So, there was the physics department, and the astronomy department, and there was also what's called the Enrico Fermi Institute, which was a research institute, but it was like half of the physics department and half of the astronomy department was in it. The one exception -- it took me a long time, because I'm very, very slow to catch on to things. So, I'm doing a little bit out of chronological order, I guess, because the point is that Brian and Saul and Adam and all their friends discovered that the universe is not decelerating. So, for the last part of our talk, I want to ask a few broadly retrospective questions about your career, and then a few looking forward. Is there something wrong about it?" There's good physics reasons. My teacher, who was a wonderful guy, thinks about it a second and goes, "Did you ever think about how really hard it is to teach people things?" I love the little books like Quantum Physics for Babies, or Philosophy for Dummies. They are . Like, here's how you should think about the nature of reality and whether or not God exists." Ted Pyne and I wrote a couple papers, one on the microwave background. I got two postdoc offers, one at Cambridge and one at Santa Barbara. In footnotes or endnotes please cite AIP interviews like this: Interview of Sean Carroll by David Zierleron January 4, 2021,Niels Bohr Library & Archives, American Institute of Physics,College Park, MD USA,www.aip.org/history-programs/niels-bohr-library/oral-histories/XXXX. It wasn't really clear. Part of that is why I spend so much time on things like podcasts and book writing. And then I could use that, and I did use it, quite profligately in all the other videos. But there's plenty of smart people working on that. Not the policy implementations of them, or even -- look, to be perfectly honest, since you're just going to burn these tapes when we're done, so I can just say whatever I want, I'm not even that fired up by outreach. Again, I did badly at things that I now know are very obvious things to do. But Villanova offered me full tuition, and it was closer, so the cost of living would be less. That was my first choice. Carroll conveys the various push and pull factors that keep him busy in both the worlds of academic theoretical physics and public discourse. Either then, or retrospectively, do you see any through lines that connected all of these different papers in terms of the broader questions you were most interested in? So, they knew everything that I had done. At the end of the interview, Carroll shares that he will move on from Caltech in two years and that he is open to working on new challenges both as a physicist and as a public intellectual. Rice offered me a full tuition scholarship, and Chicago offered me a partial scholarship. On Carroll's view the universe begins to exist at the Big Bang only in the sense that a yardstick begins to exist at the first inch. These are all things people instantly can latch onto because they're connected to data, the microwave background, and I always think that's important. In a podcast in 2018, Sam Harris engaged with Carroll. I should be finishing this paper rather than talking to you, on quantum mechanics and energy conservation. Here is a sort of embarrassing but true story, which, I guess, this is the venue to tell these things in. You're not supposed to tell anybody, but of course, everybody was telling everybody. Well, it's true. There's no delay on the line. The wonderful thing about it was that the boundaries were a little bit fuzzy. Yeah. Maybe that's not fair. I did not have it as a real priority, but if I did something, that's what I wanted to do. So, maybe conditions down the line will force us into some terrible situation, but I would be very, very sad if that were the case. When I first got to graduate school, I didn't have quantum field theory as an undergraduate, like a lot of kids do when they go to bigger universities for undergrad. What mattered was learning the material. This is an example of it. The unions were anathema. Sean Carroll: I'm not in a super firm position, cause I don't have tenure at Caltech, so, but I don't care either. Uniquely, in academia the fired professor . I love writing books so much. More the latter couple things, between collaborative and letting me do whatever I wanted on my own. Another follow up paper, which we cleverly titled, Could you be tricked into thinking that w is less than minus one? by modifying gravity, or whatever. Carroll is a vocal atheist who has debated with Christian apologists such as Dinesh D'Souza and William Lane Craig. Intellectually, do you tend to segregate out your accomplishments as an academic scientist from your accomplishments as a public intellectual, or it is one big continuum for you? Ed is a cosmologist, and remember, this is the early to mid '90s. A stylistic clash, I imagine. It's really the biggest, if not only source of money in a lot of areas I care about. This is something that is my task to sort of try to be good in a field which really does require a long attention span as someone who doesn't really have that. My biggest contribution early on was to renovate the room we all had lunch in in the particle theory group. So, I was sweet-talked into publishing it without any plans to do it. Sean, let's take it all the way back to the beginning. Sometimes I get these little, tiny moments when I can even suggest something to the guest that is useful to them, which makes me tickled a little bit. The other anecdote along those lines is with my officemate, Brian Schmidt, who would later win the Nobel Prize, there's this parameter in cosmology called omega, the total energy density of the universe compared to the critical density. I got a lot of books about the planets, and space travel, and things like that, because grandparents and aunts and uncles knew that I like that stuff, right? I think so. Drawing the line, who is asking questions and willing to learn, and therefore worth talking to, versus who is just set in their ways and not worth reaching out to? But within the course of a week -- coincidence problem -- Vikram Duvvuri, who was a graduate student in Chicago, knocked on my door, and said, "Has anyone ever thought of taking R and adding one over R to the Lagrangian for gravity and seeing what would happen?" Sean, when you got to MIT, intellectually, or even administratively, was this just -- I mean, I'm hearing such a tale of exuberance as a graduate. So, I was in my office and someone knocked on my door. I could have tried to work with someone in the physics department like Cumrun, or Sidney Coleman would have been the two obvious choices. Because you've been at it long enough now, what have been some of the most efficacious strategies that you've found to join those two difficulties? It's hard for me to imagine that I would do that. Absolutely brilliant course. She could pinpoint it there. Then, the other big one was, again, I think the constant lesson as I'm saying all these words out loud is how bad my judgment has been about guiding my own academic career. It was very long. But part of the utopia that we don't live in, that I would like to live in, would be people who are trying to make intellectual contributions [should] be judged on the contributions and less on the format in which they were presented. Anyone who's a planetary scientist is immediately interdisciplinary, because you can't be a planetary -- there's no discipline called planetary sciences that is very narrow. The South Pole telescope is his baby. Part of my finally, at last, successful attempt to be more serious on the philosophical side of things, I'm writing a bunch of invited papers for philosophy-edited volumes. I'd written a bunch of interesting papers, so I was a hot property on the job market. Well, or I just didn't care. I'm not sure how much time passed. I'm going to do what they do and let the chips fall where they may at this point. I don't think that was a conversion experience that I needed to have. I said, "Well, yeah, I did. In fact, that even helped with the textbook, because I certainly didn't enter the University of Chicago as a beginning faculty member in 1999, with any ambitions whatsoever of writing a textbook. Based on my experience as an Instructor at a major research university and now tenure-track faculty at a major public university, I would say that all of his major points are . I'm not going to let them be in the position I was in with not being told what it takes to get a job. Why do people get denied tenure? So, he won the Nobel Prize, but I won that little bottle of port. So, my other graduate school colleagues, Brian had gone to the University of Arizona, Ian Dell'Antonio, who was another friend of mine, went to, I think, Haverford. Sean Carroll Height. Being a string theorist seemed to be a yes or no proposition. So, it's sort of bifurcated in that way. He worked as a postdoctoral researcher at the Massachusetts Institute of Technology (MIT) and Kavli Institute for Theoretical Physics at the University of California, Santa Barbara[16] and as an assistant professor at the University of Chicago until 2006 when he was denied tenure. People like Wayne Hu came out of that. And guess what? Absolutely, for me, I'm an introvert. "Tenure can be risk averse and hostile to interdisciplinarity. There were so many good people there, and they were really into the kind of quirky things that I really liked. I think the departments -- the physics department, the English department, whatever -- they serve an obvious purpose in universities, but they also have obvious disadvantages. When I was very young, we went to church every Sunday. Not especially, no. So, I suspect that they are here to stay. Once I didn't get tenure, I didn't want to be there anymore. I'm a big believer that there's no right way to be a physicist. But then when it comes to giving you tenure, they're making a decision not by what you've done for the last six years, but what you will do for the next 30 years. I care a lot about the substance of the scientific ideas being accurately portrayed. It's not that I don't want to talk to them, but it's that I want the podcast to very clearly be broad ranging. You were hired with the expectation that you would get tenure. Absolutely. Young universities ditch the tenure system. In many ways, it was a great book. I think, both, actually. In other words, you have for a long time been quite happy to throw your hat in the ring with regard to science and religion and things like that, but when the science itself gets this know-nothingness from all kinds of places in society, I wonder if that's had a particular intellectual impact on you. I'm not sure, but it was a story about string theory, and the search for the theory of everything. You've got to find the intersection. They basically admitted that. Social media, Instagram. There are very few ways in which what we do directly affects people's lives, except we can tell them that God doesn't exist. The biggest reason that a professor is going to be denied tenure is because of their research productivity. The cosmological constant would be energy density in an empty space that is absolutely strictly constant as an energy. The expansion rate of the universe, even though these two numbers are completely unrelated to each other. But it doesn't hurt. If I'm going to spend my time writing popular books, like I said before, I want my outreach to be advancing in intellectual argument. It falls short of that goal in some other ways. So, it's not quite a perfect fit in that sense. I taught what was called a big picture course. No, tenure is not given or denied simply on the basis of how many papers you write. Not only did I not collaborate with any of the faculty at Santa Barbara, but I also didnt even collaborate with any of the postdocs in Santa Barbara. Sean, I wonder if you stumbled upon one of the great deals in the astronomy and physics divide. So, I wonder, in what ways can you confirm that outside assumption, but also in reflecting on the past near year, what has been difficult that you might not have expected from all of this solitary work? With over 1,900 citations, it helped pioneer the study of f(R) gravity in cosmology. As much as I love those people, I should have gone somewhere else and really shocked my system a little bit. So, we had some success there, but it did slow me down in the more way out there stuff I was interested in. And the High-z supernova team, my friends, Bob Kirshner, and Brian, and Adam, and so forth, came to me, and were like, "You know, you're a theorist. Benefits of tenure. Like, when people talk about the need for science outreach, and for education and things like that, I think that there is absolutely a responsibility to do outreach to get the message out, especially if the kind of work you do has no immediate economic or technological impact. Did you have a strong curriculum in math and science in high school? I can do cosmology, and I'd already had these lecture notes on relativity. Now that you're sort of outside of the tenure clock, and even if you're really bad at impressing the right people, you were still generally aware that they were the right people to impress. Was that something that you or a guidance counselor or your mom thought was worth even considering at that time? However, Sean Carroll doesn't only talk about science, he also talks about the philosophy of science. It doesn't really explain away dark matter, but maybe it could make the universe accelerate." You can do a bit of dimensional analysis and multiply by the speed of light, or whatever, and you notice that that acceleration scale you need to explain the dark matter in Milgrom's theory is the same as the Hubble constant. It's difficult, yes. But if you want to say, okay, I'm made out of electrons and protons and neutrons, and they're interacting with photons and gluons, we know all that stuff. I'd like to start first with your parents. theoretical physicist, I kept thinking about it. But it should have been a different conversation anyway, because I said, well, therefore it's not interesting. So, he started this big problems -- I might have said big picture, but it's big problems curriculum -- where you would teach to seniors an interdisciplinary course in something or another. One is you do get a halfway evaluation. So, I could completely convince myself that, in fact -- and this is actually more true now than it maybe was twenty years ago for my own research -- that I benefit intellectually in my research from talking to a lot of different people and doing a lot of different kinds of things. From neuroscientists and engineers to authors and television producers, Sean and his guests talk about the biggest ideas in science, philosophy, culture and much more. If literally no one else cares about what you're doing, then you should rethink. Yes, I think so. So, for you, in your career, when did cosmology become something where you can proudly say, "This is what I do. I've forgotten almost all of it, so I'm not sure it was the best use of my time. He is known for atheism, critique of theism and defense of naturalism. And that gives you another handle on the total matter density. And it has changed my research focus, because the thing that I learned -- the idea that you should really write papers that you care about and also other people care about but combined with the idea that you should care about things that matter in some way other than just the rest of the field matters. But the fruits of the labors had not come in yet. Good. The point I try to make to them is the following -- and usually they're like, sure, I'm not religious. I had that year that I was spending doing other things, and then I returned to doing other things. I knew relativity really well, but I still felt, years after school, that I was behind when it came to field theory, string theory, things like that. You feel like I've got to keep up because I don't do equations fast enough. And they had atomic physics, which I thought was interesting, and Seattle was beautiful. And he says, "Yeah, I saw that. There was a rule in the Harvard astronomy department, someone not from Harvard had to be on your committee. That was great, a great experience. Sean, just a second, the sun is setting here on the east coast. It's taken as a given that every paper will have a different idea of what that means. The idea of going out to dinner with a bunch of people after giving a talk is -- I'll do it because I have to do it, but it's not something I really look forward to. So the bad news is. That just didn't happen. But when I was in Santa Barbara, I was at the epicenter. I've been interviewing scientists for almost twenty years now, and in our world, in the world of oral history, we experienced something of an existential crisis last February and March, because for us it was so deeply engrained that doing oral history meant getting in a car, getting on a plane with your video/audio recording equipment, and going to do it in person. Being surrounded by the best people was really, really important to me. But I think, as difficult as it is, it's an easier problem than adding new stuff that pushes around electors and protons and neutrons in some mysterious way. I thought that given what I knew and what I was an expert in, the obvious thing to write a popular book about would be the accelerating universe. Not to give away the spoiler alert, but I eventually got denied tenure at Chicago, and I think that played a lot into the decision. It's a lot of work if you do it right. So, I gave a lot of thought to that question. I talked about topological defects, and it was good work, solid work, but they were honestly -- and this is the sort of weird thing -- they said, after I gave the talk and everything, "Look, everyone individually likes you, but no one is sure where you belong." When I went to MIT, it was even worse. I did an episode with Kip Thorne, and I would ask him questions. Part of it is what I alluded to earlier. Likewise, the galaxies in the universe are expanding away from each other, but they should be, if matter is the dominant form of energy in the universe, slowing down, because they're all pulling on each other through the mutual gravitational force. And I thought about it, and I said, "Well, there are good reasons to not let w be less than minus one. No one does that. Well, as in many theoretical physics theses, I just stapled together all the papers I had written. So, I think it's a big difference. Carroll provides his perspective on why he did not achieve tenure there, and why his subsequent position at Caltech offered him the pleasure of collaborating with top-flight faculty members and graduate students, while allowing the flexibility to pursue his wide-ranging interests as a public intellectual involved in debates on philosophy, religion, and politics; as a writer of popular science books; and as an innovator in the realm of creating science content online. If you just plug in what is the acceleration due to gravity, from Newton's inverse square law? But anyway, I never really seriously tried to change advisors from having George Field as my advisor. But it's not what I do research on. And it doesn't work well from your approach of being exuberant and wanting to just pursue the fun stuff to work on. I don't want that left out of the historical record. It's good to have good ideas but knowing what people will think is an interesting idea is also kind of important. We theorists had this idea that the universe is simple, that omega equals one, matter dominates the universe -- it's what we called an Einstein-de Sitter in cosmology, that the density perturbations are scale-free and invariant, the dark matter is cold. Not any ambition to be comprehensive, or a resource for researchers, or anything like that, for people who wanted to learn it. Polchinski was there, David Gross arrived, Gary Horowitz, and Andy Strominger was still there at the time. Are you so axiomatic in your atheism that you reject those possibilities, or do you open up the possibility that there might be metaphysical aspects to the universe? Philosophical reflections on the nature of reality, and the origin of the universe, and things like that. Let's put it that way. And then I got an email from Mark Trodden, and he said, "Has anyone ever thought about adding one over R to the Lagrangian for gravity?" And I could double down on that, and just do whatever research I wanted to do, and I could put even more effort into writing books and things like that. +1 516.576.2200, Contact | Staff Directory | Privacy Policy. SLAC has done a wonderful job hiring string theorists, for example. Like I said, it just didn't even occur to me. I just thought whatever this entails, because I had no idea at the time, this is what I want to do. And this time, first I had to do it all by myself, but because I was again foolishly ambitious, I typed up all the lecture notes, so equations and everything, before each lecture, Xeroxed them and handed them out. Netta Engelhardt and I did a podcast on black hole information, and in the first half, I think we were very accessible, and then we just let our hair down in the second half. The Lawrenceville Academy in New Jersey we thought of, but number one, it cost money, and number two, no one in my family really understood whether it would be important or not, etc. You can skip that one, but the audience is still there. In my book, The Big Picture, I suggested this metaphor of what I called planets of belief. I guess, the final thing is that the teaching at that time in the physics department at Harvard, not the best in the world. I don't know how public knowledge this is. He was reaching out and doing a public outreach thing, but also really investigating ideas. But he was very clear. Sean Carroll, a Cal Tech physicist denied tenure a few years back at Chicago writes a somewhat bitter guide on "How To Get Tenure at a Major Research University."While it applies somewhat less . So, the late universe was clearly where they were invested. I purposely stayed away from more speculative things. Once you do that, people will knock on your door and say, "Please publish this as a textbook." I think, to some extent, yes. One of the things is that they have these first-year seminars, like many places do. I've already stopped taking graduate students, because I knew this was the plan for a while. Audio, in one form or another, is here to stay. Now, the academic titles. Now, look, if I'm being objective, maybe this dramatically decreases my chances of having a paper that makes a big impact, because I'm not writing papers that other people are already focused on. Maybe it was that there was some mixture of hot dark matter and cold dark matter, or maybe it was that there was a cosmological constant. It's way easier to be on this side, answering questions rather than asking them. Almost none of my friends have this qualm. Sean Carroll is a tenured research physics professor at Caltech with thousands of citations. But in the books I write, in the podcasts I do, in the blog or whatever, I'm not just explaining things or even primarily explaining things. Like, ugh. At least, I didn't when I was a graduate student. Honestly, the thought of me not getting tenure just didn't occur to me, really. It's an expense for me because as an effort to get the sound quality good, I give every guest a free microphone. There was Cumrun Vafa, one person who was looked upon as a bit of an aberration. In 2017, Carroll presented an argument for rejecting certain cosmological models, including those with Boltzmann brains, on the basis that they are cognitively unstable: they cannot simultaneously be true and justifiably believed. You do get a seat at the table, in a way, talking about religion that I wouldn't if I were talking about the economy, for example. They're not in the job of making me feel good. George and Terry team-taught a course on early universe cosmology using the new book by Kolb and [Michael] Turner that had just come out, because Terry was Rocky Kolb's graduate student at Chicago. I just worked with my friends elsewhere on different things. But I don't know what started it. But do you see yourself as part of an intellectual tradition in terms of the kinds of things you've done, and the way that you've conveyed them to various audiences? So, that was with other graduate students. Again, purely intellectual fit criteria, I chose badly because I didn't know any better. The only way to do that is to try, so let's see what happens. Greg Anderson and I had written a paper. And at least a year passed. I chose wrongly again. Graduate school is a different thing. I was in Sidney's office all the time. Except, because my name begins with a C, if they had done that for the paper, I was a coauthor on, I would have been the second author. People think they've heard too much about dark energy, and honestly, your proposal sounds a little workmanlike. There was no internet back then. Another paper, another paper, another paper. Like I said, I wrote many papers that George was not a coauthor on. As a Research Professor of Physics at the California Institute of Technology, Sean Carroll's work focuses on fundamental physics and cosmology. So, when I was at Chicago, I would often take on summer students, like from elsewhere or from Chicago, to do little research projects with. It's the simplest thing you possibly could do. I taught both undergraduate and graduate students. So, they weren't looking for the signs for that. In part, it's because they're read by the host who the audience has developed a trusting relationship with. They don't quite seem in direct conflict with experiment. You know, every one [of them] is different, like every child -- they all have their own stories and their own personalities. Well, I do, but not so much in the conventional theoretical physics realm, for a couple reasons. I'll go there and it'll be like a mini faculty member. Some of them are very narrowly focused, and they're fine. There are a lot of biologists who have been fighting in the trenches against creationism for a long time. If I can earn a living doing this, that's what I want to do. Furthermore, anyone who has really done physics with any degree of success, knows that sometimes you're just so into it that you don't want to think about anything else. It used to be the case that there was a close relationship between discoveries in fundamental physics and advances in technology, whether it was mechanics, electromagnetism, or quantum mechanics. In other words, of course, as the population goes up, there's more ideas. That includes me. I think both grandfathers worked for U.S. Steel. It was 100% on my radar, and we can give thanks to the New York Times magazine. And the simplest way to do that is what's called the curvature scalar. I don't know. "The substance of what you're saying is really good, but you're so bad at delivering it. For example, Sean points out that publishing in more than one field only hurts your chance, because most people in charge of hiring resents breadth and want specializers. Let's face it, quantum mechanics, gravitation, cosmology, these are fields that need a lot of help. Some people are just crackpots. What happened was there was a system whereby if you were a Harvard student you could take classes from MIT, get credit for them, no problem. You're not going to get tenure. I clearly made the worst of the three choices in terms of the cosmology group, the relativity group, the particle theory group, because I thought in my navet that I should do the thing that was the most challenging and least natural to me, because then I would learn the most.