopic future science-fi novels? Is this what you think the world will be? And he says, no, no, no, no. I write them so that you’ll know to avoid them.

[LAUGHTER]

Kolb: Well, and you know, okay. I think…anyway, what—what I am saying to you is that, in terms of your question, the starting materials are not so important as this transition. And also, the most important thing is we will make functional equivalence of proteins, of enzymes. And there is no algorithm by which we can make an enzyme.

For example, Stuart Kauffman had this great think. He says you cannot have an algorithm for screwdriver, what screwdriver can do. You can describe two or three functions, but there are myriad more functions that screwdriver can do. So for us to lock our thinking into chemicals which could produce exact enzymes as we have, I think it’s counterproductive. It could be anything with the same function. So we are looking for functional equivalence rather than exact replica of what we have.

Tyson: Could it be that you need an enzyme to make an enzyme? So… 

[LAUGHTER]

Kolb: No. Actually, this is a very good question. And going…well, going back to the screwdriver, the primitive enzymes, and this is really fascinating, the primitive enzymes where—they could do anything. It’s like your screwdriver. If you look at what people have who are not mechanically oriented in their toolbox, they have pliers, a screwdriver, and a hammer. Okay. You can do lots of things with these primitive enzymes. And they’re kept through the evolution why? If everything goes wrong, you can always fall back on these old enzymes, which can do anything.

[LAUGHTER]

Tyson: I think a little bit of glue might help, too.

Kolb: Yes.

Tyson: Carol, let—let me ask you, the word biosphere was mentioned here, and in researching your own professional publications, I came across a shadow biosphere?

Cleland: Yes.

Tyson: Could you tell me what that is?

Cleland: Yeah. So I coined the term shadow biosphere about 2003, and a paper came out with Shelley Copley on the topic about 2005. And the basic idea behind a shadow biosphere is the idea that there may have been more than one origin of life on Earth.

[Cleland solo on-screen.]

Cleland: It’s completely compatible with the little that we do know about the origin of life on Earth, and that, you know, we know that there are…and I think Vera mentioned this…there are alternative suites, and Steve Brenner’s done a lot of this work…alternative suites of amino acids that could make proteins that were perfectly functional in the right organismal environment.

Similarly, there are nucleobases, different sugars that could make…this is, you know, nucleic acids, which are different than our nucleic acids that would be perfectly functionable in the right organismal environment. They don’t exist. All life on Earth is just select a small suite of all of the amino acids and nucleobases that are available in nature, abiotically, delivered, in some case, by a meteorite, produced in hydrothermal activities and other cases. So our core of life has just used a small suite of these.

And where…if…you know, if life originated in Earth, and Vera brings up panspermia. And certainly, that’s a possibility, that life itself or some of the basic building blocks of life, perhaps proteins or some oligonucleotides were delivered to earth by meteorites and basically seeded Earth, in some sense. But if life did originate in Earth, then it seems that all of the building blocks for alternative forms of life were available at the time, we don’t know when, that life originated in Earth. And so different, there would be different, shall way say, cradles of life with different chemistry. And I see no reason why they wouldn’t have produced early forms of life, if life is a natural phenomenon, not a scientific miracle, but a natural phenomena that arises under the right physical and chemical conditions.

Tyson: Right. So where is it now? I mean…so…because if life arose so quickly, as evidence suggests, then why doesn’t it keep arising all around the world in whole other pocket, bio pockets? Is that what you’re referring to as a shadow biosphere?

[All panelists on-screen.]

Cleland: It could be still arising, but the conditions were very different back, you know, during the—4 billion years ago. What I’m more interested in is whether or not there could be microbial forms of life. We know that multicellular organisms are fairly rare. They didn’t…they arose less than a billion years ago, and the Earth is 4.5, some 4.5 billion years. So most of the history of life on Earth had been microbial.

And the question is could there be actually unrecognized microbes on Earth that are descended from an alternative origin of life? And it seems…and it turns out that the tools that microbiologists use to explore the microbial world would not recognize it if it existed. Those are microscopy, and I don’t want to go in…go into more detail, but microscopy and cultivation and metagenomic methods. Metagenomic methods will only…they require hybridization. And hybridization requires similar, you know, nucleic acids, and nucleic acids that differed even modestly, different code…

Tyson: So it could be—it could be sitting under our noses, and we would not…

Cleland: Literally. Literally. And what we know about microbial communities is they contained a variety of low abundant varieties of microbes, and along with abundant microbes. It’s not as if they would be necessarily out competed. Microbes are quite friendly with each other, it turns out. [Indiscernible].

Tyson: What are biosignatures?

Cabrol: I’m sorry. Go ahead. Go ahead. Oh, I just wanted to…

Tyson: So, Vera, you made a comment on Carol’s…go ahead.

Cabrol: …comment on what Carol was saying is that from the astrobiology standpoint and the exploration standpoint, the search for life beyond Earth, personally, I think that, you know, engaging our self in trying to understand the shadow biosphere and how to figure out if there is another type of life on Earth that we cannot recognize is one of the best avenues and probably one of…the one that will take us the most rapidly to find life somewhere else, because this is typically, typically the kind of—of thing we need to do. We need to actually push the boxes we are…we have put our self into.

The shadow biosphere is one example of the type of individual framework, I would say, that we need to pursue, in the same way that I see theories like biocentrism today that are blowing out of the water anything we think about life, you know, and what is life, and the nature of life. I’m not saying they are true. I don’t have the—you know, the academic background to understand everything. But I know for a fact as a scientist that by exploring those avenues, we are going to understand what is right, what is wrong, and expand our horizon.

And so, this is what I am saying. I can talk to you at length about biosignature. I am going to talk to you about biosignature as we know it, you know, as we know them. And back again we are here on Earth. Biosignatures, they can be chemical. They can be physical. It can be a mound of stromatolite. Do you know those little blue and green algaes that gave the first fossil on earth 3.4 billion years ago in Australia? People are actually still debating knowing whether it’s life or not.

There are now other studies that are telling us that we have direct or indirect traces of life, and some of the indirect traces of life in those studies are right, they might be 4.28 billion years old. This, too, blew my mind away, because if that’s the case, it just mean that life was there as soon as the crust of our planet had cooled down. So that tells maybe something else about what Vera is interested in, which is panspermia, or the ability of life to be part of the planetary process.

So, you know, I’ve been hearing a lot of things tonight up to this point. But it’s all very much so into what we are used to, you know, into the individual framework and the box we are used to. It’s a lot more exciting and more thought [provocating]…provocative to just push those, you know, those walls and those boxes and collapse them. And I think that, in many ways, what Carol was saying, what biocentrism is saying is bringing those thoughts together, and it might be the best to take us to life beyond planet Earth and thinking about life as we don’t know it.

Tyson: Vera, is intelligence inevitable in an evolutionary arc? Wait. We can’t hear you. Try again.

Kolb: Can you repeat the question, please?

Tyson: Yes, I can, and we do hear you. Is…would you say intelligence is an inevitable on—on the path of the evolution of life?

Kolb: Well, I…

Tyson: And the growth of complexity, molecular complexity?

Kolb: Well, I would like to answer this question two different ways. One is we really do not know what intelligence is. So, if we… 

Tyson: Seth knows, by the way. We understand.

Kolb: Well, yes, but…

[LAUGHTER]

Kolb: …for example…

Tyson: It’s a machine sending signals. That’s intelligence.

Kolb: If we try to…if we try to define life, let’s say, by using a laundry list of characteristics of life, and one of these characteristics is intelligence, then bacteria would not be alive, because we would have intelligence, but bacteria don’t. This is one issue that we have. We always think that intelligence belongs to us, but the lower organisms don’t have it. Still, I would say that even the lowest organisms, acting to their own behalf, they know how to survive, they know how to swim upstream, bacteria, to get some sugar, not to talk about mammals, if you have a cat, let’s say. You look at in cat’s eyes, you know, you see devotion and emotion. So, okay, so this is…

Tyson: No. I see that they don’t really care about you at all. That’s just what I see when I look into a cat’s eyes. 

[LAUGHTER]

Kolb: They don’t. They don’t. Absolutely. And that’s why we desperately try to make them love you. Okay.

Tyson: Or they’re putting on a good act if—if they do. Yeah.

Kolb: Yes. However, to answer your question more directly, you were saying is intelligence inevitable? Philosophically speaking, there may be two different philosophies which claim progress of matter, evolutionary progress of matter towards the highest level that we have now, which is intelligence. I personally do not believe that intelligence of a sort that we have is inevitable. And instead of doing my own philosophy here, I would like to cite one of my favorite philosophers, Nicholas Rescher, who wrote about intelligence and science of aliens.

[Kolb solo on-screen.]

Kolb: And he had this example, out there somewhere, on some planet, there are moles who live underground. They cannot see, and they never saw the light. They do not understand the skies. They would not understand hydrogen line or anything. And since they live underground, they may communicate by the system that is not known to us, maybe some sort of electromagnetic things, which looks crazy initially. But we know now that some birds navigate through magnetic fields, and so on. So I think there are different types of intelligence, and which type of intelligence will develop depends on the circumstances of evolution.

Tyson: Okay, so the intelligence serves the organism in its environment is what you’re saying.

[All panelists on-screen.]

Kolb: That is correct. And also…

Tyson: So, Max…oh, so, go on. 

Kolb: I’m sorry. I just want to add one thing from my childhood. I know this may look like going back too much.

[LAUGHTER]

Kolb: Once I had the discussion with my father saying that how, you know, only we are intelligent, and insects, for example, are not intelligent. And he send me to the library to get a book by Maurice Maeterlinck, you know, about bees. And after I read that book about bees, I said, aha. I have to work on my own understanding, you know, that we are the only species which is intelligent. Bees just develop in a different direction than us.

Tyson: And bees communicate with each other in an abstract language that gives direction as [indiscernible]…

Kolb: Yes, they do. [Indiscernible] later, we found out recently, you know, they do dances. They have very complicated way of communicating. And so, and you know, so we have other societies, like ants and so on. So, let us not be so anthropocentric to say, oh, we are the only intelligent people on Earth. 

Tyson: So—so—so, Max, is it possible that there is a life form out there that is so vastly greater than us in intelligence that it will not see us as intelligent at all? Are we to them what worms are to us? And…and the audacity of us to say let’s look for intelligence in the universe. On that scale, they would not even notice us at all.

Tegmark: If they’re out there and can see us, I—I think they would notice us. They might find us very arrogant to…when we start talking about ourselves as the pinnacle of intelligence, as—as some humans have done, right? But I actually have a…I have a minority view on this. I’m willing to bet with anyone else on this panel, with even odds, that we are the only species in our entire observable universe that’s gotten as far as inventing telescopes. I—I can explain why that is in a little bit, but…

Tyson: What?

Tegmark: Yep.

Tyson: What? 

Tegmark: You know, and for the bet, good. What are the—what’s at stake?

Tyson: Meet me outside.

Tegmark: And…

Tyson: Wait, just to be clear. Just to be clear. Seth, on my tie is an image of the Milky Way.

[Tyson solo on-screen. He shows his tie to camera. It depicts a large glowing mass, surrounded by spiraling dust and gas.]

Shostak: Yeah.

Tyson: Show me—

Shostak: How—how’d you get that picture?

Tyson: I got people. Just…just…I got people.

[LAUGHTER]

Tyson: So how much of the Milky Way have we searched for…has SETI looked for life? 

[All panelists on-screen.]

Shostak: Well, I mean, it depends on looked, your definition of looked. But…that sounds like President Clinton, I guess. What—what I’m saying only is that if you say how much of the galaxy have we looked at very carefully over long range of the radio dial, it’s a few thousand, maybe 10,000, maybe 20,000 star systems. And as you know, there are three or 400 billion star systems.

Tyson: Yeah. You’re talking about a speck.

Shostak: Yes.

Tyson: The tiny little volume.

Shostak: Right.

Tyson: Okay.

Shostak: Yep. It’s a fly speck on your tie. Nobody’ll notice.

Tegmark: Yeah, but…but we cannot just consider the—the limits of our own technology and say we haven’t looked yet, so we—we can’t be sure, you know. If you are a lizard…

Tyson: Wait. Is this your answer to the Fermi paradox, Max?

Tegmark: Yes, it is. Because if I’m a lizard living in the rainforest, and I’ve only explored 10 square meters around where I live, and I…I can’t just draw the conclusion that that must mean that there is…there could be all of this…I can’t draw strong conclusions about what’s elsewhere in life on Earth. Right? We humans have much more advanced technology than—than the lizards, and we’ve come there and screwed over the rainforest already in a really, really major way.

[Tegmark solo on-camera.]

Tegmark: And where I’m going with this is we also know, from our own astronomical observations, right, that there’s over 1 billion solar systems, many in our own galaxy, that seem pretty inhabitable, and then there is another 100 billion or more galaxies in our observable universe.

If any of those solar systems have developed the technolo…a civilization with our level of technology a billion years ago or so, right, there’s nothing in the laws of physics, if they wanted to, preventing them from building very advanced technological life and—and going out and really doing big things in our universe. We’ve talked about the history of life, mostly, so far in the panel, which is fascinating. But I think the future of life is very interesting, too, and we pay tribute to Isaac Asimov today and to Charles Hayden. I just want to put in a tribute to Freeman Dyson as well, who—who left us this year, who may be the really first serious scientific article about the future possibilities of life in our universe. And if I had to summarize it in—in one sentence, what Freeman concluded, it was you ain’t seen nothing yet. All right? He—he basically describes our universe as a Sahara Desert with a little oasis here on Earth, and maybe there is some other oases where Seth can find E.T. But mostly it looks totally devoid of—of life.

[All panelists on-screen.] 

Tyson: We’re with you on that. Where are you coming up with that we’re the only ones with telescopes?

Tegmark: Yeah. For example, and—and so, so obviously, you have to ask, well, what does that mean? And what Enrico Fermi said is—is well, maybe it means that there isn’t, that life is for some reason much rarer than we thought. Though, yeah, it’s hard to detect life as trying to hide from us, maybe there are, in fact, billions of other civilizations on all of these planets there that are just all so excited about the video games they’ve developed that they’ve decided to not go out and do any large scale cosmic engineering projects and also…

Tyson: They’re all in their parents’ basement.

Tegmark: Yeah, in their parents’ basement. But I actually think that’s a very, very unconvincing scenario. You would only need one civilization that was like, hey, I’m going to build the Milky Way version of the Great Wall of China and start doing some Dyson spheres and rearrange my neighborhood…

Tyson: And, wait, Nathalie’s got something to say. Nathalie, what are you—what are you—what are you trying to say?

Cabrol: Yeah, and you know, of course, we can speak a little bit about so—so much around that subject. But there is one thing, and I’m not saying that this is necessarily where my heart is going in terms of—of theories, but there might be something to be said about the possibility of generational aspect of life, which means that it may be, if we want to be really anthropocentric here, that the type of star or the type of material that’s creating life as we know it is just, you know, coming in—into life in the universe right now. And basically, we are the first incarnation, manifestation of the type of life that we can recognize and can communicate with, and it will take a little bit more time. Look at us only 100 years ago or 200 years ago. The fastest way of going from Point A to Point B was the fastest horse you could buy. And now we are shooting spacecraft into space. So, I am not saying this is the right theory, but there might be something like that.

Tyson: Right. Carol. Carol…

Cabrol: [Indiscernible] somewhere that there was probably a lot more [indiscernible] bacteria in the universe than there is actually an E.T.

Tyson: Carol, you wrote a book on the universality of life as we don’t know it. Did I get that title correct?

Cleland: No. It was called The Quest for a Universal Theory of Life, but it’s about that topic. But I want to go back just briefly, because I think it’s really important, to intelligence. Philosophers normally distinguish intelligence from sentience or self-awareness. And sentience and self-awareness have to do with the subjective point of view, this capacity of us to see the world as a unique point of view.

And so, that’s what’s really hard to define. I think that could characterize. Our philosophers are still struggling with understanding what it is to have a mind…not just intelligence, but to have a mind. And so, I just wanted to mention that…that intelligence is not necessarily the same as being conscious or sentient. So, I just wanted to mention that, but you asked…

Tyson: Okay. Okay. Thank you. Seth, Seth, you’ve been trying to jump in.

Shostak: Yeah, [just very quick]. I—I have to respond to Max, because he’s essentially saying that there’s no point in my career here.

Tegmark: Oh, no, no, no.

[LAUGHTER]

Shostak: I’m going to take a paper route, Max, but I will say that I have to admire your audacity, because after all, what you’re saying is, okay, we’re the smartest things in the cosmos, and, you know, that’s great, but isn’t it a little self-referential? It could be that maybe your parents were a little too doting, right, and then they convinced you of this idea.

[LAUGHTER]

Tegmark: I would much rather, of course, have a universe which is much more alive. First of all, I love what you’re doing with SETI, and I love what everybody on this panel is doing for the professional job. When I say I’ll bet you that we are the first life that’s built telescopes, that means more than 50%. It doesn’t mean 99.999%. Of course we should look. It would be the most important discovery ever if we find it, right? But we need to be humble, also, and we can’t just dismiss this by saying, well, you know, maybe it’s too early in our universe for any of this other stuff that…

Shostak: No, no, no, no.

Tegmark: …a late bloomer solar system. We know that already.

Shostak: The universe has had…

Tegmark: There are a lot of [indiscernible] in our galaxy, right, which have been here for over a billion years longer than us. So if most of them got as far as we did, it would take less than a million years for them to spread life throughout our galaxy and do all kind of cool stuff, which they haven’t. And I think…I would just want to come back to Freeman again, because I think there’s a great optimism in—in what he says. It’s like you’re looking out over the Sahara Desert from your oasis, and Freeman Dyson is saying it doesn’t have to be this way forever. One day the Sahara can blossom with all sorts of life, right?

Tyson: It’s called global warming. Yeah.

[LAUGHTER]

Tegmark: And maybe it’s on us, actually. Maybe…

Cabrol: It was very green 2,000 years ago.

Tyson: Yes, exactly.

Tegmark: …for some lucky reason, and it’s up to us to try to not go extinct, and—and maybe we…maybe their…

Tyson: Max.

Tegmark: …first extraterrestrial life on other solar systems [indiscernible]…

Tyson: Just to summarize, you’re saying that you’re content with the answer to the Fermi paradox that there is no truly advanced civilization out there. So—so there could be one, or there’s not, but they—they encounter the same challenges we would have to populate the galaxy. That’s what you’re saying.

Tegmark: And also, though, I’m saying that these challenges are much smaller than we thought when you now factor in artificial intelligence. We don’t have to wait for human minds to invent all of the clever… 

Tyson: Let the machine do it. Vera, what were you trying to say?

Kolb: I just wanted to throw monkey wrench into discussion.

Tyson: No.

[LAUGHTER]

Kolb: I’m citing a very exciting paper…

Tyson: Oh, wait, she froze up again.

Tegmark: Those Martians.

Tyson: The Martians keep interrupting her communication.

Cleland: Martian censorship.

Shostak: Well, but one thing to note about what Max has said, there’s no way for him to prove himself right, but there is a way to prove him wrong, right?

[LAUGHTER]

Tyson: Yeah.

Cabrol: Seth is trying to save his job.

Tyson: Okay, wait. Vera is back. Vera, you’re back.

Kolb: Am I? Yeah. 

Tyson: Vera, you froze up there for a second.

Kolb: I just wanted to bring up for Max to contemplate an idea of directed panspermia, which Leslie Orgel and Francis Crick proposed in 1970s, and they were initially ridiculed for it, but now everybody’s sort of thinking about it. Namely, that life spread through the universe by intelligent bees who sent, essentially, samples of life around in their spaceships of other means. And I think now, since we know about space travel, this became more interesting, because Orgel and Crick felt that life was a rather rare event. And so, maybe some very intelligent planet, population, advanced technological population came up with this way to transfer life elsewhere through the universe.

Tyson: So there, Max.

[LAUGHTER]

Tegmark: I think we have a moral responsibility to not dismiss the possibility that—that we have this amazing responsibility on our shoulders, because I think we’re really reckless, frankly, with how we take care of our planet. We’re really terrible…

Tyson: You think?

Tegmark: …take care of it. Right? And if they just tell us that’s okay, if we go extinct because there are all of these other civilizations, we know they’re going to bail us out, then we are, like, even more reckless. I think we should be open to the possibility that maybe the destiny of life in our cosmos is up to us, and…and be better stewards of the opp…of the Earth we have.

Tyson: So we’re running short on time. I just want to make sure I hit a couple of things. So, Nathalie, you have a book…you wrote a book…or coauthored a book on habitability on Mars? Is this…do you want to terraform Mars? What’s your objective with…

Cabrol: No. No, absolutely not. In fact, it’s a collection of chapters where we are talking about the past habitability of Mars and the potential for life on Mars at the beginning of the history of Mars.

Tyson: Okay. Very good.

Cabrol: So this is really a book that’s looking at, you know, the potential for missions like Curiosity, where they should be looking at what type of environment, etc.

Tyson: To find the life that might have been there back when it was a…

Cabrol: Yeah. Yeah. Absolutely.

Tyson: A fertile haven. Very excellent there. And—and, Carol, you have to tell me…Carol, you have to tell me about your—your universal theory of life in—in 90 seconds.

Cleland: I don’t have a universal theory of life. What I do is I try to discuss…people have been searching for a universal theory of life since Aristotle. Aristotle thought he had a universal theory of life. And I argue, in my book, that biology is the only field that is still wed to fundamental Aristotelian distinctions, namely Aristotle distinguished…he distinguished, basically, what we think of as metabolism, the ability to self-organize and maintain self-organization, and the ability to reproduce, which nowadays, we have added, of course, with Darwin, with a hereditary system.

And so, we’re still—if you look at theories of the origin of life, they divide along those lines. If you look at theories of the nature of life, they divide along those lines. And if you look at chemistry, we got rid of Aristotle’s, you know, five…Aristotle thought fire, earth, wind… 

Tyson: Elements?

Cleland: …yeah, go on and on. And same with the idea…Aristotelian idea that rest is the natural state of motion. And it was getting rid of those Aristotelian ideas that actually led to the flowering of the physics and also chemistry. And yet, here we are in biology, still wedded, as revealed in theories of the origin of life, nature of life, to this bifurcation of fundamental characteristics of life. So…

Tyson: Everybody’s stuck. They’re stuck is what you’re saying.

Cleland: We need to go beyond the Aristotelian concepts. We need to do what physics and chemistry did.

Tyson: To unify.

Cleland: Well, not to unify, but to think of…to consider the possibility that our foundation, for thinking about life, is fundamentally mistaken.

Tyson: Fundamentally mistaken. Well, let me end with one final question–Nathalie, what is your favorite…this is, like, for Seth’s benefit…Nathalie, what is your favorite Hollywood alien, and why?

Cabrol: I am totally…I am a sucker when it comes to that. I am a romantic, so I go for E.T.

Tyson: E.T., ooh, E.T. Very good. By the way, Steven Spielberg told me that when he created that character, that character was a vegetable rather than an animal. And even though we want to think of it as an animal, because it walked and talked and had fingers and things, but notice how good it was with plant life. It could touch plants, and the plants would come back to life. So in—in his original thinking of that entity, it was a plant rather than an animal. So, Vera, what’s your favorite…what’s your favorite Hollywood alien? Can’t hear you. Unmute.

[Kolb solo on-screen.]

Tegmark: The Martians.

Kolb: Also E.T. for three reasons. It’s cute, it’s friendly, and there is a great representation of planetary protection during this movie. So…and also, no violence. It is just very friendly. In another emotion of E.T., he is lonely for his home. So that is a very nice feature that I like very much.

[All panelists on-screen.]

Tyson: And for those who don’t remember the film or never saw it, the planetary protection is they set up this zone with these sort of hazmat outfits when they had to operate on E.T., because they thought E.T. had died, but of course, he didn’t, because it’s a Steven Spielberg movie. So…so, Carol, who’s your favorite Hollywood alien?

[Cleland solo on-screen.]

Cleland: E.T. is not my favorite. He’s very anthropocentric in terms of a character. The Horta in Star Trek’s “Devil in the Dark” is my favorite, because it wasn’t until they had a Vulcan mind meld of all things and discovered it was a mother…talk about anthropocentric…that was protecting its young that it suddenly was thought to be conscious and sentient and worthy of saving. 

Tyson: So, the Horta was the silicon-based life that basically just looked like a rock.

Cleland: Yes.

[All panelists on-screen.]

Tyson: Silicon being one of the active ingredients in so many rocks. And I remember that the babies were these perfect, spherical eggs, but they were just rocks, right?

Cleland: Right. And nobody would have ever thought, if it hadn’t been for the Vulcan mind meld and the discovery of its anthropocentric characteristics…actually, mammalian…

Tyson: Mammalian, yeah, protecting its young. Right.

Cleland: Yeah.

Tyson: Right. Right.

Cleland: No, it was quite…

Tyson: Very cool. Very cool. And, Seth, what do you have?

[Shostak solo on-screen.]

Shostak: Yeah, well, E.T. is…

[All panelists on-screen.]

Tyson: No, I want to come to you last…

Shostak: Oh, okay.

Tyson: …because you’re the alien finder. Max, what’s your favorite alien?

[LAUGHTER] 

[Tegmark solo on-screen.] 

Tegmark: I’m going to go…I’m going to go with the aliens in the movie Contact. Because…

Kolb: Yes. That’s a good movie, too.

Tyson: That’s a little bit of a cop out, but I’ll go…

Tegmark: No, but I’ll explain it. It’s because I’m always a critic… 

[All panelists on-screen.]

Tyson: A little bit of a cop out. 

Tegmark: …when I see aliens, because they’re so…either so anthropomorphic or—or so in violation of the laws of physics. What I loved about the aliens in Contact is you don’t see them, so I didn’t cringe.

[LAUGHTER] 

Tyson: Okay. Seth? 

[Shostak solo on-scren.] 

Shostak: Yeah. Well, I—I—I got to say, I didn’t know that little E.T. was actually a vegetable. I don’t know if anybody else here is old enough to remember The Thing, a 1951 film, where The Thing from outer space was also a vegetable. They finally parboiled him with electric current. But my…my favorite is the alien from Alien. 

[All panelists on-screen.] 

SHOSTAK: I thought he was just great, and that may be because, you know, I have an uncle who was a dentist in Queens.

Tyson: And… 

Shostak: All right, if you have to think about it, it’s not even worth thinking about it.

[LAUGHTER]

Cabrol: Or maybe ALF.

Tyson: Oh, ALF was kind of fun, with a sense of humor, too.

[LAUGHTER]

Shostak: Yeah, but he didn’t have the bottom of his body.

[LAUGHTER]

Shostak: He didn’t.

Tyson: You had to imagine it. Can I tell you my favorite alien, just speaking as an astrophysicist and as a scientist, I have to say the Blob from the 1958 Steve McQueen movie. There’s one that is not anthropomorphic at all. It’s got no…no spinal column. It’s got no mouth, eyes, hands, fingers. It’s just the Blob. And most people don’t remember that when The Blob landed on Earth, it was completely transparent. Only after it ate its first human did it turn red, and it was red for the whole rest of the movie.

[LAUGHTER]

Tyson: So this was a—this was a creature that defied any biological understanding of any way life could have been. And so, that’s…I think of that every time when I want to wonder what exotic alien life might be. Well, panel, this has been highly illuminating and fun, and it’s great to see all of your expertise coming together in angular ways to enlighten our audience. And so, I just want to sort of give you an applause for that.

[Tyson applauds.]

[CHIMING MUSIC] 

[Program ends. Credit screen appears. Credits read: 

In 2020, the Museum is celebrating the legacy of Charles Hayden, whose vision made the Hayden Planetarium possible and brought the universe to New York City. 

The late Dr. Isaac Asimov, one of the most prolific and influential authors of our time, was a dear friend and supporter of the American Museum of Natural History. In his memory, the Hayden Planetarium is honored to host the annual Isaac Asimov Memorial Debate—generously endowed by relatives, friends, and admirers of Isaac Asimov and his work—bringing the finest minds in the world to the Museum each year to debate pressing questions on the frontier of scientific discovery. Proceeds from ticket sales of the Isaac Asimov Memorial Debates benefit the scientific and educational programs of the Hayden Planetarium.

Video Producers

AMNH / E. Chapman and L. Stevens

Event Producers

AMNH / A. Teruel, B. Desai, and S. Esteves

Executive Producer

Eugenia Levenson

Music

“Earth Cycles” by Richard Stephen Dutnall (PRS) / Warner/Chappell Production Music

© American Museum of Natural History