Clara Sousa-Silva: Searching for Signs of Life on Venus and Other Planets | Lex Fridman Podcast #195

1. 0:00 – 1:39

   Introduction

   1. LFLex Fridman0:00

      The following is a conversation with Clara Sousa-Silva, a quantum astrochemist at Harvard specializing in spectroscopy of gases that serve as possible signs of life on other planets, most especially, the gas phosphine. She was a co-author of the paper that in 2020 found that there is phosphine in the atmosphere of Venus, and thus, possible extraterrestrial life that lives in its atmosphere. The detection of phosphine was challenged, reaffirmed, and is now still under active research. Quick mention of our sponsors: Onit, Grammarly, Blinkist, and Indeed. Check them out in the description to support this podcast. As a side note, let me say that I think the search for life on other planets is one of the most important endeavors in science. If we find extraterrestrial life and study it, we may find insights into the mechanisms that originated life here on Earth, and more than life, the mechanisms that originated intelligence and consciousness. If we understand these mechanisms, we can build them. But more than this, the discovery of life on other planets means that our galaxy and our universe is teeming with life. This is humbling and terrifying, but it is also exciting. We humans are natural explorers. For most our history, we explored the surface of the Earth and the contents of our minds. But now with space-faring vessels, we have a chance to explore life beyond Earth, their physics, their biology, and perhaps the contents of their minds. This is the Lex Fridman Podcast, and here is my conversation with Clara Sousa-Silva.

2. 1:39 – 14:16

   Discovery of phosphine on Venus

   1. LFLex Fridman1:39

      Since you're the world expert in, uh, well, in many things, but one of them is phosphine, would it technically be correct to call you the queen of phosphine?

   2. CSClara Sousa-Silva1:53

      I go for Dr. Phosphine. Queen is an inherited title, I feel.

   3. LFLex Fridman1:56

      Yeah. But you still, uh, rule by, um, love and power, so ... But while, while having the doctor title.

   4. CSClara Sousa-Silva2:04

      Yeah.

   5. LFLex Fridman2:04

      I got it.

   6. CSClara Sousa-Silva2:05

      Kindness.

   7. LFLex Fridman2:06

      Kindness, kindness. In September 2020, you co-authored a paper announcing possible presence of phosphine in the atmosphere of Venus, and, uh, that it may be a signature of extraterrestrial life.

   8. CSClara Sousa-Silva2:21

      Big maybe.

   9. LFLex Fridman2:22

      Big maybe. There was some pushback, of course, from the scientific community that followed, friendly, loving pushback.

   10. CSClara Sousa-Silva2:30

       (laughs)

   11. LFLex Fridman2:31

       Um, then in January, another paper from, uh, University of Wisconsin, I believe, confirmed the finding. So where do we stand in this saga, in this mystery of what the heck is going on, uh, on Venus in terms of phosphine and in terms of aliens?

   12. CSClara Sousa-Silva2:48

       Okay, let's try to break it down.

   13. LFLex Fridman2:49

       Okay.

   14. CSClara Sousa-Silva2:50

       The short answer is we don't know. Um, I think you and the rest of the public are now witnessing a pretty exciting discovery, but as it evolves, as it unfolds, um, we did not wait until we had, you know, years of data from 10 different instruments across several layers of the atmosphere. We waited until we had two telescopes, uh, with independent data months apart. But still, the data is weak. It's noisy, it's delicate, it's very much at the edge of instrument sensibility, sensitivity. And so we still don't even know if it is phosphine. We don't even really know if the signal is real. People still disagree about that. And I think it ... At the most, more philosophical end of how this happened, I think it is a distinction, and myself and other co-authors were talking about this, it's a distinction between hypotheses generation and hypotheses testing.

   15. LFLex Fridman3:52

       Mm-hmm.

   16. CSClara Sousa-Silva3:52

       Now, hypotheses testing is something that I think is the backbone of, you know, the scientific method, but it has a problem, which is if you're looking through very noisy data and you wanna test a hypotheses, you may by mistake create a spurious signal. The safest, more conservative approach is hypotheses generation. You see some data, and you go, "What's in there?" with no bias. Now, this is much safer, much more conservative, and when there's a lot of data, that's great. When there isn't, you can clean the noise and take out the signal with it, the signal with a bath water or whatever the equivalent of the (laughs) -

   17. LFLex Fridman4:32

       (laughs)

   18. CSClara Sousa-Silva4:32

       ... analogy would be.

   19. LFLex Fridman4:33

       Yeah.

   20. CSClara Sousa-Silva4:33

       And so I think the healthy discourse that you described is exactly this. There are ways of processing the data, completely legitimate ways, checked by multiple people and experts, where the signal shows up, and then phosphine is in the atmosphere of Venus, and some where it doesn't, and then we disagree what that signal means. If it's real, and it is unambiguously phosphine, it is very exciting, because we don't know how to explain it without life. But going from there to Venutians is still a huge jump. And so-

   21. LFLex Fridman5:06

       Venutians. Th- so that would be the, the title for the civilization if it is a li- uh, living and thriving on Venus, is Venutians?

   22. CSClara Sousa-Silva5:14

       Until we know what they call themselves, um, that, that's the name, yes.

   23. LFLex Fridman5:18

       So this is the early analysis of data, or a da- uh, analysis of early data. It, it was nevertheless ... Y- you waited until the actual peer-reviewed publication to know?

   24. CSClara Sousa-Silva5:29

       Of course, and analysis of the two different instruments months apart, so that's ALMA and JCMT, the two telescopes.

   25. LFLex Fridman5:36

       I mean, still, I mean, it's really exciting. What, what did it feel like sort of sitting on this data, like, kind of anticipating the publication and wondering, and still wondering is it, um, is it true? Like h- how does it make you feel that a planet in our solar system might have phosphine in the atmosphere?

   26. CSClara Sousa-Silva5:56

       It's nuts.

   27. LFLex Fridman5:57

       (laughs)

   28. CSClara Sousa-Silva5:57

       It's absolutely nuts.

   29. LFLex Fridman5:59

       In a g- (laughs)

   30. CSClara Sousa-Silva6:01

       I mean ... (laughs)
3. 14:16 – 24:29

   Phosphine gas

   1. LFLex Fridman14:16

      can we talk about phosphine a little bit? Um, so you mentioned it's a pretty-

   2. CSClara Sousa-Silva14:21

      Love to talk about phosphine.

   3. LFLex Fridman14:22

      (laughs)

   4. CSClara Sousa-Silva14:22

      I love phosphine.

   5. LFLex Fridman14:22

      What's your Twitter handle? It's like Dr. Phosphine, I think.

   6. CSClara Sousa-Silva14:24

      It's Dr. Phosphine, yes. You will be surprised to hear, it wasn't taken already. I could just...

   7. LFLex Fridman14:29

      Yes.

   8. CSClara Sousa-Silva14:29

      I just grabbed it. (laughs) Didn't have to buy it off anyone.

   9. LFLex Fridman14:31

      (laughs)

   10. CSClara Sousa-Silva14:32

       (laughs)

   11. LFLex Fridman14:32

       Yeah. So what, uh... What is it? Wh- what's phosphine? Uh, you s- you already mentioned it's pretty toxic and, um, troublesome. And what... What... And outside-

   12. CSClara Sousa-Silva14:43

       Troublesome?

   13. LFLex Fridman14:43

       Troublesome. Sorry. That's the trouble-

   14. CSClara Sousa-Silva14:44

       No, I love it. I'm gonna start calling you troublesome.

   15. LFLex Fridman14:46

       (laughs) The, the, the... So maybe, what are some things that, uh, make it interesting chemically? And why is it a good sign of life, um, when it's present in the atmosphere like you've described in your paper, uh, aptly titled, Phosphine as a Biosignature Gas in Exoplanet Atmospheres? I suppose you wrote that paper before Venus, don't you?

   16. CSClara Sousa-Silva15:11

       I did, yes.

   17. LFLex Fridman15:12

       (laughs)

   18. CSClara Sousa-Silva15:13

       (laughs) I did.

   19. LFLex Fridman15:13

       (laughs)

   20. CSClara Sousa-Silva15:13

       And no one cared. You know, in that paper, I said something like, "If we find phosphine on any terrestrial planet, it can only mean life." And everyone was like, "Yeah, that sounds about right, let's go." And then Venus shows up and everyone was like, "Are you sure?"

   21. LFLex Fridman15:24

       (laughs)

   22. CSClara Sousa-Silva15:24

       I'm like, "I was sure. Before, I was sure. Now that it's right here, um, I'm less sure." (laughs) "Now that my claims are being tested." So, phosphine. Phosphine's a fascinating mos- molecule. So, it's shaped like a pyramid, with the phosphorus up top and three hydrogens. It's actually quite a simple molecule in many ways. Um, you know, it's the most e- popular elements in the universe; carbon, hydrogen, nitrogen, oxygen, phosphorous, sulfur. When you add hydrogen to them, it makes quite simple, quite famous, uh, molecules. You know, you do it to oxygen, you get water. You do it to carbon, you get methane. You do it to nitrogen, you get ammonia. These are all molecules people have heard of. When you do it to phosphorous, you get phosphine. People haven't heard of phosphine because it's not really popular on Earth. Um, we really shouldn't find it anywhere on Earth, because it is extremely toxic to life. It interacts with oxygen metabolism. And everything you know and love uses, uh, oxygen metabolism. And it interacts fatally, so it kills in several very imaginative and very macabre ways. So, it was used as, um, a chemical warfare agent in the First World War, and most recently by ISIS. So, really bad. S-... Most life avoids it. Even life that might not avoid it, so life that doesn't use oxygen metabolism, anaerobic life, still has to put crazy amounts of effort into making it. It's a really difficult molecule to make, thermodynamically speaking. It's really difficult to make that phosphorous want to be together with that hydrogen. So, it's horrible, everyone avoids it. When they're not avoiding it, it's extremely difficult to make. You would have to put energy in, sacrifice energy to make it. And if you did go through all that trouble and made it, it gets, um, reacted with the radicals in the atmosphere and gets destroyed. So, we shouldn't find it anywhere, and yet we do. It's this kind of weird molecule that seems to be made by life and we don't even know why. Life clearly finds a use for it. It's not the only molecule that life is willing to sacrifice energy to make, but we don't know how or why life is even making it. So, absolutely mysterious. Absolutely deadly. Smells horrifically. When it's made, it produces other kind of diphosphines, and it's been reported as smelling like garlicky, fishy death.

   23. LFLex Fridman17:52

       Mm-hmm.

   24. CSClara Sousa-Silva17:53

       Uh, once someone referred to it as smelling like the... Let me see if I remember. The, the rancid diapers of the spawn of Satan.

   25. LFLex Fridman18:00

       Oh, very nice.

   26. CSClara Sousa-Silva18:01

       Yeah, very, very vivid.

   27. LFLex Fridman18:03

       (laughs)

   28. CSClara Sousa-Silva18:03

       And so-

   29. LFLex Fridman18:04

       So, you're a poet after all.

   30. CSClara Sousa-Silva18:05

       (laughs)
4. 24:29 – 35:26

   Searching for molecular fingerprints

   1. LFLex Fridman24:30

      So how do you detect... You started to talk about it, but c- c- can we linger on it? How do you detect phosphine on a far away thing, rocky thing, rocky planet? What, uh, what is, uh, spectroscopy? What is this molecular fingerprint? What does it look like? You've kinda mentioned the wave, but what are we, what are we supposed to think about? What are the tools? What are the uncertainties? All those kinds of things.

   2. CSClara Sousa-Silva24:57

      So the, the path can go this way. You've got light, kind of pure light. You can crack that light open with a prism, or a spectroscope, or water, uh, and make a rainbow. That rainbow is all the colors and all the invisible colors, the ultraviolet, the infrared. And if that light was truly pure, you could consider that rainbow to just cover continuously all of these colors. But if that light goes through a gas, we may not see that gas. We certainly cannot see the molecules within that gas. But those molecules will still absorb some of that light, some, but not all. Each molecule absorbs only very specific colors of that rainbow. And so if you know, for example, that shade of green can only be absorbed by methane, then you can watch as a planet passes in front of a star. The planet's too far away, you can't see it, and it has an atmosphere. That atmosphere is far too small, you definitely can't see it. But the sunlight will go through that atmosphere, and if that atmosphere is methane, then on the other side that shade of blue, I can't remember if I said blue or green, but that color will be missing because methane took it. And so with phosphine it's the same thing. It has specific colors, 16.8 billion colors that it absorbs it and nothing else does. And so if you can find them and notice them missing from the light of a star that went through a planet's atmosphere, then you'll know that atmosphere contains the molecule. How cool is that?

   3. LFLex Fridman26:34

      That's incredible. So you can have this fingerprint within the space of colors, and there's a lot of molecules. And I mean, I w- I wonder, it's a question of, like, how much overlap there is. How, how close can you get to the actual fingerprint? Like, can phosphine unlock the iPhone with its, uh, light so on? You said it's 16.8 billion, so presumably this rainbow is discretized into little segments somehow.

   4. CSClara Sousa-Silva27:00

      Exactly.

   5. LFLex Fridman27:00

      How many total are there? How, how, how a lot is 16.8 billion?

   6. CSClara Sousa-Silva27:06

      It's a lot. You, we don't have the instruments to break these, break any light into this many tiny segments. And so with the instruments we do have, there's huge amounts of overlap. Methane, as an example, a lot of the ways it's, um, detectable is because the carbon and the hydrogens, they vibrate with one another, they move, they interact. But every other hydrocarbon, acetylene, isoprene, has carbon and hydrogens also vibrating and rotating. And so it's actually very hard to tell them apart at low resolutions, and our instruments can't really cope with distinguishing between molecules particularly well. But in an ideal world, if we had infinite resolution, then yes, every molecule's spectral features will be unique.

   7. LFLex Fridman27:58

      Yeah, like almost too un- Like, it would be too trivial. I got-

   8. CSClara Sousa-Silva28:02

      At the quantum level, they're unique.

   9. LFLex Fridman28:03

      At the quantum level, yes.

   10. CSClara Sousa-Silva28:04

       At our level, uh, there's huge overlap.

   11. LFLex Fridman28:07

       Yeah. But then you can start to then, what, try to disambiguate, like, what the mis- the fact that certain colors are missing, what does that mean? And hopefully they're missing in a certain kind of pattern where you can say with some kind of probability that it's this gas, not this gas.

   12. CSClara Sousa-Silva28:24

       Exactly.

   13. LFLex Fridman28:24

       So you're solving that g- gaseous puzzle. I got it. Okay.

   14. CSClara Sousa-Silva28:29

       We can go back to Venus actually and, and show that. So with this, I mentioned there was two molecules that could be responsible for that signal at the resolution that we have. It was phosphine and SO2, um, sulfur dioxide. And at that resolution, it could really be one of the other. But in that same bandwidth, so in the, kind of the same observations, there was another region where phosphine does not absorb. We know that, but SO2 does. So we just went and checked, and there was no signal. So we thought, "Oh, then it must be phosphine." And then we submitted the paper. (laughs)

   15. LFLex Fridman29:05

       (laughs)

   16. CSClara Sousa-Silva29:05

       And the rest is history. (laughs)

   17. LFLex Fridman29:07

       I got it. (laughs) Uh, well, yeah, that's, um, beautifully told. Is there, uh... So the telescopes we're talking about are sitting on Earth? What, uh... Can it help solving this fingerprint, molecular fingerprint problem if we do a flyby? Does it help if we get closer and closer? Or are telescopes pretty damn good for this kind of, uh, puzzle solving?

   18. CSClara Sousa-Silva29:34

       Telescopes are pretty good, but the Earth's atmosphere is a pain. I mean, I'm very thankful-

   19. LFLex Fridman29:38

       Right.

   20. CSClara Sousa-Silva29:40

       ... for it. Um, but it does interrupt a lot of measurements, and a lot of regions where phosphine would be active, they are not available. The Earth is not transparent in those wavelengths. So being above the atmosphere would make a huge difference. Then proximity matters a lot less, but just escaping the Earth's atmosphere would be wonderful. But then it's really hard to stay very stable. And if there is phosphine on Venus, there's very little of it in the clouds, and so the signal is very weak. And the telescopes we can use on Earth are much bigger and much more stable, so it's a bit of a trade-off.

   21. LFLex Fridman30:18

       So is it, um... Are you comfortable with this kind of remote observation? Is it at all helpful to, uh, strive for going over to Venus and, like, grabbing a scoop of the atmosphere?

   22. CSClara Sousa-Silva30:34

       (laughs)

   23. LFLex Fridman30:34

       Or is remote observation really a, a powerful tool?... uh, for this kind of job, like the scoop is not necessary?

   24. CSClara Sousa-Silva30:41

       Well, a lot of people want the scoop, I get it. Uh-

   25. LFLex Fridman30:44

       Yeah. (laughs)

   26. CSClara Sousa-Silva30:44

       I, I get it completely.

   27. LFLex Fridman30:45

       That's, that's my natural inclination, yeah.

   28. CSClara Sousa-Silva30:47

       I don't want the scoop specifically because if it is life, I want to know everything I can remotely before I interfere.

   29. LFLex Fridman30:54

       Yeah.

   30. CSClara Sousa-Silva30:55

       Um, so that's my, I've got ethical reasons against the scoop more than engineering reasons against the scoop. But I have some engineering reasons against the scoop. Scoop is not a technical term, but I feel like now-
5. 35:26 – 50:31

   What does a quantum astrochemist do?

   1. CSClara Sousa-Silva35:26

   2. LFLex Fridman35:26

      So you mentioned simulation, this is super interesting to me and, and this perhaps could be a super dumb question but-

   3. CSClara Sousa-Silva35:34

      Not interesting?

   4. LFLex Fridman35:35

      (laughs) I'm gonna prove you wrong on that one.

   5. CSClara Sousa-Silva35:38

      (laughs)

   6. LFLex Fridman35:38

      You simulate molecules to understand how they look from a distance is what I understand, like what does that simulation look like? So it's, uh, it's talking about the c- the, which colors of the rainbow will be missing, is that the sim- the goal of the simulation?

   7. CSClara Sousa-Silva35:54

      That's the goal but it's really just a very, very nasty Schrodinger's equation, so it's a quantum simulation.

   8. LFLex Fridman36:01

      Oh, so it's the q- it's simulating at the quantum level?

   9. CSClara Sousa-Silva36:03

      Yes. So I'm a quantum astrochemist. Hi, I'm Clara, I'm a quantum astrochemist.

   10. LFLex Fridman36:08

       Can you des-

   11. CSClara Sousa-Silva36:08

       (laughs) Is how we should've started this conversation.

   12. LFLex Fridman36:10

       Can you describe the three components of that, quantum, astro, and chemist, and how they interplay together?

   13. CSClara Sousa-Silva36:18

       So I study the quantum behavior of molecules, hence the quantum, and the chemist-

   14. LFLex Fridman36:24

       Yeah.

   15. CSClara Sousa-Silva36:25

       ... specifically so I can detect them in space, hence the astro. So what I, what I do is I figure out the probability of a molecule being in a particular state-... there's no deterministic nature to the work I do, and so it's every transition is just a likelihood. But if you get a population of that molecule, it will always happen. And so this is all at a quantum level. It's a Schrödinger equation on, I think, 27 dimensions. I don't remember it by heart. And what this means is I'm solving these giant quantum matrices, and that's why you need a lot of computer power, giant computers to diagonalize these enormous matrices, each of whom describes a single vibrational behavior of a molecule. So I think phosphine has 17.5 million possible states it can exist in, and transitions can occur between pairs of these states. And there's a certain likelihood that they'll happen. This is the quantum world, nothing is deterministic. There's just a likelihood that it'll jump from one state to another, and these jumps, they're transitions, and there's 16.8 billion of them. When energy is absorbed that corresponds to this transition, we see it in the spectrum. This is more quantum chemistry than you had asked for, I'm sorry.

   16. LFLex Fridman37:51

       No, no, I'm sorry. My brain is broken. So when the, when the transitions happen between the different states, uh, somehow the energy maps to the spectrum?

   17. CSClara Sousa-Silva38:01

       Exactly. Energy corresponds to a frequency, and a frequency corresponds to a wavelength, which corresponds to a color.

   18. LFLex Fridman38:08

       So there's some probability assigned to each color then?

   19. CSClara Sousa-Silva38:11

       Exactly, and that probability determines how intense that transition will be, how strong.

   20. LFLex Fridman38:17

       And so you run this kind of simulation for a particular... So that's 17.5 squared or something like that.

   21. CSClara Sousa-Silva38:23

       Exactly, 17.5 million energies, each one of whom involves diagonalizing a giant matrix-

   22. LFLex Fridman38:30

       Yeah.

   23. CSClara Sousa-Silva38:30

       ... with a supercomputer.

   24. LFLex Fridman38:32

       Actually, I wonder what the most efficient algorithm for dia- dia- diagonalization is. But there, there's some kind of-

   25. CSClara Sousa-Silva38:37

       There's many. (laughs)

   26. LFLex Fridman38:37

       There's many, yeah.

   27. CSClara Sousa-Silva38:38

       It depends on kind of the shape of the matrix. So they're not random matrices, so some are more diagonal than others, and so some need more treatment than others. Most of the work ends up going in describing the system, this quantum system, in different ways until you have a matrix that is close to being diagonal, and then it's much easier to, to clean it up.

   28. LFLex Fridman38:59

       So how, how many, uh, how hard is this puzzle? So you're s- solving this puzzle for phosphine, right? Um, is this s- are we supposed to solve this puzzle for every single-

   29. CSClara Sousa-Silva39:12

       Exactly.

   30. LFLex Fridman39:12

       ... molecule? Oh, boy.
6. 50:31 – 54:56

   Spectroscopic networks

   1. LFLex Fridman50:31

      What are, uh, spectroscopic networks? Those look super cool. Are they related to what we were talking about? The pictures look pretty.

   2. CSClara Sousa-Silva50:39

      Oh, um, yes, slightly. So remember when I mentioned the 17.5 million energy levels?

   3. LFLex Fridman50:44

      Yes.

   4. CSClara Sousa-Silva50:45

      There are rules for each molecule on which energy levels they can jump from and to, and how likely it is to make that jump. And so if you plot all the routes it can take, you get this energy network for... which is like a ball-

   5. LFLex Fridman51:01

      Mm-hmm.

   6. CSClara Sousa-Silva51:02

      ... of points.

   7. LFLex Fridman51:02

      So these are the constraints of the tr- the, the transitions that can be taken?

   8. CSClara Sousa-Silva51:05

      Exactly, for each molecule.

   9. LFLex Fridman51:07

      Interesting, and though, they're not... so it's not a fully connected... it's like, it's, it's sparse somehow? Like-

   10. CSClara Sousa-Silva51:14

       Yes, you get islands sometimes. You get-

   11. LFLex Fridman51:16

       Oh, cool.

   12. CSClara Sousa-Silva51:16

       ... a molecule can only jump from one set of states to another, and it's trapped now in this network. It can never go to another network that could've been available to other siblings.

   13. LFLex Fridman51:27

       Is there some insights to be drawn from these networks, like something cool that you can understand about a particular molecule because of it?

   14. CSClara Sousa-Silva51:34

       Yeah, some molecules have what we call forbidden transitions, um-

   15. LFLex Fridman51:38

       Oh, okay.

   16. CSClara Sousa-Silva51:38

       ... which aren't really forbidden 'cause it's quantum. There are no rules.

   17. LFLex Fridman51:40

       (laughs)

   18. CSClara Sousa-Silva51:40

       No, I'm not j- there are rules, it's just the rules are very often broken in the quantum world.

   19. LFLex Fridman51:45

       Yeah.

   20. CSClara Sousa-Silva51:45

       And so forbidden transitions doesn't actually mean they're forbidden.

   21. LFLex Fridman51:49

       Low probability?

   22. CSClara Sousa-Silva51:50

       Exactly. They just become deeply unlikely.

   23. LFLex Fridman51:52

       Yeah, cool. And then so you can do all the same... like I'm, uh, c- coming from a computer science world, you know, I love graph theory, so you can do all the same, like, gra- graph theoretic kind of analysis of, like, clusters or something like that or-

   24. CSClara Sousa-Silva52:05

       Exactly.

   25. LFLex Fridman52:06

       ... all, all those kinds of things-

   26. CSClara Sousa-Silva52:07

       (inhales)

   27. LFLex Fridman52:07

       ... and draw insights from it. Cool.

   28. CSClara Sousa-Silva52:09

       And they're unique for each molecule. So these... the networks that he mentioned, that's actually not too difficult a layer of quantum physics. By then, all the energies are mapped, so we've had high school children work on those networks. And the trick is to not tell them they're doing quantum physics until, like, three months in when it's too late for them to back out-

   29. LFLex Fridman52:28

       (laughs)

   30. CSClara Sousa-Silva52:29

       ... and then you're like, "You're a quantum physicist now," and it's really nice.
7. 54:56 – 57:49

   Biosignature gases

   1. LFLex Fridman54:56

      What, um, what other gases are there that we know about that are like high likelihood as biosignatures in terms of life? I mean, what are your other favorites? In t- so, (laughs) so we know, we got phosphine, but like what, uh, what else is a damn good signal to be, uh, that you think about, that we should be looking for if we're looking in another atmosphere? Is, is there gases that come to mind or are they're all sort of possible biosignatures that we should, uh, love equally?

   2. CSClara Sousa-Silva55:28

      There's many. So there's water. We know that's important for life as we know it. There's molecular oxygen on earth that's probably the most robust sign of life, particularly combined with small amounts of methane. And it's true that the majority of the oxygen in our atmosphere is a product of life. And so if I was an alien astronomer and I saw Earth's atmosphere, I'm, I would get a Nobel, I think on, you know-

   3. LFLex Fridman55:52

      (laughs) What would you notice? I mean, this is really ... (laughs) .

   4. CSClara Sousa-Silva55:55

      (laughs) I would be very excited about this.

   5. LFLex Fridman55:57

      About the oxygen?

   6. CSClara Sousa-Silva55:58

      About finding 20%, 21% of oxygen in our atmosphere, that's very unusual.

   7. LFLex Fridman56:03

      So would that be the most exciting thing to you from an alien perspective about Earth in terms of the tech, like analyzing the atmosphere? Like what are the biosignatures of life on Earth would you say in terms of the contents of the atmosphere? Is oxygen, high amount of oxygen a pretty damn good sign?

   8. CSClara Sousa-Silva56:19

      I mean, it's not as good as the TV signals we've been sending out. (laughs)

   9. LFLex Fridman56:22

      Sure. (laughs)

   10. CSClara Sousa-Silva56:23

       Those, those are slightly more robust, uh, than oxygen. Oxygen on its own has false positives for life. So there's still ways of making it, but it's, it's a pretty robust sign of life in the context of our atmosphere, with the radiation that the sun produces, our position in relation to the sun, the other components of our atmosphere, the volcanic activity we have, all of that together makes the 20% of oxygen extremely, um, robust sign of life. But outside that context, you could still produce f- um, oxygen without life.

   11. LFLex Fridman56:58

       Hmm.

   12. CSClara Sousa-Silva56:59

       But phosphine, although better in the sense of it is much harder to make, it has lower false positives, still has some. So I'm actually against looking for specific molecules, unless we're looking for like CFCs. If we find CFCs, that's definitely aliens, I f- I feel confident. Chlorofluorocarbons, and so, you know, if aliens had been watching us, they would have been going, "Oh, no CFCs. I mean ..."

   13. LFLex Fridman57:23

       (laughs) Yeah.

   14. CSClara Sousa-Silva57:23

       "They're not gonna last long." Let's, you know, everyone was writing their thesis on the end of, the end of the earth. And then we got together and we stopped using them. I like to think they're really proud of us. Um, you know, they literally-

   15. LFLex Fridman57:36

       No. (laughs)

   16. CSClara Sousa-Silva57:36

       ... saw our ozone hole shrinking. They've been watching-

   17. LFLex Fridman57:39

       Sure.

   18. CSClara Sousa-Silva57:39

       ... it and they saw it happen. How nice.

   19. LFLex Fridman57:40

       I think to be honest, they're more paying attention to the whole nuclear thing. That's just-

   20. CSClara Sousa-Silva57:44

       I don't think they care. It's not gonna bother them. Oh, I mean-

   21. LFLex Fridman57:46

       No, no, no.

   22. CSClara Sousa-Silva57:46

       ... worried about us. Oh, yes.

   23. LFLex Fridman57:48

       Oh, no, worried about us.

8. 57:49 – 1:11:06

   UFOs and aliens

   1. LFLex Fridman57:49

      They, I mean, this is why the aliens have been showing up recently. Uh-

   2. CSClara Sousa-Silva57:52

      (laughs)

   3. LFLex Fridman57:53

      ... it's like if you, if you look at ... I mean, there is inter- ... I mean, it's probably, there's a correlation with a lot of things, but what the UFOlogists, quote unquote, often talk about is that there seems to be a much higher level of UFO sightings since like in the nuclear age. So like if aliens were indeed worried about us, like if you were aliens, you would start showing up when the, the living organisms have first discovered a way to destroy the entire, the, uh, the entire colony.

   4. CSClara Sousa-Silva58:22

      Couldn't, um, the, uh, increase in sightings not have to do with the fact that people now have more cameras?

   5. LFLex Fridman58:29

      It's an interesting thing about science, like with UFO sightings, it's, it's like either 99.9 of, percent of them are false or 100% of them are false. The interesting thing to me is in that .01%, there's a lot of things in science that are like these weird outliers that are difficult to replicate. You have like, there's even physical phenomena, ball lightning. There's difficult things to artificially create in large amounts or observe in nature in large amounts in such a way that you can do it to apply the scientific method. There could be just things that like happen like a few times, like or once, and you're like, "What the hell is that?" (laughs) And that, that's very difficult for science to know what to do with. I'm a huge proponent of just being open-minded, 'cause when you're open-minded about aliens, for example, is it allows you to think outside of the box in other domains as well, and somehow that will result ... Like if you're open-minded about aliens and you don't comp- you know, don't laugh it off immediately, what happens is somehow that, that's gonna lead to a solution to P equals NP or P not equals NP. Like in ways that you can't predict, the open-mindedness has tertiary effects that will result in progress, I believe, which is why alien, I'm a huge fan of aliens, 'cause it's like, uh, 'cause too many scientists roll their eyes at the idea of aliens, alien life. And to me, it's one of the most exciting possibilities, uh, and the biggest, most exciting questions before all of human civilization. So to roll your eyes is not the right answer. To roll your eyes presumes that you know anything about this world as opposed to just knowing 0.0001% of this world. And so being humble in the face of that, uh, being open to the possibility of aliens is, uh, visiting Earth is a good idea. Not everything though. I'm not so open-minded to the flat Earth, uh, hypothesis as it's this growing number of people, uh, believing in. But even then-

   6. CSClara Sousa-Silva1:00:38

      Or the inner Earth. I've got shouted out at a public talk about it.

   7. LFLex Fridman1:00:41

      Inner the, so like the Earth is hollow?

   8. CSClara Sousa-Silva1:00:44

      Yeah. My understanding is that there's an-... this conspiracy theory that, as far as I can tell, has no grounding in reality is that there's a slightly smaller earth inside this one, which is just too cute as a concept.

   9. LFLex Fridman1:00:57

      Oh, that's awesome.

   10. CSClara Sousa-Silva1:00:57

       Um, and you can access it, I think, from Antarctica and, uh, that's where we keep, and I quote, "The mammoths and the Nazis."

   11. LFLex Fridman1:01:05

       (laughs) The mammoths and the Nazis.

   12. CSClara Sousa-Silva1:01:07

       (laughs)

   13. LFLex Fridman1:01:07

       Yeah, I- I mean, that one is ridicu- but, like, I do, like-

   14. CSClara Sousa-Silva1:01:09

       Hey, I thought you were keeping an open mind.

   15. LFLex Fridman1:01:11

       I am, this is, this is, uh-

   16. CSClara Sousa-Silva1:01:12

       I genuinely think-

   17. LFLex Fridman1:01:13

       Well-

   18. CSClara Sousa-Silva1:01:13

       ... that's more likely than aliens visiting the earth. And I say this as someone who has dedicated her life to finding, like, alien life. And, and so that's how improbable I think that visitations are.

   19. LFLex Fridman1:01:27

       I mean, it's-

   20. CSClara Sousa-Silva1:01:27

       Because interstellar distances are so huge that it's just not really worth it.

   21. LFLex Fridman1:01:32

       See, I- I have a different view on this whole thing. I think the aliens that look like little green men are, like, extremely low probability event. Uh-

   22. CSClara Sousa-Silva1:01:43

       Like mammoths and Nazis under-

   23. LFLex Fridman1:01:45

       Yeah, yeah, that- that's similar.

   24. CSClara Sousa-Silva1:01:47

       Yeah, okay, that level, okay.

   25. LFLex Fridman1:01:47

       But- w- but other kind of ideas, like, the s- the sad thing to me, and I think... (sighs) In- in my view if there's other alien civilizations out there and they visited earth, neither them or perhaps just us would be even able to detect them. Like, we- we wouldn't be open-minded enough to see it. Like, if- if, um... Because our understanding of what is life, and I just, um, talked with Sarah Walker who's, um-

   26. CSClara Sousa-Silva1:02:20

       I know Sarah.

   27. LFLex Fridman1:02:21

       Yeah. We- we talked for three hours about the question what is life? Um-

   28. CSClara Sousa-Silva1:02:26

       Sarah's a good person to talk to-

   29. LFLex Fridman1:02:27

       (laughs)

   30. CSClara Sousa-Silva1:02:27

       ... about what is life.
9. 1:11:06 – 1:28:42

   Alien civilizations

   1. LFLex Fridman1:11:07

      do you, um, do you think there's other alien civilizations out there? First, do you think there's other life out there? For- first, do you think there's life in the solar system? Second, do you think there's life in the galaxy? And, uh, third, do you think there's intelligent life in the solar system or the galaxy outside of Earth?

   2. CSClara Sousa-Silva1:11:27

      So intelligent life, I have no idea. It seems deeply unlikely. Uh, possible, but I'm not even sure if it's plausible.

   3. LFLex Fridman1:11:35

      So that's a special thing to you about Earth is somehow intelligent life came to be?

   4. CSClara Sousa-Silva1:11:38

      Yes. And it's only, you know, very briefly, probably extremely briefly. Um-

   5. LFLex Fridman1:11:44

      Uh-oh, you mean like it's always going to be, like we're gonna destroy ourselves?

   6. CSClara Sousa-Silva1:11:48

      Exactly.

   7. LFLex Fridman1:11:49

      Oh, boy.

   8. CSClara Sousa-Silva1:11:49

      And life will continue on Earth happily, uh, probably more happily. Um, so-

   9. LFLex Fridman1:11:54

      The trees and the dolphins will be here, I'm telling you.

   10. CSClara Sousa-Silva1:11:56

       And the cockroaches and the-

   11. LFLex Fridman1:11:58

       Yeah.

   12. CSClara Sousa-Silva1:11:58

       ... incredible fungi, you know?

   13. LFLex Fridman1:12:00

       Yes.

   14. CSClara Sousa-Silva1:12:01

       They'll be fine. Uh, so life on Earth will be fine, was fine before us and will be fine after us. So I'm not that worried about intelligent life, but I, I think it is unlikely. Even on Earth is unlikely out of, what is it, five billion species across the history of the Earth?

   15. LFLex Fridman1:12:16

       Yes.

   16. CSClara Sousa-Silva1:12:18

       There's been one, an intelligent one, and for a blink of an eye. Uh-

   17. LFLex Fridman1:12:21

       Yeah.

   18. CSClara Sousa-Silva1:12:21

       ... possibly not much longer than that. Uh, so I d- I wouldn't bet on that at all. Though I would love it, of course. You know, I, I wanted to find aliens since I was a little girl. And so, of course I initially wanted to find ones that I could be friends with.

   19. LFLex Fridman1:12:40

       Yeah.

   20. CSClara Sousa-Silva1:12:40

       And I've had to let go of that dream because it's so deeply implausible.

   21. LFLex Fridman1:12:44

       But see the nice, and sorry to interrupt, but the nice thing about intelligent alien civilizations, they may have more bio signatures than non-intelligent ones. So they might be easier to detect that, that would be the hope.

   22. CSClara Sousa-Silva1:12:56

       ... on Earth, that's not the case, but it could be the case elsewhere.

   23. LFLex Fridman1:12:59

       Oh, it's not the case on Earth? We-

   24. CSClara Sousa-Silva1:13:00

       Most of the biosignatures we have on Earth are created by quite simple life. If you don't count pollution. Pollution is all, all us-

   25. LFLex Fridman1:13:08

       Well, it's the garb- all, well, it's-

   26. CSClara Sousa-Silva1:13:08

       ... all us babies. (laughs)

   27. LFLex Fridman1:13:11

       (laughs) So you don't see, uh, polluting gases as a, as a possible, like...

   28. CSClara Sousa-Silva1:13:17

       I look for polluting gases. I would love to find polluting gases. Well, you know, I'll be worried for them, of course, the same way I, I think about my alien colleagues all the time, looking at us, and I'm sure they worry about our pollutions. But it would be a really good, robust, unambiguous sign of life if we found complex pollutants, so I look for those too.

   29. LFLex Fridman1:13:39

       Yeah.

   30. CSClara Sousa-Silva1:13:39

       I just don't have any hope of finding them. I think intelligent life in the galaxy at the same time that we're looking is-

Episode duration: 1:58:11