David Kipping: Alien Civilizations and Habitable Worlds | Lex Fridman Podcast #355

David Kipping 0:00 I think it's actually not that hard to imagine we are the only civilization in the galaxy right now.

Lex Fridman 0:04 Living.

David Kipping 0:05 Yeah, that's currently extant. But there may be very many extinct civilizations. If each civilization has a typical lifetime comparable to, let's say, AI is the demise of our own, that's only a few hundred years of technological development, or maybe 10,000 years if you go back to the Neolithic re- revolution, the dawn of agriculture, you know, hardly anything in cosmic time span. Um, that- that's nothing. That's the blink of an eye. And so it's not surprising at all that we would happen not to co-exist with anyone else.

Lex Fridman 0:34 Mm-hmm.

David Kipping 0:34 But that doesn't mean nobody else was ever here. And if other civilizations come to that same conclusion and realization, maybe they scour the galaxy around them, don't find any evidence for intelligence, then they have two options. They can either give up on communication and just say, "Well, it's never gonna happen, uh, we just, may as well just, you know, worry about what's happening here on our own planet," or they could attempt communication, but communication through time.

Lex Fridman 1:03 The following is a conversation with David Kipping, an astronomer and astrophysicist at Columbia University, Director of the Cool Worlds Lab, and he's an amazing educator about the most fascinating scientific phenomena in our universe. I highly recommend you check out his videos on the Cool Worlds YouTube channel. David quickly became one of my favorite human beings. I hope to talk to him, uh, many more times in the future. This is a Lex Friedman podcast. To support it, please check out our sponsors in the description. And now, dear friends, here's David Kipping.

Lex Fridman 1:41 Your research at Columbia is in part focused on what you call cool worlds, or worlds outside our solar system where temperature is sufficiently cool to allow for moons, rings, and life to form, and for us humans to observe it. So can you tell me more about this idea, this place of cool worlds?

David Kipping 2:00 Yeah. The history of discovering planets outside our solar system was really dominated by these hot planets. And that's just because of the fact they're easier to find. When the very first methods came online, these were primarily the Doppler spectroscopy method, looking for wobbling stars, um, and also the transit method. And these two both have a really strong bias towards finding these hot planets. Now, hot planets are interesting. The chemistry in their atmosphere is fascinating. It's very alien. Um, an example of one that's particularly close to my heart is TrES-2b, whose atmosphere is so dark it's less reflective than coal. And so they have really bizarre photometric properties, yet at the same time, they resemble nothing like our own home. And so, they said there's two types of astrophysicists, the astrophysicists who care about how the universe works, they wanna understand the mechanics of the machinery of this universe, why did the Big Bang happen, why is the universe expanding, how are galaxies formed, and there's another type of astrophysicist which perhaps, um, speaks to me a little bit more, it whispers into your ear, and that is, why are we here, are we alone, are there others out there? And ultimately along this journey, the hot planets aren't gonna get us there. We- when we're looking for life in the universe, seems to make perfect sense that there should be planets like our own out there, maybe even moons like our own planet around gas giants that could be habitable. And so my research has been driven by trying to find these more treacherous globes that might resemble our own planet.

Lex Fridman 3:35 So they're the ones that lurk more in the shadows, in terms of how difficult it is to detect?

David Kipping 3:39 They're much harder. Uh, they're harder for several reasons. The method we primarily use is the transit method, so this is really eclipses. As the planet passes in front of the star, it blocks out some starlight. The problem with that is that not all planets pass in front of their star. They have to be aligned correctly from your line of sight. And so the further away the planet is from the star, the cooler it is, the less likely it is that you're gonna get that geometric alignment. So whereas a hot Jupiter, about 1% of hot Jupiters will transit in front of their star, only about, uh, 0.5%, maybe even a quarter of a percent of Earth-like planets will have the right geometry to transit. And so that makes it much, much harder for us.

Lex Fridman 4:19 What's the connection between temperature of the planet and geometric alignment, probability of geometric alignment?

David Kipping 4:23 There's not a direct connection, but they're connected via an intermediate parameter, which is their separation from the star. So-

Lex Fridman 4:29 Oh, got it.

David Kipping 4:30 ... the, the planet will be cooler if it's further away from the star, which in turn means that the probability of getting that alignment correct is going to be less. On top of that, they also transit their star less frequently. So if you go to the telescope and you wanted to discover a hot Jupiter, you could probably do it in a week or so, because their orbital period is of the order of one, two, three days. So you can actually get the full orbit two or three times over, whereas if you wanted to detect an Earth-like planet, you have to observe that star for three, four years. And that's actually one of the problems with, uh, Kepler. Kepler was this very successful mission that NASA launched, um, over a decade ago now, I think, and it discovered thousands of planets. It's still the dominant source of exoplanets that we know about. But unfortunately, it didn't last as long as we would have liked it to. It died after about 4.35 years, I think it was. And so for an Earth-like planet, that's just enough to catch four transits. And four transits was kind of seen as the minimum. But of course, the more transits you see, the easier it is to detect it, because you build up signal to noise. If you see the same thing, tick, tick, tick, tick, tick, the more ticks you get, the easier it is to find it. And so it was really a shame that Kepler was just at the limit of where we were expecting it to start to see Earth-like planets. And in fact, it really found zero, zero planets that are around stars like the Sun, their orbits similar to the Earth around the Sun, and could potentially be similar to our own planet in terms of its composition. And so it's a great shame, but, um, that's why it gives astronomers more to do in the future.

Lex Fridman 6:02 Just to clarify, the transit method-

David Kipping 6:04 Mm-hmm.

Lex Fridman 6:05 ... is our primary way of detecting these things.... and what it is, is, uh, when the object passes, occludes the source of light just a tiny bit, a few pixels, and from that we can infer something about its mass and size and distance and geometry and all- all of that.

David Kipping 6:24 Mm-hmm.

Lex Fridman 6:25 That's like trying to tell, what? Uh, (laughs) at a party, you can't see anything about a- a person, but you can just see by the way they occlude others. So this is the method.

David Kipping 6:38 Yeah.

Lex Fridman 6:38 But this is super far away. How many pixels of information do we have? Basically, how high resolution is the signal that we, um, that we can get about these occlusions?

David Kipping 6:50 You're right in your description. I- I think, just to build upon that a little bit more, it might be almost like your vision's completely blurry. Like, you have an extreme, you know, eye prescription and so you can't resolve anything, everything just blurs, and – but you can tell that something was there 'cause it just got fainter for a short amount of time. Something- someone passed in front of a light.

Lex Fridman 7:09 Yeah.

David Kipping 7:09 And so that light, in your eyes, would just dim for a short moment. Now, the reason we have that problem with blurriness or resolution is just because the stars are so far away. I mean, these are- the closest stars are four light years away, but most of the stars Kepler looked at were thousands of light years away. And so you- there's absolutely no chance that the telescope can physically resolve the star or even the separation between a planet and the star, is- it's too small, especially for a telescope like Kepler. It's only a meter across. In principle, you can make those detections, but you need a different kind of telescope. We call that direct imaging. And direct imaging is a very exciting distinct way of detecting planets, but it, as you can imagine, is going to be far easier to detect planets which are really far away from their star to do that, because that's gonna make that separation really big, and then you also want the star to be really close to us, so the nearest stars. Not only that, but you would prefer that planet to be really hot, because the hotter it is, the brighter it is, and so that tends to buy us direct imaging towards planets which are in the process of forming.

Lex Fridman 8:11 Mm-hmm.

David Kipping 8:12 So things which have just formed and the planet's still got all of its primordial heat embedded within it, and it's glowing, we can see those quite easily. But for the planets more like the Earth, of course they've cooled down and so we can't see that. The light is pitiful compared to a newly formed planet. We would like to get there with direct imaging. That's the dream, is to have the pale blue dot, an actual photograph of it, maybe even just a one pixel photograph of it. But for now, the entire solar system is one pixel, with- certainly with the transit method of most other telescopes. And so all you can do is see where that one pixel, which contains potentially dozens of planets, and the star, maybe even multiple stars, dims for a short amount of time.

Lex Fridman 8:51 It dims just a little bit, and from that you can infer something.

David Kipping 8:54 Yeah, I mean, it's- it's like being a detective in the scene, right? It's very- it's indirect clues-

Lex Fridman 8:59 Yeah.

David Kipping 9:00 ... of the existence of the planet.

Lex Fridman 9:01 It's amazing that humans can do that. We're just looking out in these immense distances, and looking, you know, if there's alien civilizations out there, like let's say one exactly like our own, we're like, would we even be able to see an Earth that passes-

David Kipping 9:19 Mm-hmm.

Lex Fridman 9:19 ... in the way of its sun and slightly dims? And that's the only sign we have of that- of that alien human-like civilization out there, is it's just a little bit of a dimming?

David Kipping 9:29 Yeah. I mean, depends on the- on the type of star we're talking about. If it is a star truly like the Sun, the dip that that causes is- is 84 parts per million. I mean, that's just- it's like the same as a, um, as like a firefly flying in front of like a giant floodlight at a stadium or something. That's the- kind of the brightness contrast that you're trying to compare to. So it's- it's extremely difficult detection, and in the very, very best cases we can get down to that, but as I said, we don't really have any true Earth analogs that have been in the exoplanet candidate yet. Unless you relax that definition, you say, "It's not- just doesn't have to be a star just like the Sun." It could be a star that's smaller than the Sun, it could be these orange dwarfs or even the red dwarf stars, and the fact those stars are smaller means that, for the same size planet passing in front of it, more light is blocked out. And so a very exciting system, for example, is TRAPPIST-1, which has seven planets which are smaller than the Earth, and those are quite easily detectable, not with a space-based telescope, but even from the ground. And that's just 'cause the star is so much smaller that the relative increase in or decrease in brightness is enhanced significantly, 'cause that smaller size. So TRAPPIST-1E, it's a planet which is in the right distance for liquid water. It has a slightly smaller size than the Earth. Um, it's about 90% the size of the Earth, about 80% the mass. And it's one of the top targets right now for potentially having life. Um, and yet it raises many questions about, um, what would that environment be like? This is a star which is one eighth the mass of the Sun. Its, um... Stars like that take a long time to come off their adolescence.

Lex Fridman 11:08 Mm-hmm.

David Kipping 11:08 When stars first form, like the Sun, it takes them maybe 10, 100 million years to sort of settle into that main sequence lifetime. But for stars like these late M dwarfs, as we call them, they can take up to a billion years or more to calm down. And during that period, they're producing huge amounts of X-rays, ultraviolet radiation, that could potentially rip off the entire atmosphere, it may desiccate the planets in the system, and so even if water arrived by comets or something, it may have lost all that water due to this prolonged period of high activity. So we have lots of open-ended questions about these M dwarf planets, but they are the most accessible. And so in the near term, if we detect anything in terms of biosignatures, it's gonna be for one of these red dwarf stars. It's not gonna be a true Earth twin, as we would recognize it as having a yellow star.

Lex Fridman 12:01 Well, let me ask you, I mean, there's a million ways to ask this question, I'm sure I'll ask it, uh, about habitable worlds. Let's just go to our- our own solar system. What can we learn about the planets and moons in our solar system that...... might contain life, whether it's Mars or some of the moons of Jupiter and Saturn. What kind of characteristics, 'cause you said it might not need to be Earth-like-

David Kipping 12:28 Mm-hmm.

Lex Fridman 12:28 ... what kind of characteristics might be, we'd be looking for?

David Kipping 12:31 When we look for life, it's hard to define even what life is. Um, but we can maybe do a better job in defining the sorts of things that life does, and that provides, um, some aspects to, some avenue for looking for them. Um, in the classically, conventionally, I think we thought the way to look for life was to look for oxygen. Oxygen is a byproduct of photosynthesis on this planet. Um, we didn't always have it. Certainly if you go back to the Archean period, um, there was, you know, you have this period called the Great Oxidation Event where the Earth floods with oxygen for the first time and starts to saturate the oceans and then into the atmosphere. And so that oxygen, if we detect it on another planet, whether it be Mars, Venus, or an exoplanet, whatever it is, um, that was long thought to be evidence for something doing photosynthesis. Because if you took away all the plant life on the Earth, the oxygen wouldn't just hang around here. It's a highly reactive molecule. It would oxidize things. And so within about a million years, you would probably lose all the oxygen on planet Earth. So that was, uh, conventionally how we thought we could look for life. And then we started to realize that it's not so simple because, A, there might be other things that life does apart from photosynthesis. Um, certainly the vast majority of the Earth's history had no oxygen, and yet there was living things on it. So that doesn't seem like a complete test. Um, and secondly, could there be other things that produce oxygen besides from life? Um, a growing concern has been these false positives in biosignature work. And so one example of that would be photolysis. That happens in the atmosphere. When ultraviolet light hits the upper atmosphere, it can break up water vapor. The hydrogen splits off to the oxygen, the hydrogen is a much lighter atomic species, and so it can actually escape certainly planets like the Earth's gravity. That's why we don't have any hydrogen or, or very little helium. And so that leaves you with the oxygen, which then oxidizes the surface. And so, um, there could be a residual oxygen signature just due to this photolysis process. So we've been trying to generalize, and, um, certainly in recent years there's been other suggestions of things we could look for in the solar system beyond. Uh, nitrous oxide, basically laughing gas, is a product of microbes. Um, that's something that we're starting to get more interest in looking for. Methane gas in combination with other gases can be an important biosignature, uh, phosphine as well. And phosphine is particularly relevant to the solar system because there was a lot of interest for Venus recently. Um, you may have heard that there was a claim of a biosignature in Venus's atmosphere, I think it was like two years ago now, and the, the judge and jury are still out on that. Um, there was a very provocative claim and signature of a phosphine-like spectral absorption. Um, but it could have also have been some other molecule, in particular sulfur dioxide, which is not a biosignature. Uh-

Lex Fridman 15:24 So this is a detection of a gas in the atmosphere-

David Kipping 15:27 Yeah.

Lex Fridman 15:27 ... of Venus. And, and, uh, it might be controversial on several dimensions. So one, how to interpret that, two, is this the right gas, and three, is this even the right detection? Is this, is, is there an error in the detection?

David Kipping 15:41 Yeah. I mean, how much do we believe the detection in the first place? If you do believe it, does that necessarily mean there's life there? And, um, what gives, how can you have life in Venus's atmosphere in the first place because that's, you know, been seen as like a hell hole place for imagining life, but I guess the, the, the counter to that has been that, okay, yes, the surface is a horrendous place to imagine life thriving. Um, but as you go up in altitude, the very dense atmosphere means that there is a cloud layer, um, where the temperature and the pressure become actually fairly similar to the surface of the Earth. And so maybe there are microbes stirring around in the clouds which are producing phosphine.

Lex Fridman 16:19 Mm-hmm.

David Kipping 16:20 Um, at the moment this is fascinating. It's got a lot of us reinvigorated about the prospects of going back to Venus and doing another mission there. In fact, there's now two NASA missions, VERITAS and DAVINCI, which are gonna be going back in, before 2030 or the 2030s. Um, and then we have a European mission, I think that's slated now, and even a Chinese mission might be coming along the way as well. So we might have multiple missions going to Venus, which has long been overlooked. I mean, apart from the Soviets, there really has been very little in the way of exploration of Venus. That's certainly as compared to Mars. Mars has enjoyed most of the activity from NASA's rovers and surveys. Um, and Mars is certainly fascinating. There's, you know, the signature of methane that has been seen there before. Um, again, there the discussion is whether that methane is a product of biology, which is possible, something that happens on the Earth, or whether it's some geological process that we are yet to fully understand. Could be a, you know, for example, a reservoir of methane that's trapped under the surface and it's leaking out seasonally.

Lex Fridman 17:24 So the nice thing about Venus is if there's a giant living civilization there, it'll be airborne so you can just fly through and collect samples.

David Kipping 17:34 Yeah.

Lex Fridman 17:34 With Mars and, uh, moons of, uh, Saturn and Jupiter, you're gonna have to dig, dig under to find the civilizations...

David Kipping 17:42 Right.

Lex Fridman 17:42 ... de- dead or living.

David Kipping 17:43 Right. And so, yeah, maybe it's easier than for Venus because certainly you can imagine just a balloon floating through the atmosphere, um, that, or a drone or something, that would have the capability of just scooping up and sampling. Um, to, to dig under the surface of Mars is maybe feasible-ish with, you know, especially with something like Starship that could launch, you know, a huge digger basically to the surface and you could just excavate away at the surface. But for something like Europa, um, we really are still unclear about how thick the ice layer is, um, how you would melt through that huge, th- thick layer to get to the ocean. And then potentially also discussions about contamination.... the problem with looking for life in the solar system, which is different from looking for life with exoplanets, is that you always run the risk of, especially if you visit there, of introducing the life yourself. Right? It's very difficult to completely exterminate every single microbe and spore on the surface of your, of your rover or the surface of your lander, and so there's always a risk of introducing something. I mean, to some extent there is continuous exchange of material between these planets naturally on top of that as well, and now we're sort of accelerating that process to some degree. Um, and so if you dig into Europa's surface, which probably is completely pristine, it's very unlikely there has been much exchange with the outside world for, for its subsurface ocean, you are for the first time potentially introducing bacterial spores into that environment that may compete or may introduce spurious signatures for the life you're looking for. And so it's, it's almost an ethical question as to how to proceed with looking for life on, on those subsurface oceans. And I don't think one we really have a good resolution for at this point.

Lex Fridman 19:32 Ethical. So you mean ethical in terms of concern for the, like, for preserving life elsewhere?

David Kipping 19:40 Right. Yeah. Yeah.

Lex Fridman 19:40 Not, not to murder it? As opposed to a scientific one?

David Kipping 19:43 I mean, we always worry about a space virus, right? Coming, coming here, or, or, you know, some kind of external source, and that we would be the source of that potential contamination.

Lex Fridman 19:51 Or the other direction.

David Kipping 19:52 Yeah.

Lex Fridman 19:52 I mean, they, that, you know, the whatever, whatever survives in such harsh conditions might be pretty good at, uh, surviving all conditions. It might be a little bit more resilient and robust, so it might actually take a ride on us back home.

David Kipping 20:08 Possibly. I mean, I'm sure, I'm sure that some people would be concerned about that. I think we would, we would hopefully have some containment, uh, procedures, as if, well, if we did sample return. Or, I mean, you don't even really need a sample return. These days you can pretty much send, like, a little micro laboratory to the, the planet to do all the experiments in s- you know, in situ, and then just send them back to your planet, the data. And so I don't think there's, it's necessary, the, especially for a case like that where you might have contamination concerns, that you have to bring samples back. Um, although probably if you brought back Europan sushi, it would probably sell for quite a bit with the billionaires (laughs) in New York City.

Lex Fridman 20:43 (laughs) S- sushi?

David Kipping 20:45 Yeah.

Lex Fridman 20:45 Um, I, I would love from an engineering perspective just to see all the different candidates and designs for, like, the scooper for Venus and the scooper for Europa and, and Mars. I haven't really looked deeply into how they actually, like the actual engineering of collecting the samples, because that's, the engineering of that is probably essential for not either destroying life or, or, uh, polluting it with our own microbes and so on.

David Kipping 21:13 Mm-hmm.

Lex Fridman 21:13 Th- that's like an eng- interesting engineering challenge. I usually, for rovers and stuff, focus on the, on the robo- on the sort of the mobility aspect of it, on the robotics, the perception, uh, and the movement and the planning and the control.

David Kipping 21:26 Mm-hmm.

Lex Fridman 21:26 But there's probably, the scooper is probably where the action is, the-

David Kipping 21:28 Yeah.

Lex Fridman 21:29 ... the microscopic sample collection. So basically you have to first clean your vehicle, make sure it doesn't have any Earthlike things on it, and then you have to put it into some kind of thing that's perfectly sealed from the environment, so if we bring it back or we analyze it, it's not, um, it's not going to bring anything else, uh, ex- external in. Yeah, I don't know. It'd be, this would be, that would be an interesting engineering design there.

David Kipping 21:53 Yeah. I mean, Curiosity has been, uh, leaving these little pods on the surface quite recently, and there's some neat photos that you can find online, and it's, they kind of look like, uh, lightsaber hilts, which ... (laughs) . So, um, the, yeah, to me, I, I think I tweeted something like, uh, you know, "This weapon is your life. Like, don't lose it, Curiosity."

Lex Fridman 22:12 Yeah.

David Kipping 22:12 Because it's just dumping these little vials everywhere, and it's, yeah, it is scooping up these things, and the intention is that in the future, um, there will be a sample return mission that will come and pick these up.

Lex Fridman 22:22 Mm-hmm.

David Kipping 22:23 Um, but it's, I mean, the engineering behind those things is so impressive. The thing that blows me away the most has been the landings. Um, especially, I'm training to be a pilot at the moment, so that's the sort of, you know, watching landings has become like my pet hobby on YouTube at the moment, and how not to do it, how to do it with different levels of, uh, conditions and things. But with the, you know, when, when you think about landing on Mars, just the light travel time effect means that there's no possibility of a human controlling that descent.

Lex Fridman 22:50 Mm-hmm.

David Kipping 22:51 And so you have to put all of your faith and your trust in the computer code, or the AI, or whatever it is that you've put on board that thing to, to make the correct descent. Um, and so there's this famous, uh, period called seven minutes of hell, where you're basically waiting for that light travel time to come back to know whether your vehicle successfully landed on the surface or not. And during that period, you know in your mind simultaneously that it is doing these multi-stages of, um, deploying its parachute, deploying the crane, activating its jets to come down, and controlling its descent to the surface, um, and then the crane has to fly away so it doesn't accidentally hit the rover. And so there's a series of, uh, multi-stage points where any, any of them go wrong, you know, the whole mission could, could go awry. Um, and so the fact that we are fairly consistently able to build these machines that can do this autonomously is, to me, one of the most impressive acts of engineering that NASA have achieved.

Lex Fridman 23:51 Yes. The unfortunate fact about physics is the takeoff is easier than the landing.

David Kipping 23:55 (laughs) Yes. Yes.

Lex Fridman 23:57 It's easy. And you mentioned Starship. One of the incredible engineering feats that you get to see is the reusable rockets that take off, but they land, and they land, uh, using control, and they do so perfectly, and sometimes when it's synchronous, it's, it's just, it's beautiful to see. And then with Starship, you see the, the chopsticks that catch the ship. I mean, there's just so much incredible engineering. But you mentioned, uh, Starships is somehow helpful here. So what's your hope with Starship? What kind of science might it enable?... possibly.

David Kipping 24:28 Mm-hmm. There's two things. I mean, it's the launch cost itself, which is hopefully gonna be in per kilograms, gonna dramatically reduce the cost if it's s- sort of the lev- even if it's a factor of 10 higher than what Elon originally promised, this is gonna be a revolution for the cost to launch. That means you could do all sorts of things. You could launch, um, large telescopes, which could be basically like JWST, but you don't even have to fold them up. JWST had this whole issue with its design that it's six and a half meters across, and so you have to, there's no fuselage which is that large. At the time, Aries4 wasn't large enough for that, and so they had to fold it up into this kind of complicated origami, and so a large part of the cost was figuring out how to fold it up, testing that it unfolded correctly, repeated testing, and, you know, the n- there was something like 130 fail points or something during this unfolding mechanism, and so all of us were holding our breath during that process. But if you have the ability to just launch, you know, arbitrarily large masses, um, at least comparatively, compared to JWST, and very large mirrors into space, you can more or less repurpose ground-based mirrors. Um, the Hubble Space Telescope mirror and the JWST mirrors are designed to be extremely lightweight.

Lex Fridman 25:38 Mm-hmm.

David Kipping 25:39 And that increased their cost significantly. Um, they have this kind of honeycomb design on the back to try and minimize the, the weight. If you don't really care about weight, because it's so cheap, then you could just literally grab s- many of the existing ground-based mirrors across telescopes across the world, four meter, five meter t- mirrors, and just pretty much attach them to a chassis and have your own space-based telescope. Um, I think the Breakthrough Foundation, for instance, uh, is an entity that has been interested in doing this sort of thing. Um, and so that raises the prospects of having not just one JWST that just, you know, JWST is a fantastic resource, but it's split between all of us, cosmologists, star formation, uh, astronomers, those of us studying exoplanets, those of us wanting to study, you know, the ultra-deep fields and the origin of the first galaxies, the expansionary of the universe. Everyone has to share this resource, but we could potentially each have, (laughs) you know, one, uh, JWST each that is, uh, maybe just studying a handful of the brightest exoplanet stars-

Lex Fridman 26:42 Mm-hmm.

David Kipping 26:42 ... and measuring their atmospheres. This is important because if you, you know, we talked about this planet Trappist-1e earlier. That planet, if JWST studied it and tried to look for biosignatures, by which I mean oxygen, um, nitrous oxide, methane, it would take it of order of 200 transits to get even a very marginal what we'd call two-and-a-half sigma detection of those, which basically nobody would believe with, with that, and 100 transits, I mean, this thing transits once every six days, so you're talking about sort of four years of staring at the same star with one telescope. There'd be some breaks, but it'd be hard to schedule much else, because you have to continuously catch each one of these transits to build up your sig- signal to noise. And so JWST is never gonna do that. In principle, technically, JWST could technically have the capability of just about detecting a biosignature on an Earth-like planet around a s- around a non-sunlike star, but still, impressively, we have basically the technology to do that, but we simply cannot dedicate all of its time practically to that one resource. And so Starship opens up opportunities like that, of mass-producing these kinds of telescopes, which will allow us to survey for life in the universe, which of course is one of the grand goals of astronomy.

Lex Fridman 27:59 I wonder if you can speak to the, the bureaucracy, the political battles, the scientific battles for s- for time on the James Webb Telescope.

David Kipping 28:09 Hm.

Lex Fridman 28:09 Is n- I, is there a, uh, there must be a fascinating, it's process of scheduling that. All scientists, they're trying to collaborate and figure out what the most important problems are, and there's an interesting network of interfering scientific experiments probably they have to somehow optimize over.

David Kipping 28:26 It's, it's a really difficult process. I don't envy the TAC that are gonna have to make this decision. We call it the TAC, the Time Allocation Committee, that, that make this decision. Um, and I've served on these before. And it's very difficult. I mean, typically for Hubble, we, we were seeing at least 10, sometimes 20 times the number of proposals for telescope time versus available telescope time. For JWST, there has been one call already that has gone out. We call it cycle one. And that was oversubscribed by I think something like six to one, seven to one. And, uh, the cycle two, which has just been announced, uh, fairly recently, and the deadline is actually end of this month, so my team are totally laser focused on-

Lex Fridman 29:07 Yes.

David Kipping 29:07 ... writing our proposals right now. Um, that is expected to be much more competitive, probably more comparable to what Hubble saw. And so it's hard.

Lex Fridman 29:16 More competitive than the cycle one, you said, already? 'Cause that's already super high.

David Kipping 29:19 More, more, more competitive in the first cycle.

Lex Fridman 29:20 Yeah.

David Kipping 29:20 So I said the first cycle of James Webb was about six to one.

Lex Fridman 29:23 (laughs)

David Kipping 29:23 Um, and this will probably be more like 20 to one-

Lex Fridman 29:26 (laughs)

David Kipping 29:26 ... I would expect.

Lex Fridman 29:26 So these are all proposals by scientists and so on, and it's not like you can schedule at any time. 'Cause if you're looking for transit times-

David Kipping 29:34 Yeah.

Lex Fridman 29:34 ... uh-

David Kipping 29:34 You, you ha- you have a, a time critical element.

Lex Fridman 29:36 Yes. Time critical element.

David Kipping 29:37 If you're scheduling. Yeah.

Lex Fridman 29:38 And they're conflicting in non, like, non-obvious ways, 'cause they're, the, the frequency is different, the, the duration is different.

David Kipping 29:44 Right.

Lex Fridman 29:44 There's the co- there's probably computational needs-

David Kipping 29:46 Yeah.

Lex Fridman 29:46 ... that are different. Uh, the ty- there's the type of sensors, the direction pointing, all that.

David Kipping 29:51 Yeah. It, it's hard. And there are certain programs like doing a deep field study, where you just more or less point the telescope, and that's pretty open. I mean, you're just accumulating photons. You can just point at that, at that patch of the sky, um, whenever the telescope is not doing anything else, and just get to your month, let's say a month of integration time is your, is your goal over the lifetime of JWST. So that's m- maybe a little bit easier to schedule. It's harder, especially for us looking at cool worlds, um, because as I said earlier, these, these planets transit very infrequently.

Lex Fridman 30:20 Mm-hmm.

David Kipping 30:21 ... so we have to wait, if you're looking at the Earth transiting the Sun, an alien watching us, they, they would only get one opportunity per year to do that observation. The transit lasts for about 12 hours, um, and so if they don't get that time, it's hard. You, you, that's it, uh, if it conflicted with another proposal that wants to do, use the, uh, another time-critical element. It's much easier for planets like, uh, these hot, these hot planets or these close-in planets, um, because they transit so frequently there's maybe 100 opportunities, and so then the TAC can say, "Okay, they want 10 transits. There's 100 opportunities here." It's easier for us, to give us ti- to give them time. Um, we're almost in the worst-case scenario. We're proposing to look for exomoons around two cool planets.

Lex Fridman 31:04 Mm-hmm.

David Kipping 31:04 And so we really only have one bite of the cherry for each one. And so our sales pitch has been that these are extremely precious events, and more importantly, JWST is the only telescope, the only machine humanity has ever constructed which is capable of finding moons akin to the moons in our solar system. Kepler can't do it. Even Hubble can't do it. JWST is the first one. And so there is a new window to the universe, 'cause we know these moons exist. They, they're all over the place in the solar system. You have the Moon, you have Io, Callisto, Europa, Ganymede, Titan, lots of moons are fairly similar size, sort of 30% the size of the Earth, and this telescope is the first one that can find them. Um, and so we're very excited about the profound implications of ultimately solving this journey we're on in astronomy, which is to understand our uniqueness. We want to understand how common is the solar system. Are we the way? Are we the architecture that frequently emerges naturally, or is there something special about what happened here?

Lex Fridman 32:09 I think this is not the worst case or the best case. It's the obvious. It's super rare.

David Kipping 32:12 (laughs)

Lex Fridman 32:13 So you have to like... I would, if so, I'm, I love scheduling from a computer science perspective. That's my background. So algorithmically sche- to solve a schedule problem, I will schedule the rarest things first.

David Kipping 32:22 Yeah.

Lex Fridman 32:22 And obviously this is the, the JWST is the first thing that can actually detect a cool world, so this is a big new thing, and you can show off that new thing, happens rarely, schedule it first, perfect.

David Kipping 32:33 You should be on the TAC.

Lex Fridman 32:34 Yeah.

David Kipping 32:34 This is perfect. (laughs)

Lex Fridman 32:36 I will. I'll, I'll file my application after we're done with this. I, I, you know, this... Part of me is the OCD. Part of me is the computational aspect. I love scheduling a computing device, 'cause you have that kind of scheduling on supercomputers, on... That scheduling problem is fascinating.

David Kipping 32:51 Yeah.

Lex Fridman 32:51 How do you prioritize computation? How do you prioritize science, uh, data collection, uh, sample collection, all that kind of stuff. It's actually kind of, it's kind of fascinating, because data, in ways you expect and don't expect, will unlock a lot of solutions to, uh, some fascinating mysteries. And so collecting the data, and doing so in a way that maximizes the possibility of discovery is really interesting, like from-

David Kipping 33:15 Yeah.

Lex Fridman 33:15 ... a computational perspective.

David Kipping 33:17 I agree. There's, there's a real satisfaction extracting the maximum science per-

Lex Fridman 33:21 Yeah.

David Kipping 33:21 ... unit time-

Lex Fridman 33:21 Yeah, exactly. (laughs)

David Kipping 33:22 ... out of your telescope.

Lex Fridman 33:23 Exactly.

David Kipping 33:23 And that, that's, that's the TAC's job.

Lex Fridman 33:26 Yeah.

David Kipping 33:26 Um, but the, the TAC, uh, are not machines. They're not a piece of computer code. Um, they will make their selections based off human judgment, and, um, a lot of the telescope, uh, certainly within the field of exoplanets, 'cause there's different fields of astronomy, but within the field of exoplanets, I think a good expectation is that most of the telescope time that JWST have will go towards atmospheric retrieval, which is, uh, sort of alluded to earlier, you know, by detecting molecules in the atmospheres. Not biosignatures, 'cause as I said, it's really not designed to do that. It's pushing JWST probably too far to expect it to do that. But it could detect, for example, a carbon dioxide-rich atmosphere on TRAPPIST-1e. That's not a biosignature, but you could prove it's like a Venus in that case, or maybe like a Mars in that case. Like both those have carbon dioxide-rich atmospheres. Doesn't prove or disprove the existence of life either way, but it is our first characterization of the nature of those atmospheres. Maybe we can even tell the pressure level and the temperature of those atmospheres. So that's very exciting. But, um, there's... We, we are competing with that, and that, I, I think that science is completely mind-blowing and fantastic. We have a completely different objective, which is, in our case, to try and look for the first evidence of these small moons around these planets, um, potentially even moons which could be habitable, of course. So I think it's a very exciting goal, but, um, a TAC has to make a human judgment essentially about which science are they most excited by. Which one has the highest promise of return, the most, uh, highest chance of return? And so that's hard, because if you look at a, a planetary atmosphere, well, you know most of the time the planet has an atmosphere already, and s- and so there's almost a guaranteed success that you're gonna learn something about the atmosphere by pointing JWST at it, whereas in our case, there's a harder sell. We are looking for something that we do not know for sure exists yet or not. And so we are pushing the telescope to do something which is inherently more risky.

Lex Fridman 35:25 Yeah, but the existence, if shown, already gives a deep, uh, lesson about what's out there in the universe. But that means that other stars have similar types of variety as we have in our solar system. They have an Io. They have a Europa and so on, which means like there's a lot of possibility for icy planets, for water, for planets that enable, uh, planets and moons that, that... I mean, that, that's super exciting, because that, that means everywhere through our galaxy and beyond, there is just innumerable possibility for weird creatures-

David Kipping 36:03 I agree.

Lex Fridman 36:04 ... lifeforms.

David Kipping 36:04 Hey, you don't have to convince me. (laughs) Absolutely.

Lex Fridman 36:06 (laughs)

David Kipping 36:06 I mean-

Lex Fridman 36:07 Yeah. It's-

David Kipping 36:08 NASA, NASA has been on this quest for a long time, and it's sometimes called eater Earth. It's the frequency of Earth-like, usually they say-

Lex Fridman 36:16 Planets.

David Kipping 36:17 ... planets in the universe. How common are planets similar to our Earth in terms of...... um, ultimately we'd like to know everything about these planets, in terms of the amount of water they have, how much atmosphere they have. But for now, it's kind of focused just on the size and the distance from the star, essentially. How, how often do you get similar conditions to that? Um, that was Kepler's primary mission, and it really just kind of flirted with the answer. It didn't quite get to a definitive answer. But I always say, look, if we're looking... If, if that's our primary goal, to look for Earth-like, I would say, worlds, then moons has to be a part of that, because we know that, um, Earth-like... And so from the Kepler data, the preliminary result is that Earth-like planets around Sun-like stars is not an inevitable outcome. It seems to be something like a 1 to 10% outcome. So it's not particularly inevitable that that happens. But we do often see, about half of all Sun-like stars have either a mini-Neptune, a Neptune, or a Jupiter-

Lex Fridman 37:14 Mm-hmm.

David Kipping 37:15 ... in the habitable zone of their stars. That's a very, very common occurrence that we see. Yet we have no idea how often they have moons around them which could also be habitable. And so there may very well be... If e- if even one in five of them has an Earth-like moon, or even a Mars-like moon around them-

Lex Fridman 37:33 Mm-hmm.

David Kipping 37:33 ... then there would be more habitable real estate, in terms of exomoons, than exoplanets in the universe.

Lex Fridman 37:38 So you can essentially 2X, 3X, 5X, maybe 10X the number of habital- habitable worlds-

David Kipping 37:45 Mm-hmm.

Lex Fridman 37:45 ... out there in the universe. Uh, our current estimate for, like, the Drake equation.

David Kipping 37:49 Absolutely, yeah.

Lex Fridman 37:50 So this, this is, uh, one way to increase the confidence and increase the, the value of that parameter.

David Kipping 37:57 And just know where to look. I mean, we, we would like to know where should we listen for technosignatures? Where should we be looking for biosignatures? Um, and not only that, but what role does the, does the moon have in terms of its influence on the planet? Um, we talked about these directly imaged telescopes earlier, these missions that want to take a photo. To quote Carl Sagan, the pale blue dot of our planet, but the pale blue dot of an exoplanet. And that's the dream, to one day capture that. But as impressive as the resolution is that we are planning and conspiring to design for the future generation telescopes to achieve that, even those telescopes will not have the capability of resolving the Earth and the moon within that. It'll be a pale blue dot pixel, but the moon's gray- grayness will be intermixed-

Lex Fridman 38:43 Mm-hmm.

David Kipping 38:44 ... with that pixel. And so this is a big problem, because one of the ways that we are claiming to look for life in the universe is a chemical disequilibrium. So you see two molecules that just shouldn't be there, they normally react with each other, or even one molecule that's just too reactive to be hanging around the atmosphere by itself. So if you had, um, oxygen and methane hanging out together, those would normally react fairly easily. And so if you detected those two molecules in your pale blue dot spectra, you'd be like, "Okay, we've, we have evidence for life. Something's metabolizing on this planet." Um, however, the challenge is, what if that moon was Titan? Titan has a methane-rich atmosphere. And what if the pale blue dot was, in fact, a planet devoid of life, but it had oxygen because of water undergoing this photolysis reaction, splitting into oxygen and hydrogen separately? So then you have all of the, uh, hallmarks of what we would claim to be life-

Lex Fridman 39:38 Mm-hmm.

David Kipping 39:39 ... but all along, you were tricked. It was just a moon that was de- deceiving you. And so we are never going to... We're never gonna, I would claim, really understand the... Or, or complete this quest of looking for life, biosignatures in the universe, unless we have a deep knowledge of the prevalence and role that moons have. They may even affect the habitability of the planets themselves. Of course, our own moon is freakishly large. By mass ratio, it's the largest moon in the solar system. It's a 1% mass moon. If you look at Jupiter's moons, they're like 10 to the power of minus 4, much smaller. And so our own moon seems to stabilize the obliquity of our planet. It gives rise to tides. Especially early on when the moon was closer, those tides would have covered entire continents.

Lex Fridman 40:22 Mm-hmm.

David Kipping 40:22 And those, those rock pools that would have been scattered across the entire plateau may have been the origin of life on our planet. The moon forming impact may have stripped a significant fraction of the lithosphere off the Earth, which without it, plate tectonics may not have been possible. We'd have had a stagnant lid, because there's just too much lithosphere stuck on the top of the, of the planet. And so there are speculative reasons, but intriguing reasons as to why a large moon may be not just important, but central to the question of having the conditions necessary for life. So moons can be habitable in their own right, but they can also play a significant influence on the habitability of the planets they orbit. And further, they will surely interfere with our attempts to detect life remotely from afar.

Lex Fridman 41:15 So, uh, taking a tangent upon a tangent,

Lex Fridman 41:18 uh, you've written about, uh, binary planets.

David Kipping 41:21 Yeah.

Lex Fridman 41:21 What, what's... And that they're surprisingly common. Or they might be surprisingly common. What's the difference between a large moon and binary planets? What, what, what are binary planets? What, uh, what, what's interesting to say here about giant rocks flying through space-

David Kipping 41:38 (laughs)

Lex Fridman 41:38 ... and, and orbiting each other?

David Kipping 41:40 The thing that's interesting about binary objects is that they're very common in the universe. Binary stars are everywhere. In fact, the majority of stars seem to live in binary systems. Um, when we look at the outer edges of the solar system, we see binary Kuiper belt objects all the time, asteroids basically bound to one another. Pluto-Charon is kind of an example of that. It's a 10% mass ratio system. It almost is, by many definitions, a binary planet, but now it's a dwarf planet. So-

Lex Fridman 42:08 Yeah, it's not-

David Kipping 42:09 ... I don't know-

Lex Fridman 42:09 Yeah.

David Kipping 42:10 ... what you'd call that now. But the... We kn- we know that these... You know, the universe likes to make things in pairs.

Lex Fridman 42:15 Yeah.

David Kipping 42:15 Um...

Lex Fridman 42:16 So you're saying our sun is an incel.

David Kipping 42:19 (laughs)

Lex Fridman 42:20 It's, it's looking... So most things are dating, they're in relationships, and our- ours is, is alone.

David Kipping 42:25 ... it, it's not a complete freak of the universe to be alone, but it is, um... It's more common for Sun-like stars. If you count up all the Sun-like stars in the universe, about half of the Sun-like star systems are in binary or trinary systems, and the other half are single. But because those binaries are two or three stars, then cumulatively, maybe like a third of all Sun-like stars are single ?

Lex Fridman 42:46 I'm trying hard to not anthropomorphize the relationship-

David Kipping 42:50 (laughs)

Lex Fridman 42:50 ... that stars have with each other. But yeah-

David Kipping 42:53 The triplet, the triplets (laughs)

Lex Fridman 42:54 Yeah. That's... Yeah. I've, I've met those folks also.

David Kipping 42:57 (laughs)

Lex Fridman 42:58 Um, so is there something interesting to learn about the habitability, the... How that affects the probability of habitable worlds when they kind of couple up like that in those different ways?

David Kipping 43:08 Uh, well, it depends on if we're talking about the stars or the planets. Certainly if stars couple up, that has a big influence on the habitability. Um, of course, this is very famous from Star Wars, Tattooine in Star Wars is a binary star system, and you have Luke Skywalker looking at the sunset and seeing two stars come down. And, uh, for years we thought that was purely a product of George Lucas' incredibly creative mind, and we didn't think that planets would exist around binary star systems. It seems like too tumultuous an environment for a quiescent planetary disk, circumstellar disk, to form planets from. And yet, uh, one of the astounding discoveries from Kepler was that these appear to be quite common. In fact, as far as we can tell, uh, they're just as common around binary stars as single stars. The only, uh, caveat to that is that you don't get planets close in to binary stars. They have like a clearance region in, on the inside, where planets, maybe they form there, but they, they don't last.

Lex Fridman 44:06 Mm-hmm.

David Kipping 44:07 They are dynamically unstable in that zone. But once they get out to about the distance that the Earth orbits the Sun, or even a little bit closer in, you start to find planets emerging. And so that's the right distance for liquid water, it's the right distance for potentially life on those planets. And so there may very well be plenty of habitable planets around the binary stars. Binary planets is a little bit different. Um, binary planets, I don't think we have, um, any serious connection of planet binarity to habitability. Certainly when we investigated it, that wasn't our drive, that this is somehow the solution to life in the universe or anything. It was really just a, like all good science questions, a curiosity-driven question.

Lex Fridman 44:48 What's the dynamic? Are they legit orbiting each other-

David Kipping 44:51 Yes.

Lex Fridman 44:51 ... as they orbit the s- uh, uh, the star?

David Kipping 44:53 So the formation mechanism proposed here, um, 'cause it is very difficult to form two proto-planets close to each other like this. They would generally merge within the disk, and so that's why you normally get single planets. But you could have something like Jupiter and Saturn form at separate distances. They could dynamically be scattered in towards one another-

Lex Fridman 45:12 Mm-hmm.

David Kipping 45:12 ... and basically, not quite collide, but have a very close-on encounter. Now, because, uh, tidal forces increase dramatically as the distance decreases between two objects, the tides can actually dissipate the kinetic energy and bring them bound into one another. So that seemed, when we... Uh, you know, when you first hear that, you just think, "Well, that seems fairly contrived, that, that you'd have the conditions just right to get these tides to cause a capture." But numerical simulations have shown that about 10% of planet-planet encounters are shown to produce something like binary planets, which is a startling prediction. Um, and so that seems at odds with, naively, the exoplanet catalog, for which we know of, so far, no binary planets.

Lex Fridman 45:55 Mm-hmm.

David Kipping 45:55 And we propose one of the resolutions to this might be that the binary planets are just incredibly difficult to detect, which is also counterintuitive, because remember how they form is through this tidal mechanism, and so they form extremely close to each other, sort of the distance that Io is away from Jupiter, just a few planetary radii. They're almost touching one another, and they're just tidally locked facing each other for eternity. And so, in that configuration, as it transits across the star, it kinda looks like you can't really resolve there's two planets. It just looks like one planet to you that's going across the star. The temporal resolution of the data is rarely good enough to distinguish that. And so you would see one transit, but in fact it's two planets very close together which are transiting at once. And so yeah, we wrote a paper just recently where we developed, um, some techniques to try and get round this problem, and hopefully provide a tool where we could finally look for these planets.

Lex Fridman 46:48 Oh, the problem of detection of-

David Kipping 46:49 Yes.

Lex Fridman 46:49 ... exoplanets when they're so close together.

David Kipping 46:50 That was our focus, was how do you, how do you get round this, this merging problem? So whether they're out there or not, uh, we don't know. We w- we're planning to do a search for them, but, um, it, it remains an open question, and I think just one of those fun astrophysics curiosities questions, whether binary planets exist in the universe. 'Cause then, you know, you could have binary Earths, you could have binary Neptune, all sorts of wild stuff that would, you know, float the sci-fi imagination.

Lex Fridman 47:18 I wonder what the physics on a binary planet feels like. It might be trivial. I have to think about that. I wonder if there's some interesting dynamics. Like if you had multiple... Or, or would gravity feel different on different parts of the, the surface of the sphere when there's another large sphere? That's interesting (laughs) .

David Kipping 47:35 Yeah. I would think that the force would be, uh, fairly similar, because the shape of the object would deform to a flat geopotential, essentially, a uniform geopotential. But it would lead to a distorted shape for the two objects. I think they'd become ellipsoids facing one another.

Lex Fridman 47:52 (laughs)

David Kipping 47:52 Um, so (laughs) it would be pretty wild when you... You know, people are like, "Flat Earth or spherical Earth."

Lex Fridman 47:57 Yeah.

David Kipping 47:57 You fly from space and you see a football-shaped Earth.

Lex Fridman 47:59 Yeah.

David Kipping 47:59 (laughs) That's right, that's your home planet.

Lex Fridman 48:01 Finally, there's proof. And I wonder how, how difficult it would be to travel from one to the other. 'Cause you have to overcome the gr- well, n- well, no, it might be kinda easy. (laughs)

David Kipping 48:12 Yeah. I mean, they're so close to each other, that helps, and I think the most critical factor would be how massive is the planet.

Lex Fridman 48:17 Sure.

David Kipping 48:17 That's always... I mean, one of the challenges with escaping planets, there was a, a fun paper one of my colleagues wrote that suggested that super-Earth planets may be inescapable.

Lex Fridman 48:26 Mm-hmm.

David Kipping 48:26 If you were a civilization that were born on a super-Earth, the surface gravity is so high...... that the chemical potential energy of hydrogen or, or methane, whatever fuel you're using, simply, um, is at odds with the, with the gravity of the planet itself.

Lex Fridman 48:42 Mm-hmm.

David Kipping 48:43 And so you would, uh, you know, our current rockets, I'm not sure what the fraction, but maybe like 90% of the rocket is fuel or something, by mass. These things would have to be, um, like the size of the, the Giza pyramids of fuel, with just a tiny tip on the top, in order just to escape that planet's planetary atmosphere. And so it has been argued that if you live on a super-Earth, you may be, you may be forced to live there forever. There may be no escape unless you invent a space elevator or something. But then how do you even build the infrastructure in space to, to do something like that in the absence of a successful rocket program? Um, and so the more and more we, we look at our Earth and think about the sorts of problems we're facing, the more you see things about the Earth which make it ideally suited in so many regards. It, it's almost spooky, right? That we not only live on a planet which has the right conditions for life, for intelligent life, a sustained fossil fuel industry just happens to be in the ground, we have plenty of fossil fuels to, to get our industrial revolution going. Um, but also the chemical energy contained within those fossil fuels, um, and hydrogen and other fuels is sufficient that we have the ability to escape our planetary atmosphere and planetary gravity to have a space program. And we also happen to have a celestial body which is just within reach, the Moon.

Lex Fridman 49:59 Mm-hmm.

David Kipping 49:59 Uh, which doesn't also necessarily have to be true. Were, were the Moon not there, what effect would that have had on our aspirations of a space program in the 1960s? Would there have ever been a space race to Mars or to Venus?

Lex Fridman 50:12 (laughs)

David Kipping 50:12 That's a much harder... Certainly for a human program, that seems almost impossible with 1960s technology to imagine how to come to fruition.

Lex Fridman 50:18 So s- it's almost as if somebody constructed a set of, uh, challenging obstacles before us, challenging problems to solve. They're challenging, but they're doable. And there's a sequence to them. Gravity is very difficult to overcome, but we have, given the size of Earth, it's not so bad that we could still actually construct propulsion systems that could escape it.

David Kipping 50:40 Yeah.

Lex Fridman 50:40 And-

David Kipping 50:40 And the same with climate change, perhaps. I mean, climate change is the next major problem facing our civilization. But we know it is technically surmountable.

Lex Fridman 50:49 Yeah.

David Kipping 50:50 You know, it's, it's a, it's, it's, it is, does seem sometimes like there has been a series of challenges laid out-

Lex Fridman 50:56 Yeah.

David Kipping 50:56 ... to, um, progress us towards a mature civilization that can one day perhaps expand to the stars.

Lex Fridman 51:02 I'm a little more concerned about nuclear weapons, uh, AI, and, uh, uh, natural or artificial pandemics. But yes, climate change is-

David Kipping 51:10 Yeah. Well, there you go.

Lex Fridman 51:10 (laughs)

David Kipping 51:10 I mean, plenty, plenty of-

Lex Fridman 51:12 Plenty of fun ass...

David Kipping 51:12 ... milestones that we need to cross. Uh, and we can argue about the severity of each of them.

Lex Fridman 51:16 (laughs)

David Kipping 51:17 But, uh, there is no doubt that we live in a world that has serious challenges that are pushing our intellects and our will to the limit of whether we're really ready to progress to the next stage of our development.

Lex Fridman 51:31 So thank you for taking the tangent, and there's, there'll be a million

Lex Fridman 51:34 more. But can we step back to Kepler-1625b?

David Kipping 51:38 Mm.

Lex Fridman 51:38 What is it? And you, you've talked about this kind of journey, this effort to discover, uh, exomoons, so moons out there.

David Kipping 51:49 Mm-hmm.

Lex Fridman 51:49 Uh, or small cool objects out there. Uh, where does that effort stand? And what is Kepler-1625b?

David Kipping 51:56 Yeah. We... I mean, I've been searching for exomoons for most of my professional career. And I think a lot of my colleagues think I'm kind of, uh, crazy to, to still be doing it. You know, after, after five years of not finding anything, I think most people would probably try doing something else. I even had people say that to me, they said, um, you know, professors, and I remember at a par- a cocktail party took me to the side, an MIT professor, and he said, "Um, you know, you should just look, look for hot Jupiters. They're everywhere. It's really... You can write papers." (laughs)

Lex Fridman 52:25 (laughs)

David Kipping 52:25 "They're so easy to find." (laughs) And I was like, "Yeah, but hot Jupiters, just, they're not interesting to me. I want to do something that I feel intellectually pushes me to the edge, and, and is maybe a contribution that not no one else could do, but maybe, um, is not certainly the thing that anybody could do. I don't want to just be the first to something for the sake of being first. I want to do something that feels like a meaningful intellectual contribution to our society." And so, you know, this exomoon problem has been haunting me for years to try and solve this. Now, as I said, we looked for years and years using Kepler. And the closest we ever got was just a hint for this one star, Kepler-1625 has a Jupiter-like planet in orbit of it. And that Jupiter-like planet is on a 287 day period. So it's l- it's almost the same distance as the Earth around the Sun, but for Jupiter. Um, so that was already unusual. I don't think people realize that Jupiter-like planets are quite rare in the universe. Certainly mini Neptunes and Neptunes are extremely common, but Jupiter's... Only about 10% of Sun-like stars have Jupiters around them, as far as we can tell.

Lex Fridman 53:33 When you say Jupiter, which aspect of Jupiter?

David Kipping 53:36 In terms of its mass and, uh, its major axis. So anything beyond about half an AU, so half the distance of the Earth and the Sun, and something of order of, um, a tenth of a Jupiter mass, so that's the mass of Saturn, up to, say, 10 Jupiter masses, which is basically where you start to get to brown dwarfs. Those types of objects appear to be somewhat unusual. Most solar systems do not have Jupiters, which is really interesting, because Jupiter, again, like the Moon, seems to have been a pivotal character in the story of the development of our solar system, perhaps especially having a large influence with the development of, um, the Late Heavy Bombardment and the rate of asteroid impacts that we receive and things like this. Anyway, to come back to 1625, this, this Jupiter-like planet, um, had a hint of, of something in the data. But what I mean by that is when we looked at the transit, we got the familiar decrease in light that we always see when a planet tracks in front of the star. But we saw something extra, just on the edges, we saw some extra dips around the outside.

Lex Fridman 54:36 Hm.

David Kipping 54:36 ... it was right at the hairy edge of detectability. We didn't believe it, because, um, I think one of the challenges of looking for something for 10 years is that you become your own greatest skeptic. And no matter what you're shown, you're always thinking, "I've been..." It's like falling in love so many times and it, and it not working out.

Lex Fridman 54:56 Right.

David Kipping 54:57 You, you convince yourself it's never gonna be, it's never gonna happen. "Not for me." You know, "This just isn't, this isn't gonna happen." And so I saw that, and I, I didn't really believe it, 'cause I didn't dare let myself believe it. But being a good scientist, we knew we had an obligation to publish it, to talk about the result, and to follow it up, and to try and resolve what was going on. So we asked for Hubble Space Telescope time, which was awarded in that case, so we were one of those lucky 20 that got telescope time, and we stared at it, uh, for about 40 hours continuously. And, um, the, to provide some context, the dip that we saw in the Kepler data corresponded to a Neptune-sized moon-

Lex Fridman 55:38 Mm-hmm.

David Kipping 55:39 ... around a Jupiter-sized planet, which was another reason why I was skeptical. I was like, that... We don't have that in the solar system. That seems so strange. And then when we got the Hubble data, it seemed to confirm exactly that. There was two really striking pieces of evidence in the data that suggested this moon was there. Another was a fairly clear second dip in light, pretty clearly resolved by Hubble. It was about a five sigma detection. And on top of that, we could see the planet didn't transit when it should've done. It actually transited earlier than we expected it to, by about 20 minutes or so. And so that's a hallmark of a gravitation interaction between the planet and the moon. We actually expected that. You can also expect that if the moon transits after the planet, then the planet should come in earlier than expected-

Lex Fridman 56:25 Mm-hmm.

David Kipping 56:25 ... because the barycenter, the center of mass, lives between the two of them. They're kind of like on a, on a balancing arm between them. And so we saw that as well. So the phase signature matched up. The mass of the moon was measured to be Neptune-mass, and the size of the moon was measured to be Neptune-radius. And so everything just really lined up, and, um, we spent months and months trying to kill it.

Lex Fridman 56:50 Mm-hmm.

David Kipping 56:50 This is my strategy for anything interesting. We just try and throw the kitchen sink at it and say, "We must be tricked by something." And so we tried looking at the, you know, the centroid motion of the telescope, at the, um, the different-

Lex Fridman 57:02 (laughs)

David Kipping 57:02 ... wavelength channels of, that have been observed, the pixel level information. And no matter what we did, we just couldn't get rid of it. And so, uh, we submitted to Science, and I think at the time, Science, which is one of the top journals, said to us, "Um, would you mind calling your paper 'Discovery of an Exomoon'?" And I had to push back, and we said, "No, we're not calling it that. I don't... Even despite (laughs) everything we've done, we're not calling it a discovery. We're calling it evidence for an exomoon."

Lex Fridman 57:29 Mm-hmm.

David Kipping 57:29 Because for me, I would wanna see this repeat, two times, three times, four times-

Lex Fridman 57:33 Mm-hmm.

David Kipping 57:34 ... before I really would bet my house that this is the real deal. And maybe, and I, I do worry, as I said, that perhaps that's my own skepticism, self-skepticism going too far, but, um, I think it was the right decision. And, uh, since that paper came out, there has been continuous interest in the subject. Um, another team independently analyzed that star and recovered actually pretty much exactly the same results as us, the same dip, the same, the same wobble of the planet, and a third team looked at it and they actually got something different. They saw the dip was diminished compared to what we saw. They saw a little hint of a dip, but not as pronounced as what we saw. And they saw the wobble as well. So there's been a little bit of tension about analyzing the reduction of the Hubble data. Um, and so the only way in my mind to resolve this is just to look again. Uh, we actually did propose to Hubble straight after that, and we said, "Look, if our model is right, if the moon is there, it came in late last time. It transited after the planet. Because of the orbit, we can calculate that it should transit before the planet next time. If it's not there, if it doesn't transit before, and if we, even if we see a dip afterwards, we know that's not our moon. It's obviously some instrumental effect with the data." We had a causal prediction as to where the moon should be. And so I was really excited about that. But we didn't get the telescope time, and unfortunately, if you go further into the future, we no longer have the predictive capability, because it's like predicting the weather. You might be able to predict the weather next week to some level of accuracy, but predicting the weather next year becomes incredibly hard. The uncertainties just grow and compound as you go forward into the future more and more.

Lex Fridman 59:15 H- how were you able to know where, where the moon would be positioned? So you're able to tell the, the, the orbiting, like, geometry, and, and, and frequency?

David Kipping 59:26 Yeah, so from the, uh, basically from the wobbles of the planet itself, that tells us the orbital motion of the moon. It's the reflex motion of the moon upon the planet.

Lex Fridman 59:36 But isn't, isn't it just an estimate to where... Like, I'm concerned about you making a strong prediction here, because like if you don't get, if you don't, uh, get the moon where the moon leads on the next time around, if you did get Hubble time, w- couldn't that mean something else if you didn't see that? Like, 'cause you said it, it would be an instrumental... (laughs) I feel, I, I, I feel, um, the strong urge to disprove your, your own... (laughs)

David Kipping 1:00:01 (laughs)

Lex Fridman 1:00:01 Which is a really good, uh, uh, imperative.

David Kipping 1:00:04 Yeah. Yeah.

Lex Fridman 1:00:04 It's a good way to do science. But like, uh, this is such a noisy signal, right? Or blurry signal maybe.

David Kipping 1:00:10 Yeah.

Lex Fridman 1:00:11 Uh, low-resolutions signal maybe that's the best way to say it.

David Kipping 1:00:13 Yeah, I mean, it's, it's a five sigma signal, so that's, that's at the slightly uncomfortable edge. I mean, it's often said that for any detection of a first new phenomena, you really want like a 20, 25 sigma detection. Then there's just no doubt that what you're seeing is real. This was at that edge. I mean, I guess it's comparable to the Higgs boson, but the Higgs boson was slightly different, 'cause there was so much theoretical impetus as to expect a signal at that precise location. Um, a Neptune-sized moon was not predicted by anyone. No one... There was no papers you can find that expect Neptune-sized moons around Jupiter-sized planets, so there was a... I think we were inherently skeptical about its reality for that reason. Um, but this is science in action, and...... when we, we, you know, we fit the wobbles, we fit the dips, and we, you know, we have this 3D geometric model for the motion of the orbit. And proj- projecting that forward, we were... we found that about 80% of our projections led to the moon to be before. So it's not 100%.

Lex Fridman 1:01:07 Sure.

David Kipping 1:01:07 There is, there is maybe 20% of the cases it was over here. But to me, that was a hard enough, uh, s- a hard enough projection that we felt confident that we could refute the ex- which was... What I really wanted, I wanted a refutable... That's the basis of science, a falsifiable hypothesis. How can you make progress in science if you don't have a falsifiable, testable hypothesis? And so that was the, the, the beauty of this particular case.

Lex Fridman 1:01:31 So there's a numerical simulation with the moon, uh, that fits the data that we observed, and then you can now make predictions based on that simulation?

David Kipping 1:01:38 Yeah.

Lex Fridman 1:01:40 That is so cool. Okay.

David Kipping 1:01:42 It's fun. These are like little solar systems that we can simulate on the computer and i- imagine their motions. Um, but we are, we are pushing things to the very limits of what's possible. And that's double-edged sword. It's both incredibly exciting intellectually, but you're always, you're always risking, to some degree, the pushing too far.

Lex Fridman 1:02:03 So I, I'd like to ask you about the, uh, the, the recent paper you co-authored, "An exomoon survey of 70 cool giant exoplanets and the new candidate Kepler-1708bi."

David Kipping 1:02:15 I would say there's, I'd say there's like three or four candidates at this point, of which we have published two of them. Uh, and to me, uh, two are, are quite, uh, compelling and deserve follow-up observations. Um, and so there are... To get a confirmed detection, at least in our case, we would need to see it repeat, for sure. One of the problems with the, some of the other methods that have been proposed is that you don't get that repeatability. So, for instance, an example of a technique that would lack that would be gravitational microlensing. So it is possible, with a new telescope coming up in the future, um, called the Roman Space Telescope, which is basically a repurposed spy satellite that's the size of the Hubble mirror getting up into space. Um, it will stare at millions of stars simultaneously and it will look to see, instead of whether any of those stars get dimmer for a short amount of time, which would be a transit, it'll look for the opposite, it'll look to see if anything can get brighter. And that brightness increase is caused by another planetary system passing in front and then gravitationally lensing light around it to cause a brightening. And so this is a method of discovering an entire solar system, but only, only for a, only for a glimpse. You just get a short glimpse of it passing like a, you know, a ship sailing through the night, just that, that one photo of it. Now, the problem with that is that, um, it's very difficult... You know, the physics of, of gravitational lensing are, are not surprisingly quite complicated. And so there's many, many possible solutions. So you might have a solution which is this could be a red dwarf star with a Jupiter-like planet around it. That's one solution. But another solution is that it's a free-floating planet, a rogue planet, like Jupiter, with an Earth-like moon around it. And those two solutions are almost indistinguishable.

Lex Fridman 1:03:59 Mm-hmm.

David Kipping 1:04:00 Now, ideally, we would be able to repeat the observation, we'd be able to go back and see, well, if the moon really is there then we could predict its mass, we could predict its motion and expect it to be maybe over here next time or something. With microlensing, it's a one snapshot event.

Lex Fridman 1:04:14 Mm-hmm.

David Kipping 1:04:14 And so for me, it's intriguing as a way of revealing something about the exomoon population, but I always come back to transits because it's the only method we really have that's absolutely repeatable, that we'll be able to come back and prove everyone, prove to everyone that, look, on the 17th of October, the moon will be over here and the moon will look like this and we can actually capture that image. And that's what we see with, of course, many exoplanets. So we want to get to that same point of full confidence, full confirmation, the slam dunk detection of these exomoons. But, um, yeah, it's, it's been a, a hell of a journey, uh, to, to try and push the field into that direction. And, um, it's like-

Lex Fridman 1:04:54 Is there some resistance to the transit method in your field?

David Kipping 1:04:56 Not to the transit meth- I just said to exomoons. So the transit method is by far the most wa- the most popular method for looking for exoplanets. But, um,

David Kipping 1:05:04 yeah, as I've alluded to, exomoons is, is kind of a niche topic within the discipline of exoplanets, and that's largely because there are people like, I think, are waiting for those slam dunks. And it was like the... If you go back to the first exoplanet discovery that was made in 1995 by Michel Mayor and Didier Queloz, um, I think it was true at the time that they were seen as mavericks, that the idea of looking for planets around stars was considered fringe science. And, you know, I'm sure many colleagues told them, "Why don't you do something more safe like study eclipsing stars, two binary star systems? We know those exist. So why are you wasting your time looking for planets? You're gonna get this, um, alien moniker or something and you'll be, you'll be seen as a fringe maverick scientist." And so I think it was quite difficult for those early planet hunters to get legitimacy and be taken seriously. And so very few people risked their careers to do it, except for those that were either emboldened to try or had maybe the career, uh, maybe like a tenure or something, so they didn't have to necessarily worry about the implications of failure. And so once that happened, once they made the first discoveries, overnight, you know, everyone and their dog was getting into exoplanets, and all of a sudden, the whole, you know, the whole astronomy community shifted and huge numbers of people that were once upon a time studying eclipsing binaries, you know, changed to becoming exoplanet scientists.

Lex Fridman 1:06:28 Mm-hmm.

David Kipping 1:06:28 And so that was the first wave of exoplanet scientists. We're now in a kind of a second wave or even third wave where people like me, to some degree, kind of grew up with the idea of exoplanets as being normal. You know, I was 11 years old, I guess, when the first exoplanet was discovered. And so to me, it was a fairly, uh, normal idea to grow up with. Um, and so we've been trained in exoplanets from the very beginning. And so that brings...... a different perspective to those who have maybe transitioned from a different career path. Um, and so I suspect with exomoons and probably technosignatures, uh, astrobiology, many of the topics which are seen at the, the fringes of what's possible, they will all open up into becoming mainstream one day. But every, there's a lot of people who are just waiting, uh, waiting for that, that assuredness that there is a secure career net (laughs) ahead of them before they commit.

Lex Fridman 1:07:28 Yeah. It, it does seem to me that exomoons open wider or open for the first time the door to, to aliens, so s- more seriously academically studying, all right, let's, let's look at, like alien worlds. Like-

David Kipping 1:07:42 Mm-hmm.

Lex Fridman 1:07:42 So, um, I think it's still pretty fringe to talk about alien life, even on like on Mars and the moons and so on. You're kind of like, you know, it would be nice, but imagine the first time you disc- discover a living organism. That's gonna change, then, then everybody will look like an idiot for not focusing everything on this.

David Kipping 1:08:01 (laughs) . Yeah.

Lex Fridman 1:08:01 'Cause the, the possibility of the things we'll... It, it's possible it might, it might be super boring, it might be very boring bacteria, but even the existence of life elsewhere-

David Kipping 1:08:10 Yeah.

Lex Fridman 1:08:10 ... some, I mean, that changes everything. That means life is everywhere.

David Kipping 1:08:14 Yeah. If you knew now that in five years, 10 years, the first life would be discovered elsewhere, you knew that in advance, it would surely affect the way you approach your entire career. As a-

Lex Fridman 1:08:25 Yeah.

David Kipping 1:08:25 ... especially someone junior in astronomy, you would surely be like, "Well, this is clearly going to be the direction I have to dedicate my classes and my training and my education towards that direction."

Lex Fridman 1:08:34 All the new textbooks, all the... (laughs)

David Kipping 1:08:36 Yeah, right. (laughs)

Lex Fridman 1:08:36 ... ............................ And I mean, uh, and I, I think there's a lot of value to hedging, like allocating some of the time to that possibility-

David Kipping 1:08:45 Mm-hmm.

Lex Fridman 1:08:45 ... because the, the kind of discovery we'll, the kind of discoveries we might get in the next few decades, um, it feels what, like we're on the verge of a lot of, um, uh, getting a lot of really good data and having better and better tools that can process that data. So there's just going to be a continuous increase of the kind of discoveries that will open. Like, but a slam dunk, that's hard to come by.

David Kipping 1:09:09 Yeah, I think a lot of us are anticipating, I mean, we're already seeing it to some degree with Venus and the phosphine incident, um, but we've seen it before with Bill Clinton standing on the White House lawn announcing life from Mars. And there, there are inevitably gonna be spurious claims, or at least claims which are, um, ambiguous to some degree. There will be, for sure, a high profile journal like Nature or Science that will one day publish a paper saying, "Biosignature discovered," or something like that on TRAPPIST-1 or some other planet, and then there will be years of back and forth in the, in the literature. And that might seem frustrating, but that's how science works. It's in a... That's the mechanism of science at play, of people scrutinizing the results to intense skepticism. And it's like a crucible, you know, you burn away all the relevances until whatever is left is the truth, and so you're left with this, this product, which is that, okay, we either believe or don't believe that biosignatures are there. So there's inevitably gonna be a lot of controversy and debate and argument about it. We just have to anticipate that. And so I think you have to basically have a thick skin, to some degree, academically, to dive into that world. And you're seeing that with, um, with phosphine. It's been, uh, it's, it's been uncomfortable to watch from the outside, the kind of dialogue that some of the scientists have been having with each other about that, because, um-

Lex Fridman 1:10:35 They get a little aggressive.

David Kipping 1:10:37 Yeah.

Lex Fridman 1:10:37 (laughs)

David Kipping 1:10:37 And you can under- you can, you can understand why, because-

Lex Fridman 1:10:41 Jealousy? I don't know.

David Kipping 1:10:42 I- (laughs)

Lex Fridman 1:10:43 That's me saying, not you. That's me talking. (laughs)

David Kipping 1:10:46 It, the... I'm sure there's, I'm sure there's some envy and jealousy involved, um, on the, on the behalf of those who are not part of the original discovery.

Lex Fridman 1:10:56 Sure.

David Kipping 1:10:56 But there's also, in any case, just leave, you know, the particular people of ve- involved in Venus alone, in any case of making it a claim of that magnitude-

Lex Fridman 1:11:05 Yeah.

David Kipping 1:11:05 ... especially life, because life is pretty much one of the biggest discoveries of all time-

Lex Fridman 1:11:11 Yeah.

David Kipping 1:11:11 ... you can imagine, scientifically, um, you can see, and I'm so conscious of this in myself when I get close to, as I said, even the much smaller goal of setting an exomoon, the ego creep in. And so as a scientist, we have to be so guarded against our own egos. You see the lights in your eyes of a Nobel Prize or-

Lex Fridman 1:11:32 Yeah.

David Kipping 1:11:33 ... um, the, the fame and fortune and being remembered in the history books, and we all grew up in our training learning about Newton and Einstein, these giants of the field, Feynman, Maxwell, and you get the idea of these individual contributions which get immortalized for all time. And that's seductive. It's why many of us with the skill set to go into maybe banking instead decided actually there's something about the idea of being immortalized and contributing towards society in a permanent way that is more attractive than the financial reward of applying my skills elsewhere. So to some degree, that ego can be a benefit, 'cause it brings in skillful people into our field who might otherwise be tempted by money elsewhere. But on the other hand, it, the closer you get towards when you start flirting with that Nobel Prize in your, in your eyes or you think you're on the, on the verge of seeing something, you can lose objectivity. Uh, a very famous example of this is, uh, Barnard's Star. There was a planet claimed there by Peter van de Kamp, I think it was in 1968, '69. And at the time it would've been the first ever exoplanet ever claimed. And, um, he, he felt assured that this planet was there. He was actually using the wobbling star method, but using the positions of the stars to see them, to claim this exoplanet. It turned out that this planet was, was not there.... the subsequent analyses by both dynamicists and theorists and those looking at the instrumental data, established fairly, um, unanimously that there was no way this planet was really there. But Peter van de Kamp insisted it was there, despite overwhelming evidence that was accruing against him. Um, and even to the day he died, which was I think in like 9, in the early '90s, he was still insisting this planet was there, even when we were starting to make the first genuine exoplanet discoveries. And even at that point, I think Hubble had even looked at that star and had totally ruled out any possibility of what he was talking about. And so that's a problem. How do you get to a point as a scientist where you just can't accept anything that comes otherwise? Because you're, it starts out with the, the dream of fame, and then it ends in a stubborn refusal to ever back down.

Lex Fridman 1:13:50 Of course, the flip side of that is sometimes you need that to have the strength to carry a belief against, uh, the entire scientific community that resists your beliefs. And so it's a, it's a double-edged sword. It's like-

David Kipping 1:14:05 That can happen. But it, I guess the di- the distinction here is evidence.

Lex Fridman 1:14:09 Yes. Okay.

David Kipping 1:14:09 So in this case, the, the evidence was so overwhelming it wasn't really a matter of, um, interpretation. It was, it was you had col- you would observe this star with the same, um, the same star but with maybe 10 even 100 times greater precision, for prolonged, much longer periods of time. And there was just no doubt at this point this planet was, was a mirage. Um, and so that's why you have to be very careful. I always say don't ever name, you know, my, my wife and my daughter (laughs) like, "Name this planet after me that you discover." And I'm like, "I can't, I can't ever name a planet after you because I will be, I won't be objective anymore." How could I ever, how could I ever turn around to you and say that planet wasn't real that I named after you?

Lex Fridman 1:14:49 So you, you're somebody that talks about and is, it's clear in your eyes and in your way of being that you love the process of discovery, that joy, the magic of just, uh, you know, uh, seeing something, a new observation, a new idea. Right? Um, but th- I guess the point is when you have that great feeling, is to then switch on the skepticism. (laughs) Like to start, like, testing, um, what does this actually mean? Is, is this real? What are the possible-

David Kipping 1:15:19 Mm-hmm.

Lex Fridman 1:15:19 ... uh, different interpretations that could make this a lot less grand than I first imagined? And all-

David Kipping 1:15:25 Yeah.

Lex Fridman 1:15:25 So both have the wonder and the skepticism, all in one brain.

David Kipping 1:15:29 Uh, yeah. I think the m- generally the more I want something to be true-

Lex Fridman 1:15:33 Yeah.

David Kipping 1:15:33 ... the more I inherently doubt it.

Lex Fridman 1:15:35 Totally.

David Kipping 1:15:35 And I think that just comes from, in a way, I grew up, um, with a religious family and was just sort of indoctrinated to some degree (laughs) like many children are, that, okay, that's just normal that, you know, there's a God and this is the way the world is. Uh, God created the Earth. And then as I became more, you know, well-read and literate of, of what was happening in the world scientifically, I started to doubt. And it really just struck me that the hardest thing to let go of when you, when you do decide not to be religious anymore, and it's not really a, uh, like a light bulb moment, but it just kind of happens over my, over sort of 11 to 13 I think for me it was happening, but it's that sadness of letting go of this beautiful dream which you had in your mind of eternal life, for, you know, for, for behaving yourself, uh, on Earth you would have this beautiful heaven that you could go to and live forever. And that's very attractive. And for me personally, um, that was one of the things that pulled me against it, was this... it's, it's like it's too good to be true (laughs) and th- it's very convenient that this could be, um, this could be so, and I have no evidence directly, uh, in terms of a scientific sense, to support this hypothesis. And it just became, uh, really difficult to reconcile, um, my growth as a scientist. And I know some people find that reconciliation. I, I have not. Maybe I will one day. Um, but as a general guiding principle, which I think I, I obtained from that experience, was that I have to be extremely guarded about what I want to be true, because it's going to sway me to say things which, which are not true, if I'm not careful. And that's the, that's not what we're trying to do as scientists.

Lex Fridman 1:17:21 So you felt from a religious perspective that there was, um, a little bit of a gravitational field in terms of your opinions? Like, it was affecting how you could be as a scientist? Like, as a, as a scientific thinker. Obviously you were young.

David Kipping 1:17:35 Yeah. I, I think, um, I, I think that's, that's true. That whenever you're, whene- whenever there's something you want to be true, it's, it's the ultimate seduction, intellectually. And I worry about this a lot with, um, with, me- UFOs and with, um, it's, it's true already with things like Venus