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Eugene Chiang

Eugene Chiang

Professor of Astronomy and Earth and Planetary Science University of California at Berkeley

By David Zierler, Director of the Caltech Heritage Project

March 13, 2024

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Wednesday, March 13, 2024. It's my great pleasure to be here with Professor Eugene Chiang. Eugene, it's great to be with you. Thank you for joining me today.

EUGENE CHIANG: It's a pleasure to be here.

ZIERLER: Eugene, to start, would you please tell me your title and institutional affiliation?

CHIANG: I'm a Professor of Astronomy at UC Berkeley, cross listed with Earth and Planetary Science.

ZIERLER: For your research, what are the connecting points between planetary science and astronomy?

CHIANG: Extrasolar planets would be the connecting point, the discovery of worlds outside of our solar system. For the last 30 years, this subject has exploded with discoveries which have tied together these two communities, the planetary science community and the astronomy community. I talk with both sets of people, although I will say my home is in astronomy.

ZIERLER: Within astronomy, what kind of astronomer are you? What telescopes do you use?

CHIANG: I work in theory, so I talk to observers who use all sorts of telescopes—space telescopes in the optical and in the infrared, ground-based facilities like ALMA in the radio. But I work primarily in theory, which means that I take the observations and try to interpret them. I try to make sense of them.

ZIERLER: Have you embraced AI and machine learning? Is that now relevant for the kinds of things you do?

CHIANG: It is relevant for the sorts of things I do, although I have yet to plunge into that world. I've been reading papers on using AI to, say, assess the stability of planetary systems, multi-planet systems. Without having to integrate laboriously, computers can look for the patterns and tell whether a system is stable or not, and over what time scale. So, it's economical, using machine learning to assess dynamical stability. And that's just one application of many. But yeah, AI is providing us a set of new tools to use.

ZIERLER: These tools, is this more about just putting more power, brain power, machine brain power, as it were, to data where there are simply not enough people to look at everything? Or are we able to do things that are simply not possible even if we had unlimited people power to throw at these problems?

CHIANG: You could make the case for the latter. There are so many parameters and metrics to describe a system, and the computer is very good at looking for correlations between these parameters and seeing patterns that we wouldn't be able to see. Yeah, it's a genuinely new tool. Although I don't think we're at the stage yet, or at least I hope not, where [laughs] humans are replaceable with computers.

ZIERLER: Eugene, a terminology question. There's astrophysics, there's astronomy, there's cosmology. Where are there meaningful distinctions for you within these fields?

CHIANG: Cosmology is a subset of astrophysics. It's the study of the origin of the universe on the largest scales. I work on the other end, what some people call cosmogony, the study of the origin of the world and planets. As for the terms astronomy and astrophysics, in this day and age, they are more or less interchangeable. Astrophysics is a branch of physics. It applies physics to understanding astronomical phenomena.

ZIERLER: Cosmogony, what's the root of that word? Where does that come from?

CHIANG: [laughs] I have to look this up, but "-gon" I think means "birth," so Greek for birth. "Cosmo-" may be "world," either "world" or "universe." But I use the word in the sense of "origin of the world." Where did the Earth come from? And planets in general, where does that scale of object come from?

ZIERLER: What are some of the big debates in planetary formation?

CHIANG: The problem of planetesimal formation remains an uncertain subject. What is planet formation anyway? It's the study of how to grow micron-sized dust grains into bodies the size of Jupiter. That's many orders of magnitude in scale, from micron sizes to tens of thousands of kilometers. On that road, there is a segment that goes from a few centimeters to a few kilometers. This is the regime of planetesimals, or the building blocks of planets. There's been progress in recent years—discoveries of hydrodynamic instabilities and gravitational instabilities that can glom particles together collectively. But to trigger those instabilities, certain threshold densities need to be met. How you start the thing remains a point of contention, and we don't really know. The observations are also hard to come by because things are just so far away, and we can't resolve individual, say, kilometer-size objects. We can't see them growing in real time, so it's been a speculative field. The other problem is the problem of transport in protoplanetary disks, how they accrete. Planets form from disks. They're pancakes of gas and dust that orbit young stars, and what's not completely understood is how that gas and dust moves around. One way to transport the mass and momentum is through turbulence, but what's the source of the turbulence? How strong is it? Maybe it's not even turbulent. Maybe there's some wind which carries away the excess angular momentum so that mass can go in toward the star. These transport processes, sometimes they involve magnetic fields, sometimes they don't. So, transport in protoplanetary disks remains very much a debated subject.

ZIERLER: Absent time travel going back in time to seeing how these things actually happened, what are the technological or theoretical advances available to us that might help us answer these foundational questions?

CHIANG: [laughs] What can we say? Higher angular-resolution images of disks, in the infrared through millimeter, so we can actually detect substructures, clumps of material within the disk. To put planet formation on a more empirical footing, you need to see the planets forming. People have been able to make increasingly spectacular images of disks. We need higher angular resolution and the ability to block out the light from the central star so that we can see the little faint thing, the little planet, growing inside. So, better high-contrast imaging in the infrared to look for protoplanets that are in the process of coalescing. JWST is an instrument that's just come online, and we've been making some calculations to estimate how bright the things would be, how big they would be, and what wave bands you should look at. Bigger mirrors [laughs] and more sophisticated adaptive optics to beat down the light from the central star.

ZIERLER: The coming era of ELTs, the extremely large telescopes—the TMT, the GMT, the European Large Telescope—how will these ground-based observatories help answer these questions?

CHIANG: I mentioned bigger mirrors, I wasn't kidding. [laughs] It's the diffraction limit: the larger the diameter of the telescope, the higher the angular resolution so we can find these small-scale clumps of material. Planets are measured in tens of thousands of kilometers, and you want to compare that to the sizes of these disks which are measured in AUs, which is much larger, so it pays to have that angular resolution, and the sensitivity, which are enabled by ELTs. The trick though, is that it's not enough just to build a larger mirror; you have to beat down the atmospheric fluctuations because you could be thwarted by the weather or atmospheric turbulence, so you need to build the mirrors cleverly with adaptive optics to constantly adjust the surface of the mirror so that you can achieve that diffraction limit. The field is really driven by instrumentation and observations. As a theorist, I like doing what I do, it fits my personality, but the field is largely driven by technology and empirical data.

ZIERLER: Have you been involved in extrasolar planets since the dawn of exoplanet research?

CHIANG: Not at the dawn. [laughs] Let's put it this way: Mayor and Queloz published their paper at about the time when I was starting graduate school, so I think that's '95?

ZIERLER: Yeah, '95.

CHIANG: And they'd just won the Nobel Prize around a few years ago, so their original discovery was made when I was starting graduate school. And I remember there were debates about whether those Doppler velocity variations were due to a planet or whether they were due to stellar activity. I remember reading about that debate, so yeah, the observations were appearing at the same time that I was thinking about what I should be working on, and it was very attractive for that reason, because it seemed like a frontier field.

ZIERLER: What role does hydrodynamics play in your research?

CHIANG: It's everything! Well, maybe that's a little bit of an exaggeration. But disks, gas, all having scales larger than the mean free path between molecules, we use the fluid equations, the Navier-Stokes equations, to model the flows around disks, and within planets, and how planets interact with disks. I've been involved in planet-disk hydrodynamic simulations, and those solve, in 3D where we can afford it, the equations of hydrodynamics—coupled with thermodynamics to understand how the material heats and cools. The equations of stellar structure, which are also the same equations that govern planetary interiors, are equations of hydrodynamics, or hydrostatics when you're working on equilibrium structures. So yeah, hydro is everything. Well, not completely everything, because there's a whole complementary study, which is dynamics, which is just G(M)(m) over r squared [GMm / r^2], or the point-mass dynamics of how planets interact with one another gravitationally. I'm also interested in N-body dynamics, which you wouldn't call hydro.

ZIERLER: Your work in planetary science, does that include Earth at all? Have you ever looked at Earth as another planet?

CHIANG: I don't think I've ever written a paper about the Earth. Although I do think about it [laughs] from time to time. I'm trying to put the Earth in context. Actually, now that I think about it, it's more the other way around, that I'm trying to put extrasolar systems in the context of the Earth. Solar-system objects provide a ground truth for more uncertain questions about how extrasolar systems form. So, the history of the Earth, the giant-impacts phase that people talk about, how the Earth formed from a set of catastrophic collisions between large objects, the last one of which formed the Moon. That collisional history of the Earth is interesting to me, because we can take that picture and see how it might apply to extrasolar systems. I try to keep up with what Earth scientists are figuring out.

ZIERLER: The science of satellite formation, is it basically the same as that of planetary formation, or are there different dynamics at play?

CHIANG: This is also something I haven't spent a whole lot of time thinking about. Yes they seem the same is the short answer. I don't see any particular major differences. The same issues crop up. There's a complication in the satellite case because you can be fed from the outside, from the circumstellar disk, which couples to the circumplanetary disk.

ZIERLER: Are there advances either in hardware or software today that make research possible that wasn't at the beginning of your career?

CHIANG: Yes! [laughs] It's hard to enumerate all of them, but golly! The first one that comes to mind is, we did have email [laughs] back then and the Internet did exist back then, but we didn't have these work-sharing tools, like Google Docs and Overleaf. Overleaf changed my life! Before, we were constantly—I was shoving things under people's doors and saying, "Well, here's the latest draft." [laughs] And they'd pick it up and mark it up, and then they'd shove it back under my door; and that's how we communicated. That was fine, that worked. But now, communication is instant. We can work on it simultaneously. We can even talk to each other as we are working on the same document. There's this chat feature. [laughs] So, the communication is a lot easier. That's different. It's more efficient.

ZIERLER: It's interesting you're emphasizing technology for collaboration. What about technology for calculation, for computation?

CHIANG: The 3D hydro simulations of planet-disk interactions were barely possible when I was starting, and now there's just so much better resolution. You can get down to scales smaller than the planet's gravitational sphere of influence and resolve the flow. We've been able to test analytic theories of planet-disk interaction in a way that wasn't possible before.

ZIERLER: Eugene, your grad students and postdocs, do most of them go on to academic positions?

CHIANG: The majority, yes. They've gone on to take up faculty positions at different places.

ZIERLER: What are the skill sets for those who want to go into industry, obviously in a less fundamental area?

CHIANG: Everything revolves around computation, so, "have computer, will travel" or "will get a job." That's true in both academia and industry. I had a couple postdocs who went on to industry, and one graduate student who's very senior now, in Microsoft. And they were just whizzes at computation and programming. That's a skill set that's in tremendous demand. And the ability to think analytically—and by that I mean the ability to take a problem apart, separate it out into pieces—that's useful for all lines of work.

ZIERLER: For you being in the Bay Area, all of the startups, all of the biotech companies, is that an asset for you at all, being there?

CHIANG: [laughs] I suppose. I'm trying to think how to answer this question. [thoughtful pause] I have yet to collaborate with somebody in industry. That would be pretty exciting, but the opportunity hasn't presented itself, and I haven't looked very hard for that kind of interface. But from the point of view of building up the careers of graduate students and postdocs and undergraduates too, who are under my supervision, it's wonderful to have the Silicon Valley right there, to say, "Hey, look! There's all this available for you, and it's just right next door." So, there are job opportunities that present themselves readily. Schooling and academia, "it's all an experiment" is what I tell people. It's an experiment. Let's do some science, write some papers, great. But whether it leads to a permanent position in academia, who knows? So, it's good to have alternatives at the ready next door.

ZIERLER: Eugene, let's go back, let's establish some personal history. When you arrived at MIT, were you already on the physics and astronomy track? Were you thinking about these things early on?

CHIANG: Yeah, I was. I was one of those kids who liked reading astronomy books. As far back as I can remember. My dad got me a telescope. I still have it. It's a great little reflector. But yeah, to answer your question, I was thinking about doing astrophysics from day one, starting as an undergraduate, and I took a class taught by Saul Rappaport at MIT. I went on to work with him. In a very happy circumstance several years ago, we started up another collaboration. So yeah, from the beginning I was thinking about it—very unsure about whether I'd be able to hack it, but yeah, interested.

ZIERLER: And always more on the theory side? Did you ever consider observation?

CHIANG: I constantly considered observation. I didn't really know what was good for me or what was right for me. I've mostly worked in theory, but I did try—I made an effort to explore observation as an undergraduate working with another fellow, Ron Remillard, who took me to Kitt Peak, Arizona, the MDM telescope there. Also in the first couple years of graduate school at Caltech, I experimented with working with some observers, Mike Brown in particular. As a postdoc I got involved in some observations as well. I spread my bets around to see what would catch, but now, the last 20 odd years, I've decided. I've finally figured it out. [laughs] My personality is such that I really prefer to think about things.

Ivan King put it this way. He asked, "What's the difference between an observer and a theorist?" Here's the difference. You take a science textbook, and there are problems for every chapter. The theorist does it the way you're supposed to. [laughs] You take the problems and you work it out. And you may get it wrong! I am wrong plenty of the time. It's not something I like to talk about, but yeah, you try to work it out from first principles, starting from the beginning. What does the observer do? The observer is very happy to go to the back of the book and find the answer. [laughs] The answer is staring at you from the universe. As long as you have the correct instrumentation and you can see well, you'll have your answer. And I was just the kind of person who wanted to understand it, and it wasn't enough to look it up. So yeah, theory appeals even if I'm not that great at it. [laughs]

ZIERLER: Was there a facility in mathematics for you, also, that helped push you over to the theory side?

CHIANG: I'm okay at math, run of the mill. I don't know what to say about this. Yeah, you need to have some facility with math. There are plenty of folks out there who have [laughs] a much greater facility than I do. But there's a certain minimum, okay? [laughs] I would like to say, math, formal derivations—definitely not my strength. Where I like to work, and where I think I have some advantage or some knack, maybe, is order-of-magnitude estimation, something I got to learn in earnest in graduate school. It's my primary tool for research, sketching things out. Sketching things, back of the envelope calculations—units is everything! [laughs]—being able to estimate quantities to within a factor of ten. So, not proofs, not derivations, but intuition. "What might it be? Maybe it'll work like this." Or, "This definitely doesn't work because it's wrong by ten orders of magnitude. But this might work because I'm getting the answer right to within a factor of five, and maybe it's worth writing some code to do it better."

ZIERLER: Eugene, the intensity of an MIT undergraduate curriculum, what would you do beyond the science? What was your social scene as an undergrad?

CHIANG: [laughs] There are two ways to answer that question. One is zero. [laughs] Okay? And zero is zero; I don't think I need to elaborate. But the other way to answer that question is, I minored in theater arts, so when I wasn't doing physics problem-sets or research with Saul, I was rehearsing plays, and that was incredibly social. But it was also work. Very much work. So yeah, I was busy from the time I woke up to the time I collapsed at night. I made many good friends. I still have them today from the theater—theater friends. I learned a ton from the theater department. They were so good to me.

ZIERLER: Did you ever think about going down a very different path and pursuing theater?

CHIANG: [laughs] All the time, yeah! I mean, this physics thing, I don't know. [both laugh] It's so hard, how are you going to get these one of these academic jobs? Yeah, all the time. I was in LA, too. This sounds terrible; it sounds totally naive and foolish, but it was true. In graduate school, it was in LA—I thought, "Well, it's right there. [laughs] I could go audition for some things if this astronomy thing doesn't work out." But yeah, I thought about it, embarrassingly, more often than I care to admit.

ZIERLER: Were you aware, as an undergraduate, of Caltech's reputation in astronomy? Was that one of the places you had to consider?

CHIANG: How could you not? It's the place to be. It's like going to Hollywood to become an actor, or going to New York City to do a play. How could you not know about Caltech to do astronomy? It's where all the glass is, Palomar and Keck and all that. So yeah, super famous. My dad would tell me about it, he would say, "Oh, this place, you should go. If you're really interested in physics, you should go there." I refused to apply as an undergraduate, because I said, "No, I don't want to just do physics." [laughs] But I did spend a summer at Caltech in high school. There was a summer program run by a couple of physics undergraduates, one of whose names I remember, Dave Morton, and for two months, we just went through all of Halliday and Resnick, so I got a taste of Caltech in a high school summer program. Not research, just course work. And we went through the entire undergraduate physics curriculum [laughs] in two months.


CHIANG: All I did was do problems and study. But afterward, I knew first-year physics, [laughs] and it was very interesting. So, I got a taste of Caltech then. Yeah, astronomy and astrophysics are legendary at Caltech.

ZIERLER: What were your early impressions when you arrived in Pasadena?

CHIANG: [laughs] "Wow, the air quality is not so great!" The other thing that was different was that Pasadena was near Alhambra and Monterey Park, and that was a culture shock because I realized, my goodness, there's all this Chinese food here! It's incredible! Entire cities have been taken over by Asians, [laughs] and I'd seen nothing like this before. At other places, there's Chinatown, which is like, two streets. Here, it's entire cities, and I was dumbfounded. I shopped there all the time for groceries, ate there all the time. That was a very pleasant surprise. The other thing about Pasadena, though, is it's pretty quiet. It has a sort of a small-town feel, and that was different from Boston, Cambridge. Not what you would call a college town.

ZIERLER: No, it's Los Angeles County, but it's not Los Angeles.

CHIANG: Yeah, exactly. I would wander around campus when I first got there, and throughout grad school, I'd take walks—working—and think, "Where is everybody? [laughs]" And people would say this about Caltech, maybe you've heard this saying: "Caltech is a research institute masquerading as a school." [both laugh] I kind of believe that. I mean no offense to the students there. I married one, so I joke with her about this, and she agrees. She said, "Yeah, research." [laughs] But yeah, it's a very small, quiet place, and that took some getting used to.

ZIERLER: Did you come to Caltech knowing or hoping that you'd work with Peter Goldreich?

CHIANG: Yeah! [laughs] I did, for better or worse—oh, definitely better! I don't know how he looks at it, but for me it was one of the best things I ever did. So, here's the thing. When I was shopping around and deciding where to go for graduate school, people said, "Well, what are you interested in?" And I said, "Well, I want to work in theory, and I'm interested in planets." And they said, "Then you shouldn't come here." [laughs] They said, "You should work with Peter Goldreich." I said, "Who's Peter Goldreich?" And they said, "Well, you should get to know him. If you want to work in planets or you want to work in theory, he's the person." And they told me this everywhere I went! I was amazed. So, I wrote the guy. I said, "I'm interested in coming to Caltech, but I also want to see if you'll have me if I come." And Peter wrote back. He said, "Well, let me take a look at your application first, and I'll get back to you." I waited a couple days, and he wrote back, and he said, "Okay. Come to Caltech and I'll work with you." And that was 24 hours before I had the deadline, so I said, "Okay, I guess I'm coming over." It was a little embarrassing actually, because I had said yes to Berkeley [laughs] days before, and I had to call them back and said, "Oh, I changed my mind. I'm going to Caltech instead." But yeah, I knew beforehand. It was for better or worse. It was a gamble. I had no idea who this guy was, or what he was like, or whether we'd get along, or anything. But it's an experiment, right? We had committed, in some sense, to seeing if it could work, and lucky for me it did, so I'm tremendously grateful.

ZIERLER: Tell me about meeting Peter. What was that like?

CHIANG: Boy, his shorts are really short! [both laugh] At MIT, everybody dressed up in suits. Suit and tie. And then you meet this guy, and he's just come off the tennis court. He's like, "Okay, let's start. What did you do? Oh, I think we should do this calculation." And he would just—it was very informal, but very... [laughs] I don't know how to describe it. We'd spend hours just talking. It was really wonderful, my education in conversations. He was extraordinarily intimidating at the beginning; towards the end, less so. Still intimidating [laughs] because he's just so smart! It was very interesting. There are all kinds of stories I could tell, but one of the first times I interacted with him, meeting with him, he suggested this calculation to me. And then I came back to him a week later or something, and I said, "Oh, I did it, and let me show you how I did it." And then I would start writing on the board all this nonsense—not nonsense, just a very formal and by-the-book way of looking at it, very textbook-y—I started writing it on the board. And he very patiently just looked at me, and at some point I stopped writing, and he just looked at me. He didn't bother looking at anything I had written [laughs]. We just talked about it. We just talked about it and got to the essence of it without all this dressing up with all the algebra and all that stuff, just getting at the essence of it through order-of-magnitude calculations, or certain ways of looking at things. And that, for me, was a real eye-opener. I thought to myself, "Wow, this guy, he's an artist." He has real process. It's not by the book. It's not like accounting. He can be super-technical and formal too, but he can also—he has a very particular way of working. I can only describe it as being a creative artist. And I thought, "I want to learn how to do that."

ZIERLER: What was Goldreich focused on in the mid-1990s?

CHIANG: With me it was disks, protoplanetary disks, planet formation broadly construed. But he was also working on stellar oscillations at the time with Yanqin Wu, white dwarf oscillations. He was also working with Yoram Lithwick and Jason Maron in the physics department on turbulence, magnetized turbulence in the interstellar medium.

ZIERLER: What would be an example of an order-of-magnitude calculation where you would arrive at an answer that either was better or was not possible otherwise?

CHIANG: I don't know about not possible, [laughs] because you can do a calculation formally (or by the book), or you can do it order-of-magnitude style, and often one is a check on the other. But there are plenty, there are just an infinite number. I teach a course now, inspired by the course that he taught, except I have new problems. I have my own set of problems. [laughs] I'm very proud of my problems. But, all sorts of things. One of the first things I learned was how to calculate Einstein A coefficients on the fly, so cross sections for how atoms absorb light. That was a ton of fun. Making an analogy with a harmonic oscillator and using the Larmor power formula. We would calculate probabilities without having to do these formal quantum-mechanical calculations, just by making an analogy with a charge on a spring, you could calculate these probabilities for absorption of a photon by an atom, and that was a lot of fun.

There are plenty of other order-of-magnitude calculations. For my class, we do things like hummingbirds. Hummingbirds are birds that can hover, but why is it that hummingbirds are only limited to maybe ten grams or so? Why don't you find much larger birds that are able to hover for long periods of time? You need to know Kleiber's law for metabolism, how power scales with mass, but you also need to know the power needed to lift an object. Not glide, but lift: to push an amount of air down so that you can stay up. It's a two or three line calculation, and then you back out ten grams. You say, "Oh, well that's why hummingbirds are only this big." And that's just one of an infinite number [laughs] of order-of-magnitude calculations you can do. It's great for understanding the world around you. It just makes the world a friendlier place. You can go around the world and understand it at some level. It's a very satisfying, empowering feeling.

ZIERLER: Tell me about connecting with Mike Brown and if that's when you were still considering an observational kind of career.

CHIANG: That was at a Gordon Conference. They still hold these things every two years. They always call them the same thing: Origins of Solar Systems. I heard a talk by Anita Cochran at Texas, and it was about the Kuiper Belt and how Pluto was captured into resonance by Neptune, which had migrated out. And I had no idea about any of these things. I had never heard—the Kuiper Belt, that was also coming out at about the same time, the discovery of 1992 QB1, that Pluto and Charon weren't the only things out there, so suddenly there's a whole sea of objects out there. That was also coming online at the same time that extrasolar planets were. I was interested in both, and I did work in both. But yeah, she gave this talk, and I was like, "This looks beautiful, this resonant capture thing. What's that all about?" Mike Brown was at the conference too, and I knew he was just hired onto the Caltech faculty, so I approached him. I said, "This Kuiper Belt sounds really interesting. Is there any work that you have for me?" He said, "Yeah, I have something for you. Why don't we do a deep Keck Survey for Kuiper Belt objects, a pencil-beam survey." And that's what we did, and it was educational. Painful, but educational.

I was a theorist by day working with Peter, and then at night I'd reserve the time to reduce all the Keck data. It's a very different skill set to be an observer, the whole life is different. I should have known back then that I really wasn't cut out for it. These observers are constantly writing proposals. And the proposals don't come with money either! [laughs] It's just telescope time. And of course, you need that, but they're constantly writing proposals and constantly claiming that, "If you give me this telescope time, and I have these five hours on this telescope, I'll solve the whole thing. I'll figure it out." And I just couldn't bring myself to say those things. [laughs] I always think to myself, it's more complicated or subtle than that. You have to write these proposals pretending like you actually just need this one little thing to figure it out, and I was like, I need a lot more [laughs] to figure it out. Anyway, it was a very different life, and I spent a year, sort of schizophrenically, between Brown and Goldreich.

ZIERLER: Was Mike already in Pluto killing mode, or is this the origins of killing Pluto?

CHIANG: You'll have to ask him. [both laugh] But yes, he was very much interested in the Kuiper Belt back then. I remember when Dave Jewitt visited to give a talk, Mike would say, "Jewitt is visiting. He's one of the top 10 people I most admire, so don't make him mad. [laughs] Be properly respectful to Professor Jewitt." But yeah, he was interested in the Kuiper Belt in the 90s when he was first hired.

ZIERLER: Tell me about developing your thesis topic.

CHIANG: It's a bit of a random walk. I worked on disks, protoplanetary disks. I worked on planetary rings. I worked on the Kuiper Belt observationally. In the end, these things, they all have to do with planetary science, but the only thing tying them together—for the title of my thesis, I asked, "What's going to tie these things together?" I said, "Okay, circumstellar and circumplanetary disks." They're all disks. I was working on disks. Scott Tremaine, a famous astrophysicist, would say, "There are two kinds of objects in the universe. There's spheres, and there's disks." And I said, "Okay, well my thesis is about disks." [laughs] So, a bit of a random walk. I should say the problems were articulated by my advisors. I would ask Peter, I would say, "What are some good problems to work on?" He said, "Well, why don't you try this one?" And I made progress on that one, and then he said, "Well okay, why don't you try this one?" And then I made progress on that one too, and we wrote it up. And I've learned that problem articulation, problem identification, problem definition—people say that half the problem in research is defining the problem. I would say it's more. More than half the problem is actually just articulating it. Once you've defined it, decided, "Okay, this is a good problem"—and "good" has all kinds of dimensions. There's "good" as in yes it has a large audience, people will care if you figure this out; that's one metric of good. But another metric of good is, can you do it? Do you have a shot at it? Is this a good problem for you? So, I'm constantly—I spend all my days thinking about, what are good problems? And for every problem that I think is worth it, "good enough" that I could take a stab at it, there will be ten I've discarded. I'll say, "Oh, I don't think I can do that one," or "I don't think people care," or "I don't think this is that interesting a problem." But in graduate school, to answer your question, I relied rather heavily on my advisors for problem definition. Although I will say the solutions—and you can ask Peter and Mike whether they agree—the solutions were mostly mine. [laughs] That was a nice feeling, to think of new ideas.

ZIERLER: Why is the Kuiper Belt a rich area for studying disks?

CHIANG: It's our local, homegrown debris disk. It's the leftover material, the stuff that didn't make it, didn't get agglomerated. It can offer insights into collisional evolution, how rocks behave when they bang into each other, grinding down, how planetary systems clean up. You start with a disk, and a fraction of it—gas and dust—congeals into planets, but then there's all this stuff left over. Planet formation is not 100% efficient, so there's a cleanup phase. You have to get rid of everything. And the solar system is fairly clean. The space between the planets is pretty empty except for the Asteroid Belt and the Kuiper Belt, so in those regions maybe there are clues as to how the cleanup process unfolded, how the material collided, ground down, was transported away. We can also use the Kuiper Belt and the Asteroid Belt as tracers, like test particles that record the history of events, so not just the history of cleanup, but also the history of how planets moved around and migrated, this whole business of Pluto being captured by Neptune, originally proposed by Renu Malhotra. The Kuiper Belt may encode or record how the giant planets changed their orbits in the distant past. That dynamical history is recorded in the orbits of Kuiper Belt objects. They're our local version of a debris disk. I also study extrasolar debris disks which have their own interesting patterns and shapes. So, our solar system provides, again, some ground truth for processes that are happening in extrasolar debris disks.

ZIERLER: As a graduate student, were you following Caltech's contributions at this very early stage of extrasolar planetary research?

CHIANG: As a graduate student was I following [crosstalk] what Caltech was doing?

ZIERLER: Yeah. Was this a thing that people were talking about on campus?

CHIANG: Shri Kulkarni and Ben Oppenheimer had just discovered the first brown dwarf, so that was also happening at the same time that I was starting graduate school. Ben Oppenheimer was one year above me, and they had discovered GL229B [Gliese 229B] with Palomar, and that was quite exciting too, to see the first brown dwarf discovered. That was direct imaging, opening that door.

ZIERLER: When you finish at Caltech, were you looking at postdocs and faculty opportunities in tandem, or you wanted to do a postdoc first?

CHIANG: I looked at faculty positions at the same time, and I wouldn't have if Peter didn't tell me to. The graduate students, we were desperate even just to get a postdoc. But he said, "Well, you should apply for faculty jobs." I said, "What are you talking about? I don't even have my degree yet, and I should do a postdoc first." He said, "Well, you know, you're not getting any smarter." [both laugh] And then he said something else. He said, "I think it's crazy to have a kid when you're 30." [both laugh] I didn't know how to respond to these things. He said, "I know times have changed." I said, "Yes, Peter, times have changed! You cannot scale from your example. You're off-scale, so you cannot extrapolate, or interpolate, or do any kind of ‘-polation', okay? You're just off-scale somewhere in your world, and then there's the rest of us." And he just said, "You're not getting any smarter." So I said, "All right, well…"

I tell this to people now, I say, "You should apply when your stock is high." People's stock, [laughs] they go up and they go down. Your valuation fluctuates in time, and at the time, I guess people were paying attention to some of the things I was doing, so I said, "Why not?" So, I applied. And I got offers. [laughs] I was shocked. I was like, "Wow, these people must be really desperate to want to hire somebody fresh out of graduate school." But yeah, it was a real learning experience to apply to these positions, to faculty and postdoc positions.

ZIERLER: Did you spend a year at the Institute for Advanced Study first?

CHIANG: Yeah, I did... for worse [laughs], which people know. I've been pretty public about this.

ZIERLER: Why was that a negative experience for you?

CHIANG: Oh, it's so dull there! Sorry. [laughs] You know, Einstein died there. [laughs] No, it really wasn't a good fit for me. There are people who love the Institute. I know them, and they swear by it. Every chance they get, they'll take a sabbatical over there, and they're so productive, they don't have to think about other things. But for me, boy, if I thought Caltech was quiet, at the Institute it was so quiet you could hear yourself thinking. [both laugh] It was so quiet. I was very immature, maybe I still am, I don't know, but back then I just felt the pressure of the place. "You're at the Institute of Advanced Study, you better produce something. You better do something." And it sort of got to me. I let it get to me, and that's my problem.

There were other things that weren't a good fit. The total lack of food options. [laughs] It also depends on the particular mix of people who are there. There are no students. It's all postdocs and one or two faculty, so the whole vibe of the place, it just feels rather isolated. Small town with a capital S, or very small s. [laughs] If the chemistry doesn't quite work between, say, six people, then you're in trouble, because it's just these six people. So yeah, I had a tough time there. I left. Berkeley was good enough to give me an offer, so I left after 363 days [both laugh]. I talked to a postdoc afterwards, Scott Gaudi, now at Ohio State. He was there at the time. He was one of the six or seven. Afterward I said, "Scott, how's it going?" He was still at the Institute, or maybe he had gotten a job, I forget. And he said, "You know, after you left, it got a lot better." [laughs] I said, "That makes sense." That's consistent with my theory for why the institute doesn't work for everyone. So yeah, it was not a good match for me. I should have known better. I should have known myself better.

ZIERLER: And no hard feelings at Berkeley after you ditched them for Caltech as a graduate student?

CHIANG: Oh, I'm not sure they remember.

ZIERLER: Good. [laughs]

CHIANG: The guy I had phoned back then was James Graham. I had called him and said, "I really apologize for this, but I've changed my mind." It was very awkward, as you can imagine. We wrote papers together afterwards, when I was his colleague, and he's retired now. He never brought it up once, and I never brought it up [laughs]. We were quite friendly with one another when we were both on the faculty. He's retired now, but we never talked about my grad school decision. It just never came up as a topic of discussion.

ZIERLER: Was Berkeley a welcome change after the quietness at the Institute?

CHIANG: Night and day! With every mile that I put between me and Princeton, my heart rate went down by one beat per ten minutes. [laughs] And then it was another culture shock—a different kind, but one I could deal with—at Berkeley where everyone was just so relaxed. These students, they're everywhere, and they're on the grass, and eating, and picnics, and this is during the school days. And they're just out there on the grass, eating, not working, and I just wanted to say to them, "What are you doing? You should be working! This is a school day!" I didn't say any of those things, but I thought, "You people are so happy!" Whereas at Caltech and MIT—I don't know, I would venture I'm allowed to say this as an alumnus of both places—the culture was just the opposite. We were constantly talking to one another about—commiserating—over how miserable we were and how much work we had. The more miserable we were, the more respect we accorded each other, [laughs] it was like, "No, my horror story's worse than your horror story." But at Berkeley, that was not the case. It was instead, "Life is good." So that took some getting used to. People are quite positive here, and yeah, I've had to get used to that too.

ZIERLER: The pressure you put on yourself to produce something of import at the Institute, did that yield anything?

CHIANG: No is the short answer. [laughs] I think I wrote one paper, maybe two, and I'm not proud of those things. It was okay, and I learned some things, but no. It was just a year. It's all my fault.

ZIERLER: It was a dual appointment in Astronomy and Earth and Planetary Science from the beginning?

CHIANG: At Berkeley? Yeah.

ZIERLER: How common is that dual appointment? Do many professors have that?

CHIANG: It's what's called a 0% appointment in my case. My home is in astronomy. I don't think of myself as an Earth scientist. I think of myself as trained in astronomy. My degree is in astronomy. The courses I teach are in astronomy, so I have a 100% appointment in astronomy and a 0% appointment in Earth and Planetary Science. I like to say, "I have a 0% appointment, but I spend more than 0% of my time at McCone." Once in a while I'll attend their seminars, interact with people there. When I first got there, I co-taught a class with Raymond Jeanloz on classic papers in Earth science. That was educational for me. I learned about Oxburgh-Turcotte plate tectonics and these fun order-of-magnitude calculations to calculate plate velocities, so it was educational. I teach Earth and Planetary Science students in my cross-listed classes. Your question is how common are dual appointments. Maybe something like 10% of the faculty are formally cross-listed. We get to vote, and we get to attend their faculty meetings (if that's considered a reward). [laughs]

ZIERLER: What did you focus on during the assistant-professor years?

CHIANG: Extrasolar planets and the Kuiper Belt. The Kuiper Belt in particular. I was part of a survey of the Kuiper Belt, a wholesale survey, and what we found were a whole bunch of objects not only in the 3:2 resonance, but all these other resonances, like 2:1, 5:2, 7:4, 3:1, and using those objects to constrain the migration history of Neptune. I served as a theorist for this team of observers at Lowell Observatory and also MIT. Jim Elliott at MIT, who taught me as an undergraduate for the optical astronomy lab, I got to work with him. We had all these observers, we were all searching for Kuiper Belt objects. And I was helping to interpret the observations theoretically and classify these objects according to which resonance they were occupying. That was one effort.

The other effort was in extrasolar planets and mass loss, photoevaporative mass loss from hot Jupiters, work that I did with my first graduate student, Ruth Murray-Clay. She's now at Santa Cruz as a faculty member there. Ruth and I, we worked on a bunch of stuff. We worked on photoevaporative mass loss. We worked on other puzzles. I like puzzles, weird things. I call them X-files: weird, super weird [laughs] light curves, or some wild spectra or image, or something that's like, "What is this?! This doesn't fit anything!" So, we worked on this system, KH 15D, this bizarre light curve with a 100-year history. Ruth was very imaginative; she was able to piece together a whole story for that. So yeah, semi-random topics in extrasolar planetary systems, including disks, continuing the same themes of my thesis.

ZIERLER: When do extrasolar planets become—what's the right word?—studyable? When do you start to be able to look at these, or as a theorist, to look at what the data is telling you, and there's important work to be done here?

CHIANG: I guess your question is, when is a system ripe for study?


CHIANG: That's a judgment call that we try to make every day. There's no formula for it. You sort of have to have a feeling for it. Is there enough data? Many times I'll look at something and think—maybe here's an answer to your question: if I can think of more than one thing, say, two or three things that can explain the data, then it's not ready. It's not constraining enough. It's like, "There's just one point on your plot, and I can fit any line through it, so what's the point of that?" But if the data are extensive enough that nothing seems to work, then that becomes interesting. Like, if people tried five things and none of them work, then that's something that maybe I'll try to throw my hat into the ring and see what I can do. So yeah, the data have to be constraining enough that you can rule out things. [laughs] And if you can't explain it to within a factor of ten, then that also becomes especially interesting. If you can explain it to within a factor of two just using normal things, normal interpretations, then that's less interesting, because other people could do it.

ZIERLER: Eugene, tell me how you got involved in studying the Deepwater Horizon oil spill.

CHIANG: [laughs] It's on my website, I documented the whole thing because it was just so odd [laughs] an experience. The BP [British Petroleum] oil rig disaster happened, and I got this email from a press-relations person at Berkeley who had sent it to all faculty teaching fluid mechanics. I teach PHYS 202: Astrophysical Fluid Dynamics, so somehow I got on their list, but most of the people she sent it to were in the engineering departments. Somehow, I got on the list. I guess I was listed under astrophysical fluid dynamics. The email said, "To all fluid dynamicists at Berkeley, there's a video of this broken pipe underwater, and everyone's trying to estimate how much oil is coming out of the pipe. Can you do it? You're all fluid dynamicists, [laughs] so please try." I got this late at night, and I thought, "Well, this is my thing." [laughs] This problem could have been straight out of the Caltech order-of-magnitude class. You couldn't think of a better example. You're given this movie, there's no scale bar, there is a timer on the video, you don't know how big the pipe is, you just see oil gushing out. You don't know how big that pipe is, okay, but there's a timer on the video. Some people are attracted to these sorts of problems, it's like, "How many jelly beans are in the jar? [laughs] [dramatically] Guess how many jelly beans are in the jar! Win a prize!" And I thought, "Oh, maybe I'll get a prize [laughs] if I guess the answer right." People were guessing based on the size of the oil slick on the ocean surface and how it was growing, people were making estimates, and BP kept saying, "Oh, it's only a few thousand barrels per day." The question posed to us as a challenge was, "Does this pipe flow in this video accord with 5,000 barrels per day?"

I couldn't resist. This is a straight-up back-of-the-envelope calculation. I submitted my estimate, which was quite a bit more. I got about an order of magnitude more. I got closer to 50,000 barrels per day, higher actually, up to 200,000. It was definitely more than what the press was reporting or what BP was claiming. I said, "Here's my entry." [laughs] And I was hoping for some prize, [laughs] but the only prize I got was the next day all these reporters just clogged up my answering machine—this is back in the day when we had answering machines—my answering machine was totally clogged with reporters asking, "Where did you get this estimate? Where does this come from? This is much bigger than what BP says. Do you stand by it? Prove it!" I didn't call back any of those reporters, except for the one from NPR. The NPR one, Richard Harris, he was very sensible. I talked to him. Anyway, that's how I got involved, because it was a problem that was almost straight out of—I forget the number, Physics 101?—taught by Peter and Sterl Phinney. I think Sterl still teaches it. I put it on my problem sets now: How much oil is coming out of that pipe?

ZIERLER: Eugene, some questions about your work as an academic leader, so we'll start with the Berkeley Center for Integrative Planetary Science. What is the mission of the Center? What does it do?

CHIANG: It's an interdisciplinary unit. We're trying to get people from Earth and Planetary Science, people from McCone Hall, to talk with and interact with the people in Campbell Hall, the astronomers. We host a seminar series. It continues to this day. Burkhard Militzer is now running it. Earth scientists, solar system scientists, extrasolar planet people, disk people, it's nice and diverse—under the broad umbrella of planetary science. It's a place where we can gather and exchange expertise and learn from one another.

ZIERLER: How has the Center been important for your own research?

CHIANG: It's stimulating. Well, occasionally stimulating [laughs] to listen to these seminars. You get ideas from visitors. I've definitely gotten ideas from people who have come by and given talks. They say, "Here, check out this data that we can't explain," and I'll get interested. Sarah Stewart, whom you've interviewed, gave one of these CIPS seminars and inspired some work that Nick Choksi and I did on chondrules. Sarah was one of our CIPS speakers.

The unit also has some money. It's not just a seminar series. It also has a bit of money attached which we can use to subsidize postdocs.

ZIERLER: When you became chair of the astronomy department, was this something you were looking forward to? Did you get tapped and you said yes as a matter of service and giving back?

CHIANG: All of the above. Well, all of the above except not "looking forward to." Although, even there I was thinking—I was very naive, and I thought I'll learn lots of things. [laughs] Yeah, I did learn lots of things, but—here, let me put it this way. As most people appreciate, it's not a job that most people covet. It's very much a service position. Chair is different from Head. Chair is where you have no particular power. You have the power of the agenda to some extent, but it's very much a service role where you're really helping your colleagues and the 200 people in Campbell Hall, where at any given time there's somebody who needs something. The buck has to stop somewhere, so the chair gets involved and tries to help out. It's a full-time service position, but one which it's fair to say most people, most faculty anyway, think, "This is going to take so much time away from research, and you will suffer." And I suffered.

But let me say this. The tap on the shoulder you mentioned, yeah, the dean asked me. The way it works is, at least in our department, there's a hidden ballot, people put in names for who they want to be the chair. It's a hidden ballot—anonymous—and the dean looks at all these scraps of paper and says, "Okay," and then the dean makes the invitation. So, I guess my name showed up on at least one scrap of paper. The dean tapped my shoulder and said, "Would you be willing to do it?" I said, "Give me some time. I'll think about it." I told my wife, who's a Caltech alum, Inn Yuk, majored in chemistry. [laughs] By the way, I don't know if this is okay to say, but it's true: One of the reasons I didn't apply to Caltech, at least back in the day, was I thought the social scene must be terrible. [laughs] The male-female ratio was not in my favor, so I didn't apply, but that was just one of several reasons why I didn't want to apply to Caltech, despite what my father wanted me to do. But ironically, I found my wife at Caltech [laughs], so I guess I was wrong. Anyway, I asked Inn, "Hey, should I do this thing? The dean is asking me to do this thing for three years." And she said, "You know, you should, because maybe for once in your life you will learn not to be so selfish." [both laugh] I was blown away by that comment. That really put me in my place.

ZIERLER: Eugene, what did you learn as department chair, of the sociology of the department? Things like climate, DEI issues, hiring, and all of those things—what did you learn about Berkeley astronomy?

CHIANG: That's kind of a loaded question. You're a historian of science, so the history is that this happened around the time that our department was undergoing a sexual harassment case. So, that fell on my plate. Geoff Marcy, the whole business—became public in October of 2015. I'm not going to go into deep super-detail, but just to try to answer your question about climate in particular. The case went public in October 2015. I was not chair at the time. I was on sabbatical at the time, Fall 2015. I was scheduled to start as chair in January 2016, but because there was such chaos going on, the dean said, "Can you please start early because we need some continuity for later." And my colleagues didn't want to step up and try to handle this thing. Well, for better or worse, I stepped up, and I tried to handle it. It was a terrible time for climate. The students lost their trust in the faculty. The faculty were in disagreement with one another about what to do, so I spent the next three years trying to restore trust between people. It was a ton of work. I like to think that we were at a much better place after my three years. I made so many mistakes, though, particularly with my colleagues. "Keep your friends close, but keep your enemies closer." I did not understand that. I understand that now [laughs]. I basically worked full time on climate and tried to bring the department to a place where something like this would never ever happen again.

ZIERLER: How do you understand how it could have happened in the first place? What are the takeaways? [crosstalk]

CHIANG: I can answer that question. The takeaways are: You cannot have single points of failure. You cannot always have the chair be the one person who takes care of everything. You cannot concentrate responsibility in one person. You have to share—Berkeley as a university actually prides itself on this concept of shared governance—but the hard part is putting it into practice, creating a system where responsibility is shared, particularly among the faculty. The takeaway for me is, one can go into research, and do research, and spend close to 100% of time on research; and yes, in a research university, that is our number one priority, that's what you're rewarded for. But if you go too far in that direction and stop caring about people's lives, then it's not sustainable. You can't just be scientists all the time. You actually have to talk to people, and students, and each other, and find out what's happening. And I think the problem we had—I think this is fair to say; I hope my colleagues agree with this, but what I took away from it was— my wife's comment is apt. She said, "For once in your life, maybe you'll learn not to be so selfish. Maybe you'll learn to actually care about something other than your research." And we had to care after that incident. I don't know if that answers your question.

ZIERLER: Yeah. How did the department come out stronger as a result?

CHIANG: This is going to sound very bureaucratic [laughs], but we formed a committee, [laughs] a climate committee, which continues to this day. We created a number of things, governing bodies. Before, it was just the chair, as in, "You need this thing signed? Go talk to the chair." Or, "You have a problem? Go talk to the chair." Well, now we have a climate committee. We have also, even broader in purview, what we call Small Council. This was around the time that Game of Thrones was happening, [David laughs] so somebody said, "Oh, we should call this Small Council." I said, "Yes, we should call this Small Council, because that's what it is." So, what is Small Council? It's the chair, it's the head graduate advisor, it's the head undergraduate advisor, but it's also, very importantly, the graduate-student rep, the undergrad rep, the staff rep, the postdoc rep, and the staff-scientist rep, and we meet every so often. At the beginning, when things were in total disarray, we met every week or every two weeks. Now, things are much stabler, so we meet every four weeks. It's just a place where we all air our concerns from our respective demographics, and we try to help one another.

And it's important that there be representation from all demographics, not just faculty. This is not just a faculty meeting. It's the grads—and not all the grads! Because... it's representative government. We rediscovered representative government! [laughs] And that seems to work. And we have the same sort of structure for the climate committee, which handles incidents and people feeling disrespected in some way. We had to get educated from the rest of campus. Not just the Title IX office, but the police department, the counseling department, ombuds, health services. We got all these folks in, and they told us, "These are the services we offer. Here are the numbers to call if you ever have need." So, we all got educated, and the committee serves as a pointer to these different campus offices. Sometimes, if we feel we can, we will act to intervene and try to mediate conflict. The whole idea is to try to take a problem and solve it before it grows too big. That's the tragedy of what happened ten years ago; problems started small, and then they were allowed to snowball out of control until it was on the cover of the New York Times.

ZIERLER: Eugene, the academic response after the murder of George Floyd and all of the emphasis and interest on diversity and inclusivity initiatives, was Berkeley Astronomy ahead of the curve based on your experiences of what had happened between 2015 and 2018?

CHIANG: Ahead of the curve? Well, it's something that we've always cared about, outreach and, for lack of a better word—although I really hate this word, but for lack of a better word—diversity in our ranks, in our faculty ranks. Let me put it this way. Ahead of the curve in the sense of, yes, sometimes in the graduate applicant pool, there would be some students from diverse backgrounds and without great preparation, and we would take a chance on these folks and say, "Okay, come to graduate school. We'll admit you," and then we would shoulder the burden of bringing them up to speed. And that was a challenge which we deliberately undertook. There were not a lot of cases like this, but we did make an effort to do that. I can't claim that we were ahead of the curve, but it was certainly something that we tried to do. The admissions process is ever more complicated now, with so many factors to consider. Same goes for the search process for faculty, faculty hiring, so many dimensions in which to measure people or evaluate promise.

ZIERLER: Ultimately, does it yield better science, do you think?

CHIANG: I'm not as active as some of my colleagues are in outreach, so I may not be the best person to ask. I can try to answer your question in the abstract. I think it does yield better science in the sense that an open mind is a good thing, and to be naive can be a real advantage when you're doing research. If you're coming at a problem as an outsider, you'll sometimes have ideas that the "experts" or the "traditionalists" won't have, and that can be an advantage in research. At the risk of profiling, I think there's also something to be said about "the immigrant experience" of working really hard. When one is an outsider, there's a work ethic there that's maybe a little bit more built-in. Science is hard, and you have to throw yourself into it. When the chips are stacked against you, then you have to work that much harder, and that can be an advantage.

ZIERLER: Eugene, moving the conversation closer to the present, tell me about the CalTeach initiative and your leading work in it.

CHIANG: CalTeach takes STEM majors—science majors and math majors on campus—they major in science, but then they get a minor in education. And that minor can also lead to an accreditation to teach at the K through 12 levels, typically at the high school level. The whole mission of CalTeach is to put our undergraduates into science classrooms and math classrooms in K through 12. So, that's CalTeach. All the other UCs also have CalTeach. I think this was mandated by a call from Governor Schwarzenegger back in the day, and it continues to this day with some modest state funding.

I got involved. I've always been interested in education. My teachers mean so much to me. And it's so important to have good teachers, especially at the K through 12 level. I've always been wanting to help that effort to put good people into classrooms. So yeah, I got involved.

You could ask why I got involved that year. Well, that was the year of George Floyd. That was when I thought, "Okay, come on. You really should do something. Something!" And this was the nearest opportunity. And they were looking for a director, a faculty director, which I only learned after taking the job is really more of a faculty advisor. The hard work, the day-to-day work, the leadership work is done by the program director, currently, and has been for a while, Elisa Stone. She really runs the program. But she calls on the faculty advisor, which was me for a few years, for advice. I was the sounding board for discussions. Sometimes my involvement would be at the micro level. I would get involved with individual students, and help them along their way to graduate and become teachers. But sometimes it was more at a macro level. Once, I invited some teachers from local schools to come talk to our majors, to talk about—and they were Berkeley alumni, and they'd been teaching in the public Berkeley School districts for a number of years—I invited them to give a talk and a Q&A about their career trajectories and what their lives were like as teachers. It was a kind of recruitment activity.

I finished my term at CalTeach recently and didn't renew. I tried to do... [laugh] It was hard for me. It was very frustrating. The problems are so big. The need is so great. Berkeley High School, every other year, sometimes every year for consecutive years, puts out an advertisement for physics teachers. They say, "We need a physics teacher because the one we had left." And this is literally two streets away from campus. And we have all these physics majors, hundreds!—and astrophysics majors, hundreds! And Berkeley High School, which is just two streets away, can't staff AP physics or even regular physics. What's up with that? And that is a problem which I was utterly unable to solve. The whole culture, it was like fighting a giant monolith. I'd say to students, "Teaching, you should consider it as a career!" But then you look at the salary, look at the teaching conditions, and frankly I was at a loss as to know how to even start.

I look back, and there was one student. Her name was Sarah Kwon, and she was a physics major. She took my order-of-magnitude class. And she was in the CalTeach program, and it was obvious that she just really wanted to teach. She would talk about her experiences teaching summer programs for middle school kids, and I thought, "You should definitely go out and be a teacher. And you qualify." Not everybody qualifies. Even the people with degrees don't necessarily qualify to teach the subject. To teach a subject you have to really know it. But she was qualified. She knew her stuff, and I helped where I could. We would talk about pedagogy and career development. And she's teaching now. CalTeach helped me to help her trajectory. But I'll tell you, after three years, that's the only thing I can point to and say, "Yeah, I helped a little bit there."

ZIERLER: Okay, that's something.

CHIANG: It's something. I don't know. It's such a deeply rooted problem. I don't know where to start other than with individuals.

ZIERLER: Eugene, we'll take the story right up to the present, return to your expertise. What are you working on these days? And more broadly, what's interesting to you in the field?

CHIANG: Directly imaging planets while they're forming, the problem of accretion. It's an old problem, but the technology is now finally getting good enough. The telescopes are now finally approaching the point where we can possibly detect planets still pulling gas onto themselves and growing in mass. So, catching planets in the act of forming. With JWST or ELTs in the future, or Keck even now, there are folks—Dimitri Mawet is actively working on this. That is something I try to pay attention to. But aside from that, broad strokes, I try to track anything that's unsolved in planetary science.

I'm fortunate to be able to work with many postdocs funded by the Heising-Simons Foundation. So much of science these days, even at a public institution like Berkeley, is funded through private foundations. It's completely changed the landscape, the Simons Foundation. And those are two separate foundations, Heising-Simons and Simons. So, I've been fortunate to work with people funded by those organizations. Just recently we've been working on gravity modes in stars and how they can solve longstanding problems having to do with how planet orbits are tilted relative to their host star's spin axes. This is work with Dr. J.J. Zanazzi. It's been exciting for the last few months that we've been working together. The work is really his, but I've been helping where I can, providing sanity checks and learning about this new field. But yeah, just wandering around looking for unsolved problems. A gun for hire. [both laugh]

I will say the field feels different now than when I started because there's just so much more data. It's maturing. I feel like the problems are getting harder. There's so much data now that details matter. It's not enough to do an order-of-magnitude calculation. Once in a while, though, there will be some weird X-file [laughs], and then I'll get excited again, because then it's time to bring out the envelopes, [both laugh] start scribbling and sketching ideas.

ZIERLER: Eugene, we'll close with a retrospective question, and then we'll look to the future. Either intellectually what you learned at Caltech, or the administrative connections that keep UC and Caltech close in astronomy, the various partnerships, what has stayed with you from your Caltech days?

CHIANG: What has stayed with me administratively?

ZIERLER: No, like what you learned at Caltech, or the ongoing partnerships between Berkeley Astronomy and Caltech, if you have any.

CHIANG: Oh... [pauses] I'm trying to understand the question.

ZIERLER: Either something that you've learned at Caltech that really informs the science, or the ongoing connections that remind you of what you learned.

CHIANG: Right. The most straightforward answer to that question has nothing to do with administration. I'm not well-connected to power circles [laughs].

But Caltech, it gave me my education, particularly in physics and astrophysics research. And Feynman—he's such a presence on campus, even now, he's just so associated with the place. And the way he thought, I feel, permeates the whole place. There's knowing something, and there's knowing something. When do you really know something? It's not so much when you do all these textbook things and very formal things. OK maybe that formal path is a path to learning, it may be necessary, but it's not sufficient. So, Caltech taught me, through Peter and all the discussions I had with folks, that there are real things, and there's real knowing, and that's the goal. And there are debates about, "Oh maybe this can work and that can work." But look, there's also truth. Never forget, in this relativist world where people make arguments for this and that, that actually, in nature—Feynman put it this way: "Nature cannot be fooled." And our job is to figure out what nature is really like. And you can write pages and pages of discussion in a paper, but that's not the same as knowing. Don't be fooled. There's a truth, and if you're spending pages and pages on it, you probably don't know. [laughs] If you really know, you probably should be able to express it in a single sentence, or to a person off the street. So, there's that level of knowing, and that was the standard to which I was held at Caltech. I'm not sure if I met it, but I saw that standard. I was actually hungering for it in my undergraduate days, because I'd listen to all these lectures, and I didn't understand any of it. It was going too fast for me, or my preparation wasn't good enough, whatever, but I think it was also the instruction, the lecturers weren't getting at the heart of it. They never wrapped it up and said, "Well, this is why the electron does not spiral into the proton, why it maintains an orbit." They never tried to hit it on the nail in a concise, visceral, physical way, and I felt very unsatisfied with my undergraduate education. But at Caltech, they taught this order-of-magnitude class and it was all about that! It was about, "What's the essence of it?" And yeah, it's not getting all the details right, but this is the heart of it, and we can express it in one sentence, or in one line, and there's just such a satisfaction and beauty in that, and it makes you feel like you really know it.

ZIERLER: What a wonderful response.

CHIANG: That was the standard of knowing to which I was held, and to which everyone was held at Caltech.

ZIERLER: Great. That's great.

CHIANG: The goal is to understand it so well that you can explain it to the person off the street, and they'll get it.

ZIERLER: Finally, Eugene, looking to the future, the idea of catching planets in the act and developing technology where we can see accretion in real time, once we get there, what new questions will that compel? Where will the field head from that point?

CHIANG: What? I don't know what I'm going to do tomorrow.

ZIERLER: [laughs] Fair enough.

CHIANG: No, no. [laughing throughout] I don't even know what's going to happen this afternoon. [finishes laughing] There's so many... There's such a huge range of scales in planet formation. When I say catching planet formation in the act, what I really mean is toward the very end, like the last few doublings of gas giants, because those are the things that are the easiest to see. They're the biggest things, Jupiters pulling in gas from their circumstellar disks. So yes, in the next few years, that's where progress can be made. But then there's all the scales below that, all the way down to pebbles. And that's where we're headed, that's what we'd like to fill in, our understanding on all of those scales, from Jupiter scales, which we could actually make some progress on in the next few years, but then all the way down to—I'm thinking super ambitious—down to centimeter-sized pebble-scales. So, that's where we'd like to go. I'm not sure we'll ever get there, but that's the direction, to keep piecing together the entire road from grains to planets. But, as you know, it's turtles all the way down.


CHIANG: We already know the answer.

ZIERLER: That's part of the fun though.

CHIANG: Yeah, it's just more turtles. [both laugh]

ZIERLER: Eugene, on that note, this has been an extraordinary conversation. I want to thank you so much for spending the time with me.

CHIANG: David, it was really great.