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

Lex Fridman 0:00 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.

Lex Fridman 1:39 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?

Clara Sousa-Silva 1:53 I go for Dr. Phosphine. Queen is an inherited title, I feel.

Lex Fridman 1:56 Yeah. But you still, uh, rule by, um, love and power, so ... But while, while having the doctor title.

Clara Sousa-Silva 2:04 Yeah.

Lex Fridman 2:04 I got it.

Clara Sousa-Silva 2:05 Kindness.

Lex Fridman 2:06 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.

Clara Sousa-Silva 2:21 Big maybe.

Lex Fridman 2:22 Big maybe. There was some pushback, of course, from the scientific community that followed, friendly, loving pushback.

Clara Sousa-Silva 2:30 (laughs)

Lex Fridman 2:31 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?

Clara Sousa-Silva 2:48 Okay, let's try to break it down.

Lex Fridman 2:49 Okay.

Clara Sousa-Silva 2:50 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.

Lex Fridman 3:52 Mm-hmm.

Clara Sousa-Silva 3:52 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) -

Lex Fridman 4:32 (laughs)

Clara Sousa-Silva 4:32 ... analogy would be.

Lex Fridman 4:33 Yeah.

Clara Sousa-Silva 4:33 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-

Lex Fridman 5:06 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?

Clara Sousa-Silva 5:14 Until we know what they call themselves, um, that, that's the name, yes.

Lex Fridman 5:18 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?

Clara Sousa-Silva 5:29 Of course, and analysis of the two different instruments months apart, so that's ALMA and JCMT, the two telescopes.

Lex Fridman 5:36 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?

Clara Sousa-Silva 5:56 It's nuts.

Lex Fridman 5:57 (laughs)

Clara Sousa-Silva 5:57 It's absolutely nuts.

Lex Fridman 5:59 In a g- (laughs)

Clara Sousa-Silva 6:01 I mean ... (laughs)

Lex Fridman 6:02 In the best possible way?

Clara Sousa-Silva 6:04 ... I have been working on phosphine for over a decade. And-

Lex Fridman 6:08 Before it was cool.

Clara Sousa-Silva 6:10 Way before it was cool.

Lex Fridman 6:11 (laughs)

Clara Sousa-Silva 6:12 Um, before anyone could spell it or heard of it. And at the time people either didn't know what phosphine was or only knew it for f- being just possibly the most horrendous molecule that ever graced the Earth. And so no one was a fan. Um, and I had been considering looking for it because I did think it was an unusual and disgusting but very promising soun- sign of life. I'd been looking for it and everywhere. I really didn't think to look in the solar system. I thought it was all pretty rough around here, uh, for, for life. And so I wasn't even considering the solar system at all, never mind next door, Venus. It was only the lead author of the study, Jane Greaves, who thought to look in the clouds of Venus, and then reached out to me to say, "I don't know phosphine but I know it's weird, um, how weird is it?" And the answer is very weird.

Lex Fridman 7:09 And so the telescopes we're looking at, this is visual data. Or-

Clara Sousa-Silva 7:13 That's what I mean by visual, you wouldn't see the phosphine.

Lex Fridman 7:15 Well, but I mean it's, uh, well, it's a telescope.

Clara Sousa-Silva 7:18 It's remote.

Lex Fridman 7:19 It's remote. You're observing, y- you're what, zooming in on this particular planet? I mean, what, what, what does the sensor actually look like? How many pixels are there? What does the data kinda look like? It'd be nice to kinda build up intuition of how little data we have based on which... I mean, if you look at like... I've just been reading a lot about gravitational waves and it's kind of incredible how from just very little, like, probably the world's most precise-

Clara Sousa-Silva 7:50 (laughs) .

Lex Fridman 7:51 ... uh, instrument we can derive some very foundational ideas about our early universe. And, uh, in that same way it's kind of incredible how much data, how much information you can get from just a few pixels. So, what are we talking about here i- in terms of, um, based on which this paper saw possible signs of phosphine in the atmosphere?

Clara Sousa-Silva 8:13 So phosphine, like every other molecule, has a unique spectroscopic fingerprint, meaning it rotates and vibrates in special ways. I calculated how many of those ways it can rotate and vibrate, and it's 16.8 billion ways. What this means is that if you look at the spectrum of light, and that light has gone through phosphine gas on the other end, there should be 16.8 billion tiny marks left, indentations left in that spectrum. We found one of those on Venus, one of those 16.8 billion. So now the game is can we find any of the other ones?

Lex Fridman 8:53 (laughs) Yeah.

Clara Sousa-Silva 8:53 But they're really hard to spot. They're all in terrible places in the electromagnetic spectrum. And the instruments we use to find this one can't really find any other one. There's another one of the 16.8 billion we could find but it would take many, many days of continuous observations and that's not really in the cards right now.

Lex Fridman 9:13 I mean, how do you... there's all kinds of noise first of all.

Clara Sousa-Silva 9:16 Yes.

Lex Fridman 9:16 There's, uh, all kinds of other signal.

Clara Sousa-Silva 9:20 Mm-hmm.

Lex Fridman 9:20 So how do you separate all of that out to pull out just this particular s- signature, uh, that's associated with phosphine?

Clara Sousa-Silva 9:31 So the data kind of looks somewhat like a wave.

Lex Fridman 9:34 Mm-hmm.

Clara Sousa-Silva 9:34 And a lot of that is noise and it's a baseline. And so if you can figure out the exact shape of the wave, you can cancel that shape out and you should be left with a straight line, and if there's something there, an absorption, so a, a signal.

Lex Fridman 9:48 Mm-hmm.

Clara Sousa-Silva 9:48 So that's what we did, we tried to find out what was this baseline shape, cleaned it out, and got the signal. That's part of the problem, if you do this wrong you can create a signal. But that signal is at 8.904 wave numbers. (laughs)

Lex Fridman 10:03 Mm-hmm.

Clara Sousa-Silva 10:03 And we actually have more digits than that, but I don't remember by heart. And, and ALMA in particular is a very, very good, um, telescope, array of telescopes, and it can focus on exactly that frequency. And in that frequency there are only two known molecules, um, that absorb at all. So that's how we do it, we look at that exact spot where we know phosphine absorbs. The other molecule is SO2.

Lex Fridman 10:30 If there is extraterrestrial life whether it's on Venus or on, uh, exoplanets where you looked before, how does that make you feel? How should it make us feel? Should we be scared? Should we be excited? Um, let's say it's not intelligent life. Let's say it's m- microbial life. It's, um... Is it a threat to us? Are we a threat to it? Or is it only, not only but mostly, a possibility to understand something fundamental, something beautiful about life in the uni- in the universe?

Clara Sousa-Silva 11:04 Hard to know. You would have to bring on a poet or a philosopher on the show. Uh, I-

Lex Fridman 11:10 You don't feel-

Clara Sousa-Silva 11:11 I feel those things, I just don't know if those are the right things to feel. I don't, certainly don't feel scared. I think it's rather silly to feel scared. Definitely don't touch them. Um, you know, sometimes in-

Lex Fridman 11:21 Wear a glove. (laughs)

Clara Sousa-Silva 11:22 ... the movies you... Don't go near it. Don't interfere.

Lex Fridman 11:25 Yeah.

Clara Sousa-Silva 11:25 Um, I think-

Lex Fridman 11:27 Yeah.

Clara Sousa-Silva 11:27 ... one of the things with Venus is because of phosphine, now there is a chance that Venus is inhabited. And in that case we shouldn't go there. We should be very careful with messing with them, um, bringing our own stuff there that contaminates it. And Venus has suffered enough. If there's life there it's probably the remains of a living planet, the very last survivors of what once was potentially a thriving world. And so I don't want our first interaction with alien life to be a massacre. So I definitely wouldn't want to go near out of a, let's say, galactic responsibility-

Lex Fridman 12:11 Mm-hmm.

Clara Sousa-Silva 12:12 ... (laughs) galactic ethics.... and I often think of, you know, alien astronomers watching us and how disappointed they would be if we messed this up, so I really... I really want to be very careful with anything that could be life. But certainly, I wouldn't be scared. Humans are plenty capable of killing one another. We don't, you know... We don't need extraterrestrial help to-

Lex Fridman 12:33 Yes.

Clara Sousa-Silva 12:33 ... destroy ourselves.

Lex Fridman 12:34 Scared mostly of other humans, so...

Clara Sousa-Silva 12:36 Exactly.

Lex Fridman 12:36 But these... This life, if there is life there, it does seem, just like you said, it would be pretty rugged. It's like the cockroaches or... (laughs) Or Chuck Norris, I don't know. It's the... Some kind of, um... It's something that's survived through some very difficult conditions.

Clara Sousa-Silva 12:53 That doesn't mean it would handle us, you know. It could be like War of the Worlds.

Lex Fridman 12:57 Yeah.

Clara Sousa-Silva 12:58 You come... Just because you're resilient in your own planet doesn't mean you can survive another. Even our extremophiles, which are very impressive, we should all be very proud of our extremophiles, they wouldn't really make it in the Venusian clouds. So, I wouldn't expect because you're tough, even Chuck Norris tough, that you would survive-

Lex Fridman 13:18 Yeah.

Clara Sousa-Silva 13:18 ... on an alien planet.

Lex Fridman 13:20 Uh, and... And then from the scientific perspective, you don't want to pollute the, um, the data gathering process by show-

Clara Sousa-Silva 13:27 Absolutely.

Lex Fridman 13:27 ... showing up there. The observer can, can affect the observed. Okay.

Clara Sousa-Silva 13:32 How heartbreaking would it be if we found life on another planet and then we're like, "Oh, we, we brought it with us. It was my sandwich."

Lex Fridman 13:38 But that's... But that's always the problem, right? And it's certainly a problem with Mars because we visited the, the... The... If there is life on Mars or, like, remains of life on Mars, it's always going to be a question of, like, "Well, maybe we planted it there."

Clara Sousa-Silva 13:53 Let's not do the same with Venus. It's harder, 'cause when we try to go to Venus, it... Things melt very quickly.

Lex Fridman 13:58 Yes.

Clara Sousa-Silva 13:59 And so-

Lex Fridman 13:59 It's a pretty, uh-

Clara Sousa-Silva 14:00 It's, it's a little harder to pollute Venus. Um, it's very good at destroying foreigners.

Lex Fridman 14:08 Yeah. Well, in terms of Elon Musk and terraforming planets, uh, Mars is stop number one, and V- Venus may be after that. So,

Lex Fridman 14:17 can we talk about phosphine a little bit? Um, so you mentioned it's a pretty-

Clara Sousa-Silva 14:21 Love to talk about phosphine.

Lex Fridman 14:22 (laughs)

Clara Sousa-Silva 14:22 I love phosphine.

Lex Fridman 14:22 What's your Twitter handle? It's like Dr. Phosphine, I think.

Clara Sousa-Silva 14:24 It's Dr. Phosphine, yes. You will be surprised to hear, it wasn't taken already. I could just...

Lex Fridman 14:29 Yes.

Clara Sousa-Silva 14:29 I just grabbed it. (laughs) Didn't have to buy it off anyone.

Lex Fridman 14:31 (laughs)

Clara Sousa-Silva 14:32 (laughs)

Lex Fridman 14:32 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-

Clara Sousa-Silva 14:43 Troublesome?

Lex Fridman 14:43 Troublesome. Sorry. That's the trouble-

Clara Sousa-Silva 14:44 No, I love it. I'm gonna start calling you troublesome.

Lex Fridman 14:46 (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?

Clara Sousa-Silva 15:11 I did, yes.

Lex Fridman 15:12 (laughs)

Clara Sousa-Silva 15:13 (laughs) I did.

Lex Fridman 15:13 (laughs)

Clara Sousa-Silva 15:13 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?"

Lex Fridman 15:24 (laughs)

Clara Sousa-Silva 15:24 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.

Lex Fridman 17:52 Mm-hmm.

Clara Sousa-Silva 17:53 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.

Lex Fridman 18:00 Oh, very nice.

Clara Sousa-Silva 18:01 Yeah, very, very vivid.

Lex Fridman 18:03 (laughs)

Clara Sousa-Silva 18:03 And so-

Lex Fridman 18:04 So, you're a poet after all.

Clara Sousa-Silva 18:05 (laughs)

Lex Fridman 18:05 (laughs)

Clara Sousa-Silva 18:05 I didn't... I didn't call it that, someone else did.

Lex Fridman 18:08 Okay, all right.

Clara Sousa-Silva 18:08 And so, it's just this horrific molecule, but it is produced by life.

Lex Fridman 18:12 Mm-hmm.

Clara Sousa-Silva 18:12 We don't know why. And when it is produced by life, it's done with enormous sacrifice, and the universe does not sacrifice life-... sacrifices. And so it's this strange, contradictory molecule that we should all be avoiding, and yet seems to be an almost unambiguous sign of life on rocky planets.

Lex Fridman 18:32 Okay. C- can we dig into that a little bit? So w- on rocky planets, what, um... Is, is there biological mechanisms that can produce it? I mean, is there, is there... You said that why is unclear, why life might produce it, but is there an understanding of what kind of mechanisms might be able to produce it, this very difficult to produce molecule?

Clara Sousa-Silva 18:56 We don't know yet. The enzymatic pathways of phosphine production by life are not yet known. This is not actually as surprising as it might sound. I think something like 80% of all the natural products that we know of, so we know biology makes them, we don't know how. It is much easier to know life produces something, because you can put, you know, bacteria in a Petri dish and then watch, and then that gas is produced, you go, "Oh, life made it."

Lex Fridman 19:21 Yeah.

Clara Sousa-Silva 19:21 That actually happened with phosphine. But that's much easier to do, of course, than figuring out what is the exact metabolic pathway within that life form that created the, this, uh, molecule. So we don't know yet. Phosphine was really understudied. Um, no one had really heard of it until (laughs) now-ish.

Lex Fridman 19:40 S- what you were presenting is the fact that life produces phosphine, not the, the process by which it produces phosphine. Is there an urgency now? Like, if you were to try to understand the mechanisms, the... What did you call them, enzymatic pathways-

Clara Sousa-Silva 19:56 Hmm.

Lex Fridman 19:57 ... uh, that produce phosphine, how difficult is that of a problem to crack?

Clara Sousa-Silva 20:00 It's really difficult. If I'm not mistaken, even, you know, the scent of truffles, obviously a billion-dollar industry, huge deal, until quite recently it wasn't known exactly how those scents, those molecules that create this incredible smell were produced, and this is a billion-dollar industry.

Lex Fridman 20:18 Wow.

Clara Sousa-Silva 20:18 As you can imagine, there is no such pressure, there's no phosphine lobby or anything (laughs) -

Lex Fridman 20:24 (laughs)

Clara Sousa-Silva 20:24 ... that would push for this research.

Lex Fridman 20:25 (laughs)

Clara Sousa-Silva 20:25 But I hope someone picks, picks it up and does it. And it isn't crazy, because we know that phosphine is really hard to make. We know it's really hard for it to happen accidentally. You know, even lightning and volcanoes that can produce small amounts of phosphine, it's extremely difficult for even these extreme processes to make it. So it's not really surprising that only life can do it, because life is willing to make things at a cost.

Lex Fridman 20:52 So maybe on the topic of phosphine, what... Uh, again, you, you're, you've gotten yourself into trouble with it. I'm gonna ask you all these, like, high-level poetic questions. I apologize. But-

Clara Sousa-Silva 21:02 No, I would love it.

Lex Fridman 21:03 Okay. (laughs) When, when did you first fall in love with phosphine?

Clara Sousa-Silva 21:08 (laughs) It, it wasn't love at first sight. It was somewhere between a long relationship and Stockholm syndrome.

Lex Fridman 21:18 Uh, yeah. (laughs)

Clara Sousa-Silva 21:19 When I, when I first started my PhD, I knew I wanted to learn about molecular spectra and how to simulate it. I thought it was really outrage- outrageous that we as a species couldn't detect molecules remotely. We didn't have this perfect catalog ready of the molecular fingerprint of every molecule we may want to find in the universe. And something as basic as phosphine, the fact that we didn't really know how it interacted with light, and so we couldn't detect it properly, you know, in the galaxy, just

Narrator 21:48 12%

Clara Sousa-Silva 21:48 Just I was so indignant. And so initially I just started working on phosphine because people hadn't before, and I thought we should know what phosphine looks like. And that was it. And then I read every paper that's ever been published about phosphine. It was quite easy because there aren't that many. Um, and that's when I started learning about where we had already found it in the universe and what it meant. Um, I started finding out quite how little we know about it and why. And it was only when I joined MIT and I started talking to biochemists that the, that it be became clear that phosphine wasn't just weird and special and understudied and disgusting. It was all these things for oxygen loving life. And it was the anaerobic world that would welcome phosphine. And that's when the idea of looking for it on other planets became crystallized. Because oxygen is very powerful and very important on Earth, but that's not necessarily going to be the case on other exoplanets. Most planets are oxygen poor. Overwhelmingly most planets are oxygen poor. And so finding this sign of life that would be welcomed by everything that would live without oxygen on Earth seemed so cool.

Lex Fridman 23:12 (lauger) But ultimately the project that first is born out of the idea that you want to find that molecular fingerprint of any, o- of a molecule. So and this is just one example. And that's connected to then looking at for, looking for that fingerprint elsewhere in the, in a remote way. And obviously that then at that time were exoplanets already when you were doing your PhD. And by the way I should say your PhD thesis was on phos-

Clara Sousa-Silva 23:41 It was all on phosphine. 100% on phosphine. (laughs) With a little bit of ammonia. I have a chapter that I, I did where I talked about phosphine and ammonia. So I-

Lex Fridman 23:51 Got it. (laughs)

Clara Sousa-Silva 23:53 But no, it, phosphine was very much my thesis.

Lex Fridman 23:55 But at that, that, at that time when you're writing it there's already a sense that exoplanets are out there and uh, we might be able to be looking for biosignatures for um, on those exoplanets.

Clara Sousa-Silva 24:08 Pretty much. So I finished my PhD in 2015.

Lex Fridman 24:11 Mm-hmm.

Clara Sousa-Silva 24:11 We found the first exoplanets in the kind of mid to late 90s. So exoplanets were known. Uh, it was known that some had atmospheres. And from there it's not a big jump to think well if some have atmospheres some of those might be habitable and some of those may be inhabited.

Lex Fridman 24:30 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.

Clara Sousa-Silva 24:57 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?

Lex Fridman 26:34 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.

Clara Sousa-Silva 27:00 Exactly.

Lex Fridman 27:00 How many total are there? How, how, how a lot is 16.8 billion?

Clara Sousa-Silva 27:06 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.

Lex Fridman 27:58 Yeah, like almost too un- Like, it would be too trivial. I got-

Clara Sousa-Silva 28:02 At the quantum level, they're unique.

Lex Fridman 28:03 At the quantum level, yes.

Clara Sousa-Silva 28:04 At our level, uh, there's huge overlap.

Lex Fridman 28:07 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.

Clara Sousa-Silva 28:24 Exactly.

Lex Fridman 28:24 So you're solving that g- gaseous puzzle. I got it. Okay.

Clara Sousa-Silva 28:29 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)

Lex Fridman 29:05 (laughs)

Clara Sousa-Silva 29:05 And the rest is history. (laughs)

Lex Fridman 29:07 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?

Clara Sousa-Silva 29:34 Telescopes are pretty good, but the Earth's atmosphere is a pain. I mean, I'm very thankful-

Lex Fridman 29:38 Right.

Clara Sousa-Silva 29:40 ... 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.

Lex Fridman 30:18 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?

Clara Sousa-Silva 30:34 (laughs)

Lex Fridman 30:34 Or is remote observation really a, a powerful tool?... uh, for this kind of job, like the scoop is not necessary?

Clara Sousa-Silva 30:41 Well, a lot of people want the scoop, I get it. Uh-

Lex Fridman 30:44 Yeah. (laughs)

Clara Sousa-Silva 30:44 I, I get it completely.

Lex Fridman 30:45 That's, that's my natural inclination, yeah.

Clara Sousa-Silva 30:47 I don't want the scoop specifically because if it is life, I want to know everything I can remotely before I interfere.

Lex Fridman 30:54 Yeah.

Clara Sousa-Silva 30:55 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-

Lex Fridman 31:06 Yeah, thank you, thank you-

Clara Sousa-Silva 31:06 ... it's too late to-

Lex Fridman 31:06 ... for going along with this.

Clara Sousa-Silva 31:07 (laughs) It's too late to take it back.

Lex Fridman 31:08 I appreciate it. (laughs)

Clara Sousa-Silva 31:10 We don't understand the clouds well enough to plan the scoop very well.

Lex Fridman 31:14 Because it's not that, uh, saturated, like there's not that much of it present.

Clara Sousa-Silva 31:19 No, and the place is nasty. You know, it's not, (laughs) it's not going to be easy to build something that can do the task, uh, reliably and can be trusted, the measurements can be trusted, and then pass that message on. So actually I'm for an orbiter. I think we should have orbiters around every solar system body whose job is just to learn about these places. I'm disappointed we haven't already got an orbiter around every single one of them. But they're small, it can be a small satellite.

Lex Fridman 31:49 Just collecting data.

Clara Sousa-Silva 31:49 Just collecting data, figuring out, you know, how do the clouds move? What's in them? How often is there lightning and volcanic activity? Where's the topography? Is it changing? Is there a biosphere actively doing things? We should be monitoring this from afar. And so I'm for a over the atmosphere, hopefully around Venus, that would be, that would be my choice.

Lex Fridman 32:12 Okay, so now, recently Venus is all exciting about phosphine and, and everything. Is there, is there other stuff maybe before we were looking at Venus or now looking out into other solar systems, is there other promising exoplanets or other planets within the solar system that, uh, might have phosphine or might have other strong, uh, biosignatures that we should be looking for like phosphine?

Clara Sousa-Silva 32:42 There's a few, but outside the solar system all are kind of promising candidates. We know so little about them. For most of them, we barely know their density. Um, most of them we don't even know if they have an atmosphere never mind what that atmosphere might contain. So we're still very much at the stage where we have detected promising planets, but they're promising in that they're about the right size-

Lex Fridman 33:07 Yeah.

Clara Sousa-Silva 33:07 ... uh, about the right density, they could have an atmosphere, and they're about the right distance from their host star. But that's really all we know. Near future telescopes will tell us much more, but for now we're just guessing.

Lex Fridman 33:21 So you said near future, so there's hope that there will be telescopes that can see that far enough to, to d- determine if there's an atmosphere and perhaps even the contents of that atmosphere?

Clara Sousa-Silva 33:31 Absolutely. JWST launching later this year will be able to get a very rough sense of the main atmospheric constituents of planets that could potentially be habitable, and that's this year, you know.

Lex Fridman 33:45 What's the name of the-

Clara Sousa-Silva 33:46 JWST, the James Webb Space Telescope.

Lex Fridman 33:49 Okay. And that's going to be out in space past the atmosphere?

Clara Sousa-Silva 33:53 Yes.

Lex Fridman 33:53 Is there something interesting to be said about the engineering aspect of the telescope?

Clara Sousa-Silva 33:57 I mean, it's an incredible beast, but it's a beast of many burdens. Um, (laughs) so it's going to do... (laughs) It's going-

Lex Fridman 34:05 See, you are a poet.

Clara Sousa-Silva 34:07 (laughs)

Lex Fridman 34:07 You are, yeah. I love it. (laughs) This is very eloquent. I lo- you're speaking to the audience which I appreciate. (laughs)

Clara Sousa-Silva 34:14 (laughs)

Lex Fridman 34:14 Uh, so, so yeah, so it's a giant engineering project and, uh, is it orbiting something, do you know?

Clara Sousa-Silva 34:20 So it's going to be above the atmosphere, um, and it will be doing lots of different astrophysics and so some of its time will be dedicated to exoplanets. But there's an entire astronomy field fighting for time before the cryogenic lifetime of the, um, instrument. And so when I was looking for the possibility of finding phosphine on distant exoplanets, I used JWST as a, uh, way of checking with this instrument that we will launch later this year could we detect phosphine on an oxygen-poor planet. And there I put very much a, a hard stop where some of my simulations said, "Yes, you can totally do it, but it will take-"

Lex Fridman 35:03 (laughs)

Clara Sousa-Silva 35:03 ... "a little under the cryogenic lifetime of this machine." So then I had to go, "Well that, that's not going to, no one's going to dedicate all of JWST to look for my molecule that no one cared about." So we're very much at that edge, but there'll be many other telescopes in the coming decades, um, that will be able to tell us quite a lot about the atmospheres of potentially habitable planets.

Lex Fridman 35:26 So you mentioned simulation, this is super interesting to me and, and this perhaps could be a super dumb question but-

Clara Sousa-Silva 35:34 Not interesting?

Lex Fridman 35:35 (laughs) I'm gonna prove you wrong on that one.

Clara Sousa-Silva 35:38 (laughs)

Lex Fridman 35:38 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?

Clara Sousa-Silva 35:54 That's the goal but it's really just a very, very nasty Schrodinger's equation, so it's a quantum simulation.

Lex Fridman 36:01 Oh, so it's the q- it's simulating at the quantum level?

Clara Sousa-Silva 36:03 Yes. So I'm a quantum astrochemist. Hi, I'm Clara, I'm a quantum astrochemist.

Lex Fridman 36:08 Can you des-

Clara Sousa-Silva 36:08 (laughs) Is how we should've started this conversation.

Lex Fridman 36:10 Can you describe the three components of that, quantum, astro, and chemist, and how they interplay together?

Clara Sousa-Silva 36:18 So I study the quantum behavior of molecules, hence the quantum, and the chemist-

Lex Fridman 36:24 Yeah.

Clara Sousa-Silva 36:25 ... 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.

Lex Fridman 37:51 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?

Clara Sousa-Silva 38:01 Exactly. Energy corresponds to a frequency, and a frequency corresponds to a wavelength, which corresponds to a color.

Lex Fridman 38:08 So there's some probability assigned to each color then?

Clara Sousa-Silva 38:11 Exactly, and that probability determines how intense that transition will be, how strong.

Lex Fridman 38:17 And so you run this kind of simulation for a particular... So that's 17.5 squared or something like that.

Clara Sousa-Silva 38:23 Exactly, 17.5 million energies, each one of whom involves diagonalizing a giant matrix-

Lex Fridman 38:30 Yeah.

Clara Sousa-Silva 38:30 ... with a supercomputer.

Lex Fridman 38:32 Actually, I wonder what the most efficient algorithm for dia- dia- diagonalization is. But there, there's some kind of-

Clara Sousa-Silva 38:37 There's many. (laughs)

Lex Fridman 38:37 There's many, yeah.

Clara Sousa-Silva 38:38 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.

Lex Fridman 38:59 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-

Clara Sousa-Silva 39:12 Exactly.

Lex Fridman 39:12 ... molecule? Oh, boy.

Clara Sousa-Silva 39:14 Yes, I calculated if I, if I did the work I did for phosphine again for all the molecules for which we don't have spectra, for which we don't have a fingerprint, it would take me 62,000 years, a little over.

Lex Fridman 39:28 62,000 years. Well, time flies when you're having fun.

Clara Sousa-Silva 39:31 (laughs)

Lex Fridman 39:31 Okay. But you, um, you write that there are about 16,000 molecules we care about when looking for a new Earth or when we try to detect alien biosignatures. If we want to detect any molecules from here, we need to know their spectra, and we currently don't. Solving this particular problem, that's my job. I think-

Clara Sousa-Silva 39:53 Where was that? That, I mean, that's absolutely correct.

Lex Fridman 39:55 Yeah.

Clara Sousa-Silva 39:55 I couldn't have s- couldn't have not said it better myself. Did you take that from my website?

Lex Fridman 39:59 Yeah, I think I-

Clara Sousa-Silva 39:59 Oh, okay.

Lex Fridman 39:59 ... stole it. And your website is excellent, so it's worthy place to steal stuff from.

Clara Sousa-Silva 40:04 Thank you.

Lex Fridman 40:05 How do you solve this problem, uh, of, uh, for the 16,000 molecules we care about, of which phosphine is one?

Clara Sousa-Silva 40:12 Yes.

Lex Fridman 40:13 And so, um, so taking a step a little bit out of phosphine, is there, uh-

Clara Sousa-Silva 40:22 But we were having so much fun.

Lex Fridman 40:23 We were having so much fun. No, we're not saying-

Clara Sousa-Silva 40:25 No, no, no.

Lex Fridman 40:26 ... bye. It's sticking around.

Clara Sousa-Silva 40:27 (laughs)

Lex Fridman 40:27 I'm just saying with joining more friends coming to the party, how do you choose other friends to come to the party that are interesting to study as we solve one puzzle at a time through the space of 16,000?

Clara Sousa-Silva 40:40 So we've already started. Out of those 16,000, we understand water quite well, methane quite well, ammonia quite well, s- carbon dioxide. I could keep going. And then we understand molecules like acetylene, hydrogen cyanide, more or less. And that takes us to about 4% of those 16,000. We understand about 4% of them, more or less. Phosphine is one of them. But the other 96%, we just really have barely any idea at all of where in the spectrum of light they would leave a, a mark. I can't spend the next 62,000 years doing this work, um, and I don't want to, even if, you know, somehow I was able, that- that's not... that- that wouldn't feel good. So one of the things that I try to do now is move away from how I did phosphine. So I did phosphine really the best that I could, the best that could be done with the computer power that we have, you know, trying to get each one of those 16.8 billion transitions mapped accurately, calculated. And then I thought, "What if I do a worse job? What if I just do a much worse job?"

Lex Fridman 41:52 (laughs)

Clara Sousa-Silva 41:53 And can I just make it much faster, and then-

Lex Fridman 41:55 Yes.

Clara Sousa-Silva 41:55 ... it's still worth it?

Lex Fridman 41:56 Yes.

Clara Sousa-Silva 41:57 Like how bad can I get before it's worthless? And then could I do this for all the other molecules?

Lex Fridman 42:05 Yes.

Clara Sousa-Silva 42:05 So I created exactly this terrible, terrible-

Lex Fridman 42:09 Mm, yeah, so how bad-

Clara Sousa-Silva 42:10 ... system.

Lex Fridman 42:10 ... is how bad... So how... what's the answer to that question, that fundamental question I ask myself all the time in other domains?

Clara Sousa-Silva 42:15 How crappy can I be before I'm useless?

Lex Fridman 42:17 (laughs) Before somebody notices. (laughs)

Clara Sousa-Silva 42:19 Turns out pretty crappy, because-

Lex Fridman 42:22 Excellent.

Clara Sousa-Silva 42:22 ... no one has any idea what these molecules look like. Anything is better than nothing.

Lex Fridman 42:28 Mm-hmm.

Clara Sousa-Silva 42:28 And so I thought, "How long will it take me to create better than nothing spectra for all of these molecules?" And so I created RASCAL, Rapid Approximate Spectral Calculations For All.... um, and what I do is I use organic chemistry and quantum chemistry and kind of cheat at them both. I just try to figure out what is the fastest way I could run this, and I simulate rough spectra for all of those 16,000, so I managed to get it to work. It's really shocking how well it works, considering how bad it is. (laughs)

Lex Fridman 43:03 Is there insights you could give to like the- the tricks involved in making it fast? Like, what are the, um, maybe some insightful shortcuts taken that still result in some useful information about the spectra?

Clara Sousa-Silva 43:18 The insights came from organic chemistry from decades ago. When organic chemists wanted to know what a compound might be, they would look at a spectrum and see a feature, and they would go, "Mm, I- I've seen that feature before." That's usually what happens when you have a carbon triple bonded to another carbon, and they were mostly right. Almost every molecule that has a carbon triple bonded to another one looks like that. Has other features different from, that distinguish them from one another, but they have that- that feature in common. We call these functional groups. And so most of that work ended up being abandoned because now we have mass spectrometry, we got nuclear magnetic resonance spectroscopy, so people don't really need to do that anymore. But these ancient textbooks still exist, and I've collected them all, as many as I could, and there are hundreds of these descriptions where people have said, "Oh, whenever you have a, um, a- a iodine atom connected to this one, there's always a feature here, and it's usually quite sharp, and it's quite strong." And some people go, "Oh, yeah, that's a really broad feature every time that combination of atoms and bonds..." So I've collected them all, and I've created this giant dictionary of all these kind of puzzle pieces, these Lego parts of molecules.

Lex Fridman 44:36 Mm-hmm.

Clara Sousa-Silva 44:37 And I've written a code that then puts them all together in some kind of like Frankenstein's monster of molecules. So you ask me for any molecule, and I go, "Well, it has these bonds, and this atom dangling off this atom, and this cluster here," and I tell you what it should look like. And it kinda works.

Lex Fridman 44:56 (laughs) So this creates a whole, uh, portfolio of just kind of, uh, signatures that we could look for.

Clara Sousa-Silva 45:03 Rough, very rough signatures.

Lex Fridman 45:05 Rough, but still useful enough to analyze the atmospheres, the- the- t- telescope-generated images of oth- of other planets?

Clara Sousa-Silva 45:14 Close. Right now, it is so complete, so it has all of these molecules, that it can tell you, say you look at an alien atmosphere, and there's a feature there. It can tell you, "Oh, that feature? That's familiar. It could be one of these 816 molecules."

Lex Fridman 45:31 Then there's the ...

Clara Sousa-Silva 45:32 "Best of luck."

Lex Fridman 45:33 Yes. (laughs)

Clara Sousa-Silva 45:34 So I think the next step, which is what I'm working on, is telling you something more useful than it could be one of those 816 molecules. That's still true. I wouldn't say it's useful. So it can tell you, "But only 12% of them also have a feature in this region, so go look there. And if there's nothing there, it can't be those," and so on. It can also tell you things like, "You will need this much accuracy to distinguish between those 816." So that's what I'm working on, but it's a lot of work.

Lex Fridman 46:03 (laughs) So, uh, this is really interesting, the- like, the role of computing in- in this whole picture. You mention code. So, like, you, as a quantum astrochemist, there is some role of- for programming in your life, in your past life, in your current life, in your group?

Clara Sousa-Silva 46:20 Oh, yeah, almost entirely. I'm a computational quantum astrochemist.

Lex Fridman 46:23 Okay.

Clara Sousa-Silva 46:24 But that doesn't roll off the tongue very easily.

Lex Fridman 46:25 So is, is, this is fundamentally computational, like if you wanna be successful in the 21st century in doing quantum astrochemistry, you wanna be computational?

Clara Sousa-Silva 46:33 Absolutely. All of quantum chemistry is computational at this point.

Lex Fridman 46:36 Okay. What, uh, does, um, machine learning play a role at all? Is there some extra shortcuts that could be discovered through, uh, like you see all that success with protein folding, right? A problem that thought to be extremely difficult to apply machine learning to because it's, um, um, I mean, mostly because there's not a lot of already solved puzzles to train on. I suppose the same exact thing is true with this particular problem, but is there hope for machine learning to help out?

Clara Sousa-Silva 47:11 Absolutely. Currently, you've laid out exactly the problem. The training set is awful, and because they're so... A- a lot of this data that I'm basing it on is literally many decades old. The people who worked on it and data that I get, often they're dead, and, um, the files that I've used, they- some of them were hand-drawn by someone tired in the '70s.

Lex Fridman 47:34 Yes. (laughs)

Clara Sousa-Silva 47:35 So I can, of course, have-

Lex Fridman 47:36 Yeah. Yeah.

Clara Sousa-Silva 47:36 ... have a- a program training on these, but I would just be perpetuating these mistakes without hope of actually verifying them. So my next step is to improve this training set, um, by hand, and then try to see if I can apply machine learning on the full code of the full 16,000 molecules and improve them all. But really, I need to be able to test the outcomes with experimental data, which means convincing someone in a lab to spend a lot of money putting very dangerous gases in chambers and measuring them at outrageous temperatures. So, it's a work in progress.

Lex Fridman 48:13 And so collecting huge amounts of data about the- the actual gases, uh, so you're- you're- so you- so you- you are up for doing that kind of thing too? So actually, like, doing the full end-to-end thing, which is like having a gas, collecting data about it, and- and then doing the kind of analysis that creates the fingerprint, and then also analyzing, using that library of the data that comes from other planets? So you do the full... (laughs)

Clara Sousa-Silva 48:41 Full from birth to...... death.

Lex Fridman 48:44 Interesting.

Clara Sousa-Silva 48:44 Um-

Lex Fridman 48:45 That's fascinating.

Clara Sousa-Silva 48:45 Yes, I worked in an industrial chemistry laboratory when I was much younger in Slovenia, and there I worked in the lab actually collecting spectra-

Lex Fridman 48:53 Right.

Clara Sousa-Silva 48:53 ... and, and predicting spectra.

Lex Fridman 48:56 Wh- what's it like to work with a bunch of gases that are, like, not so human-friendly? Is it-

Clara Sousa-Silva 49:01 Terrifying. It's horrific.

Lex Fridman 49:03 (laughs)

Clara Sousa-Silva 49:03 It's so scary, and I love my job. I'm willing to clearly sacrifice a lot for it-

Lex Fridman 49:08 Yes.

Clara Sousa-Silva 49:08 ... you know, job stability-

Lex Fridman 49:11 Yes.

Clara Sousa-Silva 49:11 ... money-

Lex Fridman 49:12 Yes.

Clara Sousa-Silva 49:13 ... sanity. But I only worked there for a few months. It, it was really terrifying. There's just so many ways to die. You know, usually you only have a handful of ways to die every day, you know? But i- if you work in a lab, there's (laughs) so many more, like orders of magnitude more, and I, I was very bad at it. I'm not a good hands-on scientist. I want a laptop connected to a remote supercomputer or a laptop connected to a telescope.

Lex Fridman 49:43 Yes.

Clara Sousa-Silva 49:43 I don't, I don't need to be there to believe it, and I am not good in the lab.

Lex Fridman 49:48 (inhales) Yeah, when there's a bunch of things that can poison you, a bunch of things that could explode-

Clara Sousa-Silva 49:53 Yeah.

Lex Fridman 49:53 ... and they're gaseous, and they're often... maybe they might not even have a smell, or they might not be visible, it's like if you-

Clara Sousa-Silva 50:00 So many of them give you cancer.

Lex Fridman 50:02 Yeah.

Clara Sousa-Silva 50:02 It's just so cruel, and some people love this work, but I've, I've never enjoyed experimental work. It's so ungrateful, so lonely.

Lex Fridman 50:12 Well, most... I mean, so much work is lonely. Y- you finally join it, but you e- you enjoy the results of it.

Clara Sousa-Silva 50:19 Yes. I'm very thankful for all the experimentalists in my life. But I-

Lex Fridman 50:25 (laughs)

Clara Sousa-Silva 50:25 ... I'll do the theory, they do the experiment, and then we talk to one another and make sure it matches-

Lex Fridman 50:29 (laughs)

Clara Sousa-Silva 50:29 ... you know?

Lex Fridman 50:30 Uh, okay, beautiful.

Lex Fridman 50:31 What are, uh, spectroscopic networks? Those look super cool. Are they related to what we were talking about? The pictures look pretty.

Clara Sousa-Silva 50:39 Oh, um, yes, slightly. So remember when I mentioned the 17.5 million energy levels?

Lex Fridman 50:44 Yes.

Clara Sousa-Silva 50:45 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-

Lex Fridman 51:01 Mm-hmm.

Clara Sousa-Silva 51:02 ... of points.

Lex Fridman 51:02 So these are the constraints of the tr- the, the transitions that can be taken?

Clara Sousa-Silva 51:05 Exactly, for each molecule.

Lex Fridman 51:07 Interesting, and though, they're not... so it's not a fully connected... it's like, it's, it's sparse somehow? Like-

Clara Sousa-Silva 51:14 Yes, you get islands sometimes. You get-

Lex Fridman 51:16 Oh, cool.

Clara Sousa-Silva 51:16 ... 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.

Lex Fridman 51:27 Is there some insights to be drawn from these networks, like something cool that you can understand about a particular molecule because of it?

Clara Sousa-Silva 51:34 Yeah, some molecules have what we call forbidden transitions, um-

Lex Fridman 51:38 Oh, okay.

Clara Sousa-Silva 51:38 ... which aren't really forbidden 'cause it's quantum. There are no rules.

Lex Fridman 51:40 (laughs)

Clara Sousa-Silva 51:40 No, I'm not j- there are rules, it's just the rules are very often broken in the quantum world.

Lex Fridman 51:45 Yeah.

Clara Sousa-Silva 51:45 And so forbidden transitions doesn't actually mean they're forbidden.

Lex Fridman 51:49 Low probability?

Clara Sousa-Silva 51:50 Exactly. They just become deeply unlikely.

Lex Fridman 51:52 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-

Clara Sousa-Silva 52:05 Exactly.

Lex Fridman 52:06 ... all, all those kinds of things-

Clara Sousa-Silva 52:07 (inhales)

Lex Fridman 52:07 ... and draw insights from it. Cool.

Clara Sousa-Silva 52:09 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-

Lex Fridman 52:28 (laughs)

Clara Sousa-Silva 52:29 ... and then you're like, "You're a quantum physicist now," and it's really nice.

Lex Fridman 52:32 Yeah. Okay, but, like, the, the promise of this, even though it's 16,000, even just a subset of them, that's really exciting 'cause then you can do... as the telescope data get better and better, especially for exoplanets, but also for Venus, uh, you can then start, like, getting your full... like, you know how you get, like, blood work done or, like, you get your genetic testing to see what your ancestors are? You can get the same kinda, um, like, high-resolution information about interesting things going on on a particular planet based on the atmosphere, right?

Clara Sousa-Silva 53:02 Exactly. How cool would that be if we could, you know, scan an alien planet and go, "Oh, this is what the clouds are made of. This is what's in the surface. These are the molecules that are mixing. Here are probably oceans because you can see these types of molecules-"

Lex Fridman 53:16 Mm-hmm.

Clara Sousa-Silva 53:16 "... above it, and here are the Hadley cells. Here are how the biosphere works." We could map this whole thing.

Lex Fridman 53:24 Wouldn't it be cool if the aliens, like, are aware of these techniques and, like, would spoof, like, the wrong gases just to, like, pretend... that's how they can be... it's like an invisibility cloak. They can generate gases that would throw you off or, like... or do the opposite, that pretend... they would artificially generate phosphine so, like, like, the, the dumb, the dumb apes on Earth again, like, go out, like, flying in different places 'cause it's just fun. It's like some teenager alien-

Clara Sousa-Silva 53:52 Pranking us.

Lex Fridman 53:52 ... somewhere just pranking, yeah. Uh, but-

Clara Sousa-Silva 53:54 I was asked that exact question this Saturday-

Lex Fridman 53:57 (laughs)

Clara Sousa-Silva 53:57 ... by a, by a 7-year-old boy in Canada.

Lex Fridman 53:59 How old? Seven?

Clara Sousa-Silva 54:00 Seven, yeah. (laughs)

Lex Fridman 54:03 (laughs)

Clara Sousa-Silva 54:03 Um, but it was the first time I'd been asked that question. This is the second in, in a week, um.

Lex Fridman 54:08 (laughs)

Clara Sousa-Silva 54:09 (laughs)

Lex Fridman 54:10 We're kindred spirits, him and I.

Clara Sousa-Silva 54:12 We can. Um, w- they can prank us to some extent, but the, this work of interpreting an alien atmosphere means you reading the atmosphere as a message-

Lex Fridman 54:23 Mm-hmm.

Clara Sousa-Silva 54:23 ... and it's very hard to hide signs of life in an atmosphere-

Lex Fridman 54:27 Yeah.

Clara Sousa-Silva 54:27 ... because you can try to prank us, but you're still going to fart and breathe-

Lex Fridman 54:33 Yeah.

Clara Sousa-Silva 54:33 ... and somehow metabolize the environment around you-

Lex Fridman 54:36 Yeah.

Clara Sousa-Silva 54:36 ... and call that whatever you call that, uh, and release molecules, and so that's really hard to hide. You know, you can go very quiet. You can...... throw out some weird molecule to confuse us further, but we can still see all your other metabolites.

Lex Fridman 54:51 Yeah. I- it's hard to fake. Uh, is there ... So you kind of mentioned like water.

Lex Fridman 54:56 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?

Clara Sousa-Silva 55:28 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-

Lex Fridman 55:52 (laughs) What would you notice? I mean, this is really ... (laughs) .

Clara Sousa-Silva 55:55 (laughs) I would be very excited about this.

Lex Fridman 55:57 About the oxygen?

Clara Sousa-Silva 55:58 About finding 20%, 21% of oxygen in our atmosphere, that's very unusual.

Lex Fridman 56:03 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?

Clara Sousa-Silva 56:19 I mean, it's not as good as the TV signals we've been sending out. (laughs)

Lex Fridman 56:22 Sure. (laughs)

Clara Sousa-Silva 56:23 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.

Lex Fridman 56:58 Hmm.

Clara Sousa-Silva 56:59 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 ..."

Lex Fridman 57:23 (laughs) Yeah.

Clara Sousa-Silva 57:23 "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-

Lex Fridman 57:36 No. (laughs)

Clara Sousa-Silva 57:36 ... saw our ozone hole shrinking. They've been watching-

Lex Fridman 57:39 Sure.

Clara Sousa-Silva 57:39 ... it and they saw it happen. How nice.

Lex Fridman 57:40 I think to be honest, they're more paying attention to the whole nuclear thing. That's just-

Clara Sousa-Silva 57:44 I don't think they care. It's not gonna bother them. Oh, I mean-

Lex Fridman 57:46 No, no, no.

Clara Sousa-Silva 57:46 ... worried about us. Oh, yes.

Lex Fridman 57:48 Oh, no, worried about us.

Lex Fridman 57:49 They, I mean, this is why the aliens have been showing up recently. Uh-

Clara Sousa-Silva 57:52 (laughs)

Lex Fridman 57:53 ... 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.

Clara Sousa-Silva 58:22 Couldn't, um, the, uh, increase in sightings not have to do with the fact that people now have more cameras?

Lex Fridman 58:29 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-

Clara Sousa-Silva 1:00:38 Or the inner Earth. I've got shouted out at a public talk about it.

Lex Fridman 1:00:41 Inner the, so like the Earth is hollow?

Clara Sousa-Silva 1:00:44 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.

Lex Fridman 1:00:57 Oh, that's awesome.

Clara Sousa-Silva 1:00:57 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."

Lex Fridman 1:01:05 (laughs) The mammoths and the Nazis.

Clara Sousa-Silva 1:01:07 (laughs)

Lex Fridman 1:01:07 Yeah, I- I mean, that one is ridicu- but, like, I do, like-

Clara Sousa-Silva 1:01:09 Hey, I thought you were keeping an open mind.

Lex Fridman 1:01:11 I am, this is, this is, uh-

Clara Sousa-Silva 1:01:12 I genuinely think-

Lex Fridman 1:01:13 Well-

Clara Sousa-Silva 1:01:13 ... 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.

Lex Fridman 1:01:27 I mean, it's-

Clara Sousa-Silva 1:01:27 Because interstellar distances are so huge that it's just not really worth it.

Lex Fridman 1:01:32 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-

Clara Sousa-Silva 1:01:43 Like mammoths and Nazis under-

Lex Fridman 1:01:45 Yeah, yeah, that- that's similar.

Clara Sousa-Silva 1:01:47 Yeah, okay, that level, okay.

Lex Fridman 1:01:47 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-

Clara Sousa-Silva 1:02:20 I know Sarah.

Lex Fridman 1:02:21 Yeah. We- we talked for three hours about the question what is life? Um-

Clara Sousa-Silva 1:02:26 Sarah's a good person to talk to-

Lex Fridman 1:02:27 (laughs)

Clara Sousa-Silva 1:02:27 ... about what is life.

Lex Fridman 1:02:29 But, like, the whole point is we don't really, we have a very narrow-minded view of what is life and when it shows up, and it might be already here, um, trees and dolphins and so on...

Clara Sousa-Silva 1:02:40 (laughs) Good, good choices.

Lex Fridman 1:02:42 (laughs) And or- or- or ro- or mountains or, I don't know, or the- or the molecules in the atmosphere or, um, or, like, I, people make fun of me but I do think that ideas are kinda aliens themselves, or consciousness could be the aliens, or it could be the method by which they communicate. We don't know shit about the way our human mind works and the fact that this thing is-

Clara Sousa-Silva 1:03:05 Could be a quantum process.

Lex Fridman 1:03:07 Please don't, I- I understand this.

Clara Sousa-Silva 1:03:09 (laughs)

Lex Fridman 1:03:09 It's not woo-woo, I'm not, I-

Clara Sousa-Silva 1:03:11 (laughs)

Lex Fridman 1:03:11 We could, but it very well could be, there could be something at the qu- uh, at the physics level, right? It could be at the chemical or the biological level, things that are happening that we're just close, too close-minded because our conception of life is at the level of, like, us, like, at the jungle level of- of mammals and on the timescale that's the human timescale. We may not be able to perceive what alien life is actually like. Uh, what, uh, the scale at which their intelligence realizes itself we may not be able to perceive. And the other thing that's really important about alien visitations, whether it happened or not, is, especially after COVID in 2020, I am losing a little bit of faith of our government being able to handle th- that well. Not our government, but us as a society, as a collective, being able to deal with new things in an effective way that's inspiring, that's efficient, that, uh, like, whether it's w- if- if it's a- a dangerous thing to deal with it to alleviate the danger. Whether it's the possibility of s- um, new discoveries and something inspiring, to ride that wave and make it inspiring, all those kinds of things. I honestly think if aliens showed up, they would look around, everybody would ignore them and the government might, like, hide it, try to, like, see, to keep it from the Chinese and the Russians if it's the United States, uh, call it a military secret in a very close-minded way, and then the bureaucracy would drown it away to where, uh, through paperwork the poor aliens would just, like, waste away in a cell somewhere. Like, there's a certain-

Clara Sousa-Silva 1:04:51 That would not happen, that would never happen. Part of the reason that I feel so confident that aliens have not visited is because they would have had to visit just to have a look remotely, you know, from Neptune or something, which makes no sense because interstellar travel is so difficult that it would be quite a ridiculous proposition. But that's the bit that I think is technically possible. If they did come here and they were visible by anyone, detectable by anyone, the thought that any government, no matter, or any military could just contain them, these beings are capable of traveling interstellar distances when we can barely go to the moon.

Lex Fridman 1:05:29 Yeah.

Clara Sousa-Silva 1:05:29 Like, barely go to the moon.

Lex Fridman 1:05:31 So these things would be way, way, way more intelligent.

Clara Sousa-Silva 1:05:32 Way... And the fact that we think our puny, uh, military-

Lex Fridman 1:05:36 Yes, is true.

Clara Sousa-Silva 1:05:36 ... if any, even if all the military in the world got together, and the fact that they could somehow contain the- this- it's, that's the bit that's laughable-

Lex Fridman 1:05:44 It's like ants trying to contain a human-

Clara Sousa-Silva 1:05:45 Exactly.

Lex Fridman 1:05:45 ... that visited them.

Clara Sousa-Silva 1:05:46 Exactly.

Lex Fridman 1:05:47 But I-

Clara Sousa-Silva 1:05:48 And scientists, you would have to bring scientists on board. You've met a lot of scientists-

Lex Fridman 1:05:51 Yeah.

Clara Sousa-Silva 1:05:52 ... how good are they at keeping secrets? 'Cause in my experience they're absolutely appalling at keeping secrets.

Lex Fridman 1:05:58 Yeah, that's terrible.

Clara Sousa-Silva 1:05:59 Even the phosphine on Venus thing which was a pretty well-kept secret.

Lex Fridman 1:06:03 Oh, this is true, you had a bunch of people that were th-

Clara Sousa-Silva 1:06:05 I told my dad.

Lex Fridman 1:06:06 Yeah.

Clara Sousa-Silva 1:06:06 You know, my dad knew (laughs) and hopefully he didn't tell anyone but if there had been an alien visiting, he probably would have told the mate, you know? And so these secrets could not be kept by any scientist that I know and certainly not collaborative scientists which would be needed, you would need all sorts of, um, scientific teams. So between the pathetic power of any world's military compared to any civilization, uh, capable of traveling and our absolute inability to keep secrets, uh, uh, a- absolutely not. I will bet everything that we have not been visited because we are too-

Lex Fridman 1:06:45 Okay.

Clara Sousa-Silva 1:06:45 ... pathetic to hold that-

Lex Fridman 1:06:47 Well, let me, uh-

Clara Sousa-Silva 1:06:47 ... (laughs) To hold that truth.

Lex Fridman 1:06:48 ... let me push back. If we're do- making a, like, a $10 bet-

Clara Sousa-Silva 1:06:51 (laughs)

Lex Fridman 1:06:51 ... the possibility here...... that the main alien, say, say there exists one alien civi, other intelligent alien civilization in the galaxy. The po-, to me, the, if they visit Earth, what's going to visit Earth is like the crappy-

Clara Sousa-Silva 1:07:09 (laughs)

Lex Fridman 1:07:09 ... like the really crappy broken draw-

Clara Sousa-Silva 1:07:10 Short straw, yeah, yeah. (laughs)

Lex Fridman 1:07:12 ... draw-, like, like, this, this like really dumb thing that's, uh, I don't know, like the early Game Boys or something like.

Clara Sousa-Silva 1:07:19 I think there's a cartoon about this. There's an alien that gets sent to Earth, Commander Spiff or something, and it's kind of-

Lex Fridman 1:07:26 Good.

Clara Sousa-Silva 1:07:26 ... a punishment or something. Uh, but that's not possible. That's the thing, because interstellar distances are so hard to-

Lex Fridman 1:07:33 Yeah.

Clara Sousa-Silva 1:07:33 ... to cross and-

Lex Fridman 1:07:34 You have to do it on purpose.

Clara Sousa-Silva 1:07:35 You have to do it on purpose. It has to be a big, big deal. And we know this because, yes, you're right, we don't know enough about galactic biology. We don't know what the universal rules of biology or biochemistry are, because we only have the Earth. But we do know that the laws of physics are universal. We can predict behavior in the universe and then see it happen based on these laws of physics. We know that the laws of chemistry are universal. We know the periodic table is all they have to choose from. So yes, there may be some sort of unimaginable intelligence, but they still have to use the same periodic table that we have access to. They still have a finite number of molecules they can do things with. So, they still have to use the resources around them, the stars around them, the universe around them. And we know how much energy is in these places. And so, yes, they may be very capable, capable beyond our wildest dreams, but they're still in the same universe and we know a lot of those rules. We're not completely blind.

Lex Fridman 1:08:36 But there's a colleague of yours at Harvard, uh, uh, Kamran Vafa, he's a theoretical physicist. I don't know if you know him.

Clara Sousa-Silva 1:08:45 I've only joined Harvard about, uh, six months ago.

Lex Fridman 1:08:48 Okay. It's time to meet all the theoretical physicists. Uh, so he's a string theorist, but, uh, his idea is that, uh, aliens that are sophisticated enough to travel interstellar s- like that, those kinds of distances, will figure out actually ways to hack the, the fabric of the universe enough to have fun in other ways. Like, "This universe is too boring."

Clara Sousa-Silva 1:09:12 (laughs)

Lex Fridman 1:09:12 Like you would figure out ways to create other universes or like you, you, you go outside the physics as we know it. Uh, so the reason we don't see aliens visiting us all over the place is they're having fun elsewhere. This is like way too boring. We humans think this is fun, but it's actually mostly empty space that noth- no fun is happening. Like, there's no fun in visiting Earth for a super advanced civilization. So he thinks like if alien civilizations are out there, they found outside of our current standard models of physics ways of having fun that don't involve us. But-

Clara Sousa-Silva 1:09:47 And that, that's probably true. But even the notion of visiting, that's so literally pedestrian, you know?

Lex Fridman 1:09:52 Yeah.

Clara Sousa-Silva 1:09:52 Of course we want to go there, 'cause going there is the only thing we know. We see a thing we want, we wanna go there and get it.

Lex Fridman 1:09:58 Yeah.

Clara Sousa-Silva 1:09:58 But that is probably something they've n- no longer got need for. I specifically don't particularly wanna go to space. Sounds awful. Uh, you know, none of the things I like are gonna be there. And (laughs) I, my whole work is, my whole career is finding life and understanding the universe. So I care a lot.

Lex Fridman 1:10:19 Mm-hmm.

Clara Sousa-Silva 1:10:20 But I care about knowing about it, and I feel no need to go there to learn about it.

Lex Fridman 1:10:24 Mm-hmm.

Clara Sousa-Silva 1:10:25 And I think as we develop better tools, hopefully people will feel less and less a need to go everywhere that we know about. And I would expect any alien civilization worth their salt have developed observation tools and, and tools that allow them to understand the universe around them and beyond without having to go there. This, this going is so wasteful.

Lex Fridman 1:10:48 Yeah, so more focused on the knowledge and learning versus the colonization, like the, the conquering and all those kinds of things. That-

Clara Sousa-Silva 1:10:55 That's, you know, beneath them.

Lex Fridman 1:10:57 (laughs) That's beneath them. That, I mean, that said, do you think there's, um, in your hopeful search for life through phosphine other, um, gasses,

Lex Fridman 1:11:07 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?

Clara Sousa-Silva 1:11:27 So intelligent life, I have no idea. It seems deeply unlikely. Uh, possible, but I'm not even sure if it's plausible.

Lex Fridman 1:11:35 So that's a special thing to you about Earth is somehow intelligent life came to be?

Clara Sousa-Silva 1:11:38 Yes. And it's only, you know, very briefly, probably extremely briefly. Um-

Lex Fridman 1:11:44 Uh-oh, you mean like it's always going to be, like we're gonna destroy ourselves?

Clara Sousa-Silva 1:11:48 Exactly.

Lex Fridman 1:11:49 Oh, boy.

Clara Sousa-Silva 1:11:49 And life will continue on Earth happily, uh, probably more happily. Um, so-

Lex Fridman 1:11:54 The trees and the dolphins will be here, I'm telling you.

Clara Sousa-Silva 1:11:56 And the cockroaches and the-

Lex Fridman 1:11:58 Yeah.

Clara Sousa-Silva 1:11:58 ... incredible fungi, you know?

Lex Fridman 1:12:00 Yes.

Clara Sousa-Silva 1:12:01 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?

Lex Fridman 1:12:16 Yes.

Clara Sousa-Silva 1:12:18 There's been one, an intelligent one, and for a blink of an eye. Uh-

Lex Fridman 1:12:21 Yeah.

Clara Sousa-Silva 1:12:21 ... 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.

Lex Fridman 1:12:40 Yeah.

Clara Sousa-Silva 1:12:40 And I've had to let go of that dream because it's so deeply implausible.

Lex Fridman 1:12:44 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.

Clara Sousa-Silva 1:12:56 ... on Earth, that's not the case, but it could be the case elsewhere.

Lex Fridman 1:12:59 Oh, it's not the case on Earth? We-

Clara Sousa-Silva 1:13:00 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-

Lex Fridman 1:13:08 Well, it's the garb- all, well, it's-

Clara Sousa-Silva 1:13:08 ... all us babies. (laughs)

Lex Fridman 1:13:11 (laughs) So you don't see, uh, polluting gases as a, as a possible, like...

Clara Sousa-Silva 1:13:17 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.

Lex Fridman 1:13:39 Yeah.

Clara Sousa-Silva 1:13:39 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-

Lex Fridman 1:13:47 Yeah.

Clara Sousa-Silva 1:13:47 ... deeply implausible. But life, I think, is inevitable, and if it is inevitable, it is common, so I think there'll be life everywhere in the galaxy. Now, how common that life is I think will depend a lot on whether there's life in the solar system beyond Earth. So I'll adjust my expectations very much based on there being life in the solar system. If there's life in the Venusian clouds, if there's life in the, if there are biosignatures coming out of the plumes of Enceladus, if there's life on Titan.

Lex Fridman 1:14:23 Oh, yeah, that's right. Encel- yeah, yeah, plumes of Enceladus, that's the, um, that's the Saturn one?

Clara Sousa-Silva 1:14:28 It's the moon that has the geysers that come out.

Lex Fridman 1:14:30 Yeah.

Clara Sousa-Silva 1:14:30 And so you can't see the under- the subterranean oceans, but...

Lex Fridman 1:14:34 It's supposed... It's, so it would be in the atmosphere. I was gonna ask you about that one. Uh, have you looked at that? Uh, have you... Is, is that a hope for you to use the tools that you're using with RASCAL, uh, and other (laughs) ways for detecting the 16,000 of, um, molecules that might be biosignatures to look at Enceladus?

Clara Sousa-Silva 1:14:56 Yes, that's absolutely the plan. It's-

Lex Fridman 1:14:59 Is there... What's the, what's the limiting factor currently? Is it the s- the, the quality of the telescopes? Is, what's the, what's the, the, the quality of the data?

Clara Sousa-Silva 1:15:07 Yeah, the quality of the data, the observational data, and also the quality of RASCAL and other (laughs) associated things. So we're missing a lot of fundamental data to interpret the data that we get, and we don't have good enough data. Um, but hopefully we will, in the coming decades, we'll get some information on Titan. We have Dragonfly going over. Uh, we'll get the plumes of Se- Enceladus. We will look at the clouds of Venus, and there's other places. And so if we find any life or any sign of life ever, like on Mars, then I'll adjust my calculations, and I'll say, "Life is not just inevitable and common, but extremely common." Because all of these places we've mentioned, the subterranean oceans on Enceladus, the methane oceans of Titan, the clouds of Venus, the acidic clouds of Venus, these are places that are very different from the places where we find life on Earth, even the most extreme places. And so if life can originate in all of these completely different habitats, then life is even more resourceful than we thought.

Lex Fridman 1:16:12 Yeah, that's really-

Clara Sousa-Silva 1:16:13 Which means it's everywhere.

Lex Fridman 1:16:14 That's really exciting if it's everywhere. If, if there's life on just one, uh, one of the moons, if it's on Mars.

Clara Sousa-Silva 1:16:21 Anywhere, anywhere in the solar system, and I will bet everything I own...

Lex Fridman 1:16:25 That's a good point.

Clara Sousa-Silva 1:16:25 ... that every solar system, every planetary system has a potential for habitability, you know, because even if they don't have a habitable planet, they'll have moons around other giant planets, and there'll be so much life. So for me, that's the only thing to figure out now, whether life is inevitable and quite common throughout the galaxy or everywhere.

Lex Fridman 1:16:49 Mm-hmm.

Clara Sousa-Silva 1:16:49 But it's somewhere between those two. Intelligent life, I make no bets.

Lex Fridman 1:16:54 See-

Clara Sousa-Silva 1:16:54 And if I had to bet, I would be against.

Lex Fridman 1:16:58 See, uh, to me, like, two discoveries in the 21st century would change everything. One is, and maybe I'm biased, but one is the discovery of life in the solar system. I feel like that would change our whole conception of how unique we are in the universe. I, I think I'm much more eager than you are to jump from basic life to intelligent life. I feel like we- if there's life everywhere, like, the odds are, there has... Like, we cannot... Like, you ha-... Oh, I see, you're, you're saying it, there could have been many intelligent civilizations out there, th- but they just keep dying out as like little-

Clara Sousa-Silva 1:17:38 Yeah, us detecting them, you know, ships in the night.

Lex Fridman 1:17:41 Ships in the night. Oh, that's f- now that's ultra sad, just like-

Clara Sousa-Silva 1:17:46 Is it sad?

Lex Fridman 1:17:47 ... a graveyard of just-

Clara Sousa-Silva 1:17:47 The Earth is not better for having us. Is it... We...

Lex Fridman 1:17:51 There's-

Clara Sousa-Silva 1:17:51 It doesn't owe us anything.

Lex Fridman 1:17:53 There's b-

Clara Sousa-Silva 1:17:53 Wouldn't you be sad to find alien giraffes? Would you be disappointed if you found alien giraffes? 'Cause I would not.

Lex Fridman 1:18:00 No, well, giraffes, f- first of all, they look goofy with their necks and everything, but-

Clara Sousa-Silva 1:18:03 But, no, we do not shit on giraffes.

Lex Fridman 1:18:05 (laughs) Okay, all right.

Clara Sousa-Silva 1:18:06 Giraffes are wondrous animals that are deeply understudied. We still know so little about them 'cause no one does PhDs in giraffes. I am disappointed. I made a PhD in phosphine when people aren't doing PhDs in giraffes. We do not know enough about giraffes.

Lex Fridman 1:18:19 I think it was, like, Ricky Gervais that did a whole, like, long thing about-

Clara Sousa-Silva 1:18:23 You can't trust Ricky Gervais (laughs) to talk about giraffes.

Lex Fridman 1:18:25 (laughs)

Clara Sousa-Silva 1:18:25 That is not his expertise.

Lex Fridman 1:18:26 (laughs) Yeah, but it's the stupid necks. It doesn't make any sense.

Clara Sousa-Silva 1:18:30 Why...

Lex Fridman 1:18:30 I, it, the, the, I mean, that's fine that-

Clara Sousa-Silva 1:18:32 Giraffes are very resourceful animals who do incredible things and can kick a lion in the face.

Lex Fridman 1:18:36 Why don't you climb the tree? Why don't you climb the tree? You don't need to grow, uh, through the, uh, the, the lengthy evolutionary process.

Clara Sousa-Silva 1:18:42 Don't be shitting on giraffes.

Lex Fridman 1:18:43 I d- okay. Fine.

Clara Sousa-Silva 1:18:44 Giraffes are wondrous animals.

Lex Fridman 1:18:46 I would very appreciate it.

Clara Sousa-Silva 1:18:47 I take it back.

Lex Fridman 1:18:48 I, uh, I take it back. I apologize. I, I trust, I trust your expertise on this. Uh, the, the, the thing that makes humans really fascinating and I think the Earth-... but I'm a human, is where we create-

Clara Sousa-Silva 1:19:03 Disclaimer.

Lex Fridman 1:19:04 (laughs) Yeah. We create things that are... Yes, there's all the ugliness in the world, there's all the- on the- on the bio- biological and the chemical level, there's the pollution, but we create beauty. If you, if you even from a physics perspective look at symmetry as somehow capturing beauty, the breaking of symmetries, stuff grounded in all the different definitions of symmetry, we're good at like creating things.

Clara Sousa-Silva 1:19:31 So are spiders.

Lex Fridman 1:19:34 But not giraffes. Okay. But yes, this is a... (laughs)

Clara Sousa-Silva 1:19:37 Spiders-

Lex Fridman 1:19:38 Yes, this is a good point.

Clara Sousa-Silva 1:19:38 There are spiders that create-

Lex Fridman 1:19:39 This is a very strong point.

Clara Sousa-Silva 1:19:40 ... little bubbles of air so they can breathe under water. They can literally scuba dive. There are spiders that can create parachutes so they can glide.

Lex Fridman 1:19:48 Yeah.

Clara Sousa-Silva 1:19:48 And talk about symmetry, look what spiders can do. And I just thought of spiders, but if I was an alien species coming to Earth, there'll be plenty to wonder and we would just be one-

Lex Fridman 1:20:00 One of the things.

Clara Sousa-Silva 1:20:01 ... yeah, clunky-

Lex Fridman 1:20:03 Yeah.

Clara Sousa-Silva 1:20:04 ... naked monkey.

Lex Fridman 1:20:05 Yeah. The ants might be even more fascinating.

Clara Sousa-Silva 1:20:07 Exac- The ants. Ants can figure out exactly through some emergent consciousness what the maximum distance between their trash, their babies, and their food is, just from, without any of them knowing how to do this, and collectively they've learned how to do this.

Lex Fridman 1:20:25 Yeah.

Clara Sousa-Silva 1:20:25 If I was an alien species, I'd be looking at that.

Lex Fridman 1:20:27 Well, so that was the other thing I was gonna mention, the second thing is, I tend to believe we- we can engineer consciousness, but at the- at the basic level, understand the source of consciousness. Because if consciousness is- is unique to humans, and if we can engineer it, that gives me hope that it could be present elsewhere in the universe. That's the other thing that makes... It's an-

Clara Sousa-Silva 1:20:50 Debride.

Lex Fridman 1:20:50 ... open question that makes humans perhaps special is not maybe the presence of consciousness but some kind- somehow a presence of like elevated consciousness. It does, again, may be human-centric, but it feels like we're more conscious than giraffes, for example, and spiders. Uh-

Clara Sousa-Silva 1:21:06 Yes, I won't deny that. I, I, there is something special about humans. I, you know, they're my favorite species. I-

Lex Fridman 1:21:13 They are.

Clara Sousa-Silva 1:21:14 They are, you know.

Lex Fridman 1:21:15 Yeah.

Clara Sousa-Silva 1:21:16 Some of my best friends are humans.

Lex Fridman 1:21:18 (laughs) Yeah.

Clara Sousa-Silva 1:21:18 And I, (laughs) I, I think highly of humans. It's-

Lex Fridman 1:21:23 Yeah.

Clara Sousa-Silva 1:21:24 ... it's great. I just don't have great hope for our longevity, and specifically I don't have great hope given that we're the only species out of five billion that did this cool consciousness trick. I just, I don't wanna bet on finding, um, a kinship elsewhere.

Lex Fridman 1:21:42 That's quite interesting to think about. I don't think I've even considered that possibility that the, that there would be life in the solar system, so that indicates that very possibly life is r- like literally everywhere.

Clara Sousa-Silva 1:21:57 Yeah, everywhere it can happen it does.

Lex Fridman 1:21:58 Yeah.

Clara Sousa-Silva 1:21:59 You know?

Lex Fridman 1:21:59 And the mo- like especially what we're discovering with exoplanets now, uh, they're, how numerous they are, are Earth-like habitable quote/unquote planets. There's, th- fr- like they're everywhere.

Clara Sousa-Silva 1:22:12 The most common type-

Lex Fridman 1:22:13 It's-

Clara Sousa-Silva 1:22:13 ... of planet-

Lex Fridman 1:22:13 Yeah.

Clara Sousa-Silva 1:22:14 ... is rocky it seems.

Lex Fridman 1:22:15 And so f- but I didn't consider the possibility that life is like literally everywhere and yet intelligent life is nowhere long enough to, uh, to communicate with each other, to form little clusters of, um, civilizations that expand beyond the solar system and so on. (sighs) Man, maybe becoming a multi-planetary species is, uh, is a less likely pursuit than, um, than we imagined, but-

Clara Sousa-Silva 1:22:44 I agree.

Lex Fridman 1:22:44 ... but one of the things that makes humans beautiful is we hope.

Clara Sousa-Silva 1:22:49 But I, I hope for humanity. And one of the things I hope for is that we become less obsessed with conquering, and we become less obsessed with spreading ourselves. I hope that we transcend that, that we're happy with the universe without having to go and take it. So you can hope for the species without hoping for a multi-planetary existence. That is only, I think, the drive of our most primitive instincts to go and take, to go and plant a flag somewhere. We love planting a flag somewhere. And maybe we could overcome that minor drive.

Lex Fridman 1:23:35 And once we do, the AI systems we build will destroy us because we're too peaceful, and they will go and conquer and plant the flags.

Clara Sousa-Silva 1:23:43 Best of luck to them. The cockroaches will be happy to-

Lex Fridman 1:23:46 (laughs)

Clara Sousa-Silva 1:23:46 ... um, keep their, (laughs) keep to their business-

Lex Fridman 1:23:49 I tend to-

Clara Sousa-Silva 1:23:50 ... as they always have.

Lex Fridman 1:23:50 ... I tend to believe that robots can have the same, um, elegance, and consciousness, and all the qualities of kindness, and love, and hope, and fear that, that humans have. Yeah.

Clara Sousa-Silva 1:24:02 In principle they could, yes.

Lex Fridman 1:24:05 Well-

Clara Sousa-Silva 1:24:05 I don't really trust the people who make them.

Lex Fridman 1:24:09 (laughs) This is about the giraffe comment, isn't it? Okay.

Clara Sousa-Silva 1:24:13 It is. (laughs)

Lex Fridman 1:24:13 (laughs)

Clara Sousa-Silva 1:24:13 I haven't forgiven you for shitting on giraffes.

Lex Fridman 1:24:16 (laughs)

Clara Sousa-Silva 1:24:16 What have they done to you?

Lex Fridman 1:24:17 You, um, j- just as a small tangent, uh, your master's thesis is also fascinating. Um, maybe we could talk about it for just a little bit. It's, uh, titled Influence of a Star's Evolution on its Planetary System. So this interplay between a star and a planet, is there something interesting you could say about what you've learned about this, this journey that a star takes and the planets around it?

Clara Sousa-Silva 1:24:42 Well, I- eh, when I was younger and I was told what would happen ultimately to the Earth as the sun expands towards a red giant and, you know, Mercury would just like fall in, (laughs) and then, you know, Venus would fall in, and the sun doesn't care, and it just seemed-... so... I felt so small. I felt like the earth and everything on it, it just... The universe doesn't care. Even our sun doesn't care. And I think I felt like our sun should feel some sort of responsibility-

Lex Fridman 1:25:15 (laughs)

Clara Sousa-Silva 1:25:16 ... for its planets, you know?

Lex Fridman 1:25:17 Yes, yeah.

Clara Sousa-Silva 1:25:17 And it just felt like such a violent and neglectful parent and-

Lex Fridman 1:25:21 It's like a parent eating its own children.

Clara Sousa-Silva 1:25:23 It's horrible.

Lex Fridman 1:25:24 (laughs)

Clara Sousa-Silva 1:25:24 It's just a horrible notion. Uh, but it made me think, what if this, there's some sort of generation, and so at the time, when I was doing my masters, there was a notion of the white dwarf cemetery, which is this idea that when stars become white dwarfs, that death is so horrible that planets, potentially habitable planets that could have been habitable before, they're now gone. There's no, there's no s- chance for life. But then I thought, "What if life returns?" You know,