Dennis Whyte is a nuclear scientist at MIT and the director of the MIT Plasma Science and Fusion Center. Please support this podcast by checking out our sponsors:
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EPISODE LINKS:
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OUTLINE:
0:00 - Introduction
0:32 - Nuclear fusion
18:31 - e=mc^2
32:58 - Fission vs fusion
38:10 - Nuclear weapons
41:56 - Plasma
49:07 - Nuclear fusion reactor
1:04:27 - 2022 nuclear fusion breakthrough explained
1:25:04 - Magnetic confinement
1:44:14 - ITER
1:49:01 - SPARC
2:03:00 - Future of fusion power
2:11:33 - Engineering challenges
2:30:14 - Nuclear disasters
2:34:58 - Cold fusion
2:49:14 - Kardashev scale
2:58:38 - Advice for young people

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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.

The following is a conversation with Dennis White, nuclear physicist at MIT and the director of the MIT Plasma Science and Fusion Center.

To support it, please check out our sponsors in the description.

And now, dear friends, here's Dennis white.

It's the underlying process that powers the universe.

So as the name implies, it fuses together or brings together 2 different elements, technically nuclei, that come together and if you can push them together close enough that you can trigger essentially a reaction, what happens is that the element typically changes, so this means that you change from 1 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 were the initial elements, typically hydrogen, and they had a particular mass, rest mass, which means just the mass 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?

But mass and energy are the same thing, which is what E equals MC squared means.

And the conversion of this comes into kinetic energy, namely energy that you can use in some way, and that's what happens in the center of stars.

So fusion is literally the reason life is viable in

So fusion is happening in our sun, And what are

The elements are hydrogen that are coming together.

It goes through a process which is probably gets a little bit too detailed, but it's a somewhat complex catalyzed process that happens in the center of stars.

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.

And it's essentially a sequence through which these processes occur that you end up with helium.

And the reason for this is because helium has features as a nucleus, like the interior part of the atom, that is extremely stable.

And the reason for this is helium has 2 protons and 2 neutrons.

These are the things that make up nuclei, that make up all of us, along with electrons.

And because it has 2 pairs, it's extremely stable.

And for this reason, when you convert the hydrogen into helium, it just wants to stay helium, and it wants to release kinetic energy.

So stars are basically conversion engines of hydrogen into helium.

And this also tells you why you love fusion.

I mean, because our sun will last 10 billion years approximately.

But to do that kind of conversion, you have to have extremely high temperatures.

It is 1 of the criteria for doing this, but it's the easiest 1 to understand.

It's because effectively what this requires is that these hydrogen 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 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 4 fundamental forces in the universe.

This is the strongest 1, but it has a strange property is that 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?

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 out 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.

And on Earth, this means it's 1 of the first things we teach, you know, entering graduate students, you can do a quick, basically, power balance and you can determine that on Earth it requires a minimum temperature of about 50 million degrees Celsius on Earth.

To get enough fusion that you would be able to make, get energy gain out of it.

So you can trigger fusion reactions at lower energy, but they become almost vanishingly small at lower temperatures than that.

First of all, let me just link around some crazy ideas.

So, 1, the strong force, just stepping out and looking at all the 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 they're all very specific and the standard model describes 3 of those forces extremely well and there's.

Did you step back and almost look at the philosophy of physics?

So it's interesting, because as a scientist, I see the universe through that lens of essentially the interesting things that we do are through the forces that get used around those, and everything works because of that.

Richard Feynman had, I don't know if you've ever read Richard Feynman, it's a little bit of a tangent, but-

He's never been on the podcast, he's unfortunately passed away, but like a hero to almost all physicists.

And a part of it was because of what you said, he kind of looked through a different lens at these, what typically look like very dry equations and relationships, and he kind of, I think he brought out the wonder of it in some sense, right, for those.

He posited what would be, if you could write down a single, not even really a sentence, but a single concept that was the most important thing scientifically that we knew about, that in other words, you had only 1 thing that you could transmit like a future or past generation.

So it's not what you think, it wasn't like, oh, strong nuclear force or fusion or something like this.

And it's very profound, which 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.

Which is like, wow, that's so simple, but it's not so simple.

It's because who thinks about atoms that they're made out of?

This is a good question I give to my students, how many atoms are in your body?

Almost no students can answer this, but to me, that's like a fundamental thing.

So that's a trillion, million, trillion, trillion or something like that, yes.

So 1 thing is to think about the number and the other is to start to really ponder the fact...

Yeah, it all holds together and you're actually that.

No, I mean, there are people who do 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 2 or something, I was like, oh, this would all not work.

It's like, so it turns out that there are key reactions that if they had slightly lower probability, no star would ever ignite.

It does seem like the universe set things up for us that it's possible to do some cool things, but it's challenging.

I mean, the multiverse model is an interesting 1 because there are 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 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 1 of the interesting ones by default.

Yeah, 1 of the somewhat interesting, but there's probably super interesting ones where we, I tend to think of humans as incredible creatures.

Our brain 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 in ways we can't even comprehend in terms of their ability to construct models of the world, to do physics, to do physics and mathematics.

I would see it in a slightly different way.

It's actually, it's because we have creatures that live with us on the earth that have cognition, that understand and move through their environment, but they actually see things in a way, or they sense things in a way which is so fundamentally different it's really hard.

The problem is the translation, not necessarily intelligence, so it's the perception of the world.

So I have a dog and when I go and I see my dog 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, optical 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 1 of my areas of research is spectroscopy, so this means the study of light.

And I get this quote unquote, see things or representations of them from the far infrared all the way to hard, hard x-rays, which is several orders of magnitude of the light intensity, but our own human eyes see a teeny, teeny little sliver of this.

So that even bees, for example, see a different place than we do.

I think if you think of, there's already other intelligences around us in a way, in a limited way, because of the way they can communicate.

But those are already baffling in many ways, yeah.

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.

For example, whatever the heck consciousness is, could actually be a door into understanding some physical phenomena we haven't even begun understanding.

So just like you said, spectroscopy, it could be a similar kind of spectrum for consciousness that we're just like, we're like these dumb descendants of apes walking around.

It sure feels like something to experience the color red.

But we don't have, it's the same as in the ancient times you experienced physics, you experienced light.

It's like, oh, it's bright, and you know.

We might actually experience this faster than we thought, because we might be building another kind of intelligence.

Yeah, and that intelligence will explain to us how silly we are.

Well, there was an email thread going around the professors in my department already of, so what is it going to look like to figure out if students have actually written their term papers or its chat… Chat GPT.

So as usual, we tend to be empiricists in my field, so of course they were in there like trying to figure out if it could answer like questions for a qualifying exam to get into the PhD program at MIT.

Which was, they didn't do that well at that point, but of course this is just the beginning of it, so we have some interesting ones to

Eventually both the students and the professors will be replaced by Chad GPT.

I really recommend, I don't know if you've ever seen them, it's called The Day the Universe Changed.

He's a science historian based in the UK.

He had a fairly famous series on public television called Connections, I think it was, but the 1 that I really enjoyed was The Day the Universe Changed.

And the reason for the title of it was that it 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 moments of perception in the history of humanity that changed what we were, right?

And so as I was thinking about coming to discuss this, people see fusion, oh, it's still far away, or it's been slow progress.

It's like when my godmother was born, people had no idea how stars worked.

So you talk about that day, that insight, the universe change, it's like, oh, this is the, I mean, and they still didn't understand all the parts of it, but they basically got it.

It's like, oh, 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 1 of those days the universe changed, right?

It seems like technology is developing faster and faster and faster.

I tend to think, just like with Chad GPT, I think this year might be extremely interesting, just with how rapid and how profitable the efforts in artificial intelligence are, that just stuff will happen where our whole world is transformed like this, and there's a shock, and then next day, you kind of go on and you adjust immediately.

You probably won't have a similar kind of thing with nuclear fusion with energy because there's probably going to be an opening ceremony and stuff like this.

But with digital technology, you can just have a immediate transformation of society.

And it'll be this gasp, and then you kinda adjust, like we always do.

And then you don't even remember, just like with the internet and so on, how the days were before.

I mean, fusion will be, because it's energy, it's nature is that it will be, and anything that has to do with energy use tends to be a slower transition, but they're the most, I would argue, some of the most profound transitions that we make.

I mean, the reason that we can live like this and sit in this building and have this podcast and people around the world is, at its heart, is energy use,

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 a bedrock, actually, of all of these, but it doesn't tend to come overnight.

Yeah, and some of the most important, some of the most amazing technology is 1 we don't notice, because we take it for granted, because it enables this whole thing.

which is energy, which is amazing for how fundamental it is to our society and way of life is 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, which are very important.

So for example, you buy an electric car and you go, oh good, I have an emission-free car.

And ah, but it's like, so why do you say that?

Well, it's because if I draw the circle around the car, I have electricity and it doesn't emit anything.

Okay, but you plug that into a grid where you follow that wire back, there could be a coal power plant or a gas power plant at the end of that.

Oh, 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.

Plus there's also a story of how the raw materials are mined in which parts of the world with sort of basic respect or 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 the particular electric car with a circle around it.

And the physics or the science of it too is the energy use that it takes to do that digging up, which is also important and all that.

Yeah, anyway, so we wandered away from fusion, but yes.

But it's very important actually in the context of this, just because, you know, those of us who work in fusion and these other kinds of sort of disruptive energy technologies, it's interesting, I do think about like what is it going to mean to society to have an energy source that is like this, that would be like fusion, which has such completely different characteristics.

For example, free unlimited access to the fuel, but it has technology implications.

What does it mean for how we distribute wealth within our society?

It's very difficult to know, but probably profound.

We're gonna have to find another reason to start wars.

Instead of resources, we're gonna have to figure

We've done a pretty good job of that over the course of our history.

So we talked about the forces of physics, and again, sticking to the philosophical before we get to the specific technical stuff, E equals mc squared you mentioned.

How amazing is that to you, that energy and mass are the same?

And what does that have to do with nuclear fusion?

It's the fact that energy and mass are equivalent to each other.

They're just, the way we usually comment to it is that they're just energy, just in different forms.

I haven't for a while, but often I teach the introductory class for incoming nuclear engineers.

And so we put this up as an equation, and we go through many iterations of using this, how you derive it, how you use it, and so forth.

And then usually in the final exam, I would give, I would basically take all the equations that I've used before and I flip it around.

I basically, instead of thinking about energy is equal 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 to get that intuition, yeah.

So in the end, it's interesting is that this 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 though we used equals MC squared, this is burning coal and burning gas and burning wood is actually still 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, which is that E equals mc squared.

It tells you that the amount of energy that is liberated in a particular reaction when you change mass has to, because C squared, that's the speed of light squared.

It's a very large number and it's totally constant everywhere in the universe, which is the most- Which is another weird thing.

Which is another weird thing and in all rest frames and actually, the relativity stuff gets more difficult conceptually until you get through it.

Anyway, so you go to that and what that tells you is that it's the relative change in the mass, we'll 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, it's 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 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.

So of whatever you do, if you're thinking about, and why do I care about this?

Well, because 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, the environmental impact it would have.

And fusion will always have 20 million times the amount of energy release per reaction that you could have those.

So this is why we consider it the ultimate like environmentally friendly energy source is because of that.

So is it correct to think of mass broadly as a kind of storage of energy?

You mentioned it's environmentally friendly.

It's cheap, clean, safe, so easy access to fuel and virtually unlimited supply, no production of greenhouse gases, little radioactive waste produced allegedly.

Can you sort of elaborate why it's cheap, clean, and safe?

It is not cheap yet, because it hasn't been made at a commercial scale.

Actually, we'll come back to that, because this is cheaper, or a more technically correct term, that it's economically interesting, is really the primary challenge, actually, of fusion at this point.

So cheap, actually, when we're talking about cheap, we're thinking like asymptotically.

If you take it forward several hundred years, that's sort of because of how much availability there is of resources to use.

The fuel is already cheap, it's basically free, right?

So if we were to be using fusion fuel sources to power your, 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.

This is why it's hard to, in 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 gas or oil, or we chop wood, or we find coal, or these things.

And it's also, it's not an intermittent renewable energy source like wind and solar.

So if you're saying the fuel is free, 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, in the center of stars, in fact.

So there's only 1 natural place in the universe that fusion energy occurs that's in the center of stars.

So that's going to bring a price to it depending on the size and complexity of the technology that's needed to recreate those things.

And we'll talk about the details of those technologies and which parts might be expensive today and which parts might be expensive in 200 years.

It will have a revolution, I'm certain of it.

So about clean, so clean is, at its heart, what it does is convert, it basically converts hydrogen into, it's heavier forms of hydrogen, the most predominant 1 that we use on Earth, and converts it into helium and some other products, but primarily helium is the product that's left behind.

In fact, that's actually what our sun is doing.

It's eventually going to extinguish itself because it'll just make so much helium that it doesn't do that.

So in that sense, clean because there's no emissions of carbon or pollutants that come directly from the combustion of the fuel itself.

We're talking about very high temperatures.

Yeah, so this is also the counterintuitive thing.

So I told you temperatures, which like 50 million degrees or it actually tends to be more like about 100 million degrees is really what we aim for.

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, this is the technology that I just described, is it fundamentally, what it does is it takes this fuel and it isolates it from any terrestrial conditions so that it has no idea it's on Earth.

It's not touching any object that's at room temperature.

Even including the walls of the containment building or containment device or even air or anything like this.

So it's that part that makes it safe And there's actually another aspect to it.

But that fundamental part makes it so safe.

And in the mainline's approach to fusion is also that it's very hot, where there's very, very few particles at any time in the thing that would be the power plant.

Actually, the more correct way to do it is you say there's very few particles per unit volume, so in a cubic centimeter, in a cubic meter, something like that.

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 because if I wave my hand, I can feel the air pushing against my face.

That means we're in a fluid or a gas which is around us that has a particular number of atoms per cubic meter, right?

So it's what, this actually turns out to be 10 to the 25th, so this is 1 with 25 zeros behind it per cubic metre.

So we can figure out what a cubic, like cubic metre is about like this.

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