Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas - 24 | Kip Thorne on Gravitational Waves, Time Travel, and Interstellar

Episode Date: November 26, 2018

I remember vividly hosting a colloquium speaker, about fifteen years ago, who talked about the LIGO gravitational-wave observatory, which had just started taking data. Comparing where they were to where they needed to get to in terms of sensitivity, the mumblings in the audience after the talk were clear: "They'll never make it." Of course we now know that they did, and the 2016 announcement of the detection of gravitational waves led to a 2017 Nobel Prize for Rainer Weiss, Kip Thorne, and Barry Barish. So it's a great pleasure to have Kip Thorne himself as a guest on the podcast. Kip tells us a bit about he LIGO story, and offers some strong opinions about the Nobel Prize. But he's had a long and colorful career, so we also talk about whether it's possible to travel backward in time through a wormhole, and what his future movie plans are in the wake of the success of Interstellar. Kip Thorne received his Ph.D. in physics from Princeton University, and is now the Richard Feynman Professor of Theoretical Physics (Emeritus) at Caltech. Recognized as one of the world's leading researchers in general relativity, he has done important work on gravitational waves, black holes, wormholes, and relativistic stars. His role in helping found and guide the LIGO experiment was recognized with the Nobel Prize in 2017. He is the author or co-author of numerous books, including a famously weighty textbook, Gravitation. He was executive producer of the 2014 film Interstellar, which was based on an initial concept by him and Lynda Obst. He's been awarded too many prizes to list here, and has also been involved in a number of famous bets. Caltech page Wikipedia page Nobel Prize citation Nobel Lecture Amazon.com author page Internet Movie Database page

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And I'm sure that most of the listeners remember back just February 2016, two and a half years ago, I guess, by now, when scientists announced the first direct detainees. of gravitational waves from elsewhere in the universe. The LIGO Observatory, the laser interferometric gravitational wave observatory, announced that they had seen these signals of black holes, 30 times the mass of the sun, spiraling into each other a billion years ago, giving off gravitational waves, and we had finally detected them. They were actually detected back in September of 2015,

and then announced in February 2016. And enormous excitement because of this. I mean, it's a truly groundbreaking. discovery, even though we've been anticipating it for years and years. It's one of those things which will go down in the textbooks and in the history books as a real cornerstone of how we think about the universe. What is less clear is the enormous amount of not only work, but perseverance that went into this discovery. It's always a lot of work to do an enormous experiment or observation in physics or astronomy. If you discover the Higgs boson, you have to build a large

Hadron Collider, and that takes $10 billion in many, many years. and thousands of people working. The difference being that I don't want to in any way disparaged the people who found the Higgs boson. I did write a book about them and I admire them enormously. But they kind of knew it was there and how to find it, right? I mean, they were following a tradition of high-energy particle physics. They had to invent new technology and so forth, but the basic path had been laid. Whereas with gravitational waves, there were a lot of people who thought that there just weren't any gravitational waves of sufficient magnitude to be found,

or even more people who thought that even if there were, we wouldn't be able to build a detector with a sufficient sensitivity to actually find them. Today's guest is Kip Thorne, who along with Ray Weiss and Ron Drever, was a driving force behind the LIGO Observatory collaboration all the way since the 1970s. And so much effort involved not only intellectually,

you know, as a theorist, Thorne would have to figure out how many sources of gravitational waves there are in the universe, how strong they would be, what they would look like in the detector and so forth, but also, you know, navigating the waters of getting funding and getting support from the community over a course of decades to build this enormous machine. And LIGO in particular had a history where the first version of LIGO wasn't really expected to see anything.

You know, they spent a billion dollars to build something that they didn't expect to see anything in the sky, and they were right. They had to upgrade it to what is called advanced LIGOs. Ligo before they eventually saw something. So it was really a testimony to humankind in some sense, because we really stuck with it. But there's certain particular examples, exemplars of humankind who made it happen, and Kip Thorne is absolutely one of them. Of course, Kip is a very famous scientist for many reasons. He's written books. He's done enormous amounts of research in other areas of gravitational physics. That's his expertise. One of his famous results

was introducing the idea that you can use wormholes as time machines. As long as you first find a wormhole, you might be able to travel backward in time. That was Kip and his students, who originally came up with that idea. And this led to his second career as a movie writer and producer. Kip was also one of the guiding forces behind the movie Interstellar. So over the course of the podcast, we'll talk about LIGO, of course, in gravitational waves, but also quite a bit about time travel and movie making and things. like that. This is a really good one. I think you're going to enjoy it. And before we dive in, let me just

remind you that we have a Patreon page if you want to pledge a little bit of support per episode to Minescape. And because of popular demand, I've added a PayPal page as well. So if you don't like this recurring payment kind of idea, you can just donate in one lump sum whenever you want to. It's all on the podcast web page, preposterousuniverse.com slash podcast. You can find the links on the right hand side. And I greatly appreciate it. Sometimes I say we greatly appreciate it, but really the whole operation is me here in my office. So thanks for keeping the lights on here at Minescape. It's, it's very, very gratifying to see the support. So let's go. When Toyota builds an electric vehicle, we don't start with a blank slate. We start with everything we know. The BZ brings Toyota's

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All welcome. All free. Search Fremont Street Experience for the full lineup and dates. Kip Thorne, welcome to Mindscape Podcast. Wonderful being here. I mean, among your other distinctions, I'm sure that you'll be very proud to know, you are the first Nobel Prize winner to be interviewed for the Mindscape podcast. I'm not sure that that's an honor or not.

You know, Nobel Prize winners who usually has been. No, well, that's not true because I was going to say I came very close to getting Francis Arnold on the podcast. Well, that would be a real coup. There you go, you see? Like all the other Nobel Prize winners are good. So there are a few, yes. Yeah, so you won last year, not this year, 2018, but it was last year, right? 2017, Nobel for gravitational waves.

I'm sure people know the general story, but before we jump into the physics, was it mostly relief that you felt when you finally discover the gravitational waves, or were you excited? I mean, this is a long-term project. Yeah, for me, it had been a half a century. Right. That's kind of long. Very long. Yeah, you started young.

It was good. It consumed essentially all my career, though, as a theorist, I was able to do a lot of other things on the side. But more than half my career was spent on it in terms of time. For me, when I woke up in the morning and I had an email from Christianotte, a good friend and a member of the collaboration saying, hey, go look at this such and such a website. We may have a detection. I went and looked at it. It was obvious. It was too good to be true. It had something had to be wrong. It must have been what we call a blind injection to test the system. Right. You're faking yourself, right? People are intentionally putting in fakes. That's the best way to test the system. is an end-to-end test where a group of about something like three or four members of the collaboration are assigned the test to go in and electronically wiggle the mirrors in this instrument, which is just precisely what the gravity way would do.

And then the wiggling mirrors send signal through the whole system all the way through the electronics to the computer, and then through the human beings and through the human beings to the point of writing a paper. and then after the paper is written, you discover, well, no, that was a blind injection. So we'd been through that, and I figured this is a blind injection, obviously. And, well, it wasn't, but we weren't absolutely sure for several months, really. So even you don't get told, right? Oh, no, not even. I might be the last one to be told.

But, yeah, so, but it gradually became clear that this was probably the real thing. And my reaction was simply one of profound satisfaction that I had indeed put a huge fraction of my energy of my career in the right direction and a direction that really paid off. So there's a kind of excitement you feel when you're told that your experiment has found something amazing. What about the excitement you feel when you hear you won the Nobel Prize? Yeah, well, let me tell you about that. So it was October 3rd of last year. 15 in the morning, telephone call came in from, I think it was the Secretary General of the Swedish Academy of Sciences. I was asleep, sound asleep, woke me up, though I had been expecting it.

Okay. And I mean, by the way, for the audience out there, everyone in the physics world thought that Daigo would win the Nobel Prize. So at the other end, he announced himself, he says, it will not surprise you. that we are awarding the Nobel Prize to Rainer Weiss at MIT, Barry Barish, and you at Caltech. And I responded, it does not surprise me, but I'm exceedingly disappointed. And he was a bit taken aback. Right. That's not usually what he hears. That's not usually what he hears.

But I said to him, this prize should have gone to the LIGO team who pulled this off. Right. And not to just three people. in this case, this could never have been done by the three of us. It really was a team effort. And I thought you had learned your lesson about this in the case of the Nobel Prize for the Higgs boson several years ago, where it should have gone to the team.

Well, it went to three theorists and zero experimenters. That's right. It should have gone to the experimenter team, at least maybe some theorists too. And so he said, well, we've been discussing that, but we don't do it. we don't give it to teams. Right.

And he said, but we can continue this discussion in Stockholm. So in Stockholm, we did continue. And I told him in no uncertain terms, the Nobel Committee has an obligation to educate the public about the importance of collaborations.

There are some kinds of major scientific breakthroughs that are going to only be done by a big collaboration, and that the process of collaboration is absolutely crucial for success. And you're not doing a good job of education. the public about that. And he said, well, yes, he said, I've been sensitive to this. There are a number of members of the committee that do not, don't agree that our principal goal with an OLL prize is to educate the public about the importance of science, the value of science, what has been done, and three individuals are better icons for science than a big team. And so that's how the conversation

went, and they're still struggling with this question. You know, I'll be honest, I get that argument. I don't have strong feelings one way or the other. I think that if your goal of the prize was to do the best possible job honoring good science, then it's clear that the large team should win. But, I mean, obviously winning, it does change the lives of the individual winners, but maybe the best public thing that it does is bring the excitement of science to a wider audience and identifying some real human faces with that is the right way to go.

I really don't know. Yeah, well, that may be the case, but the breakthrough prize, which is only in physics, but is a huge prize in physics. I think there's some biology version too. Yeah, that's right. I guess you're right. Anyway, the breakthrough prize does it in a manner that they, and with LIGO, they gave two-thirds of the prize to the collaboration.

Right. And one-third to three individuals. And I thought that worked well. Yeah, I mean, they give the Peace Prize to organizations. Peace Prize is a mess for other reasons. And I know other prizes, my friend Brian Schmidt, who helped discover the accelerating universe,

sort of insisted for some prizes that rather than it be himself, it should be the team, but the Nobel said, no, we don't work that way. But it might change. Do you think that they're open to changing down the room? Some of them are open to change. And I was told they, do have the power to change. This is not set in stone legally by Alfred Nobel's will.

Yeah, apparently Alfred Nobel's will is very different than what they actually do anyway, right? Do you think overall, I know Richard Feynman had a story or an article called Alfred Nobel's other mistake. Do you think that overall the Nobel is good for science? I think it is. It's it is more effective at reaching the broadly throughout the world to non-scientists and giving them some sense of the importance, the power, and the beauty of science, more effective than anything else that we have. Yeah. And so 50 years ago, what were you thinking? Like, what was it? Well, I guess I want to ask you, what was the opinion about gravitational waves and so forth? But for those out there in podcast land, what is a gravitational wave?

The gravitational wave can be described heuristically as a ripple in the fabric or the shape of space or of space and time that is produced, in our case, by two colliding black holes, travels across the universe bringing information about its source. The word ripple is meant to evoke the idea of a ripple on the surface of a pond if you throw a pebble into the pond. pond, and it's a very quiet pond. You see the waves propagating out. In fact, these waves are quite different, whereas the surface of the pond is disturbed. It goes up and down and up and down in a wave. Here, what happens is space is stretched and then squosen in one direction, perpendicular to the direction of the wave is propagating. And then in the other perpendicular direction is squosen and stretched. That is, it's a stretch on one direction and squeeze on the other. Now, what does it mean for space to be stretched and squeezed?

We could just think of particles or little tiny asteroids out there floating in space as the wave goes by, and they're at rest with respect to each other initially, and they each ride on the stretching and squeezing space. And so they get pushed apart and then together, apart and together. So the distance between them changes. When Toyota builds an electric vehicle, we don't start with a blank slate. We start with everything we know. The BZ brings Toyota's proven engineering to electric. With impressive range, intuitive technology, and Toyota reliability,

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Like his opinion about whether or not these were even a real thing changed over time. It did. There were times when he lost faith in gravitational waves. And very quickly, however, he recovered and realized, well, yeah, they ought to be real. But it was controversial among theorists who worked in relativity theory, at least among some fraction of the community. all the way up into the 1980s. And so really quite surprising. It took so long for the community to totally sort this out.

And what's so difficult about figuring it out? The difficulty is you have a theory that's a mathematical theory. And it's a question of truly understanding the physical consequences of the mathematics. And to me it was obvious. But, you know, I was of the younger generation. And so I was taught in what I would call the right way by my mentor, John Wheeler, to think about it. But to people of an earlier generation who struggled to understand the mathematics, it was not totally clear until after we started planning these gravitational wave detectors.

Wasn't there a famous thought experiment by fine men that was trying to show that gravitational waves were physically real? That's right. And so that's one of the compelling things in which, he said, let's take a stick and we'll put some beads on the stick. And there's a little bit of friction between the beads and the stick. And when the gravitational waves go by, they move the beads back and forth because they can slide. The stick is stiff and it resists being stretched and squeeze. So it doesn't move hardly at all because of its resistance. The beads don't resist. So the beads go back and forth and they rub on the stick. They heat the stick up. And if you have strong enough ways they might even start a fire.

I just love that example for so many reasons. I mean, everyone else is sitting there with equations, trying to figure out what the symmetries are and what's going on and he has this stick and B. But he is relying on a particular equation called the equation of geodesic deviation. It was another

physicist, mathematical physicist, Felix Pirani, who first said, hey, this is the equation we should be using to discuss gravitational waves. And that was so, so Feynman's remark about this was at a conference in Chappell Hill, North Carolina, uh, 1956 or seven, I think it's 57, 57, okay. It might have been 56.

It was anyway, Felix Perani was almost that same time, just within a year or so that same time. So the people hadn't identified really the right way mathematically to discuss waves until then. And it was Feynman, who. as far as I'm aware, who first gave this beautiful description, but it did come from the mathematics. And that's a remark about Feynman, who, of course, was a close friend of mine. Feynman would, at conferences like this, he would come up with some really remarkable statement that would startle people.

And this was not the only one. And if you would then afterwards ask Feynman, where did this come from? Where did you get this sudden insight? He would say, well, I did some long calculations back several years ago, just trying to understand how things work. And once I understood, I was satisfied. I didn't need to write a paper describing this. I just understood and I was satisfied.

Just wait to the right moment at the conference to pull it out. That's a sudden insight. Right. But he was driven by his own personal curiosity. Yeah. And he had an enormous storehouse of information that came from the curiosity-driven questions he had asked to himself over the decades. I know about this. Among other things that this famous conference in Chapel Hill did is it helped

launch the many worlds interpretation of quantum mechanics, which I'm thinking about that, because John Wheeler was Hugh Everett's advisor and Richard Feynman's advisor and your advisor. And John Wheeler, who promoted this, didn't believe it. He didn't believe it. No, that's right. Anyway, that's a separate story. Separate story. That's another podcast. So there was skepticism about gravitation. waves, there was arguably even more skepticism about black holes back in the day.

Indeed. And for the same reason, the issue of really understanding what the mathematics were saying was even harder in the case of black holes than gravitational waves. And so that skepticism also, well, that lasted, I think, up until the early 1970s when it was finally laid to rest. And that's about the time you started thinking about LIGO or gravitational waves more generally? That's about the time I started thinking about experiments. So I was thinking about theory of gravitational waves beginning in the mid-60s when I was John Wheeler's student and just finishing working with him. It was after Joseph Weber in 69 had announced tenity of evidence for gravitational waves that I really began thinking deeply about, fairly deep, as deeply as I could about experiments. Although I had been a champion, enthusiast of Weber earlier, it was really only triggered by that.

And it was 1972 that I wrote with Bill Press, a student of mine at the time, my first paper about a vision for what you can do with gravitational waves if you could detect them. And it was that same year that Reiner Weiss, or Ray, as I call him, at MIT, wrote a marvelous technical paper where he described his invention of the kind of gravitational wave detector we would ultimately build, identified all of the major things that could go wrong, all the major noise sources, as we say, and described ways of dealing with each one and estimated what kind of accuracy you could get after you dealt with them. all tour to force. And that was really the beginning, I think, 72 for him and for me, of the research that led directly to LIGO. And so, very quick footnote, LIGO, for those who don't know at all, if you've not been paying attention, which is probably a tiny fraction of the audience, the laser interferometric

gravitational wave observatory, they found gravitational waves. But also for people who are not physics experts, let's talk a little bit about the difference between being a theorist, such as yourself, and being an experimenter or an instrument builder like Ray Weiss. Well, there's not a very clean distinction between the two, but most physicists work essentially entirely in theory, developing models for the universe or for things that happen in the universe, mathematical models, trying to understand the consequences of experiments that have been done. in the past and the implication implication for things you might do in the future. But working with the mathematics and with physical intuition to try to deduce what's going on in the universe from observation and mathematical laws of nature. An experimenter designs experiments, builds apparatus to perform them in order to investigate the laws of nature and their predictions.

So Ray Weiss, a consummate experimenter, who also understands theory quite deeply, but focused his career on experiment primarily. He was the primary designer and inventor of these gravitational wave detectors, though the basic idea underlying them had been also found independently by other people, even earlier. But he was the person who really built these and made them happen. I was a theorist who set some vision for where we might be going, but I also spent along with my students a lot of time and energy helping identify things that go wrong in these gravity wave detectors and through theoretical calculations with the mathematics and physical understanding, identifying ways to deal with them, but I didn't go in and actually build the apparatus. Right, that's right. Now, you did, that was a long sentence that I think you might have, no, no, it was good, except I think that you might have said most physicists are theorists. And I think that you wanted to say most physicists are theorists or experimenters. Yeah. Most physicists or experimenters, but in my case, and I think this was essential, when I was a PhD student at Princeton, I had made a decision I was going to work in relativity. Relativity was a wonderful field. I thought it was going to take off. It had been more abundant for.

several decades. And I knew it could really only take off if it had some experimental underpinnings. And so I actually spent much of a year working on experiment just sort of to prepare myself so I could interact with the experimenters. It didn't matter what kind of experiment. I happened to work in nuclear physics using a machine called a cyclotron. And then in terms of research groups at Princeton, I had worked within a theory research group led by John Wheeler. but I also participated in the weekly group meetings of an experimental research group that Ray Weiss was a postdoc in. Oh, okay.

It was led by Bob Dickie, a different professor. And so I prepared myself for the possibility, the likelihood, that I would be able to work at the interface between theory and experiment. Dickie's famous gravity group was partly responsible for major research in the microwave background back in the day. Precisely. Yeah. Yes. Yeah. So let's skip ahead and then.

we can come back, but what was the final product of all this thinking? To explain to us LIGO, what it is, how it looks. So LIGO is a set of instruments called gravitational wave detectors or gravitational wave interferometers that are designed to detect these gravitational waves coming from the distant the universe and extract the information they carry. So we could use that information to live. learn about the universe. Right.

Each of these instruments is something that measures the stretching and squeezing of space, monitors the stretching and squeezing of space, monitors the pattern of stretch and squeeze. What we have is we have four mirrors. Each of them weighs about 40 kilograms, 100 pounds. That doesn't sound so bad. I could do this in my backyard, right? That's right.

That's right. Yeah. They need to be near perfect mirrors. Okay. And they hang from overhead supports by quartz fibers. I don't have any of those, but, you know, Amazon probably send some. That's right. That's right.

And you put two mirrors along one arm of an L and the other two along the other arm. So you have two arms that are perpendicular with mirrors at each end of an arm. and when the gravitational wave comes along, it pushes the mirrors on one arm together while it's pushing the ones on the other arm apart. The amount of the push and squeeze is the relevant thing. And for what we finally did detect, it was 1-100th, the diameter of a proton

or the nucleus of a hydrogen atom. That seems very small. That is about roughly a... trillion times smaller than the wavelength of the light that we use to make the measurement. And these mirrors are... How far apart? They are four kilometers apart. Is it underground or just in tubes?

They're in tubes. That you shoot the laser down. They shoot the laser down the tube. And so you use laser beams to monitor this stretching and squeezing using this technique of interferometry. But the key thing is how the hell do you measure motions of mirrors that are four kilometers apart when the motions are about a trillion times smaller than the wavelength of the light that you're using.

How do you do it when that size is a hundred times smaller than a proton? A proton is 100,000 times smaller than an atom. And there's got lots of individual atoms in the face of this mirror. So we're talking about 10 million times smaller than the individual atoms that make up the face of the mirror that are jickling around in the mirror all the time because they're warm by distances, amplitudes of motion that are also huge. So if someone said, you know, can you find the location of this proton to within this accuracy, you would say, no, that's impossible. But you're measuring the changes in location due to the

gravitational weight. But you're measuring the changes in location of huge numbers of them. You're measuring actually the average position of all the atoms in the mirror. Yeah. And that's a big part of why it's hard. You have to design your experiment as Ray showed us how so that you're losing light that bounces off the face of these of the jiggling faces, thermally jiggling faces of these mirrors. But you want the signal that's put onto the light to only be influenced by the motion of the center of a mirror and not by the jiggles of the faces. One of the things you have to worry about is just that any graduate student nearby who sneezes

is going to make the mirror jiggle by much more than the gravitational wave will jiggle it by, right? Yeah, so that graduate student better not be too close. But there must be like baffles and noise can't. Yeah, there's huge, huge numbers of things to deal with. And so that's why this thing, why this whole experiment cost over a billion U.S. tax pair dollars. Right, that's right. a huge amount because there are so many things that go wrong.

One way to describe how many things can go wrong is the number of data channels carrying information out of the instrument and out of the environment, that each of which could tell you something was going wrong is not 100, not 1,000, not 1,000, not 10,000, but 100,000. 100,000 data channels telling you things that, monitoring things that might go wrong. might go wrong. And one data channel carrying gravitational wave information about the pattern of stretch and squeeze. That's about, yeah, that's about right. That's about the challenge you face.

I mean, how much of this was clear in 1972 or how quickly did you come to it? No, it wasn't clear. It was going to be that complex. But one of the best experimenters I ever worked with, aside from Ray and Ron Drever at Caltech, was Vladimir Brighinsky in Moscow. He was absolutely superb, became a close personal friend. And he was, aside from Joseph Weber, the other person, the second person, to really jump into this field and make a mark. He was enthusiastic about this, but said it wasn't for him because there were so many things that go wrong,

that it was very dangerous to pursue this approach. So he pursued a simpler approach. Through the 1970s and 80s, he came to visit Caltech and MIT, where we were working on LIGO in the late 1980s, looked at the progress, looked at the plans, went home and shut down his whole operation, and joined LIGO. He joined our effort. But he was superb, and he was just so very skeptical for about 15 years because of the complexity that these instruments would have to have. And one of the worries was certainly, like, what if the instrument works perfectly well, but there's nothing out there making large enough gravitational waves to see, right?

No, I wasn't worried about that. You're not hooked up to a polygraph right now. No, it was a worry of the community, but it seemed clear to me. Not with 100% confidence, but up in the 95% confidence level at least, that we would have black holes that orbit around each other and merged, and neutron stars that orbited around each other and merged. And those already became our primary source. sources that we were planning to go after that dictated things about the design of these

instruments already by about 1980. And were you surprised at the exact thing that you saw? Was it, what, 2016 when they saw the first event? Yeah, 2015. It was the down to 2016. That's right. It was precisely what I had expected, except the black holes were a little heavier than I expected. 30 times the mass of the sun each. Yeah, and I figured maybe 15. times the mass of the sun each. But again, this is what I had been expecting since about 1980. We knew enough about the universe that that seemed like a pretty good bet then, about the universe and about these instruments. A key part of that knowledge was that heavier objects emit stronger waves. And so black holes, if they were 15 times heavier than the sun, that makes them

10 times heavier than a neutron star. And our primary sources we thought were, in fact, the things we have seen. Neutron stars orbiting around each other, colliding, black holes doing the same thing. With the black holes 10 times heavier, you can see them 10 times farther. That means the volume of the universe you can see them through is 10 cubed, the cubed for the three dimensions of space. Greater, a thousand times greater volume. And it just seemed very likely to me that the number of black holes,

it would be less than neutron stars, but it would be less by a factor of maybe 100, not 1,000. And so that would be the first thing we saw that is what we saw. And that's what I was aiming for is the most likely thing to happen. And these events are quite rare sort of on a galaxy by galaxy basis. That's right. I mean, in our galaxy, how often do two 30 solar mass black holes coalesce? Do you have a guess?

one in a million years. Yeah, okay. Right. But there's a lot of galaxies out there. That's how we win, right? Precisely. What have we learned about the universe so far by these experimental results? Well, we've learned that black holes do collide in merge.

They do form binaries as we expected, similarly neutron stars. But let's not forget. We truly didn't know that for sure. No, you didn't know that for sure. To me, one of the most interesting things we have learned is the fact that when two black holes collide, you're colliding two objects that aren't made from matter. They have no solid surfaces. They have nothing solid in them at all.

They're made only from warped space and warped time. And so when they collide and merge, they create a veritable storm in the shape of space and the rate of flow of time, wildly oscillating rate of flow of time, wildly oscillating shape of space like the surface of the ocean and a huge storm out at sea.

And we didn't know anything about storms in the fabric of space and time, even theoretically, until maybe three or four years ago. And just a little bit before we discovered gravitational waves from these things, the supercomputer simulations, solving Einstein's equations on supercomputers, began to tell us about these storms.

We have now seen the waves from these storms. we have now seen the ways from these storms, the agreement between the predictions of the simulations and the observations is absolutely remarkable. And so for the first time now, we have both a theoretical understanding and an observational verification of storms in the fabric of space and time.

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Toyota, let's go places. And I think that there's an aspect of this story that maybe isn't as popularly appreciated as it could be. We have general relativity, Einstein's theory of space and time. He gives us what we call an equation, Einstein's equation, but in some sense it's really multiple equations talking to each other, and it's very complicated to solve. And you can't get complicated, interesting solutions on pencil and paper. You need a computer.

And just a number of years ago, the idea of getting accurate, real-world, useful, numerical calculations from Einstein's equation seemed very, very difficult and maybe not feasible, right? Precisely. the effort to create the technology and the techniques for these simulations for solving Einstein's equations on computers lasted just as long as our experimental effort lasted half a century. And in the early 2000s, well, in the 1990s, I was following that effort with great interest

because I was expecting that the first things we would see would be colliding, black holes and we wouldn't be able to say for sure what we were seeing unless we had predictions and predictions required these simulations. We would need the predictions to compare with the observations in order to deduce the details of what the black holes were doing, the details of these storms. And the progress was painfully slow. I was chairing a advisory committee to the collaboration of all the leading groups in the world that were trying to do these simulations. And as the chair of their advisory committee, I was aghast, the slowness of their progress. I mean, it was very hard.

It wasn't they were dumb. They were the best people in the world, but it was very, very hard. And so, in fact, I personally left the LIGO project in terms of day-to-day involvement in the early 2000s. In order to start an effort at Caltech in doing these simulations in collaboration with what I viewed as the strongest group in the world, a group of Saul Ticolski at Cornell, in the early 2000s. It's not that I wrote code,

computer code, anymore than I built the apparatus for LIGO, but at least I had some sense of where we needed to be going and what questions needed to be asked and what accuracy's needed to be achieved and so forth in these simulations. And so that's where I was putting my effort when the gravitational waves were discovered.

I was not a major participant in the end game experimentally. But we did make amazing we, the Royal Wii made quite impressive progress over the last 10 years. That's right. Huge progress on the simulations and huge progress experimentally. And the two came together on just the time scale it was required. And it was the marriage of the simulations with the observations that really led to our being able to understand in depth what was being seen. So where does a 30 solar mass black hole come from, much less a pair of two 30 solar mass black holes right next to each other, ready to coalesce. Now, you tell me.

These were not expected. They were not expected. Of course, in many, maybe in most cases, when something unexpected is seen, theorists can come up with explanations. Right. We have options. We have options. That's right. Kind of up with options. And so my personal, the option that I think is most likely to turn out to be true

is that you begin with smaller black holes that form inside what we call globular clusters or big clusters of stars. And they sink to the bottom of the cluster through gravitational interactions with the smaller stars, with the less massive stars. they sink to the bottom, they find each other, they collide and merge, and that merged hole merges with another merged hole. And you build up fairly quickly to 30 solar mass black holes. And these are very different than the supermassive black holes we have at the centers of galaxies.

They are very different. So we're dealing with 30 solar mass black holes. They ones at the center of our own galaxy is what, about four million times the mass of the sun. one at the center of the Andromeda galaxy and the nearest big galaxy to our own is more like a hundred million times the mass of the sun. So they are completely different kinds of beasts. There are any hope for someday seeing those

in gravitational waves? Yes, I'm sure we will see them. Will LIGO see them? No. Ligo hasn't done us ever prayer. So the bigger the black holes when they emerge, the slower the oscillations of the waves as they pass, which means the longer, the wavelength of the waves. And on the earth, when you get down to those oscillations that are this slow,

now we're talking about 10 minutes, an hour, 10 hours. Noise on the earth is horrendous. Yeah, a lot of things happen at an hour time scale. It's hopeless on earth. You have to get away from the earth and far away from the earth. And the noise on the earth that comes from, weather, humans,

and so forth. And so that has to be done out in interplanetary space. And also you would like to have your mirrors or the equivalent of your mirrors roughly 10 light minutes apart, right? That's right. And how big is the Earth in light seconds?

Well, it's about a tenth of a light second. Okay, there you go. A few tenths. About a tenth. A 10th or a few hundreds of a light second. And so we had this plan. When I was a kid, there was this plan called Lisa to put satellites in space that would bounce lasers off of each other.

And people then decided it was too expensive. But then you and your friends discovered gravitational waves and there's an effort to bring it back. Do you have any idea how that's going? Well, I think the history is a little different from that. Oh, okay. I think the problem is that NASA had a big cost overrun on the James Webb Space Telescope. and NASA pulled out of a signed agreement with the European Space Agency to do this mission. Yeah, okay.

It was not the first time that NASA pulled out of agreements with the East. Europeans are getting accustomed to this. The U.S. is not a great partner for some of these big long-term missions. It's a result of the nature of our political system. It's not something that NASA can control. It's a result of the way the congressional election system and the way things swing with new administrations, unfortunately, for science. But anyway, so NASA pulled out, and then it was too expensive for the Europeans alone to do right.

So they scaled emission down. They made it less robust in a way that was really quite dangerous, but in order to be able to do it. Now, as you say, now the gravitational waves have been seen by LIGO, but fast gravitational waves rapidly oscillating, not the slow ones that Lisa would see. Now that that's been seen, and the Europeans have flown test apparatus that verifies that the most serious sources of noise that had been identified are under control. We expect Lisa to be on a fast track,

very likely with NASA rejoining as a junior partner, not an equal partner. Well, that's what they get. Yeah, that's what happens. And in parallel, the Chinese are pushing very hard to do this, to do a simpler analog to Lisa faster. So they're the first ones to see these gravitational waves in space. That can often be very, very useful, right?

That's a quick, dirty thing just to see the scope of the land and then go back and do it right. And this is, you know, one of the things, again, we take for granted, but it's worth emphasizing is here's Albert Einstein a hundred years ago, almost a little bit over 100 years ago, you know, from very, you know, thought-experimenty kind of inputs, right? Like, there was no data that said, oh, you have to throw out Newtonian gravity, roughly speaking. And, but he had principles. He knew about special relativity. He knew about other things that he wanted to be true, the principal equivalence.

And he came up with general relativity, which both you and I have written textbooks about, by the way, or competitors in that way. Well, hardly competitors. My textbook was written decades before your textbook. So you sold a lot more copies than I had, yes. Yeah, we don't sell today nearly what you sell, I think. They're making younger ones, I'm sure. And he was right.

And in some sense, not only was he right about the predictions for the experiments, which it took us, like you say, years to figure out, but the feature, the fact that space time is curved and that curvature is gravity, we're still learning about what that really means at a deep level. Is that fair to say? Yes, I think that's very fair to say. What do you think is the future of what do we need to learn? about space time and general relativity, even though we have the equation written down?

Well, that's far. The key thing, the recent thing, and the thing that excites me for the next five years, maybe a little longer, is understanding these storms in the shape of space and time. So, for example, we've come to understand first through computer simulations and then understanding it in the equations directly, that sticking out of each spinning black hole is a twisting, vortex of space. Okay. It's very much like the twist of a tornado. So two tornadoes sticking out of a black hole.

One of them, at the north pole of the black hole, it has a counterclockwise twist of space. South pole, a clockwise twist of space. And these vortices, when you have two black holes collide and merge, you wind up then with four vortices sticking out of a pair of, out of the merged black hole. hole plus two more of vortices that are created by the orbital angular momentum. So you can have as many as six vortices sticking out. Black holes don't like to have any more than two vortices. And so these vortices have to fight with each other in some manner and do a shape down to two vortices.

So there's a very interesting behavior of empty space. Yeah, yeah. I mean, we had no idea about this until we saw some of this in simulations and then started thinking about it theoretically. So these black holes are spinning. very rapidly. We say those words, but really just like you said, it's empty space. It's as if it were spinning very rapidly, right? So if I fall into one of these black holes, can I travel across the universe? Probably not. Almost certainly not. Well, how would I then travel across the universe if I

wanted to do that? I think this is a leading question because I know a famous colleague of yours back in the day asked a similar question. Yeah, well, it was a guy, a close friend, Carl Sagan had written a novel called Contact. Well, he'd originally written a screenplay, and then he turned it into a novel when the screenplay wasn't getting made into a movie very fast. Why would anyone make a movie like that?

Anyway, so he wanted his heroine who became Jody Foster to travel through a black hole to the vicinity of the Star Vega. And so he sent me the page proofs of his book. He was already at a point, nearly ready to publish. He waited a long time, yeah, I know.

And said, you know, I might realize I might be in trouble. Can you help me? And I read them driving up to see, I think it was driving up to see my daughter graduate from Santa Cruz. You see Santa Cruz. Okay. Read them in the car and fired off a response and said, well, you can't do it with black holes. She's going to die.

inside. That's a short movie, yes. And so you want to use a wormhole, a hypothetical object that is somewhat similar to a black hole in the sense that it has a spherical mouth that is sort of like the horizon of a black hole, except you can travel two ways through this mouth. You can travel in and back out,

and you go through it, and it leads to another place in the universe. And just so we're not getting in trouble with the physics police here, black holes really exist. Wormholes not only are hypothetical, but what are the chances that wormholes exist in the real world? I think the chances that they exist naturally are exceedingly small.

The chances that they can be made by an artificial, very advanced civilization are bigger but still small. And if they get made by advanced civilization, they probably implode before you can travel through them. the chances that the civilization can stabilize them so you can travel through, again, are small, but not zero. And so the issue is that motivated by Carl Sagan's question and by my suggesting that he used wormholes in what became the movie contact, I and other of my physicist colleagues started working hard to try to understand, do the laws of physics allow them. And it was obvious already from the beginning that they would, unless you did something very strange with them, they would self-destruct. They would implode. And sorting, trying to sort that out. And to my surprise, we couldn't get it sorted out fully. But the work that has been done points rather strongly to a conclusion that probably they can't

exist. And if they can't exist, they very probably can't exist naturally. Yeah. So this was circa late 80s, early 90s. So the work on this continues to do today, but a small level. The bulk of the research on this was done late 80s, early to mid 90s, but it still continues because the answer isn't in. Right. We still don't know. So Carl Sagan wants to let L.E. Arrow A travel across the galaxy. You say it should be a wormhole, not a black hole. And then you realize, you know, wormholes were again coined by John Wheeler. Is that true? The phrase? So the phrase was coined by John Wheeler. The concept actually goes back to Herman Vile about 1922. I did not know. I would have given Einstein credit, but yeah. So it was conceived perhaps independently by Einstein and his

colleague Rose and Einstein and Rosen in 36. But you go back. you find it in Herman Vile in around in 1920 but it was John Wheeler who really pushed hard to understand these initially because he had intuition which may have been right that

on very small scales what we call the plank length the scale where space and time as we know them must become probabilistic they fluctuate like anything in the universe fluctuates due to quantum physics On those very small scales, John Wheeler argued that you would likely find a froth of fluctuating wormholes. Right.

And so that was his central focus. There's this rough problem. Maybe this is getting a little bit too technical, but I can't resist. So Einstein gives us this equation for general relativity, Einstein's equation. And we might want to say, well, why can you just solve the equation? And part of the problem is there's a left-hand side, which says space time is curved. And there's a right-hand side which says there's stuff in the universe, matter and energy and so forth, causing space time to curve. And the left-hand side with the curvature is very pretty and understandable, and the right-hand side with stuff is kind of a mess.

Is that about why we don't understand wormholes very well? Well, that's maybe a piece of it. That's a piece of it because although wormholes are things that are made from warped space time without matter. If you have them made from warped space time without matter, then they self-destruct. Right. So you have to put some kind of matter in them to hold them open. And that's where it becomes tough. It's where the rest of physics becomes.

And that's all a messy, terrible thing. But the other issue, and this was the issue for Wheeler, is that when you get down to these very tiny length scales, associated with quantum effects, that there you don't even know the correct laws of physics at all well. And so then you have to start speculating. and that's where he gave, I think, some pretty plausible arguments that you would have this quantum foam of fluctuating wormholes.

But there the problem is you don't understand the laws of physics. For a big wormhole, you don't understand the matter well enough to be sure whether you can hold the wormhole open with it. When Toyota builds an electric vehicle, we don't start with a blank slate. We start with everything we know. The BZ brings Toyota's proven engineering to electric, With impressive range, intuitive technology, and Toyota reliability, BZ reflects decades of experience, reimagined for what's next. The BZ isn't just electric, it's Toyota Electric.

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but if you have a big wormhole and you can use it to travel across the galaxy very quickly don't you worry because special relativity says i can't go faster than the speed of light it's like going backward in time Oh, come on. I'm leading you down somewhere. Sure you can go faster to the speed of life. We all know. But not locally. Right. So let's be more precise.

So the universe is expanding, as we know. You're a cosmologist. You understand this far better than I do, Sean. And the most distant part of the universe is moving away from us faster than the speed of light. So we can't see it because light can't get to us from it, but it's doing it. And so what the speed limit really says is that if you have two objects that are close enough to each other, that there's no significant warping of space and time between them, then they can't move fast in the speed of light with respect to each other.

But when you've got a wormhole, you've got lots of warping with space and time, and all bets are off. Right. So you can just, and ever since, I don't know if contact was the first movie to use wormholes to get people across the, And now every movie does it. So, yeah, Star Trek is fun and everybody else. But then, I don't know whether it was you or your collaborators, but you began to realize that if you can travel across great distances of space,

maybe you can also go backward in time. Yeah. So that was me in this case. I mean, other people had working in relativity had seen other ways that you might be able to go backward in time. This was just one more way. Right. but one that became particularly popular, maybe because of contact. To be more fair, I would say that it was, you know, you could imagine building it.

Like a lot of the other ways to build time machines started by saying, imagine you have an infinitely long cylinder, right? And at least the wormhole that's contained in some region. And once you have a wormhole. Once you have a wormhole. Oh, yeah. So with a couple of. my students, Mark Morris and Ulvey-Eertsever, I worked out if you had a wormaha, how you would use it to

make a time machine. It's fairly simple. You just take one mouth and I put my wife in one mouth. She carries that mouth out through the universe in her spaceship and comes back at high speed. and time for her slows down, as seen in the external universe. I said on earth it doesn't slow down, but as seen through the wormhole, our clocks run at the same rate. So you begin, the clocks always run at the same rate, hers and mine, as seen through the wormhole. When she comes back, she's very young and I'm very old, seen through the exterior, seen through the interior of the wormhole, we're the same age. And so there's something crazy going on.

the craziness is that you created a time machine. Right. So that was fairly simple and fairly obvious, but I think, yes, you're right. This was something that if you had a wormhole, you could actually make it. And so then the question became, what did the laws of physics say about this? Could you really do it? And there comes in the key thing that things, if you're an engineer in a very advanced civilization, and you can do anything that is allowed by the laws of physics, you've got to,

to look at more than the laws of relativity. The laws of relativity say, yeah, sure, you can make a time machine. Yeah. But you've also got to look at the laws of quantum physics and the behavior of matter. There's always going to be some matter present because of quantum physics. There's always at least a little bit of fluctuating matter present. And so you then ask, okay, now you've got a wormhole. You turned into a time machine.

Relativity allowed it. What did quantum physics do? What did it say? And the answer is that quantum physics says with high probability that the wormhole is going to self-destruct the moment you turn it into a time machine. It seems like from various different perspectives, the universe is kind of reluctant to let you build a time machine. It does seem that way, isn't it?

Do you, would it bother you if we could build a time machine? I mean, there are logical paradoxes involved, right? I think you're wonderful. And anything that says that the laws of nature are different than you expect is wonderful. You're going to learn wonderful things. Is that how you knew in the early 70s to think about gravitational ways? Because you visited yourself in the past, gave you a hint. Well, but.

Yeah, no, yeah. So, yes, so then you immediately do worry about paradoxes. And so that's what I did with, again, with students and colleagues. And so we asked. we asked ourselves, okay, suppose you do have a wormhole, you did turn it into a time machine successfully, it didn't self-destruct in the process, then how do you deal with these paradoxes? How does nature deal with these paradoxes? And so what we did was we, well, a dear colleague of mine in yours, Joe Polchinsky, who just passed away sadly fairly recently, a really great theoretical

physicist. He had been a student of mine years ago, decades ago. And Joe sent me an email. I think it was an email. It was a letter in those days. This is about 19-19. The dawn of the email day. And he said, well, here's a little thought experiment. You send a billiard ball into a one wormhole mouth and it comes back out of the other mouth before it went in and it hits itself and prevents itself from going in. How do you solve that paradox? So we call this

Bolchinsky's paradox. And so together with some students I worked out how what does nature say about Blanchinsky's paradox? We found that there are multiple ways that nature can get out of it. Okay.

The beater ball goes in it gets hit a very gentle blow by itself on its way in. So it goes in, it comes out on a slightly different trajectory than it was supposed to and hits itself a very gentle blow. So everything's all right. But there are a number of different ways that can do these gentle blows. And so you wind up with more than one solution to the laws of physics instead of just one solution, where you thought there were none. You thought there's no way, no answer to what happens to the bitterer ball when it goes in

because you've got a paradox. First night you say the bigelry ball goes in, it comes back out, it hits itself, and prevents it from itself going in. That's the trajectory. And then you find a trajectory where it's modified itself, and then you find another one, and then another one. And in the laws of classical physics, there had not ought to be multiple solutions when you pose initial. conditions, there should not be multiple answers. And so then you go to quantum physics. And you ask what does quantum physics say. And so it becomes a very interesting game intellectually, trying to figure out how does nature get out of this? And it's much easier to deal with this with billiard balls than with

human beings who go back in time and try to kill their grandparents. That's the more common thing. But Joe is a good physicist honed in on the simple physics problem. So it's interesting because on basic features of sort of logical consistency, we would not want to have a true paradox. We're two incompatible things happened. And you're saying that it seems, at least at the classical level, what nature gives up on is not logical consistency, but predictability.

There's more than one possible way out. But then we pay attention to the fact that the world is really fundamentally quantum at the bottom. And so where you have these multiple solutions classically, you go in and analyze them quantum mechanically. And what is you and I would call a WKB approximation. This is getting jar. We'll flip note that.

Okay. There's a good approximation scheme we can use. And so you see that the quantum physics probably has a solution to get around this, and there's probably one unique solution. So my bottom line with this, and my problem is that I was just deep into this and felt like I was making some progress in understanding how you would deal with paradoxes when LIGO got funded. And I said, do I spend the rest of my career now working hard on making gravitational ways of success,

or do I think about time travel with paradoxes? I love time travel, but you made the right choice. But when you mentioned quantum mechanics there, just because I know probably some people know a little bit about the idea of branching the universe off because you have a time machine and creating a new timeline, and that's not what you're talking about. No, it's not at all what you're talking about.

You're just using quantum mechanics to find the one consistent, most probable trajectory of what actually happens. So what you really want to do is ask how do you formulate quantum mechanics in the presence of a time machine. Right. And in fact, there is a way to do it. And it's using a formulation of quantum mechanics due to our dear friend Richard Feynman. Yeah.

But a generalization of Feynman's ideas due to his colleague, Murray Gallamont. and Jim Hardle. And so the tools are there. Very Caltechy field. Very Caltechy field. That's right. Well, with Hardle, it's Caltech in Santa Barbara. But the tools are there to do this.

But wasn't Jim a grad student at Caltech? Back in the day. He was Murray Galamon's grad student. Yeah, all right. And John Wheeler's undergraduate and postdoc. But anyway, so you can formulate quantum mechanics in a way that handles all this. in the presence of what we call a closed time machine. But for me, the beautiful thing about this is that once you've done that,

you discover that information gets lost. Right. Physicists don't like this. And physicists don't like that. Some physicists don't like this. But I think it's quite wonderful that anyway. And so then you get caught up in the so-called information loss paradox. And a view of this that I have that's iconoclass.

that differs from that of the majority of physicists. But it's a good little lesson about how you're fooling around in some sense, right? Like you weren't trying to build a time machine. You were inspired by a question from Carl Sagan, but it leads you to some maybe interesting insights into questions people really care about. Precisely. And so I came to appreciate that in areas where you're dealing with physics, beyond where we can actually do experiments today,

someday we will, but not today. Thought experiments like these, simple thought, experiments, like what happens to billiard balls if they collide through a wormhole that has a time machine built into it. A simple thought experiments can sometimes take pretty deeply into the laws of nature. And nevertheless, I remember a footnote or the acknowledgments one of your papers saying that the National Science Foundation wouldn't let pay you to work on this anymore. That was a half tongue-in-cheek remark, only half. So the story is that I was working on this in parallel with gearing up to Bill Ligo.

And we had our major funding for LIGO, in the end, $1.1 billion for LIGO, coming from the National Science Foundation. And I had a conversation about this research with Richard Isaacson, a superb director, a program director for our field at NSF, a person who I regard, Ray Weiss and Bear Barry Barrage and I regard as really our collaborator in Washington who really made this happen. Anyway, so Isaacson said to me, you don't want to screw things up for LIGO if some congressman comes in and starts hacking at you for working on time machines. And maybe you can find funding elsewhere for that work just to keep yourself safe from being attacked. by some.

It sounds like good advice. It was very good advice. But I also tweet back at Richard, Isaacson, and put in these acknowledgments. This work was not supported by the National Science Foundation. Instead, it was supported by the Richard Chase Feynman Research Fund at Caltech. Tolman, Tolman. It was the Tolman Funds.

That's right. Well, no, wait a minute. It's a question of point. It was. Okay. I know these were, these were, this was in the 90s. So I became the Feynman professor, 91.

Yeah, I don't know. I think it was Feynman funds, actually. Okay, that could be. I think it was Feynman funds, you know. So, but there's another spinoff of this fortuitous conversation you had with Carl Sagan was that you got interested in the phenomenon of Hollywood making science fiction movies, right? Yeah. And is it exactly right, or maybe you can correct me, like, you were not perfectly happy

with how the movie version of Contact turned out? Yeah, so that's right. So George Miller was the original director of Contact, and he was working very hard to perfect the last, the tail end of the movie involving Wormholes and the ultimate denouement at the end of the movie. Right. And he got canned.

by the studio for taking too long. Hollywood, yep. Yep. And so they brought in Zemeckis with an order. You finish things off. You don't dittle any longer with the screenplay. You finish things off and we want to get into production. And so he did.

And basically all the efforts that were being put into really perfecting the last part of the movie and went down the tubes. And so I was disappointed in that. So did that inspire you to say someday I'll do it right? No. No, no, I never had any intention, any intention to do that. But, yeah, it was always in the back of my mind. But I got into this simply because Linda Ops, who had been Carl's partner in Hollywood on contact,

a movie producer, a great movie producer. She called me up one day in 2004 and said, would you like to brainstorm with me for a science fiction movie? Okay. And that's what led to interstellar. That's what led to interstellar. But I had no plan to do that. So we just, I mean, we have Hollywood people on the podcast,

so we don't need to rehearse the entire process. But how do you go from brainstorming to seeing your name up there as an executive producer? Oh, that happens by having a very good attorney. Important lesson for the young Hollywood strivers out there. Yes, absolutely. So Linda said to me, once we had brainstormed, and she had brought on a studio which bought an option to make the movie

from the treatment that she and I had created through brainstorming. The treatment is just a description of a story. And in our case, of science embedded in the story. So she brought in a studio, and she said, you have to negotiate with a studio. You can't do it yourself. You have to have an attorney. Okay. So with the help of a Caltech president

who went to a member of the board of trustees who was well connected in Hollywood, I got a great attorney, Ken Ziprin. Good to know people in high places. And Ken negotiated and got me an executive producer credit off the bat based on the brainstorming that we had done initially and on the expectation that I would stick with the project all the way through and would be the lead science advisor and make and realize. the vision that Linda and I had formulated of a film with science embedded deeply into it from the outset.

And what happened? What was the first step? Was it getting the director or the screenwriter? So Linda brought on, well, the story is that Linda brought on Stephen Spielberg to direct it. And the two of them were both with Paramount at the time. And so then they brought on Paramount. Stephen then was the director through the early creative phase on making the movie. The early creative phase lasted for a few years. They brought on Jonathan Nolan or Jonah, as he's known to his friends, to write the screenplay. Jonah had written a couple of screenplays previously with his brother, Christopher Nolan, but that was the extent of his experience in Hollywood.

Since then, his created a person of interest. Yeah, West World. And West World. He's doing okay. He's doing okay. The West World with his wife, Lisa Joy. Right. And so, but he, he was really pretty green and young at the time, but superb and wonderful to work with.

So he went through three drafts of the screenplay. And then Stephen always carries more movies in the creative phase than he can possibly make. And he came, the crunch time came. And he was going to make Lincoln. Okay. Or he was going to make Interstellar. And I don't know, he may have had other choices as well, but he did make the choice to make Lincoln.

He certainly had like over a dozen movies in development any one time. That's right. So that was his choice. And Christopher Nolan, being Jonathan's brother, had said to Linda before Stephen dropped out, he had said, if Stephen drops out, I would be interested in considering making this movie. Pretty good backup possibility.

You'd have that in your knowledge. And so when Stephen dropped out, then Linda and Paramount started to try to negotiate with Chris. Chris said, no, I won't negotiate until after my next movie comes out and has been out for maybe six months. So then I'll negotiate. Because he's the opposite, right? He's the opposite. He does one thing at a time. He does one thing at a time.

And he doesn't even make a decision about the next thing. he's going to do until the previous movie has been out for a few months. He sees how it's been done. He's gone through all of the publicity on it and so forth. And then he starts thinking seriously about what he'll do next. And so we waited for two and a half years while he did Batman, the Dark Night Rises. Right. And then a few months after that came out, he negotiated seriously with Paramount. He, by then, Linda had had a divorce with Paramount,

as had Stephen. And Chris was not about ready to work with Paramount. Okay. And so Chris said, I only work with Warner Brothers. And so. And none of your physics education had prepared you for any of this.

Well, but fortunately, I had a great attorney. Had a great partner in Linda. Right. Linda was superb. She knows. knows their ropes and Ken knows their ropes.

So I just sat back and waited and got briefed by phone and email from time to time. And so anyway, it was obvious that Chris was the person who should make this movie obvious to everybody. And so Paramount negotiated with Warner Brothers, that Warner Brothers would have the rights, all the foreign rights of this movie. Paramount would have the domestic U.S. rights and they would do it jointly, but the production would be in the hands of of Warner Brothers because that's where Chris works. Okay. And as you say, this is not part of my training.

So I watched this all. A wonderful education, right? Yeah, real education. And speaking of education, you figured out you had some good science projects come out of the attempts to get the science right in the movie. Yeah. Yeah.

So I very much enjoyed working. Well, I enjoyed brainstorming with the Nolan brothers. I enjoyed my interactions with the actors, and particularly with the computer graphics team, Double Negative, Limited in London, led by Paul Franklin, who was one of the founders and leaders of double negative. And together then, at Christopher Nolan's request,

enthusiastic request, which I was expecting, He wanted everything that involved visualizations of black holes and wormholes and astrophysical objects to be done as accurately as possible through computer simulations. And solving the equation for propagation of light from the source of the light through the environment to an IMAX camera, through the optics of the IMAX camera, with all of the vagaries of the optics of the IMAX camera, to the film at the end. And so that was how it was done, and I provided the equations for the propagation of the light

to Oliver James, who was the chief scientist at Double Negative, and he programmed the equations, and the artist there created the images, the sources of the light, and it all came together quite beautifully. And I remember, if I remember correctly, you saying that not all the science

in the movie might be plausible, but it's absolutely compatible with what we currently know about the laws of physics. Not everything, almost everything. Almost everything. Well, that's better than that. The agreement between Christopher and all and me from the outset was,

I told him I wanted everything to be compatible to the laws of nature, and he said, I'm enthusiastic to do that, as long as it doesn't get in the way of making a great movie. Which is fair. It was fair. That's perfectly fair.

Absolutely. And he was afraid, however, I would play the role of science police. And I was afraid he wouldn't respect the science. And within a few hours of brainstorming together, it became obvious that we were on the same wavelength that we could work together as beautifully as I had worked with his brother on the screenplay,

and it became a marvelous collaboration. There did come one point when we had these wonderful images of the wormhole and of the spacecraft traveling around and through around the wormhole. And then they had to make the computer graphics for the trip through the wormhole. And I got a telephone call from Christopher Nolan and said, Kip, would you come over to my house?

We got a problem. Okay. I went over and he said, we've tried various sizes and shapes of wormholes. This is what the trip through the wormhole looks like with this shape and size of the wormhole. That's what it looks like with another one. None of them are very exciting. They're all pretty dull. Because they would be, actually, right?

They would be. And so he says, so what do we do? I said, you use creative license. And that's the one place where there was a substantial departure from what things would really be like. Everywhere else, there were a number of other places with little departures. If you want to know all of the places that I was aware of at the time the movie came out, there were a few I missed, where there were... little glitches with regard to laws of physics.

You go to my book, The Science of Interstellar. First you buy the book, the Science of Interstellar. And for Christmas presents, too, yeah. Anyway, you go to the subject index, but you look up a person in the subject index. You look up Christopher Nolan, and then under Christopher Nolan in the subject index, you see all of the compromises that he made

with a science in order to make a great movie. So your conscience is gleeiness. You know, you list. It's also, with most books that I've written over my career, there are little gems like this hidden in them. That's a good thing to do. And you may find them if you're clever in an index, or you may be told. The authors have to keep themselves entertained as well as everybody else. So do you have another movie in the pod?

So Stephen Hawking and Linda Opson and I wrote the treatment for a follow-on movie several years ago before Steve. even passed away. And we're very enthusiastic about the movie. Again, a science fiction movie. Again, with science, real science, built into it. We, whereas, well, so with this movie, then, we went through the same process. Linda identified a studio. We sold an option.

Well, she and my lawyer, my liar, Ken Zephran, and his team sold an option to make the movie from our treatment to a studio. The studio hired the screenwriter that we wanted. They now have an offer out to the director we want. And it may go forward. But I'm not allowed to say anything more than that's probably more than I'm allowed to say. Not even asking. Probably that much is on IMDB already, right?

So much goes out now. So you've enjoyed the process? I've enjoyed the process. Very much, very much. And I should say with Interstellar, the Nolan brothers changed the story so much. It wasn't Linda's in my story at all. The way things work in Hollywood, if you've written the story for a movie, then you go and you ask the Screenwriters Guild that you want a credit for story by.

We didn't even ask for a credit for story by because they had changed the story in very positive ways. We were enthusiastic about the change. they had made. So this wound up as the Nolan's movie, but with a science that came from Linda and me and then additional science from the brainstorming with the Nolan brothers. In this second movie, so far it's followed pretty closely the story that we began with in the dream. So maybe Stephen and I and Linda will get credit for story by. I will see. Well, Kepler, I think that one thing everyone who's listened to the podcast will be able to say is you've been very successful. You've had a great life.

I've had great fun. I've had a great fun. Yeah, and I love the variety of it. We didn't even get into the various books that you've written, but, you know, great science, a little bit of fun living here in L.A. It's been a great conversation. Thanks so much for being on the podcast. Thank you.