Dennis Whyte: Nuclear Fusion and the Future of Energy | Lex Fridman Podcast #353

Dennis Whyte 0:00 Why weren't we pushing towards economic fusion, and new materials, and new methods of heat extraction, and so forth? Because everybody knew fusion was 40 years away. And now it's four years away.

Lex Fridman 0:13 The following is a conversation with Dennis White, nuclear physicist at MIT and the director of the MIT Plasma Science and Fusion Center. This is the Lex Fridman podcast. To support it, please check out our sponsors in the description. And now, dear friends, here's Dennis White.

Lex Fridman 0:32 Let's start with the big question, what is nuclear fusion?

Dennis Whyte 0:35 It's the underlying process that powers the universe. So, as the name implies, it fuses together or brings together two different elements, technically nuclei, that come together. And if you can push them together close enough that you can trigger essentially a, a reaction, what happens is that the, the element typically changes. So, this means that you change from one element to another, chemical element to another. Underlying what this means is that you change the nuclear structure. This rearrangement, through E equals MC squared, releases large amounts of energy. So, fusion is the fusing together of lighter elements into heavier elements. And when you go through it, you say, "Oh, look. So, here are the initial elements, typically hydrogen, and they had a particular mass, rest mass." Which means just the mass with a, with no kinetic energy. And when you look at the product afterwards, it has less rest mass. And so you go, "Well, how is that possible? Because you have to keep mass." But mass and energy are the same thing, which, which is what E equals MC squared means. And the, the conversion of this comes into kinetic energy, namely energy that you can use in some way. Um, and that's what happens in the center of stars. So, fusion is literally the reason life is, is viable in the universe.

Lex Fridman 1:57 So, fusion is happening in our sun. And what are the elements?

Dennis Whyte 2:01 The elements are hydrogen that are coming together. Um, it goes through a process, which is probably gets a little bit too detailed. But there's, it's, it's, it's a somewhat complex catalyzed process that happens in the center of stars. Um, but in the end, stars are big balls of hydrogen, which is the lightest, it's the simplest element, the lightest element, the most abundant element. Most of the universe is hydrogen. Um, and it's essentially a sequence through which these processes occur that you end up with helium. So, those are the primary things. And the reason for this is because helium has, uh, features as a nucleus, like the interior part of, of the atom, that is extremely stable. And the reason for this is helium has two protons and two neutrons. These are the things that make up nuclei that make up all of us, along with electrons. And because it has two pairs, it's extremely stable. And for this reason, it, when you convert the hydrogen into helium, it just wants to stay helium, and it wants to release, uh, kinetic energy. So, stars are basically conversion engines of hydrogen into helium. And, uh, I mean, this also tells you why you love fusion. I mean, 'cause our, our sun will last, you know, 10 billion years appro- approximately. Uh, that, that's how long the fuel will last.

Lex Fridman 3:23 But to do that kind of conversion, you have to have extremely high temperatures.

Dennis Whyte 3:26 It is one of the criteria for doing this, but it's the easiest one to understand. And why is this? It's because effectively what this requires is that these hydrogen, uh, ions or, which is really the bare nucleus, so they have a positive charge. Everything has a positive charge of those ones. Is that to get them to, to trigger this reaction, they must approach within distances which are like the size of the nucleus itself, because the nature... In fact, what it's really using is something called the strong nuclear force. There's four fundamental forces in the universe. This is the, the strongest one, but it has a strange property is that it, while it's the strongest force by far, it only has impact over distances which are the size of a nucleus. So, to get, let's put that into, what does that mean? It's a millionth of a billionth of a meter, okay? Incredibly small distances. But because the distances are small and the particles have charge, they want to push strongly apart. Namely, they have repulsion that wants to push them apart. So, it turns, when, when you go through the math of this, the average velocity or energy of the particles must be very high to have any significant probability of the reactions happening. And so the center of our sun is at about 20 million degrees Celsius. Um, and on Earth, this means, it's one of the first things we teach, you know, entering graduate students, you can do a quick, uh, you can do a quick, uh, basically power balance, and you can, you can determine that on Earth, it, it requires a minimum temperature of about 50 million degrees Celsius on Earth.

Lex Fridman 5:02 To perform fusion?

Dennis Whyte 5:03 To get enough fusion, uh, that you would be able to make, uh, get energy gain out of it. So, you can trigger fusion reactions at lower energy, but they, they become almost vanishingly small at lower temperatures than that.

Lex Fridman 5:18 First of all, let me just linger on some crazy ideas. So-

Dennis Whyte 5:20 Yeah.

Lex Fridman 5:21 Uh, one, the strong force, just stepping out and looking at all of physics, is it weird to you that there's these forces, and they're very particular? Like, it operates at a very small distance, and then gravity operates at a very large distance, and, and they're all very specific. And the standard model describes, uh, three of those forces extremely well, and there's-

Dennis Whyte 5:42 And this is one of them, and- (laughs)

Lex Fridman 5:43 Yeah, this is one of them.

Dennis Whyte 5:44 Yeah.

Lex Fridman 5:44 And it just all kind of works out.

Dennis Whyte 5:46 Yeah.

Lex Fridman 5:46 There's a, a big part of you that's, uh, you know, an engineer. So, do you stu- step back and almost look at the philosophy of physics?

Dennis Whyte 5:55 So, it's interesting 'cause as, as a scientist, I see the universe through that lens of essentially the interesting things that we do are through the forces that are, get used around those. And everything works because of that.... Richard Feynman had a, a... I don't know if you've ever read Richard Feynman. It's a little bit o- of a tangent, but-

Lex Fridman 6:12 He's never been on the podcast.

Dennis Whyte 6:13 He's never been on the podcast.

Lex Fridman 6:14 Yeah.

Dennis Whyte 6:14 He was, unfortunately passed away, but one of, like a, a, like a hero to almost all, all physicists.

Lex Fridman 6:19 Yeah.

Dennis Whyte 6:19 And then part of it was because of what you said. He kind of looked through a different lens at these what are, typically look like very dry, like equations and relationships, and he kind of s- I think he brought out the wonder of it in some sense, right, for, for those. He posited what would be, if you could write down a single, not even really a sentence but a s- a single concept that was the most important thing scientifically that we, that we knew about that, in other words, you had only one thing that you could transmit to like a future or past generation. It was very interesting. It was, um... So it's not what you think. It wasn't like, oh, strong nuclear force or-

Lex Fridman 6:56 (laughs) Yeah.

Dennis Whyte 6:56 ... fusion or something like this. And it's very profound, which was he was, that the reason that matter operates the way that it does is because all matter is made up of individual particles that interact each other through forces. That was it.

Lex Fridman 7:13 So just-

Dennis Whyte 7:14 The atomic theory basically. Yeah.

Lex Fridman 7:16 Yeah.

Dennis Whyte 7:16 Which is like, wow, that's like so simple, but it's not so simple. It's because, like w- who thinks about atoms, that they're made out of? Like I, I... This is a good, this is a good question I give to my students. How many atoms are in your body? Like almost no student's gonna answer this. But to me that's like a fundamental thing.

Lex Fridman 7:32 Yeah.

Dennis Whyte 7:33 By the way it's about 10 to the 28th. (laughs)

Lex Fridman 7:36 10 to the 28th.

Dennis Whyte 7:36 So that's, uh, you know, trillion or, you know, million trillion trillion or something like that. Yes, yeah.

Lex Fridman 7:41 So one thing is to think about the number, and the other is to start to really ponder the fact-

Dennis Whyte 7:46 That it all holds together.

Lex Fridman 7:47 Yeah, it all holds together, and you're actually that. You're more that than you are anything else.

Dennis Whyte 7:51 Yes, exactly, yeah. No, I mean, there, there are people who do s- study such things of the fact that if you look at the, for example, the ratios between those fundamental forces, people have figured out, "Oh, if this ratio was different by some factor," like a factor of two or something like that, oh, it's like, "Oh, this would all, like not work."

Lex Fridman 8:09 Mm-hmm.

Dennis Whyte 8:10 And I look, you look at the sun, right? It's like, so it turns out that there are key reactions that if they had slightly lower probability, no star would ever ignite.

Lex Fridman 8:19 Mm-hmm.

Dennis Whyte 8:20 And then life wouldn't be possible.

Lex Fridman 8:21 It does seem like the-

Dennis Whyte 8:23 (laughs)

Lex Fridman 8:23 ... the universe-

Dennis Whyte 8:24 Yes. (laughs)

Lex Fridman 8:24 ... set things up for us-

Dennis Whyte 8:26 Yeah.

Lex Fridman 8:26 ... that it's possible to do some cool things, but it's challenging, so that, that, that keeps it fun for us.

Dennis Whyte 8:33 Yeah. Yeah, that's the way I look at it. I mean the, you know, the multiverse model is an interesting one, uh, because there are, you know, quantum scientists who look at it and figure... It's like, oh, it's like, oh yeah. Like quantum science perhaps tells us that there are almost an infinite, you know, variety of other universes. But the way that it works probably is it's almost like a form of natural selection. It's like, well, the universes that didn't have the correct or interesting relationships between these forces, nothing happens in them. So almost by definition, the fact that we're having this conversation means that we're in one of the interesting ones by default.

Lex Fridman 9:07 Yeah, one of the somewhat interesting, but there's probably super interesting ones where we, I, I tend to think of humans as incredible creatures. Our brain is, is an incredible computing device, but I think we're also extremely cognitively limited. I can imagine alien civilizations that are much, much, much, much more intelligent, uh, in ways we can't even comprehend in terms of their ability to com- to construct models of the world and to do physics, to do physics and mathematics.

Dennis Whyte 9:37 I would see it in a slightly different way. It's, it's actually it's because we have, um, we have c- we have creatures that live with us on the Earth that have cognition, right, that understand and move through their environment. But they, they actually see things in a way or they sense things in a way which is so fundamentally different, it's really hard. Like the tr- it's, it, the it's the problem is the translation, not necessarily intelligence, so it's the perception of the world. So I have a, a dog. And when, when I go and I see my dog, like s- smelling things, there's a realization that I have that he sees or senses the world in a way that I can never, like I can't understand it because I can't translate my way to this. We get little glimpses of this as humans though, by the way, because there are some parts of it, for example, o- optical, uh, information, which comes from light is that now because we've developed the technology, we can actually see things. You know, I've had... I get this, you know, as a, one of my areas of research is spectroscopy, so this means the study of light, you know? And I, and I get this, quote-unquote see things or representations of them from, you know, the far infrared all the way to like hard, hard X-rays which is several orders of magnitude of the, of the light intensity. But our own human eyes-

Lex Fridman 10:52 Mm-hmm.

Dennis Whyte 10:52 ... like see a teeny, teeny little sliver of this.

Lex Fridman 10:55 Yeah.

Dennis Whyte 10:55 So that even like bees, for example, see a different place than we do. So I, I don't... I, I think if you think of there's already other intelligences like around us in a way, in a limited way, um, because of the way they can communicate, but it's like tho- those are already baffling (laughs) in many ways, yeah.

Lex Fridman 11:14 Yeah. Uh, see, if we just focus in on the senses, there's already a lot of diversity. But there's probably things we're not even considering as possibilities.

Dennis Whyte 11:21 Yes.

Lex Fridman 11:22 For example, uh, whatever the heck consciousness is could actually be a, a door into understanding some physical phenomena we're not, haven't even begun understanding. So just like you said spectroscopy, there could be a similar kind of spectrum for consciousness that we're just like, we're like these dumb, uh, descendants of apes like walking around. It sure feels like something to experience the color red, but like we don't have...It, it's the same as in the ancient times you experience physics, y- you experience light.

Dennis Whyte 11:52 Yeah.

Lex Fridman 11:52 It's like, oh, it's bright and, you know... (laughs)

Dennis Whyte 11:54 Y- yeah. Yeah. (laughs)

Lex Fridman 11:55 And you construct kind of a semi-religious kind of explanations.

Dennis Whyte 11:57 Well, it's interesting. We, we, we, we, we might actually experience this faster than we thought 'cause we might be building another, another kind of intelligence.

Lex Fridman 12:05 Yeah. And that, that intelligence will explain to us-

Dennis Whyte 12:07 (laughs)

Lex Fridman 12:08 ... (laughs) how silly we are.

Dennis Whyte 12:09 Well, (laughs) w- there was an email thread going around the professors in my department already o- of, uh, "So what is it going to look like to figure out if students have actually written their term papers, or it's chat, uh, the, the-"

Lex Fridman 12:21 ChatGPT?

Dennis Whyte 12:22 ChatGPT. Um-

Lex Fridman 12:24 (laughs)

Dennis Whyte 12:24 Um, uh, it was... So, a- as usual, as em- as empir- we're u- we tend to be empiricists in my field, so of course they were in there, like, trying to figure out if, uh, if it could answer, like, questions for a qualifying exam to get into the PhD program (laughs) at MIT. Which was... It, it, they didn't do that well at that point, but of course this is just the beginning of it, so-

Lex Fridman 12:44 Yeah.

Dennis Whyte 12:44 ... we have some interesting ones to go forth, yeah.

Lex Fridman 12:46 Eventually both the students and the professors will be replaced by ChatGPT.

Dennis Whyte 12:49 Yeah. (laughs)

Lex Fridman 12:50 And we'll sit on the beach.

Dennis Whyte 12:52 I really recommend, you know, the s- I don't know if you've ever seen them. It's called The Day the Universe Changed. This is-

Lex Fridman 12:57 Is that a movie?

Dennis Whyte 12:58 ... James Burke.

Lex Fridman 12:59 Oh.

Dennis Whyte 12:59 He's a science historian based in the UK. Um, he had a, had a fairly famous series on, on public television called Connections, I think it was. Uh, but the one that I really enjoyed was The Day the Universe, uh, Changed. And the, the reason for the title of it was that, um, he says the universe is what we know and perceive of it. So, when there's a fundamental insight as to something new, the universe, for us, changes. Of course, the universe from an objective point of view is the same as it was before, but for us, it has changed. So, he walks through these, these moments of perception in, in, in, in the history of humanity that, like, changed what we were, right? And so, as I was thi- thinking about coming to, to, to discuss this, you know, people see fusion, "Oh, it's still far away," or, "We've been, it's been slow progress." It's like, when my, when my godmother was born, like, people had no idea how s- stars worked.

Lex Fridman 13:58 (laughs) Yeah.

Dennis Whyte 13:59 So, you talk about, like, that day, that insight-

Lex Fridman 14:01 Yeah.

Dennis Whyte 14:01 ... the universe changed. It's like, oh, this is the ... I mean, they, and they still didn't understand all the parts of it, but, you know, th- they basically got it. It's like, oh, because of the, because of the understanding of these processes, it's like we unveiled the reason that there can be life in the universe. That's probably one of those days the universe changed, right?

Lex Fridman 14:20 Mm-hmm.

Dennis Whyte 14:20 Yeah.

Lex Fridman 14:21 And, uh, it s-

Dennis Whyte 14:22 And that was around the 1930s, yeah.

Lex Fridman 14:23 It seems like technology is developing faster and faster and faster.

Dennis Whyte 14:28 Yeah.

Lex Fridman 14:28 I tend to think, just like with ChatGPT, I think this year might be extremely interesting just with how rapid-

Dennis Whyte 14:34 Mm-hmm.

Lex Fridman 14:35 ... and how profitable the efforts in artificial intelligence are, that just stuff will happen where our whole world is transformed like this, and we're, there's a shock. And then next day, you kinda go on, and you adjust immediately. Uh, you probably won't have a similar kind of thing with, uh, nuclear fusion with energy 'cause there's, there's probably going to be an opening ceremony and stuff. (laughs)

Dennis Whyte 14:57 Yes. (laughs)

Lex Fridman 14:58 An announcement. It could take months.

Dennis Whyte 15:00 (laughs) Yeah.

Lex Fridman 15:00 But with the, with digital technology, you can just have a immediate transformation of society, and then there'll be this (gasps) gasp, and then you kinda adjust-

Dennis Whyte 15:08 Yeah.

Lex Fridman 15:08 ... like we always do. And then you d- don't even remember, just like with the internet and so on-

Dennis Whyte 15:12 Yeah.

Lex Fridman 15:12 ... how the days were before.

Dennis Whyte 15:14 And how it worked before, right. Yeah. I mean, fusion will be, because it's energy, it's, it's, its nature is that it will be, um, and anything that has to do with energy use tends to be a slower transition. But they are the most, I would argue, pro- some of the most profound-

Lex Fridman 15:28 Yes.

Dennis Whyte 15:28 ... transitions that we make. I mean, the reason, uh, that we can l- live like this and sit in this building and have this podcast and people around the world is, is, at its heart, is energy use.

Lex Fridman 15:39 Mm-hmm.

Dennis Whyte 15:39 And it's intense energy use that came from the evolution of starting to use intense energies at the beginning of the Industrial Revolution up to now. It's that, it's like, it's a bedrock actually of all of these. But it doesn't tend to come overnight.

Lex Fridman 15:53 Yeah.

Dennis Whyte 15:53 Yeah.

Lex Fridman 15:53 And some of the most important, some of the most amazing technology is one we don't notice 'cause we take it for granted 'cause it enables this whole thing.

Dennis Whyte 16:00 Yeah. Exactly.

Lex Fridman 16:01 (laughs) And-

Dennis Whyte 16:01 Which is energy, which is am- amazing for how fundamental it is to our society and way of life. It's a very poorly understood concept actually, just even energy itself. People confuse energy sources with energy storage with energy transmission. These are different physical phenomena-

Lex Fridman 16:21 Mm-hmm.

Dennis Whyte 16:21 ... which are very important. For, so for example, you know, you buy an electric car, and you go, "Oh, good, I have an emission-free car." And, uh, ah, but it's like, so, so wh- why do you say that? Well, it's 'cause if I draw the circle around the car, I have electricity, and it doesn't emit any- anything. Okay, but you plug that into a grid where you follow that wire back, there could be a coal power plant-

Lex Fridman 16:44 Mm-hmm.

Dennis Whyte 16:45 ... or a gas power plant at the end of that. Oh, really? You mean, so this isn't, like, carbon free? Oh. B- and it's not their fault. It's just, you know, they don't... Like, the car isn't a source of energy. The underlying source of energy was the combustion of the fuel back somewhere.

Lex Fridman 17:00 Yeah. Plus there's also the story of how the raw materials are mined-

Dennis Whyte 17:05 Yeah.

Lex Fridman 17:05 ... in which parts of the world, uh, with sort of basic respect or, or a deep disrespect of human rights that happens in that mining. So, the whole supply chain, there's a story there that's deeper than just a particular electric-

Dennis Whyte 17:17 Yes.

Lex Fridman 17:17 ... car with a circle around it.

Dennis Whyte 17:18 Yeah. And the physics or the science of it too is the energy use that it takes to do that digging up-

Lex Fridman 17:23 Yeah.

Dennis Whyte 17:23 ... which is also important and all that. Yeah. Anyway, so-

Lex Fridman 17:26 Yeah.

Dennis Whyte 17:27 ... we wandered away from fusion, but yes.

Lex Fridman 17:28 Oh, it's a beautiful stroll.

Dennis Whyte 17:30 But it, but it, but it's very important actually to, in the, in the context of this just because, you know, those of us who work in, in fusion and these other kinds of, um, sort of disruptive energy technologies, it's, it's interesting. I, I do think about, like, what would it, what is it going to mean to society to have an energy source that is like this, um, that it w- that would be like fusion, you know, which has, which has such completely different characteristics.... you know, for example, you know, free unlimited access to the fuel, but it has technology implications. So, what does this mean geopolitically? What does it mean for how we, how we distribute wealth within our society? It's, it's- it's very difficult to know. (laughs) But probably profound.

Lex Fridman 18:12 Yeah.

Dennis Whyte 18:12 Yeah.

Lex Fridman 18:12 We're gonna have to find another reason to start wars.

Dennis Whyte 18:15 (sighs)

Lex Fridman 18:15 (laughs) For s- instead of resources, we're gonna have to figure something else out.

Dennis Whyte 18:18 Uh, we- we've done a pretty good job of that over the-

Lex Fridman 18:20 Yeah, perfect.

Dennis Whyte 18:21 ... the- the- the-

Lex Fridman 18:21 We're very clever.

Dennis Whyte 18:21 ... course of our history, yeah.

Lex Fridman 18:23 Uh, so w- we talked about, uh, the forces of physics, and again, sticking to the philosophical before we get to the s- specific technical stuff.

Lex Fridman 18:31 E equals MC squared, you mentioned. How amazing is that to you, that energy and mass are the same?

Dennis Whyte 18:35 Yeah.

Lex Fridman 18:36 And what does that have to do with nuclear fusion?

Dennis Whyte 18:39 So, it has to do with everything we do. It's the fact that energy and mass are equivalent to each other. They're just, the way th- th- we usually comment to it is that they're just energy, just in different forms.

Lex Fridman 18:49 Can you intuitively understand that?

Dennis Whyte 18:52 Yes.

Lex Fridman 18:53 (laughs)

Dennis Whyte 18:53 But it takes a long time. (laughs) I (laughs) um ha- haven't for a while, but usually, uh, often I've, I- I teach the, um, uh, the inter- introductory class for incoming nuclear engineers, and, and so we put this up as an equation, and we go through many, um, iterations of, of using this, uh, to, to, how- how you derive it, how you use it and so forth. And then u- usually in the final exam, I would give, uh, I would basically take all the equations that I've used before and I flip it around. I basically, instead of thinking about energy as equal to, to mass, it's sort of mass is equal to energy. And I ask the question a different way, and usually about half the students don't get it. It takes a while i- t- to get that intuition. Yeah. Um, so, so in the end, it's interesting is that th- this is a- is actually the source of all free energy because that energy that we're talking about is kinetic energy if it can be transformed from mass. So, it turns out even, even though we, we used E equals MC squared, this is burning coal and, and burning gas, or/and burning wood is actually still E equals MC squared. The problem is that you would never know this because the relative change in the mass is incredibly small. By the way, which comes back to fusion, is which is that E equals MC squared. Okay, so what does this mean? It tells you that the r- the amount of energy that is liberated in a particular reaction when you change mass has to d- because C squared is, that's the speed of light squared.

Lex Fridman 20:19 It's a large number.

Dennis Whyte 20:19 It's a very large number, and it's totally constant everywhere in the universe, which is the-

Lex Fridman 20:23 Which is another weird thing.

Dennis Whyte 20:24 Which is another weird thing, and in all rest frames and th- actually, the relativity stuff gets more (laughs) difficult conceptually un- until you get through. Anyway, so you go th- you g- you go to that and, and it's, and what that tells you is that it's the relative, it's the relative change in the mass will tell you about the relative amount of energy that's liberated. And this is what makes fusion, and you asked about fission as well too, this is what makes them extraordinary is because the relative change in the mass is very large as compared to what you get, like, in a chemical reaction. In fact, it's about, it's about 10 million times larger. And that is at the heart of why you use something like fusion. It's because that is a fundamental of nature. Like, you can't beat that. So, uh, whatever you do, if you're thinking about l- and why do I care about this? Well, 'cause mass is, like, the fuel, right? So, this means gathering the resources that it takes to gather a fuel, to hold it together, to deal with it, th- the environmental impact it would have. And fusion will always have 20 million times the amount of energy released per reaction that you could those. So, this is why, you know, we consider it the ultimate, like, environmentally friendly energy source is because of that.

Lex Fridman 21:40 So, is it, is it correct to think of mass broadly as a kind of storage of energy?

Dennis Whyte 21:46 Yes.

Lex Fridman 21:47 You mentioned it's environmentally friendly. So, nuclear fusion is a source of energy. It's cheap, clean, safe, so easy access to fuel and virtually unlimited supply, no production of greenhouse gases, little radioactive waste produced allegedly.

Dennis Whyte 22:03 Mm-hmm.

Lex Fridman 22:03 Uh, can, can you sort of elaborate why it's cheap, clean, and safe?

Dennis Whyte 22:07 I'll start with the easiest one, cheap. It is not cheap yet because it hasn't been made at a commercial scale.

Lex Fridman 22:14 Time flies when you're having fun but yes.

Dennis Whyte 22:15 It d- yeah, yeah. (laughs)

Lex Fridman 22:18 But yes, not yet.

Dennis Whyte 22:19 Yeah, but-

Lex Fridman 22:19 We'll talk about-

Dennis Whyte 22:20 And actually, we'll- we'll- we'll- we'll come back to that because it- it- it- this is cheaper, m- or, or a more technically correct term that it's econom- that it's economically interesting is, is really the primary challenge actually of, of fusion at this point. Um, but I think we can get back to that. So, what were the other ones? You said, um-

Lex Fridman 22:38 So, so cheap, we're ta-

Dennis Whyte 22:39 Huh?

Lex Fridman 22:39 We're, uh, actually when we're talking about cheap, we're thinking, like, asymptotically, like-

Dennis Whyte 22:43 Oh.

Lex Fridman 22:43 ... if you take it forward-

Dennis Whyte 22:45 Yeah.

Lex Fridman 22:45 ... several hundred years, uh, th- that's sort of because of how much availability there is of resources to use.

Dennis Whyte 22:52 Of the fuel, yeah.

Lex Fridman 22:53 Yeah, of the fuel.

Dennis Whyte 22:54 We should separate those two. The fuel will al- uh, the fuel is already cheap. It's basically-

Lex Fridman 22:58 Yeah.

Dennis Whyte 22:58 ... free, right?

Lex Fridman 22:59 Yeah.

Dennis Whyte 23:00 And what do you mean by basically free? So, if, if we were to be using fusion, um, uh, fuel sources to power your, and, and it's like that's all we had was fusion power plants around, and we were doing it, the fuel cost per person are something like 10 cents a year. It's like fr- it's free. Okay? This is why it's hard to, in some- some ways I think it's hard to understand fusion because people see this and go, "Oh, if the fuel is free, this means the energy source is free" because we're used to energy sources like this, so we, you know, we spend resources, and drill to get a- gas or oil, or we chop wood, or we make coal, we find coal, or these things, right? So, f- fusion, th- this is what makes fusion, and it's also, um, it- it's not an intermittent renewable energy source like wind and solar. So, it's like but this is, this makes it hard to understand. So, if you're saying the fuel is free, why isn't the, like, why isn't the energy source free? And it's because of the necessary technologies which must be applied to basically recreate the conditions which are in stars.

Lex Fridman 24:03 Mm-hmm.

Dennis Whyte 24:03 In the center of stars, in fact. So there's only one natural place in the universe that fusion occur- fusion energy occurs. That's in the center of stars. So that's going to bring a price to it, depending on the, the cost and com- or sorry, the size and complexity of, of the technology that's needed to recreate those things.

Lex Fridman 24:22 And we'll talk about the details of-

Dennis Whyte 24:24 Yeah, we'll get... yeah, yeah.

Lex Fridman 24:24 ... those technologies-

Dennis Whyte 24:25 Yeah.

Lex Fridman 24:25 ... and which parts might be expensive-

Dennis Whyte 24:27 Yeah.

Lex Fridman 24:27 ... today and which parts might be expensive in 200 years from now.

Dennis Whyte 24:29 Ex- e- exactly. I- it will have a revolution. I'm, I'm certain of it. Um, so about clean, so clean is, at its heart, what it does is convert, um, it basically converts hydrogen into, it's, it's, it's, it's heavier forms of hydrogen, the one, the most, um, predominant one that we use on Earth, and converts it into helium and some other products, but primarily helium is the product that's left behind. So helium, safe, inert gas, you know?

Lex Fridman 24:57 Mm-hmm.

Dennis Whyte 24:57 In fact, like, that's actually what our sun is doing is eventually going to extinguish itself because it'll just make so much helium that it doesn't, uh, it doesn't do that. So in that sense, clean because there's no, there's no emissions of, of carbon or pollutants that come directly from the combustion of the fuel itself.

Lex Fridman 25:15 And safe.

Dennis Whyte 25:16 Safe, yeah.

Lex Fridman 25:18 We're talking about very high temperatures.

Dennis Whyte 25:19 Yeah, yeah. So this is also the counterintuitive thing. So you, you, I told you temperatures which are like 50 million degrees, or it actually tends to be more like about 100 million degrees is really what we aim for. So how can 100 million degrees be safe? And it's safe because it is, this is so much hotter than anything on Earth, where everything on Earth is at around 300 kelvin, you know? It's around a few tens of degrees Celsius. And what this means is that in order to get a medium to those temperatures, you have to completely isolate it from anything to do with terrestrial environment. It can have no contact, like, with anything on Earth basically. So this means what we... th- this is (laughs) the technology that I just described, is it- it fundamentally, what it does is it takes this fuel, and, uh, it isolates it from any terrestrial conditions so that it has no idea it's on Earth. It's not touching any object that at, that's at room temperature or-

Lex Fridman 26:16 Including the walls of the containment that it's separating from?

Dennis Whyte 26:18 Even the, including the walls of the containment building or con- containment device or even air or anything like this. So, so it's that part, um, that makes it safe in this... and, and there's, there's actually another aspect to it. But that, that fundamental part makes it so safe. Um, and in, in the mainline, um, uh, approach to fusion is also that it's very hot where there's very, very few particles in, at any time in, in the thing that would be the power plant. And actually, the more correct way to do it is you say there's very few particles per unit volume, so in a cubic centimeter or cubic meter or something like that. So we can do this. So right now, we're... although we don't think of air really as a... there's atoms floating around us, and there's a density 'cause if I wave my hand, I can feel the, the air pushing against my face. That means we're in a fluid or a gas which is around us. That has a particular, um, number of atoms per cubic meter, right? So it's about... thi- this actually turns out to be 10 to the 25th, so this is one with 25 zeros behind it-

Lex Fridman 27:22 Mm-hmm.

Dennis Whyte 27:22 ... per cubic meter. So we can figure out what a cubic... like, a cubic meter's about like this-

Lex Fridman 27:27 Yeah.

Dennis Whyte 27:27 ... the volume of this table, like the whole volume of this table.

Lex Fridman 27:30 Mm-hmm.

Dennis Whyte 27:30 Um, okay, very good. So, like, fu- fusion, there's a f- a few of those. So fusion, like, the mainstream one of fusion, like what we're working on at MIT, will have 100,000 times less particles-

Lex Fridman 27:41 Mm-hmm.

Dennis Whyte 27:42 ... per unit volume than that. So this is very interesting because it's extraordinarily hot, 100 million degrees, but it's very tenuous. And what matters from the engineering and safety point of view is the amount of energy which is stored per unit volume because this tells you about the in- the scenarios of the... and that, and that's what you worry about 'cause when en- those kinds of energies are released suddenly, it's like, what would be the consequences, right? So the cons- sequences of this are essentially zero-

Lex Fridman 28:14 Mm-hmm.

Dennis Whyte 28:14 ... because that's less energy content than boiling water.

Lex Fridman 28:20 Because of the low density of the-

Dennis Whyte 28:21 Because of the low density. So if you take... uh, water is at about 100 million to a billion times more dense than this. So even though it's at much lower temperature, it's actually still... it has more energy content. So for this reason, um, you know, one, one of the ways that I explain this is that if you imagine a power plant that's, like, powering Cambridge, Massachusetts, like, if you were to... which you, you wouldn't do this directly, but if you went (blows air) like this-

Lex Fridman 28:48 Mm-hmm.

Dennis Whyte 28:48 ... on it, it actually extinguishes the fusion-

Lex Fridman 28:51 Mm-hmm.

Dennis Whyte 28:51 ... because it gets too cold immediately.

Lex Fridman 28:55 (laughs)

Dennis Whyte 28:55 Yeah. So that's the other one. And, and the other part is that it does not... in the, because it works by staying hot rather than a chain reaction, it can't run out of control. That's the other part of it. So th- by the way, this is what very much distinguishes it from fission. It's not a process that can run away from you 'cause it's, it's basically thermally stable.

Lex Fridman 29:15 What does thermally stable mean?

Dennis Whyte 29:16 That means is that you want to run it at the optimization in temperature such that if it deviates away from that temperature, the reactivity gets lower. And it, and the reason for this is because it's hard to keep the reactivity going.

Lex Fridman 29:28 Yeah.

Dennis Whyte 29:28 Like, it's a very hard fire to keep going ba- basically.

Lex Fridman 29:31 Oh, so it doesn't, it doesn't run away from you?

Dennis Whyte 29:33 It can't run away from you.

Lex Fridman 29:33 So the con- how difficult is the control there to keep it at that?

Dennis Whyte 29:37 It varies from, from concept to concept, but in general, it, it's fairly, it's fairly easy, um, uh, to do that. And the, the easiest thing, it, it can't, it can't physically run away from you because the other part of it is that there's just, at any given time, there's a very, very small amount of fuel available to fuse a- anyway. So this means that that's always intrinsically limited to this. So if it, ev- even if the power consumption of the device goes up, it just kind of burns itself out immediately. Yeah.

Lex Fridman 30:05 So you are the, just to take a tan- another tangent on a tangent, you're the director of MIT's Plasma Science and Fusion Center.

Dennis Whyte 30:11 That's right. Yeah.

Lex Fridman 30:13 We'll talk about, maybe you can mention some interesting aspects of the history, uh, of the center i- in the broader history of, uh, MIT, and maybe broader history of science and engineering and the history of human civilization.

Dennis Whyte 30:26 (laughs)

Lex Fridman 30:26 But also just to linger on the safety aspect-

Dennis Whyte 30:29 Yeah.

Lex Fridman 30:29 ... you know, um, how, how do you prevent, you know, so- some of the amazing reactors that you're designing, h- how do you prevent from destroying all of human civilization in the process?

Dennis Whyte 30:42 (laughs) It's like-

Lex Fridman 30:42 What, what's the safety protocols?

Dennis Whyte 30:44 Fusion is, um, interesting 'cause it's not really directly weaponizable because, what, what I mean by that is that you have, you have to work very hard to make these-

Lex Fridman 30:54 Yes.

Dennis Whyte 30:54 ... conditions at which you can get energy gain from, from fusion. Um, and, uh, this means that the, the, wh- when we design these d- devices with respect to application in the energy field is that they, you know, you, you, th- uh, whi- while, while, while they will pr- because they're producing large amounts of power, and they will have hot things inside of them-

Lex Fridman 31:17 Mm-hmm.

Dennis Whyte 31:17 ... this means that they have a, a, like a level of industrial hazard, which is very similar to, like, you would have, like, in a chemical processing plant or-

Lex Fridman 31:24 Mm-hmm.

Dennis Whyte 31:25 ... anything like that. An- any kind of energy plant actually has these as well too. But the underlying, under- underneath it core technology, like, can't be directly used, uh, in, in a nefarious way because of the power that's being emitted. It just basically will s- if you try to do those things, typically it just stops working.

Lex Fridman 31:43 So, the safety concerns have to do with just regular things that, uh, like equipment malfunctioning, uh, m- melting of equi- like all, all this kind of stuff that-

Dennis Whyte 31:52 Yeah.

Lex Fridman 31:53 ... has nothing to do with fusion necessarily.

Dennis Whyte 31:54 Yeah, I mean, u- usually what we worry about is the viability 'cause in the end we build pretty complex objects to realize these requirements. And so what we try really hard to do is, like, not damage those components, which, but those are things which are internal to the, to the fusion device. And, and it's, this is not something that you would, um, uh, consider about, like, it would, uh, as you say, destroy human civilization because that release of energy is just inherently limited because of the fusion process. So, it doesn't say that there's zero... So, you asked about the other feature of it, that it's safe. So, it is, the process itself is intrinsically safe, but because it's a complex technology, you still have to take into amount, uh, consideration aspects of the safety. So, it produces ionizing radiation instantaneously, so you have to take care of this, which means that you shield it. Think of, like, your dental X-rays or, or treatments for cancer and things like this. We, we always shield ourselves from this. So, we get the beneficial effects, but we minimize the harmful effects of those. So, there, there, there are those aspects of it, uh, uh, as well too. Yeah.

Lex Fridman 32:58 So, we'll return to MIT's Plasma Science and Fusion Center-

Dennis Whyte 33:01 Sure.

Lex Fridman 33:01 ... but let us linger on the, uh, destruction of human civilization, uh, which brings us to the topic of nuclear fission. What is that? Wh- uh, so the, the process that is inside, uh, nuclear weapons and current nuclear power plants.

Dennis Whyte 33:16 So, it relies on the same underlying physical principle, but it's exactly the opposite-

Lex Fridman 33:22 Mm-hmm.

Dennis Whyte 33:22 ... of fu- which actually the names imply. Fusion means bringing things together. Fission means splitting things apart.

Lex Fridman 33:28 Mm-hmm.

Dennis Whyte 33:28 So, fission, uh, requires the heaviest instead of the lightest and the most unstable versus the most stable, uh, uh, elements. So, this tends to be uranium, uh, or plutonium, p- primarily uranium. So, take uranium. So, uranium-235 is one of the he- uh, that, this is one of the heaviest unstable elements. And what happens is that this is, uh, and f- uh, fission is triggered by the fact that one of these subatomic particles, the neutron, which has no electric charge, basically gets i- in proximity enough to this, uh, and, and triggers an instability, uh, effectively inside of this uns- what is teetering on the border of instability and basically splits it apart. And that's the fission, right? The fis- fissioning. Um, and so when that happens because the products that are in, in kind of, it roughly splits in two, but it's not even that. It's actually more complicated. It splits into this whole array of lighter elements and nuclei. A- and when that happens, there's less rest mass, uh, uh, l- left than the, than the original one. A- so it's actually the same. So, it's again, it's rearrangement of the strong nuclear force that, that's happening. Um, but that's the source of the energy. And so in the end, it's like, so this is a famous graph that we show everybody is, is basically it turns out every element that exists in the periodic table, all the things that make up everything-

Lex Fridman 34:55 Mm-hmm.

Dennis Whyte 34:56 ... have, uh, have a, remember y- you asked a good question. It was like, "So, should we think of mass as being the same as stored energy?" Yes. So, you can make a plot that basically shows the relative amount of stored energy in all of the elements that are stable and make up basically the world, okay, and the universe. And it turns out that this one has a maximum amount of, of stability or storage, uh, at iron.

Lex Fridman 35:23 Okay.

Dennis Whyte 35:24 So, it's kind of in the middle of the periodic table because this goes from, you know, it's r- it's roughly that. And so this, what that means is that if, um, if you take something heavier than iron, like uranium, which is, which is more than twice as heavy th- that, and you split apart, if somehow just magically you can just split apart its constituents, and you get something that's lighter, that will, because it moves to a more stable energy state, it releases kinetic energy. That's the energy that we use. Kinetic energy meaning the movement of things. So, it's actually an energy you can do something with. And fusion sits on the other side of that because it's also moving towards iron, but it's do, it has to do it through fu- fusion together. So, this leads to some pretty profound differences. As I said, they have some underlying physics or science, um, uh, proximity to each other, but they're literally the opposite. So, fusion, uh, why is this... It actually goes into practical implications of it, which is that fission can happen at room temperature. It's because there's, this neutron has no...... electric charge, and therefore roo- it's literally room temperature neutrons that actually trigger the reaction. So this means, um, a-in order to establish, uh, what's going on with it, and it works by chain reaction, is that you can do this at room temperature. So Enrico Fermi did this, like, on a, on a university campus, University of Chicago campus. The first sustained, you know, chain reaction was done underneath a squash court with big blocks of graphite, you know? It was still an, I mean, don't get me wrong, an incredible human achievement, right? But that's, you know... And then you think about fusion. I have to build a contraption of some kind that's going to get to 100 million degrees. Okay, wow, that's a big difference. The other one is about the chain reaction, that namely fission works by the fact that when that fission occurs, it actually produces free neutrons. Free neutrons, particularly if they get slowed down to room temperature, trigger, can trigger other fission reactions if there's other uranium nearby or fissile materials. So this means that the way that it releases energy is that you set this up in a very careful way such that every, on average, every reaction that happens exactly releases enough neutrons and slows down that they actually make another reaction, one, exactly one. And th- what this means is that because each reaction releases a fixed amount of energy, blah, blah, blah, you do this, and then in time, this looks like just a constant power output. So that's how our fission power plant works.

Lex Fridman 37:52 And so there control the fi- the chain reactions-

Dennis Whyte 37:54 Yes.

Lex Fridman 37:54 ... is extremely difficult and extremely important for-

Dennis Whyte 37:56 It's very important.

Lex Fridman 37:58 ... fission.

Dennis Whyte 37:58 And when you intentionally design it that it, it creates more than one-

Lex Fridman 38:01 Mm-hmm.

Dennis Whyte 38:02 ... fission reaction per, per starting reaction, then it exponentiates away.

Lex Fridman 38:07 Mm-hmm.

Dennis Whyte 38:08 But which is, which is what a nuclear weapon

Dennis Whyte 38:10 is.

Lex Fridman 38:10 Yeah, so h- how does an atomic weapon work? How does a hydrogen bomb work? Asking for a friend.

Dennis Whyte 38:15 Yeah. (laughs) Yeah, so, um, a- at its heart, what it ha- what you do is you very quickly put together enough of these materials that can undergo fission with room temperature neutrons.

Lex Fridman 38:28 Mm-hmm.

Dennis Whyte 38:28 And you put them together fast enough that what happens is that the, this process can essentially grow mathematically, like very fast.

Lex Fridman 38:36 Hm.

Dennis Whyte 38:36 And so this releases large amounts of energy. So that's the underlying reason that it works. So you've heard of a fusion weapon. So this is interesting is that it is, it, but it's dislike fusion energy in the sense that what happens is that you're using fusion reactions to, but it's simply, it increases the gain actually of the weapon rather than, um, it- it- it's not a pure... At- at its heart, it's still a fission w- weapon. You're just using fusion reactions as a sort of intermediate catalyst basically to ma- to get even more energy out of it. But it's not directly applicable to, to be used in, in energy source.

Lex Fridman 39:14 Does it terrify you, just, again, to step back at the philosophical, that humans have been able to use physics and, uh, engineering to create such powerful weapons?

Dennis Whyte 39:28 I wouldn't say terrify. I mean, we should be... (laughs) This is the, this is the progress of, of human- every time that we've gotten access, you talk, you know, the day the universe changed, things really changed when we got access to new kinds of energy sources. But every time you get ac- and typically what this meant was you get access to more intense energy, right? That's, and that's what that was. And so the ability to move from burning wood to using coal to using gasoline and petroleum and then finally to use this is that, is that both the potency and the consequences a- are elevated a- around those things.

Lex Fridman 40:08 It's just like you said, the, the way that fusion, nuclear fusion would change the world, I don't think, u- unless we think really deeply, we'll be able to anticipate some of the things we can create. There's go- going to be a lot of amazing stuff.

Dennis Whyte 40:22 Yeah.

Lex Fridman 40:22 But then that amazing stuff is gonna enable more amazing stuff and more, unfortunately, or, uh, depending how you see it, m- more powerful weapons.

Dennis Whyte 40:31 Well, yeah, but see, that's the thing. Fusion breaks that trend-

Lex Fridman 40:36 Mm-hmm.

Dennis Whyte 40:36 ... in the following way. So one of the... So fusion doesn't work on a chain reaction. There's no chain reaction. Zero. So this means it cannot physically exponentiate away on you 'cause it works... And actually this is why star... By the way, we know this already. It's why stars are so stable, why most stars and suns are so stable. It's because they are regulated through their own temperature and their heating. Because what's happening is not that there's some probability of this exponentiating away, it's that the energy that's being released by fusion basically is keeping the fire hot.

Lex Fridman 41:11 (laughs)

Dennis Whyte 41:11 Um, and these tend to be, you know, and when it comes down to thermodynamics and things like this, there's a reason, for example, it's pretty easy to keep a constant temperature like in an oven and things like this. It's the same thing in fusion. So this is actually one of the features that I would argue fusion breaks the, breaks the trend of this is that it's, it has more energy intensity than, than, than fission on, on paper, but it actually does not have the consequences of control and sort of rapid release of the energy because it's actually... It, it, the physical system just doesn't want to do that. Yeah.

Lex Fridman 41:48 We're gonna have to look elsewhere for the weapons with which we fight World War III. Fair enough. Uh, so

Lex Fridman 41:56 what is plasma-

Dennis Whyte 41:58 Hm.

Lex Fridman 41:58 ... that you may or may have not mentioned? You mentioned ions and electrons and so on.

Dennis Whyte 42:01 I did not mention plasma.

Lex Fridman 42:02 So what is plasma? What is the role of plasma in nuclear fusion?

Dennis Whyte 42:06 So plasma is a phase of matter or a state of matter, so-Unfortunately, our schools don't... (laughs) It's like, I'm not sure why this is the case, but, eh, all, all children l-learn the three phases of matter, right? So, and what does this mean? So, we'll take, like, water as an example. So if you c- if it's cold, it's ice. It's in a solid phase, right? And then if you heat it up, the temp- it's the temperature that typically depends, uh, uh, sets the phase, although it's not, it's, it's not only temperature. So, you heat it up, and you go to a liquid, and obviously it changes its physical properties 'cause it can, you can pour it and so forth, right? And then if you heat this up enough, it turns into a gas, and a gas behaves differently because there's a very sudden change in the density. Actually, that's what's, what's happening. So, it, it changes by about a factor of 10,000 in density from the, from the liquid phase into when you make it into steam at atmospheric pressure. All very good, eh, except the problem is they forgot, like, what happens if you just keep elevating the temperature?

Lex Fridman 43:03 You don't wanna give kids ideas.

Dennis Whyte 43:04 (laughs)

Lex Fridman 43:05 They're gonna start experimenting. They're gonna start heating up the gas.

Dennis Whyte 43:08 Well, they're like, "It's good to, it's good to start to..." Anyway, so you, um, yeah, it turns out that once you get above, it's approximately 5,000 or 10,000 degrees Celsius, then you hit a new phase of matter. And actually, that's the phase of matter that is for all, uh, pretty much all the temperatures that are above that, uh, as well too. Um, and so what does that m-mean? So, it actually changes phase, so it's a different state of matter. And the reason that it becomes a different state of matter is that it's hot enough, that what happens is that the atoms that make up, remember, go back to Feynman, right? Everything's made up of these individual things, these atoms, but atoms can actually themselves be, um, w- which are c- which are made of nuclei, which contain the positive, uh, particles and the neutrons and then the electrons, which are very, very light, very much less mass than, than the nucleus, and that surround this. This is what makes up an atom. So, a plasma is what happens when you start pulling away enough of those electrons that, that they're free from the ion. So almo- all the atoms that make up, uh, uh, us, up and this water and all that, the electrons are in tightly bound states, and basically they're extremely stable. Once you're at about 5,000 or 10,000 degrees, you start pulling off the electrons. And what this means is that now the medium that is there, its constituent particles have mostly have net charge on them. So, why does that matter? It's because n- now this means that the particles can interact b- through their electric charge. In some sense, they were when it was in the atom as well too, but now that they're free particles, this means that they start, it fundamentally changes the behavior. It doesn't behave like a gas. It doesn't behave like a solid or a liquid. It behaves like a plasma, right? And so wh- why is this, (laughs) why is it disappointing that we don't speak about this? It's because 99% of the universe is in the plasma state. It's called stars. And in fact, our own sun, at the center of the sun is, well, clearly a plasma, but actually the surface of the sun, which is around 5,500 Celsius, is also a plasma 'cause it's hot enough, that is, uh... In fact, the things that you see... Sometimes you see these pictures from the surface of the sun, amazing f- (laughs) like, satellite photographs of, like, those big arms of things and of light coming off of the surface of the sun and solar flares, those are plasmas.

Lex Fridman 45:27 What are some interesting ways that this fourth state of matter is different than gas?

Dennis Whyte 45:32 Let's go to how a gas works, right? So, the reason a ga- and it goes back to Feynman's brilliance in saying that this is the most important concept. The reason g- actually solid, f- (laughs) liquid, and gas phases work is because the w- the nature of the interaction between the atoms changes. And so in a gas, you can think of this as being this room and the things, uh, although you can't see them, is that the molecules are flying around, but then with some frequency they basically bounce into each other.

Lex Fridman 46:00 Mm-hmm.

Dennis Whyte 46:00 And when they bounce into each other, they exchange momentum and energy around on this. And so it turns out that the probability and the distances and the scattering of those, of what they do, it, it's, it's those interactions that set the, uh, about how a gas behaves.

Lex Fridman 46:19 Mm-hmm.

Dennis Whyte 46:19 So, what does he mean by this? Well, so for example, if I take a t- a, a, an i- a, an imaginary test particle of some kind, like I spray something into the air that's got a particular color, or in fact you can do it in liquids as well too, like, how it, uh, gradually will s- disperse away from you. This is s- this is fundamentally set because of the way that those particles are bouncing into each other.

Lex Fridman 46:40 The, the probabilities of those, uh, particle bouncing.

Dennis Whyte 46:43 Yeah, the rate that they go at and the distance that they go at and so forth. So, this was figured out by Einstein and others at the beginning of the, b- Brownian motion, all these kinds of things. These were, these were set, um, up at the beginning of the last century, and it was really, like, this great revelation. "Wow, this is why matter behaves the way that it does, like, wow." Um, um, so but it's really like... And, and also in liquids and in solids, like, what really matters is, is, is, is how you're interacting with your nearest neighbor.

Lex Fridman 47:12 Mm-hmm.

Dennis Whyte 47:13 So, you think about that one. The gas particles are basically going around. Until they, until they actually hit into each other though they don't really exchange information And it's the same in a liquid. You're kind of beside each other, but you can kinda move around. And in a solid, you're literally, like, stuck beside your neighbor. You can't move, like Yeah. Plasmas are, uh, are weird in the sense is that they're, it's not like that. So, and it's because the particles have electric charge, this means that they can push against each other without actually being in c- close proximity to each other. It's, it's not, that's not an infinitely true statement, which if we go together, it's a little bit more technical. But basically, this means that you can start having action or exchange of information at a distance. And that's, in fact, the definition of a plasma is that it says the, these have a technical name, it's called a Coulomb collision, it just means that it's dictated by this force which is being pushed between the charged particles, is that, uh, the definition of a plasma is a, is a medium in which the collective behavior is dominated by these collisions at a distance. So, you can imagine, then, this starts te- to, to give you some strange...... behaviors, um, uh, which I could, I could quickly talk about, like, for exa- one of the most (laughs) counterintuitive ones is as plasmas get more hot, as they get h-h-high in temperature, then the collisions happen less frequently. It's, like, like, "What? That doesn't make any sense." When particles go faster, you think they would collide more often. But because the particles are interacting through, interacting through their electric field when they're going faster, they actually spend less time-

Lex Fridman 48:51 Mm-hmm.

Dennis Whyte 48:51 ... in the influential field of each other, and so they talk to each other less in an energy and momentum exchange point of view.

Lex Fridman 48:58 Interesting.

Dennis Whyte 48:58 It's just, well, just one of the count- one of the counterintuitive aspects of plasmas. (laughs)

Lex Fridman 49:02 Which is probably very, uh, relevant for nuclear fusion.

Dennis Whyte 49:06 Yes, exactly.

Lex Fridman 49:07 So if I can try to summarize what a nuclear fusion reactor is supposed to do, so you have, what, a couple of elements? What are usually the elements?

Dennis Whyte 49:19 Usually deuterium and tritium, which are the heavy forms of hydrogen.

Lex Fridman 49:22 Hydrogen. You have those, and you start heating it. And then as you start heating it, I forgot the temperature you said, but it becomes plasma.

Dennis Whyte 49:29 About 100 million, yeah.

Lex Fridman 49:29 No, first. First, it becomes-

Dennis Whyte 49:31 Oh, first, it becomes plasma.

Lex Fridman 49:32 ... plasma.

Dennis Whyte 49:32 So it's, it's a gas-

Lex Fridman 49:33 Yeah.

Dennis Whyte 49:33 ... and then it turns into a plasma-

Lex Fridman 49:35 Right.

Dennis Whyte 49:35 ... at about 10,000 degrees.

Lex Fridman 49:36 And then so you have a bunch of electrons and ions flying around, and then you keep heating the thing.

Dennis Whyte 49:41 Yep.

Lex Fridman 49:42 And, uh, I guess as you heat the thing, the ions hit each other rarer and rarer?

Dennis Whyte 49:47 Yes.

Lex Fridman 49:47 So, oh man, that's not fun.

Dennis Whyte 49:48 (laughs)

Lex Fridman 49:49 So you have to keep hea-

Dennis Whyte 49:50 Yes.

Lex Fridman 49:50 ... heating it, um, such that, uh, you, you have to keep hitting it until the probability of them colliding becomes reasonably high.

Dennis Whyte 50:00 And so it turns-

Lex Fridman 50:01 And also on top of that, and sorry to interrupt, you have to prevent them from hitting the walls-

Dennis Whyte 50:07 Exactly.

Lex Fridman 50:07 ... of the reactor-

Dennis Whyte 50:08 Yes, exactly.

Lex Fridman 50:09 ... somehow.

Dennis Whyte 50:09 So you asked about the r- the, the definitions of the requirements for fusion, so the most famous one or in some sense the most intuitive one is the temperature. And the reason for that is that you, you can make many, many kinds of plasmas that have zero fusion going on in them. And the reason for this is that the average, so , you can make a plasma at around 10,000. In fact, if you come ... By the way, you're welcome to come to our laboratory at the PSFC. I can show you a demonstration of a plasma-

Lex Fridman 50:37 Mm-hmm.

Dennis Whyte 50:38 ... that you can see with your eyes, and it's at about 10,000 degrees. And you can put your hand up beside it and all this, and it's like, and nothing, there's zero fusion going on.

Lex Fridman 50:47 So you have, uh, sorry, what was the temperature of the plasma you put your-

Dennis Whyte 50:49 About 10,000 degrees.

Lex Fridman 50:50 You can stick your hand in?

Dennis Whyte 50:51 Well, you can't stick your hand into it, but there's a glass tube, and you can basically see this-

Lex Fridman 50:55 See it right there.

Dennis Whyte 50:56 ... with your bare eye, yeah. And you can put your hand on the glass tube because it's, it's-

Lex Fridman 50:59 What's the color? Is it purple?

Dennis Whyte 51:00 It's, yeah, it's purple, yeah, yeah.

Lex Fridman 51:01 Blue and purple.

Dennis Whyte 51:02 It's blue and purple. Uh, it is, it is kind of beautiful. Um, yeah, pla- plasmas are actually quite, uh, astonishing sometimes in their beauty. Actually, o- uh, uh, one of the most amazing forms of plasma is lightning, by the way, which is, is instantaneous form of plasma that exists on Earth but immediately goes away because everything else around it is at room temperature.

Lex Fridman 51:20 That's fascinating.

Dennis Whyte 51:21 Yeah, so there's different requirements in this, so making a plasma takes about this. But at 10,000 degrees, even at a million degrees, there's almost no probability o- of the fusion reactions occurring. And this is because while the, the charged particles can hit into each other if you went, go back to the very beginning of this, remember I said, "Oh, these charged particles have to get to within distances which are like this size of a nucleus because of the strong nuclear force." Well, (laughs) unfortunately, as the particles get closer, this, the repulsion that comes from the charge, the Coulomb force, increases like the inverse distance squared.

Lex Fridman 52:04 Oh, no.

Dennis Whyte 52:04 So as they get closer, it, they are pushing harder and harder apart. So then it, then, then it gets a little bit more exotic, which you, maybe you will like though, that it turns out that you, people understood this in the, at the beginning of the, um, uh, of, of the age after Rutherford discovered the nucleus. It's like, "Oh, yeah." It's like, "How are we going to, how is this gonna work," right? 'Cause how do you get anything within these distances? It's g- it's gonna require extraordinary energy, and it does. And in fact, when you look at those energies, they're very, very high. Um, but it turns out quantum physics comes to the rescue because the particles aren't, aren't actually just particles. They're also waves. This is the point of quantum, right? The, you can treat them both as waves and as, as particles. And it turns out if you get, if they get in close enough proximity to each other, then the particle pops through, basically, this energy barrier through a c- an effect called quantum tunneling, which is really just the transposition of the fact that it's a wave so that it has a finite probability of this. It's, it's this, by the way you talk about, like, do, do you have a hard time, like, conceptualizing this? These are, this is one of them.

Lex Fridman 53:14 So quantum tunneling-

Dennis Whyte 53:15 Yeah.

Lex Fridman 53:15 ... is one of them?

Dennis Whyte 53:15 Yeah. This is like throwing a ping pong ball, like, at a, a piece of paper, and then every, like, you know, 100 of them just, like, magically show up on the other side of the paper without seemingly breaking the paper. I mean-

Lex Fridman 53:26 Yeah.

Dennis Whyte 53:27 ... to use a physical (laughs) analogy. Yeah.

Lex Fridman 53:29 And that, that phenomena is import- is, uh, is, uh, critical for the function of nuclear fusion-

Dennis Whyte 53:34 Yes.

Lex Fridman 53:34 ... uh, from a-

Dennis Whyte 53:35 For, for ev- all kinds of fusion, so this, this is the reason why stars can work as well too. Like, the pro- stars would have to be much, much hotter, actually, to be able to. In fact, it's not clear that they would actually ignite, in fact, uh, with- without this effect. And, so we get to that-

Lex Fridman 53:50 Interesting.

Dennis Whyte 53:50 ... so this is why there's another requirement. It's, it's not, so you must make a plasma, but you als- also must get it very hot in order for the reactions to have a significant probability to actually fuse.

Lex Fridman 54:01 Mm-hmm.

Dennis Whyte 54:01 And it actually falls effectively almost to zero for lower temperatures, eh, eh, as well too.

Lex Fridman 54:07 And so th- there's a, some nice equation-

Dennis Whyte 54:09 Yes.

Lex Fridman 54:09 ... that gets you to 50 million degrees?Or, like, uh-

Dennis Whyte 54:13 Yeah.

Lex Fridman 54:14 ... the, or the you said practically speaking 100 million.

Dennis Whyte 54:17 So, it's a really simple equation. It's the ideal gas law, basically, almost. So it's the, in the end, you've got a certain number of particle, of these fusion particles in the plasma state. They're in the plasma state. There's a certain number of particles. And if the confinement is perfect, if you put in a certain content of energy, then basically, eventually they just, they come up in a temperature, and they become, they be, they, they go up at, they go up to high temperature. This turns out to be, by the way, extraordinarily small amounts of energy. And you go, "What? It's like I'm getting something to, like, 100 million degrees? That's gonna take the biggest flame burner that I've ever seen." N- no. And the reason for this is b- it goes back to the energy content of, of this. So yeah, you have to, there's, you have to get it to high average energy, but there's very, very few particles.

Lex Fridman 55:05 Which is low density.

Dennis Whyte 55:07 It's low density.

Lex Fridman 55:07 How do you get it to be low density in a, in a reactor? Is this-

Dennis Whyte 55:09 So, you, well, the way that you do this is primarily, again, this is not exactly true in all kinds of, of fusion, but in the pri- in, in the primary one that we work on, magnetic fusion, this is all happening in a hard vacuum. So it's like it's happening in outer space. So basically, you've gotten rid of all the other particles except for these specialized few particles.

Lex Fridman 55:27 So you add them one at a time? Okay.

Dennis Whyte 55:30 Uh, no, actually, it's even e- easier than that. You, you connect a gas valve, uh, and you basically leak gas into it.

Lex Fridman 55:36 In a controlled fashion.

Dennis Whyte 55:37 Yeah. Yeah.

Lex Fridman 55:38 Wow.

Dennis Whyte 55:39 Yeah.

Lex Fridman 55:39 This is beautiful. How do you get it-

Dennis Whyte 55:40 It's a gas cylinder. (laughs)

Lex Fridman 55:41 How do you get it from hitting the walls?

Dennis Whyte 55:43 Yeah. So now you've touched on the other necessary requirements. So it turns out it's not just temperature that's required. You must also confine it. So what does this mean, confine it?

Lex Fridman 55:53 And there's two types of confinement, as you mentioned.

Dennis Whyte 55:55 Yeah.

Lex Fridman 55:55 You mentioned the magnetic one.

Dennis Whyte 55:56 Magnetic one, and there's the one they're called inertial as well too. But the general principle actually has nothing to do with, w- in particular with what you're, what, what the technology is that you use to confine it. It's because this goes back to the fact that the requirement in this is high temperature and thermal content. So it's like building a fire, right? And what this means is that if you, when you release the energy into this, or, or, or apply heat to this, if it just instantly leaks out, it can never get hot, right? So you're familiar with this. It's like if you've got something that you're, you're, you're trying to apply heat to, but you're just l- throwing the heat away very quickly. This is why we insulate homes, by the way, and things like this, right? It's like you don't want the heat that's coming into this room to just immediately leave 'cause you'll just start consuming infinite amounts of heat to try to keep it hot. So in the end, this is one of the requirements, and it ha- actually has a, a name. We call it the energy confinement time. So this means if you release a certain amount of energy into this fuel, um, kind of how long, you sit there, and you look at your watch. Well, how long does it take for this energy to, like, leave the system? So you could imagine that in this room that, you know, these heaters are putting energy into the air in this room, and you waited for a day. Would all the heat have gone to outside if I open up the windows? Oh, there, that's the energy confinement time. Okay, so it's the same concept as that. Um, so this is an important one. So all fusion must have confinement. Uh, there's another more esoteric reason for this, which is that people often confuse temperature and energy. So what do I mean by that? So this is literally a temperature, which means that it is a system in which all the particles, every particle has high kinetic e- energy and is actually in a fully relaxed state, namely that entropy has been maximized. I think it's a little bit more technical, but-

Lex Fridman 57:45 (laughs)

Dennis Whyte 57:45 ... m- this means that basically it is, it is a thermal system. So it's like the air in this room. It's like the water. It's the water in this. These all have temperatures, which means that there's a distribution of those energies 'cause the particles have collided so much that it's there. So we, th- this is distinguished from having high energy particles, like what we have in, like, particle accelerators like CERN and so forth. Those are high kinetic energy, but it's not a temperature, so it actually doesn't count as confinement. So we go through all of those. You have temperature, um, and then the other requirement, not too surprising, is actually that there has to be enough density of the fuel.

Lex Fridman 58:22 Enough, but not too much.

Dennis Whyte 58:23 Enough, but not too much, yes. And so in the end, um, the way that it, uh, there's a fancy name for it. It's called the Lawson criterion because it was, it was f- it was formulated by a scientist in the United Kingdom about 1956 or 1957, and this was essentially the realization o- oh, this is what it's going to take regardless of the confinement method. These are, this is the basic, what it is, is actually p- power balance. It just says, oh, there's a certain amount of heat coming in, which is coming from the fusion reaction itself, 'cause the fusion reaction heats the f- the fuel, um, versus how fast you would lose it. And it re- it, it basically summarize, it summarized by those three parameters, which is fairly simple, so temperature, and then the reason we say 100 million degrees is because almost alwa- in, and for th- for this kind of fusion, deuterium-tritium fusion, the minimum in the density and the confinement time product is at about 100 million. So you almost always design your device around that minimum, and then you try to get it contained well enough, and you try to get enough density. So, you know, so that temperature thing sounds crazy, right? That's what we've actually achieved in the laboratory. Like our experiment here at MIT, when it ran at its optimum configuration, it was at 100 million degrees.

Lex Fridman 59:39 Mm-hmm.

Dennis Whyte 59:40 But it wasn't actually the... The product of the density and the confinement time wasn't sufficient that we were at a place that we were getting high net energy gain, but it was making fusion reactions. So this is the sequence that you go through. Make a plasma. Then you get it hot enough, and when you get it hot enough, the fusion reactions start happening so rapidly that it's overcoming the, the rate at which it's leaking heat to the outside world. And at some point, it just becomes like a star, like a sun, and our own, our, our own sun, and a star doesn't have anything plugged into it. It's just keeping itself hot through its own fusion reactions. In the end, that's really close to what a fusion power plant would look like.

Lex Fridman 1:00:18 What does it visually look like? Does it-

Dennis Whyte 1:00:19 Yeah.

Lex Fridman 1:00:19 Does it look like, like you said, like, purple plasma in a-

Dennis Whyte 1:00:22 Yeah. Actually, it's, it's invisible to the eye 'cause it's so hot that it's basically emitting light in frequencies that we can't detect.It's literal, it's vi- invisible. (laughs) In fact, light goes through it. Visible light goes through it so easy that if you were to look at it, what you would see... In, in our own particular configuration, what we make is, in the end, is a donut shaped, um, it's vacuum vessel to keep the, uh, the air out of it. And when you in, and when you turn on the plasma, it gets so hot that most of it just disappears in the visible spectrum.

Lex Fridman 1:00:52 Mm-hmm.

Dennis Whyte 1:00:52 You can't see anything. And there's very, very cold plasma, which is between 10 and 100,000 degrees, which is out in the very periphery of it, which is kind of... So, the very cold plasma is allowed to interact with the, kind of has to interact with something eventually at the boundary of the vacuum vessel. And this kinda makes a little halo around it, and it glows this beautiful purple light basically. And these are, that's the em, that's the vi, that's what we can sense in the human spectrum, yeah.

Lex Fridman 1:01:20 I, I, uh, remember reading on a subreddit called Shower Thoughts, uh, which people should check out. It's just fascinating philosophical ideas that strike you while you're in the shower, and one of them was, it's lucky that, uh, fire, when it burns, communicates that it's hot using visible light.

Dennis Whyte 1:01:39 Yeah.

Lex Fridman 1:01:39 Otherwise, hum- humans would be screwed.

Dennis Whyte 1:01:41 Yeah.

Lex Fridman 1:01:42 Um, I don't know if there's a deep profound truth to that, but nevertheless, I did find it on Shower Thoughts subreddit.

Dennis Whyte 1:01:47 Yes. Actually, I do have the, there... (laughs)

Lex Fridman 1:01:49 (laughs)

Dennis Whyte 1:01:49 This, this goes off on a bit of a... You're, you're right. This is actually, it's interesting 'cause, uh, you know, as a scientist you also think about evolutionary functions and how we got like, why do we have the senses that we do?

Lex Fridman 1:01:59 Yeah.

Dennis Whyte 1:01:59 It's an interesting question, right? Like, why can bees see in the ultraviolet and we can't? Then you go, "Well, it's natural selection." For some reason, this wasn't really particularly important to us, right?

Lex Fridman 1:02:08 Mm-hmm.

Dennis Whyte 1:02:08 Why can't we see in the infrared and other things can? It's like, "Hmm, mm."

Lex Fridman 1:02:13 (laughs) 'Cause the people that could are-

Dennis Whyte 1:02:14 Yes, it's a, it's, it's a fascinating question, right?

Lex Fridman 1:02:15 (laughs)

Dennis Whyte 1:02:15 Obviously, there's some, there's some advantage that you have there that isn't there, and even color distinguishing, right, of something safe to eat is not safe, what- whatever it would be. Uh, I'll actually go back to this because it's something that I, that I tell all, all of my, my students when I'm teaching, um, ionizing radiation and radiological safety. Whatever you say, there's a cultural concern or that when people hear the word radiation, like, what does this mean? It, it literally just means light is what it means, all right? But it's light in different parts of the spectrum, right? And so it turns out besides the visible light that we can see here, we are immersed in almost the totality of the electromagnetic spectrum. There is visible light. There's infrared light. There is microwaves going around us. That's how our cellphone works. You can't... Th- it's, it's way past our detection capability. But also higher energy ones which have to do with ultraviolet light, how you get a sunburn. Um, and even x-rays and things like this at, at small levels are continually being c- like from the concrete in this wa- in the walls of this hotel, there's x-rays hitting our body continuously. Like, I can, I can bring out a... And we can go down to the lab at MIT. I can bring out a detector and show you. Every single room will have, will have these.

Lex Fridman 1:03:26 And by our body-

Dennis Whyte 1:03:27 Yeah.

Lex Fridman 1:03:27 ... you mean the 10 to the 28 atoms that make up us.

Dennis Whyte 1:03:29 Yeah, the, the 10 to the 28 atoms, and they're coming in-

Lex Fridman 1:03:31 (laughs)

Dennis Whyte 1:03:31 ... and they're interacting with those things. And those, particularly the ones where the light is at higher average energy per, per light particle, those are the ones that can possibly have an effect on human health. So, we, we have... It's interesting humans and all animals have evolved on Earth where we're immersed in that all the time.

Lex Fridman 1:03:51 Yeah, we are.

Dennis Whyte 1:03:51 There's natural sources of radiation all the time, yet we have zero ability to detect it, like zero.

Lex Fridman 1:03:57 Yeah, and our ability, cognitive ability to filter it all out and not-

Dennis Whyte 1:04:01 Right.

Lex Fridman 1:04:01 ... not give a damn.

Dennis Whyte 1:04:01 It would probably overwhelm us actually if we could see all of it. But my main point is, goes back to your thing about fire and, and self-protection. If, if these ionize, if ionizing radiation was such a critical aspect of the health of organisms on Earth, we would almost certainly have evolved methods to detect it, and we have none. (laughs)

Lex Fridman 1:04:20 (laughs)

Dennis Whyte 1:04:20 And, uh, yes.

Lex Fridman 1:04:21 The physical world that's all around-

Dennis Whyte 1:04:23 Yeah.

Lex Fridman 1:04:23 ... is just incredible. You're blowing my mind, uh, Dr. Dennis White. Okay.

Lex Fridman 1:04:27 Let's, so you have experience with, uh, magnetic confinement. You have experience with inertial confinement. Most of your work has been in magnetic confinement.

Dennis Whyte 1:04:33 Yes, yeah.

Lex Fridman 1:04:34 But let's sort of, um, talk about the, the, the, the sexy recent thing for, for a bit of a time. There's been a breakthrough in the news, uh, that, uh, laser-based inertial confinement was used by DoE's National Ignition Facility at the Lawrence Livermore National Laboratory. Can you explain this breakthrough that happened in December?

Dennis Whyte 1:04:56 Yeah. So, it goes to the set of criteria that I talked about before about getting high energy gain. So, in the end, what, what are we after in fusion is that we, we basically assemble this plasma fuel in some way, and we provide it a starting amount of energy. Think of lighting the fire. And what you want to do is get back, like, m- significant excess gain-

Lex Fridman 1:05:23 Mm-hmm.

Dennis Whyte 1:05:23 ... from the fact that the fusion is, is making more, uh, is releasing the energy. So, it's, it's like the equivalent of, like, we wanna have a match, a small match light a fire, and then the fire keeps us hot.

Lex Fridman 1:05:34 Mm-hmm.

Dennis Whyte 1:05:34 It's like, it's, it's very much like that. So, as I said, we've, we've made many of the, and what do we mean by we? It's like the fusion community has pursued aspects of this through a variety of different confinement, uh, methodologies. Um, is that the, um, the key part about what happens... So, what was a threshold we had never gotten over before was that if you only consider the plasma fuel, not the, not the total engineering system but just the plasma fuel itself, we had not gotten to the point yet where basically the size of the match was, was smaller than the amount of energy that we got from the fusion.

Lex Fridman 1:06:11 Mm-hmm. Is there a good term for when the output is greater than the input?

Dennis Whyte 1:06:17 Yes, yes. It, it, there is. Well, there's several special definitions of this. So, one of them is that if you l- if you, like in a fire, if you light a match-... and you have it there, and it's an infinitesimal amount of energy compared to what you're getting out of the fire. We call this ignition.

Lex Fridman 1:06:32 Mm-hmm.

Dennis Whyte 1:06:33 Which makes sense, right? This is like what the s- the, the what our own sun is as well too. So, that, that was not ignition in that sense, uh, as well too. So, what we call this is scientific, what the one that we, I just talked about, which is for, for some instance, when I get enough fusion energy released compared to the size of the match, we call this scientific breakeven.

Lex Fridman 1:06:54 Breakeven.

Dennis Whyte 1:06:55 Breakeven. And it's because you've gotten past the fact that this is unity now at this point.

Lex Fridman 1:07:00 What is a fusion gain or as, uh, using the notation Q from the paper overview of the-

Dennis Whyte 1:07:05 Yeah.

Lex Fridman 1:07:05 ... SPARC tokamak before to-

Dennis Whyte 1:07:07 Yeah.

Lex Fridman 1:07:07 ... using just the same kind of terminology-

Dennis Whyte 1:07:08 Yeah, actually, so there's, uh, sorry, the technical term is Q, uh, capital Q.

Lex Fridman 1:07:13 Oh, so it's good. People actually use Q for this purpose.

Dennis Whyte 1:07:15 We actually use capital Q, yeah. Or sometimes it's called Q-

Lex Fridman 1:07:18 So, Q's taken?

Dennis Whyte 1:07:18 Q sub p or something like this.

Lex Fridman 1:07:20 Okay.

Dennis Whyte 1:07:20 Okay, so this is, which, which means the, which wha- what it means is that it's in the plasma. So, all we're considering is, is the energy balance or gain that comes from the plasma itself.

Lex Fridman 1:07:30 Mm-hmm.

Dennis Whyte 1:07:30 We're not considering the technologies which are around it which are providing the containment and so forth. So, wh- why, why the excitement and so f- well, because f- for one reason, it's a rather sim- it's a rather simple threshold to get over, to understand that you're getting more energy out from the fusion, even in a theoretical sense than you were from the, you know, from the ini- uh, starting match.

Lex Fridman 1:07:52 Do you mean conceptually simple?

Dennis Whyte 1:07:53 It's conceptually simple that you get past one that everyone under- like, when you're less than one, that's much less-

Lex Fridman 1:07:59 I see.

Dennis Whyte 1:07:59 ... interesting than getting past one because obviously you start-

Lex Fridman 1:08:00 So there's a really big-

Dennis Whyte 1:08:01 ... you start to get energy again, yeah.

Lex Fridman 1:08:03 ... threshold to get past.

Dennis Whyte 1:08:03 But it's, it's really, it really is a scientific threshold 'cause what QP actually, um, denotes is the relative amount of self-heating that's happening in the f- in the plasma.

Lex Fridman 1:08:16 Mm-hmm.

Dennis Whyte 1:08:17 So, what, what I mean by this is that in the end, in these systems for, and, uh, what you, what you want is something that where the, the relative amount of, of heating, which is keeping the fuel hot, is dominated by from the fusion reactions themselves.

Lex Fridman 1:08:34 Mm-hmm.

Dennis Whyte 1:08:35 And, and so it becomes, it's, it's, it's sort of like thinking, like, a bonfire is a lot more interesting physically than just holding a blowtorch to a wet log, right? There's a lot more dynamics. It's a lot more self-evolved and so forth. And what we're excited as, as scientists is that it's clear that the, uh, th- in that experiment, that they actually got to a point where the fusion reactions themselves were actually altering the state of the plasma.

Lex Fridman 1:09:02 Mm-hmm.

Dennis Whyte 1:09:03 It's like, wow. I mean, we'd seen it in glimpses before in magnetic confinement at relatively small levels, but apparently it, it seems like in this experiment, it's likely to be a dominant, do- dominated by self-heating. That's a very important, that's a very in- in-

Lex Fridman 1:09:16 So, that makes it a self-sustaining type of reaction.

Dennis Whyte 1:09:18 It's more self-sustaining. It's a more self-referential system, uh, in, in a sense. And it sort of self-evolves in a way. Again, it's not that it's going to evolve to a dangerous state. It's just that we want to see what happens when the, when the fusion is the dominant heating source.

Lex Fridman 1:09:32 And we'll talk about that, but-

Dennis Whyte 1:09:33 Yeah.

Lex Fridman 1:09:33 ... so there's also another element which is the, uh, inertial confinement. Uh, laser-based inertial confinement is kinda the, a little bit of an underdog. And so a lot of the co- and the broad nuclear fission community has been focused on magnetic confinement.

Dennis Whyte 1:09:47 Yeah.

Lex Fridman 1:09:47 Can you explain just how laser-based inertial confinement works? So, it says, uh, 192 laser beams-

Dennis Whyte 1:09:56 Yeah.

Lex Fridman 1:09:56 ... were aligned on a-

Dennis Whyte 1:09:57 Yes.

Lex Fridman 1:09:57 ... deuterium-tritium DT target smaller than a pea.

Dennis Whyte 1:10:01 Yes.

Lex Fridman 1:10:02 Uh, this is like-

Dennis Whyte 1:10:03 Or a BB actually, yeah.

Lex Fridman 1:10:04 Thr- b- okay, well, you know, it depends. Uh, not all peas are made the same. But, uh, this is like, uh, throwing a perfect strike in baseball from a pitch. This is like a journalist wrote this, I think.

Dennis Whyte 1:10:14 (laughs)

Lex Fridman 1:10:14 This is like, oh, no, it's not a journalist. It's a DoE wrote this.

Dennis Whyte 1:10:16 Yeah, yeah, could be. Yeah.

Lex Fridman 1:10:17 Department of Energy which-

Dennis Whyte 1:10:18 We, we try to use all these analogies as-

Lex Fridman 1:10:20 This is like throwing a perfect strike in baseball from a pitcher's mount 350 miles away from the plate. There you go.

Dennis Whyte 1:10:28 (laughs)

Lex Fridman 1:10:28 Department of Energy, the United States Department of Energy wrote this.

Dennis Whyte 1:10:31 (laughs)

Lex Fridman 1:10:32 Okay. (laughs) So, can you explain-

Dennis Whyte 1:10:33 Interesting.

Lex Fridman 1:10:34 ... what the, what the lasers, uh, Department of Energy

Dennis Whyte 1:10:36 ... what, what, what actually happens?

Lex Fridman 1:10:37 Yeah.

Dennis Whyte 1:10:37 Actually, there's usually mass confusion about this, so, um, so what's going on in this form of energy? So, the fuel is, is, is delivered in a discreet, the fusion fuel, the deuterium and tritium-

Lex Fridman 1:10:49 Mm-hmm.

Dennis Whyte 1:10:50 ... is in a discreet spherical, it's more like a BB. Let's call it a BB. So, it's in, it's a small one, and all the fuel that you're gonna try to, to burn is basically there, okay, and it's about that size. So, what's hap- so how are you going to get... and it's at li- literally it's a, it's like at 20 degrees above absolute zero because the deuterium and tritium are kept in, in a liquid and, and a solid state, so it's, it's, it-

Lex Fridman 1:11:11 Oh, wow, so the fuel is injected not as a gas but as a, as a solid or-

Dennis Whyte 1:11:15 Yeah. Uh, yeah. It, it's actually, and it's very, and, and in these particular experiments, they can introduce one of these, you know, pa- these targets once per day approximately, something like that, 'cause it's very, it's v- very, uh, it's kind of amazing technology actually (laughs) that I know some of the people that worked on this, uh, back in the days. Um, they actually make these things at a BB l- size of this frozen fuel. It's actually at cryogenic temperatures.

Lex Fridman 1:11:38 Mm-hmm.

Dennis Whyte 1:11:38 And they're almost, like, smooth to the atom level. I mean, they're am- amazing pieces of technology. So, what you do in the end is think, you, what you have is a spherical assembly of this fuel, like a ball, and what, what is the purpose of the lasers? The purpose of the lasers is to provide optical energy to the very outside of this. And what happens is the, that energy is absorbed because it's a s- it's, it's in the solid phase of matter, so it's absorbed really in the surface. And then what happens is that, but when it's absorbed in a something called the ablator, what does that mean? It means it goes instantly from the solid phase to the gas phase. So, it becomes like a rocket engine. Uh, but you hit it, like, very uniformly. So, all, there's, like, rocket engines coming off this surface. Think of, like, an asteroid almost where there's, like, rockets coming off-

Lex Fridman 1:12:32 Mm-hmm.

Dennis Whyte 1:12:32 ... and all those things. So, what does that do? Well, what does a rocket do? It actually pushes-... by, by Newton's law, right? It pushes the other thing on the other side of it, equal and opposite reaction, it pushes it in. So, what it does is it ac- the, the lasers actually don't heat. This is what was, was confusing. People think the lasers, "Oh, we're gonna get it to 100 million degrees." In fact, you want the exact opposite of this. What you want to do is get, like, essentially a rocket going out like this-

Lex Fridman 1:12:58 Mm-hmm.

Dennis Whyte 1:12:58 ... and then what happens is that the sphere, like, r- and this is happening in a billionth of a second or, or less actually, this rapidly, tha- that force, like, so rapidly compresses the fuel that what happens is that you're squeezing down on it and, and, and, you know, it's like... What was the... See BB to... That's bad actually. BB... I should have started with a basketball. Basket. Goes from, like, a basketball down to something like, like this-

Lex Fridman 1:13:23 Mm-hmm.

Dennis Whyte 1:13:24 ... in a billionth of a second.

Lex Fridman 1:13:26 (laughs)

Dennis Whyte 1:13:26 And whe- when that, when that happens, I mean, you scale that in your mind. So, when that happens, and in... This c- this comes from, almost from classical physics. So, there's s- some quantum in it as well too, but basic- if you can do this, um, like, very uniformly and so-called adiabatically, like, you're not actually heating the fuel, what happens is that you get adiabatic compression such that the very center of this thing all of a sudden just spikes up in temperature because it's- it's- it's- it's actually done so fast. So, why is it called inertial fusion? It's because you're doing this on such fast time scales that the inertia of the hot fuel basically is still finite, so it can't, like, push itself apart before the fusion happens.

Lex Fridman 1:14:08 Oh, wow.

Dennis Whyte 1:14:09 Yeah.

Lex Fridman 1:14:09 So, so how do you make it so... How do you make it so fast?

Dennis Whyte 1:14:12 This is why you use lasers, because you're applying this energy in very, very short periods of time, like under a fraction of a billionth of a second, and so basically that... And then the force which is coming from this comes from the energy of the lasers, which, which is basically the rocket action which g- does the compression quite quickly.

Lex Fridman 1:14:30 Well, so is the force... Is the, uh, inward-facing force...

Dennis Whyte 1:14:34 Is, is-

Lex Fridman 1:14:34 Is that, is that increasing the temperature-

Dennis Whyte 1:14:36 No.

Lex Fridman 1:14:36 ... exponentially?

Dennis Whyte 1:14:37 You wanna keep the fuel c- cold and then, and just literally just ideally compress it, and then in something which is at the very center of that compressed sphere, because you've compressed it so rapidly, the laws of physics basically require for it to increase in temperature.

Lex Fridman 1:14:53 So, the- the change in pressure-

Dennis Whyte 1:14:54 The, the effect is that, is like if you know the thing... So, adiabatic cooling we're actually fairly familiar with. If you take a spray can, right-

Lex Fridman 1:15:01 Mm-hmm.

Dennis Whyte 1:15:01 ... and you push the button, when it, when it rapidly expands, it cools. This is the nature of a lot of cooling technology we use actually. Well, the opposite is true, that if you would take all of those particles and jam them together very fast back in, they wanna heat up, and that's what happens. And then what happens (laughs) is you, you basically have this very cold, compressed set of fusion fuel, and at the center of this, it goes to this 100 million degrees Celsius, and so if it gets to that 100 million degrees Celsius, the fusion fuel starts to burn, and when that fusion fuel starts to burn, it wants to heat up the other cold fuel around it, and, and it just basically propagates out so fast that what you would do ideally, you would actually burn, in a fusion sense, most of the fuel that's in the pellet. So, this was very exciting because what they had done was they, it's clear that they propagated this. They got this what they call a hotspot and then the fact that this heating had