Theories of Everything with Curt Jaimungal - Einstein Would Fail Modern Grant Applications | David Deutsch

Episode Date: October 6, 2025

David Deutsch argues that Einstein would struggle to secure modern research grants, exposing how funding systems favor incremental work over bold, fundamental ideas. He connects this bias to quantum computing, constructor theory, free will, and the role of creativity in scientific breakthroughs.- 00:00 - Einstein's Grant Application- 07:00 - Funding People, Not Projects- 12:35 - Is Physics Stagnant?- 17:34 - The "Checkbox" Problem- 26:05 - Physics vs. Math Departments- 32:42 - Fundamental vs. Foundational- 40:08 - Physicists and Philosophy- 45:44 - Why Academics Are Silent- 51:20 - The Problem of Quantum Gravity- 58:31 - Qubit Field Theory- 1:03:18 - Problem-Solving in Physics- 1:17:14 - Deutsch's "Impossible" List- 1:24:23 - Meeting Hugh Everett- 1:35:01 - Susskind's MWI Objections- 1:46:44 - Everett and Quantum Computing- 1:56:20 - Constructor Theory- 2:03:01 - Free Will and Knowledge- 2:09:08 - Follow The FunSPONSORS:- The Economist: 20% off - https://www.economist.com/toe- Claude: 50% off Claude Pro - http://claude.ai/theoriesofeverythingRESOURCES:- Beginning Of Infinity [Book]: https://www.amazon.com/Beginning-Infinity-Explanations-Transform-World/dp/0143121359- How To Reverse Academia’s Stagnation [YouTube]: https://youtu.be/Em-85baHx0A- Qubit Field Theory [Paper]: https://arxiv.org/pdf/quant-ph/0401024- Quantum Theory, The Church–Turing Principle And The Universal Quantum Computer [Paper]: https://royalsocietypublishing.org/doi/10.1098/rspa.1985.0070- ArXiv: https://arxiv.org/- Scott Aaronson [TOE]: https://youtu.be/1ZpGCQoL2Rk- Wayne Myrvold [TOE]: https://youtu.be/HIoviZe14pY- Neil Turok [TOE]: https://youtu.be/zNZCa1pVE20- String Theory Iceberg [TOE]: https://youtu.be/X4PdPnQuwjY- Alex Honnold [TOE]: https://youtu.be/D4oXvxqzSyA- Michael Levin Λ Anna Ciaunica: https://youtu.be/2aLhkm6QUgA- Stephen Wolfram [TOE]: https://youtu.be/FkYer0xP37E- The Heisenberg Picture: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Advanced_Statistical_Mechanics_(Tuckerman)/09%3A_Review_of_the_basic_postulates_of_quantum_mechanics/9.04%3A_The_Heisenberg_Picture- Jacob Barandes Λ Emily Adlam: https://youtu.be/rw1ewLJUgOg- Everett’s Letter To DeWitt: https://www.pbs.org/wgbh/nova/manyworlds/orig-02.html- The Many-Worlds Interpretation Of Quantum Mechanics [Book]: https://www.amazon.com/Interpretation-Quantum-Mechanics-Princeton-Library/dp/069161895X- Leonard Susskind [TOE]: https://youtu.be/2p_Hlm6aCok- Sean Carroll [TOE]: https://youtu.be/9AoRxtYZrZo- David Wallace [TOE]: https://youtu.be/4MjNuJK5RzM- Chiara Marletto [TOE]: https://youtu.be/40CB12cj_aM- Roger Penrose [TOE]: https://youtu.be/sGm505TFMbU- Robert Sapolsky [TOE]: https://youtu.be/z0IqA1hYKY8- Yang-Hui He [TOE]: https://youtu.be/spIquD_mBFk- Maria Violaris [TOE]: https://youtu.be/Iya6tYN37ow Learn more about your ad choices. Visit megaphone.fm/adchoices

Why would Einstein fail a modern grant application? Fortunately, I'm not very familiar with the way that grant applications are dealt with. I only know the gross features in both senses of the word gross. That is where I notice that grants that should have been awarded aren't fairly reliably. when it comes to fundamental research, which is what I'm mainly interested in. So, judging by my experience, and I certainly don't know what it was like over 100 years ago in Germany,

but judging by my experience today in Britain and in America, he wouldn't have stood a very good chance. because he wouldn't have been able to say what the application – well, first of all, he wouldn't have been able to say very clearly what he was trying to do because there was no one versed in relativity on the panel that judged physics applications. So none of them would have known what a manifold is. what the Riemann tensor is. So his application would have had to explain that in very elementary terms,

and they would have had in front of them a pile of applications, which from their point of view had much more merit because they could see that these were open research problems that needed to be solved, only in the bigger picture, they were incremental, whereas Einstein's was fundamental. So I think he would have had difficulty getting a grant, and I think in historical fact he did have such difficulty.

It was only when Max Planck saw that there was something interesting about him that he got him a job. And again, that isn't possible nowadays because there'd be anti-nepotism rules, there'd be rules about the procedure, and every procedural rule is an impediment to any new kind of thing being tried. Anti-nepotism sounds positive.

What's the negative side to it? well so um nepotism literally if it means not giving a job to your nephew then perhaps perhaps that perhaps that has merit but what it means is in practice that if you know someone personally you can't take part in the selection process for that person and you certainly can't get the university to let that person in. So it all has to be at arm's length in order to ensure fairness. Now, the amount of unfairness that can be caused by not having that rule is very tiny compared with the enormous unfairness of having that rule,

because having that rule means that only people who know nothing about the candidate can rule on whether the candidate's accepted. So the natural question that arises in someone's mind is why is it that we need grants anyhow? So professors of the past, like, and I'm speaking about fundamental physics, not just a generic professor, but say Einstein or Feynman or Everett, which I know you have some personal stories on Everett. Yes. And I'd like to get to those at some point. But I'd never heard them complain about the grant system. However, I hear complaints, especially off air from contemporary professors about it frequently.

So why does one require grants if they're all. already paid a salary, what are the grants for? What if you don't get a grant? Are you just sitting around twiddling your thumbs? Are you then seen as a net cost to the university and they just make you lecture? Yeah, I, yeah, that's what it is. I repeat, I'm not very familiar with the system and that's not an accident. I have intentionally distanced myself from any knowledge of the system because it is a very unpleasant thing to be connected with. But yes, professors can do full-time teaching, most of them don't want to, and that's not because they don't like teaching, I think, in many cases,

but because they have to teach to a regimented curriculum and syllabus, and they can't exercise their creativity and reveal to students why they are passionate about the subject and they have to get through a lot of it because the students are all competing with each other to get the exam results which are a very inaccurate measure of how suitable they are for future research. It's not even intended for that. It's intended for displaying their qualifications, usually to do something else, which is by two orders of two orders of remove away from suitability for research. And then here in Britain, I don't know what it's like in the US.

The professor has to apply for a grant to do research, which is going to, and some of that money goes to the university, so he doesn't have to do as much teaching. but the student or graduate student has to separately apply for a grant the mere fact that the professor wants to include him on his research team is not enough to provide for subsistence for the student and again the university takes a cut

notionally because of desk space or lab space or whatever it is so I think this whole superstructure is contrary to what is needed for fundamental research, and actually for all the functions of a university, but particularly for fundamental research, what it should be is that the grant-giving authority or the entity that pays for somebody to do fundamental research, whether it's a private charity, a private individual, the government or various branches of the government, the military, whichever it is, what they should be doing is

awarding the grant to one person. And sometimes that one person alone, like it would have been with Einstein, that one person alone is the research group. But in a more general case, that person would then spend part of his grant on hiring postdocs and graduate students and undergraduate students. I mean, this whole hierarchy is counterproductive. And in the research group, I believe in flat hierarchies. So ideally, it should be the boss and everyone else. and the boss and everyone else

should be equal as well so that no one's commanding anything they're all there on a joint project which they believe passionately in and that reminds me of another incident with my former supervisor Dennis Sharma by the way I've been very lucky

with my supervisors he was once told by the higher-ups that they would be instituting a, what do you call it, not time and motion, but yes, clocking in system, where the students and postdocs in the morning, they would sign the whatever it was, the register that they had, and they had to be in by 9 a.m. And so Dennis Sharma objected to this,

saying, if any of my people is in the department at 9 a.m., it's because they've been up all night. Right. There's a story about Schwinger who was told, can you lecture at 10 a.m.? And then he paused and thought, I don't know if I could stay up that late. Yeah, yeah, yeah. Well, that is the way, you know, when physics was a small enterprise, and there weren't that many physicists in the world, and they were all rather eccentric. and they were all supported by various other means other than a system. They were all rather eccentric, and they all had their quirks, and whatever it was that sustained them,

approved of those quirks. So like in the Institute of Advanced Study as well, The first thing someone was told when they were given their 10-year or 15-year grant or whatever is do whatever you like. That's what the grant holder should be told. And that's what the grant holder, in my opinion, should tell the postdocs and the graduate students and whoever else is working with him. you might think, well, if they're told that, why shouldn't they just spend all their time drinking and, well, it's because they've been hired for the purpose.

They've been hired because they are passionate about something. And when you want to do a joint project, you interview someone, you want to see whether they are passionate about that project, nor whether they have some standardized qualification for it. There is no such thing if you're working on something new. Yeah, enthusiasm is there for everything. Peter Higgs said, I believe this was a decade ago now, that he wouldn't be able to get an academic job in today's environment.

I think he said it's quote unquote as simple as that, that he wouldn't be productive or something akin to that? Yes, nor would I. Could quantum computing get invented today? I think what would happen. I think probably yes, but the way it would happen is that, which is happening a lot already,

which is that people who are really passionate about some new fundamental thing, apply for a grant to do something else. to do something incremental. And they do the incremental thing to the minimum level required to sort of pass the various tests. They publish, they publish again,

they publish again. Meanwhile, they're passionate thing. They don't necessarily publish because they're grappling with very difficult problems that don't admit of successive papers doing it better and better. They're waiting for a breakthrough. So they do that in their spare time.

And that is highly unsatisfactory. I imagine the retort would be, look, there's plenty of great work occurring. It would be foolish to paint all of academia with a brush of stagnation, although that word hasn't come up. I would like to talk about that as you had a whole conversation with the Conjecture Institute. I'll place a link on screen to that. It was fantastic about that subject. Anyhow, we don't want to paint all of academia with a brush.

So some would say, even to say physics is stagnant, they would quit. While I wish the field was stagnant, I wouldn't have so much to do. I could catch up on the archive, for instance. So what do you say to those who argue, look, there's been innovation, there's gravitational waves, black hole imagery, topological insulators and phases, time crystals, exoplanes have been discovered, quantum advantage. So I don't want to appear to be trashing incremental research. And also, in that list of things you just mentioned, I don't want to classify all of those as incremental research. Some of them are indeed fundamental.

What I want to say is that the research landscape taken as a whole is heavily biased against fundamental discoveries. Everything we've talked about, the criterion for getting a grant, the structure of careers, the structure of university departments, all of them are heavily biased against fundamental research such that it is much more done in people's spare time than it is done. in pursuance of the grant that they're getting. So, by the way, I also think that you mentioned what do I mean by grants. Somebody pays for research, which is blue sky research. It used to be that aristocrats did it. They funded their own research.

So that's one way to go. but so in regard to who funds it the main thing that is wrong with the existing setup is that there are too few sources of funding because the government has entered the field not only have they sort of crowded out other means of funding

and also prevented it in various ways, but the private charity, for example, who funds research, they're going to use the same criteria because they are, what they do is they have a committee whom they assign the task of searching through, sifting through all the applications and picking the best ones. And they don't know how to do that either. They can't possibly know. And they're forbidden from using one of the few ways that they could, namely to ask their colleagues, do you know someone who is worthy of this grant? They're not allowed to ask that. So, in other words, broadly speaking, the government has now contributed, it sounds like a positive to physics, to

fundamental research. They've given plenty of money. However, with that money comes some poor practices. these poor practices are then adopted by the individuals who previously used to donate without these poor practices? Yes, and the result is not stagnation. I mean, there is a kind of stagnation, but that's a different story. It's not that the result is stagnation, or rather indirectly it is. The result is de-emphasis of the fundamental in favor of the incremental. Not that there's anything bad about incremental research, as I said.

Yes, yes. And I would like to get to this definition of fundamental research. But just to pause here about government funding, I see public funding, which is a synonym for government funding, as a net good. So am I incorrect in that, or do I have to delineate between different types of public funding in my mind? When the government funds something,

it's very rarely doing harm. I mean, that does happen as well. But on the whole, the things it funds are worth doing, but they're not always worth the money, especially when there are other things that could be done, which are prevented by the system by which the funds are allocated. Now, on the archive, for those people who are, are listening who aren't researchers, there's something called A-R-X-I-V pronounced archive, sometimes at least

pronounced archive, where researchers post and also researchers look on a weekly to daily basis for new research. There's HEP, so high-energy physics, and then there's quant physics. Is there a specific subcategory of the archive for this quote-unquote fundamental research that you speak of, or does it just get pooled into one of these two? It's done by subject. There is no a category for fundamental. And of course, there is no category either there or in grant application forms for things that haven't been invented yet. So when I applied for a grant to do research in quantum computation, of course there

was, there were, there were, one of the things you had to do is, is check the checkboxes for what kind of physics you're doing, solid state physics, astrophysics, and, and none of them were quantum computing because computing wasn't considered a branch of physics in the first place, and, um, and especially not quantum computing. Now, there is a checkbox for quantum computing. And consequently, now you can get a grant to do incremental research in quantum computing, but you can't get a grant for inventing a new thing that would go on that list. Yes. And that's impossible. It's impossible there could be. I'm not saying there should be a thing on that list. It's impossible to put something like that on the list. And therefore, it's

impossible to judge applications according to classify applications according to what they're trying to do like that. And if you could, if you had another box for fundamental none of the above, for example, the people on the committee wouldn't know how to judge that. The only way to judge that is, for example, with quantum computing, there would have been some people like Wheeler and Feynman, who were aware that there was something to be learned in the physics of computation or the physics of information that hadn't yet been incorporated into physics. And they might have been able to point to young researchers who would be deserving of getting a grant.

But they weren't on the committee. And the committee couldn't consult them. So, okay, do you think that there should be a new box, maybe the same. not the solution, but let me just posit it. Do you think there should be a new box that is for new boxes? I've been using Claude to prep for theories of everything episodes, and it's fundamentally changed how I approach topics. When I'm exploring, say, gauge theory or consciousness

prior to interviewing someone like Roger Penrose, I demand of an LLM that it can actually engage with the mathematics and philosophy and physics, etc., at the technical level that these conversations require. I also like how extremely fast it is to answer. I like Claude's personality. I like its intelligence. I also use Claude code on a daily basis and have been for the past few months. It's a game changer for developers. It works directly in your terminal and understands your entire code base and handles complex engineering tasks. I also used Claude, the web version, live, during this

podcast with Eva Miranda here. Oh my God. This is fantastic. That's actually a feature named artifacts and none of other LLM providers have something that even comes close to it. And no coding is required. I just describe what I want and it spits out what I'm looking for. It's the interactive version of, hey, you put words to what I was thinking. Instead, this one's more like you put implementation into what I was thinking. That's extremely powerful. Use promo code, theories of everything, all one word capitalized, ready to tackle bigger problems, sign up for Claude today and get 50% off Claude Pro, which includes access to Claude code when you use my link, clod.a.ai slash theories of everything. Do you think there should be a new box that is for new boxes?

As I said, if you had such an application, suppose I had an application, suppose I was on the committee and I had an application in front of me for a new propulsion system for spacecraft. let's say. Now, I know nothing about that and I know no way of judging. I mean, I could probably tell if it's a crank or crackpot. Sure.

But if it's something which is viable but is not a modification of something in existence already, obviously I can't give you an example of that right now because I'm giving you an example of something that I don't know about. Yes. So who should get such a grant? Well, that person who deserves such a grant

will have been talking to somebody. With luck, they will have been talking to somebody who already has a reputation for making progress somewhere in physics. And that person should be listened to there should be a mechanism for that person to cause somebody to be funded to do some fundamental research. I have several times tried to recommend such people, people that don't fit into the standard categories and without success. Only private entities have funded them, but even that was very very,

difficult because, as I say, they use very similar system and very similar criteria. But at least there's diversity. At least there's more than one place you can apply to. There ought to be dozens of places you can apply to. Okay, so about the quantum computing checkbox, I imagine, and I know that you mentioned that you're not as familiar with the grant system as one could be or even maybe you do not want to be, But I imagine that it's not as simple as the checkbox for quantum computing. I imagine there's sub-checkboxes like quantum hardware or cryptography or fault tolerance or algorithms or what have you in the quantum computing space.

Now there would be, yes. But when I was doing it, there were none of those. Right. Okay. For the creation of these new checkboxes, are you saying that they would be done inadvertently? You can't predict ahead of time. So what you should do is you should fund people with, potential. Yes. Fun people. That's how it should be, that's how it should be in incremental

research as well. The whole of scientific research should be like that. I thought you were about to say you'd be allowed to make a new box and say what should be in it and all the subboxes. I wouldn't have known what the subboxes are. They were, they too were only invented later and not by me. So the communities that I also traffic in other than physics are philosophy and math, and the grant situation there doesn't seem to be as dire. There's no expectations of grants as a prerequisite for tenure, for instance. There's just the hope and the promoting of people who have strong publications.

So a math department meeting may say something like congratulations on your annals paper, but I imagine that a physics department meeting would include like your grant expires next year. What's your renewal plan? So what's the difference here between physics and math? And I'm speaking about fundamental physics. Because you can always say, well, if it's experimental physics, it's quite clear you do need plenty of money to fund your machines and your computers and your servers and your students and so on. But fundamental physics. Yes. So for the, in the structure that I advocated earlier, the research group leader should indeed be judged not on his past papers, not on his, but on his previous success in advancing the subject.

It should be a well-known figure in the field who has a, who has a, track record of making progress. And now he wants to make progress in a way that can engage several other people. Maybe, maybe, you know, if he's an experimentalist, he wants to build this with a machine, or if he's a theoretician, then the field has broadened enough for him to see that there is potential there that he doesn't yet know what it is. But he knows. But he knows who he wants that's that's the thing 10 years earlier he knew what he wanted to do now he knows what kind of person he wants to work with and he wants to he knows that he wants to hire five of them or 10 of them but not 500 of them so he he's funded not because he can say what

his next paper is going to be about. He's funded because he says he's very interested in stuff and he's going to do research on it and somebody who funds him will be saying, I think that this guy is good. Or gal. Yeah, well, I don't want to use gender neutral language because I think it's silly. Obviously, when I say he, I mean he or she. And if I said Mr or Mrs, I might also mean his majesty or master so-and-so. So, yes, it's completely natural in this whole scheme of things that I'm advocating, that everything is tuned to doing the research, creating the new knowledge.

Everything is subordinate to that. If somebody is going to care whether the graduate student is male or female, then they're not the founder that I want. They need to be obsessed with the thing itself,

and so should be the people they hire. Suppose right now there's a wealthy patron or multiple, and you could speak directly to them, and these people who are watching, they care about fundamental physics, maybe foundational research in computer science as well, just foundational in general, which we can get to distinguish in between fundamental and

foundational. To me, I see them as quite close. I can't distinguish them. Maybe you can, but anyhow, what is your message to them? What are they to do? They have this money. What are they to do? They want to help. Yeah, so each one of them is different. Each one of them has interest. Each one of them has reasons for wanting to promote fundamental physics, and each one of them has a different conception of what fundamental physics is, and they might also have a conception that it's being slowed down by various sociological facts and so on, so they want to get around that. They need to find somebody that they think is good.

somebody usually this will be somebody who has already done some of the thing that they want done and then they should approach that person and say could you use some money often the answer will be no

but often it will be yes because with money they can do a lot of things in parallel that they would otherwise have to do in series by themselves or with a smaller group. Now, there is a thing that's just started up the Conjecture Institute, and I don't know how they make their choices,

but what I've seen seems to be following the pattern that I advocate quite closely. So they fund the person, not the research project. and they seem to fund people who are interested in foundations. I don't know whether that's because their thing is to fund foundations or whether their thing is to fund things which aren't normally funded because of... So I don't know which of those it is. But either of those would do.

And lots of variations on them. that would also do. Like I said, I would like there to be dozens of such entities and all with the different ethos, all with a different theory of what foundations are or what they're for and all with the different theory of what's wrong with the present thing, why somebody hasn't already funded the thing that they want to fund, that sort of thing. Firstly, what is the difference between fundamental research and foundational research? I don't make much difference between those things, but foundational suggests to me that you have a field and you're drilling into its foundations. So you want to understand it more deeply than it has been before.

Fundamental means to do with fundamental knowledge, that is, knowledge that is needed for all sorts of different areas. You know, for example, quantum computation, I think, is fundamental or was, because it has to do with mathematics and epistemology as well as physics and computation and computer engineering. So there's a whole bunch of things that it might unite, it works. But it's fundamental in its conception that it's not it's not like working at existing foundations of anything. Okay. So someone who's listening, who doesn't care about fundamental

or foundational research, they hear you keep bringing it up. Why is it so important to you? And of course, you are not saying that the incremental, conformational research that's done on existing theories is not important. But that the fundamental and foundational, foundational has been somewhat excluded or not incentivized properly, but that implies that why should we even care that it's incentivized properly? What is it about foundational and fundamental research that's so vital to your conception of knowledge in the world? The thing that unites them, so the growth of knowledge can't be regimented. there's there's uh you know if you tell somebody like like henry ford said something like

uh you know if i'd ask people what they want they would they would have said a better horse um so uh the um the essential thing to intellectual progress of all kinds whether incremental fundamental whatever, is interest, that somebody is interested in doing this. If they weren't paid, they'd still do it. They'd get a job doing something else and they'd do it in their spare time. Like Van Gogh with his painting. Nobody ever bought a painting from him in his lifetime. Even though his brother owned an art gallery. I mean, I don't know the story of that, but it's obviously not it's not the standard story of slotting into an existing structure. So some, but yeah, sorry, I've gone off to subject slightly.

What unifies fundamental and incremental research is that someone's interested in it. And it's that interest that drives all progress. It's true that fundamental research eventually, typically, eventually drives something useful as well but not always and you know you could ask well if the general theory of relativity hadn't been invented for another 60 years let's say after Einstein nothing practical would have been affected then then it was needed for the GPS system then now it's being needed for other things. But perhaps if you were interested in purely utilitarian outputs, you would have delayed Einstein. But then if you take that kind of utilitarian attitude to Einstein,

you would have taken the utilitarian attitude to everything and you would never have had antibiotics and rocketry and satellites and that sort of thing. And the reason that it's all connected is not so much that the progress in the whole of science and engineering comes from fundamental research as a sort of wellspring. that also happens, but the main thing is that the whole of progress in human ideas is a single thing, an indivisible thing, which is all powered by interest, by curiosity, by dissatisfaction with the way things are currently thought of. Okay, so it's not an argument to pursue foundational research

because in your mind, maybe a decade from now, maybe 200 years from now, it will prove to be useful. No, it's not that. I thought what you're going to say, it's an in and of itself argument, but it doesn't sound like that. It sounds like pursue it because this is part of a larger knowledge creation process. Exactly.

Exactly. It's needed for that. And if you suppress the impulse to create, the impulse to improve anywhere, you're going to affect everywhere, or you may affect everywhere. I mean, you could be lucky and not affect the theory of evolution or whatever. But in practice, you usually do.

Interesting. Okay, sorry to interrupt you. So it sounds like you're saying that, Look, a child has a natural curiosity. As you get older, your curiosity morphs into various subjects. One of those subjects could be foundational research in physics. But that is an example of foundational research curiosity. And that is important. Yes. And therefore, if you're talking about your hypothetical rich person, a hypothetical rich person who has that interest or who wishes they could have pursued that interest when they didn't have time to do it when they were younger or that kind of thing. Somebody who, for reasons of their own, thinks that that is important and they're curious as to where that will go, and they want it to, they want to get the answer before they die. That is the thing that this hypothetical rich person should be funding. Yes, and I imagine this hypothetical rich person was not able to pursue foundational research because you hypothetically

don't get rich by pursuing fundamental research. That's the whole point of our conversation for the past 30 minutes. Yes. Yes. Presumably something else interested in. And that involved making money. I don't think, by the way, I don't think there's hardly anybody

who's interested in making money per se. They make money because that is what they need to do the thing that they're interested in. Right. Should physicists study philosophy? Well, if it's relevant to their research, now, in the case of quantum computing, it's rather paradoxical because I think philosophy is extremely important in the foundations of quantum computing. but the state of the art in academic philosophy is terrible and people who study that and internalize it

become less proficient at the kind of philosophy that's needed to make progress in physics. Now there are exceptions to that and I won't name them because then the people I don't name will be offended but there are certainly philosophers who take the right attitude to philosophy, but the overwhelming majority do not. So, you know, physicists should know philosophy, provided they find the right philosophy.

Speaking of naming, can you name a physics department that is doing extremely well in your eyes? Now, I said department, but it could also be institute, like the perimeter institute, for instance. Again, I'd rather not for the same reason. I don't want to single people. I'm a theorist. I prefer to talk theory rather than practice. If the things that I'm saying are true or even half true, people will really recognize it. People will recognize that they've seen this happening.

And when I speak to people about this, I've very rarely had anyone contradict to what I'm saying. They usually agree, but they say, yes, but what can I do about it? I, what was it about? About five years ago, I was trying to get the rules changed about how foreign postdocs are treated in the British visa system. So that may seem to be a rather esoteric thing, but it was important to me at the time because, well, never mind.

Longbandy Twizzlers candy keeps the fun going. Keep the fun. Going. Twizzlers, keep the fun going. So I thought, well, who can I go to? The head of the physics department, well, the head of the physics department told, said to me, I've got no power over that. That's for my superiors.

The superiors said, we have no power over that. So I thought, well, I'll go to the vice chancellor of the university. No, the Vice-Chancellor doesn't deal with such things at all. So then it happened to come into my email box. The Royal Society had a document saying the structure of research funding, this is one of the reasons why I avoid this whole field, by the way, structure of fundamental research funding in Britain. So I downloaded it.

It's like, you know, I don't know, a big, fat thing. and I looked at it, and I found that if I had pursued this line of who should I ask to change this rule, there is no one. Basically, the structure of decision-making goes right up to the Minister, the Minister for Science and Education, but the Minister is required to consult various committees before making any decision. So there is nobody I can go to to make the change I wanted to. And that's why I gave up on that. Well, this sounds hopeless, so there must be some hope here. Indeed.

Physicists, professors of physics, who watch this channel, they're listening and they're thinking, look, I don't like this, quote-unquote, system that I'm in. Yeah. And I would like to change it in various specific ways that are important to them. David, what is your advice? I suppose what they would need to do is get together and form a proposal to take to government. Because it's pointless taking it to the minister

because the minister doesn't have that power. It's the government that has to change the rules under which the minister makes these decisions. And then that can go right down through the hierarchy. And somehow these people would have to present it in such a way that it bubbles up to the top of what the government wants to do. I don't know how to do that. I don't know how to politically campaign

and I so but but perhaps there are such people perhaps they're watching what do you think the reason is that more physicists aren't actively critiquing the academic organization that that they're a part of so I hear plenty of critiques off air from professors that I speak to but on air they're much more reluctant and one reason may be that that occurs to people who are listening could be well the academic positions are precarious, especially without tenure. So when you speak, it's like you're biting the hand that feeds you. And so maybe you have the incentive to do the opposite to say, no, no, I love everything about where I work and everything is copacetic. I think very few people say that. Okay, so you're one of maybe 10 people that I know

who are currently in the academic institution. Right. Yes. who are willing to say there's something rotten at the core of the institution. And the difficulty here is when most people say something is rotten at the core of an institution. They get labeled as a conspiracy theorist. The mental image people have of what you think is, okay, at some point people sat around with cigars thinking, how can we make this less efficient and more beneficial to myself? And there are distributions of notes that said burn after reading. Yeah, yeah, nothing like that.

This is nobody's fault. nobody is to blame that is part of why why it's hard to change so why is it that you're a part of a small handful of people who are willing to publicly

talk about this well I'm again I can't psychologize sorry I'm being that's fine and you can feel free to disagree with the premise you can also say no no I think that's that's false

I think it's true that few people want to criticize it, especially in public. But I can't speculate on why. Is it because of their career, like you said, is it because they consider their position precarious? A whole load of other considerations come in once you have tenure, because you're not a free agent when you have tenure. It's supposed to make you to free you from peer pressure or whatever you call it or public pressure. But in practice, that doesn't really happen.

Very many people who get permanent jobs just slot into the system. him. And I don't know why, but some sociological reason, perhaps. Again, you're making me speculate about things I don't know about. So I'm extremely vexed with you. Good. Yes, that's worth being. It's rare that there's a physicist who's made significant contributions, even to their own field. That's something to note. To make contributions to the philosophy of physics as something else. And then with your book the beginning of infinity, which I'll place a link on screen and in the description. You've made contributions to philosophy proper. So that's vexing. What is it about you? I've been very lucky. As I said earlier, when I was a graduate student and

postdoc, I was very lucky to have supervisors who did exactly this what I advocate. They said, I came in on day one, or rather even in my interview before I was even accepted, they said, what is it you want to work on? And I didn't say anything specific because I didn't know anything specific at the time. So I just described what kind of thing I want to work on. And I remember saying, for example, to Dennis Sharma, in my first interview, that it seems to me that the most urgent problem in physics is quantum gravity. So I'd like to work on that. I know a bit of quantum field theory, but I don't know enough for relativity yet. And so on. Now, it turned out that that was a bad idea. And I've

decided to turn from quantum gravity, which I thought was too difficult to work on at my stage yet. And I was getting interested in other things, which eventually led to physics of information and to quantum computation and so on. And Dennis somehow saw, that I had the thing he wants in his students. And so he hired me. And when I wanted to change to study something completely different, he not only did he not object in any way, he was interested.

He said, you know, he was interested in what I want to do and why and so on, but he never tried to direct my research because he assumed that I wanted what he wanted. You mentioned that quantum gravity was too difficult. What do you mean? So at the time, I didn't know what was so difficult about it. I took the, like, I think I'd absorbed the standard view that what we're trying to do is cure the infinities and cure the non-linearities and that kind of thing. So that, so that, so that, uh, the answer would be like an equation which had the desired properties.

And I realized, as I got into the subject, that those are trivial problems. It wouldn't matter if we didn't solve that. But the chances are that we will solve that once we've got the deeper incompatibility between the two theories, sorted out. So the fundamental, I keep saying fundamental, I don't always mean fundamental in the same sense.

We have to unpick this. At root, all the existing field theories are theories of fields on space space, time, whereas general relativity is a theory of space time itself, and it's not a field. You can think of it as a fixed space time with a field on top of it, so it's the sort of static part and the varying part which people then try to quantize. But that's very alien to general relativity. General relativity is the theory of space time as a

dynamical thing itself. And there are theories, I mean, people have tried everything in quantum gravity and in my view, everything has failed. The the

the um oh and in every other part of physics um these fields evolve in time and what you're

looking for a dynamical equation an equation of motion that says how they evolve in time but in general relativity viewed in that sense there is no time it's just a either it's a four-dimensional thing or it's a in the quantum sense

it's a manifold where every point is a three geometry and evolution in time is just a strip of things with a higher wave function than the rest. But how that turns into time, there are various proposals. Anyway, it's, what can I say?

It's conceptually very incompatible. The way we conceive of quantum fields, which have its own problems, by the way, and the way we conceive of spacetime is fundamentally incompatible. And there are also problems with quantum field theory itself. Now, I think general relativity in itself would be a viable theory. That's okay. Okay, there's the big bang and black holes, and we're not sure what, how to deal with singularities.

But basically, it's a viable theory, and there's no kind of contradictions in it. whereas quantum field theory is full of contradictions in its own right, let alone before you try to unify it with gravity. Such as? So the, well, my favorite one at the moment. So I like being baffled, and this is one of my favorite problems with quantum field theory because it's so baffling. One of the basic axioms of quantum field theory is that field quantities at space-like

separated points, that is at points at the same time, that those quantities should commute with each other. That is, if there's a quantity A and B, then A-B equals B-A. and at a later time they don't commute and that's the whole reason why quantum fields evolve in time is because the later thing doesn't commute with the earlier thing.

So now if two things let's say in the same space there is a quantity here and a quantity there that don't commute it means they must be described by separate algebras. And no matter how close they are, they must still be described by separate algebras, which means that these separate algebras all commute. So no matter how close together these algebras are,

they still commute. And yet when they coincide, they don't commute because field quantity, is at the same point, don't commute, because that's what drives the whole thing forwards. So, this axiom of commutativity at space-like separations is disastrous. One way of looking at the infinities of quantum field theory is that they are precisely caused by that axiom. Interesting.

And yet, if you try to remove that axiom, which I have tried to do, then you run into problems of causality and other problems and problems of interpretation and what the meaning of the different quantities are. It's like you're not in Candace anymore. Just that tiny change in quantum theory leads to a theory that can't even be interpreted in the normal way as being things having values at different points. so it becomes something else you're not in Kansas anymore

so that's that's one of the problems and I like thinking about it so you'll have to stop me talking about it oh I don't want to stop you talking about it I want to know what were some of your attempted solutions so I tried to set up a quantum

theory where the fields at each point don't range over the real numbers for their possible values, but they just range over plus and minus one. So they're qubits, as I call this qubit field theory. So you have a field of qubits, and there's a qubit at each point in space, and they don't have to commute with each other at different points. You just assume that somehow dynamically, when they're far enough apart, they'll approximately commute, but they won't commute.

And as they get, when you choose two points closer and closer together, you'll find that their algebras become more and more the same until when they coincide. There's no blowing up or anything. It's just a perfectly well-behaved theory. So then I worked out what the possible equations of motion for such a theory are. And I worked out that there, I think it was. was, this was several years ago that I did this.

I worked out, I think, that there are 13 possible second-order differential equations that are capable of being equations of motion for qubit field theory. And then, so the question then arose, what counts as a measurement? Because in ordinary quantum theory, if you measure something, you're putting it, you're putting the value of it into another thing, which then commutes with the original thing. So you can think of it as having a value, which if it's a good measurement, it'll be the same value as in the thing you were measuring. But in qubit field theory, that's not true, because when you measure something, the result of the measurement will still not commute

with the original thing. And when you measure that, the non-commutativity will spread a bit like entanglement, but this is spreading a different thing. It's spreading non-commutativity, and I couldn't solve that problem. And so although the papers on the archive, you can read it if you want to. I'll place a link on screen to it. Right. So it's a nice little theory. I have no idea what it means physically, and I failed in finding a thing it could mean.

so I never published it except on the archive. Is it a non-local quantum field theory? No, no, it's perfectly local. That is the right question. Because normally, when things don't commute, there'll be problems with causality. But in qubit field theory, there are no problems with causality. It all works, no infinities, no non-localities.

there is no Schroding a picture for that theory. There's only a Heisenberg picture. So that seems to be an important thing, but I haven't put my finger on exactly how. Okay, so most of the time, when people are thinking of combining general relativity with QFT, the mathematical problem is non-renormalizability. Yes.

There are said to be three or so, conceptual problems that are distinct from the non-renormalizability. So one is just QFT requires a fixed background like you mentioned. Background independence is the issue here, conceptually speaking. Then there is, well, what does it mean for you to have a superposition of geometries operationally? And then there's the problem of time that you mentioned. Now, the current leading theory of quantum gravity is string theory. At the time when you were a graduate student, it may not have been there. But either way, you have heard of it at some point during your career and what attracted you to it or what did not attract you to

it? What dissuaded you or persuaded you to? I've never worked on it because I don't think that progress in fundamental physics, well, one should never say never, but I don't think progress in fundamental physics ever or almost ever comes by trying to find a better mathematical object and then wondering what kind of what it means as a bit of physics. So, for example, finding a different group for the fundamental particles to belong to, I don't think you can find the answer to a sophisticated problem that way. What you need to do is have an idea about what physical thing you want. For example, as I was saying with cubic field theory, you want the commutation relations of different field quantities not to be pathological.

So you want everything to be smooth. Okay, now what kind of mathematics can give that to you? That's the kind of thing that I think can make progress in physics. And string theory, it seems to me, is entirely the other way. around. It's saying, suppose that the fundamental things in nature are not point particles but strings. Okay, now let's find out what kind of a world that would look like. You know, I can't prove that that will never work, but I don't think it can work. So it was more their approach to landing on string theory that you disagreed with rather than string theory itself? Yes, well,

string theory itself then just becomes trying to find, trying to find some equations that will make it work. And that, that, that's not, you know, you should be trying to look for equations that do the physical thing that you, that you think physics is going to be like. Why should the approach matter? So let's just analogize this to scaling a mountain and you think you should be hiking to find the mountain with your flashlight and they think, no, you should be using a you could tell I'm not a

mountain climber but whatever those picks are that they use I did speak to Alex Hennold who's a rock climber and I've

already forgotten petons I believe their names are but regardless yeah okay sure so there are

two approaches and you find something on the mountain to me it doesn't matter how you got to what you found

you found it so you just evaluate this it's not it's not how you got there it's what the problem was

so you as I said you know as we're saying in the part of the conversation, someone has to be passionate about it, someone has to be obsessed with the problem and trying to solve it, not being expert at mathematics and making up a new

mathematical thing and then throwing that over to the physicist and saying, is it this? And they say, no, it's not that. Then you say, well, is it this? that's the approach that I couldn't really shouldn't really call that approach I mean that's not problem based that that's not that's not somebody trying to solve a problem maybe you should say you could say it's somebody trying to solve someone else's problem

but but from the physics point of view the conceptual thing is this fundamental that's again fundamental okay the sexual the the conceptual thing is where the whole what motivates the whole procedure it you you want to make the theories work and you have an idea about how reality should be that would make it work or what kind of reality would make that work not what kind of equation of motion would make it work. I think you'll never get there that way. If you try to make general relativity by that method, you would absolutely never have got there because you would never have had the theory of a dynamical space time. You'd just have been thinking of, you know, what terms can we add to

Newton's laws to make it compatible with, let's say, electromagnetism? Well, add a couple of terms, And so you can do that. You might even get as far as the relativistic formulation of Maxwell's equations, which might then get you to special relativity. I mean, this is already assuming a lot of luck. But you'd never get to general relativity because the idea of a dynamical space time, a dynamical curved space time, was needed to make that progress. And you'd never have found those equations without first having that idea.

So what if the string theorist says, well, who cares about what motivated us to get to our answers? Firstly, we're a diverse group of people. We all have different motivations. It's unclear to speak of the motivation of the field of string theory itself. But regardless, look, David, we've given you, we the string theorists have given you ADSC of T correspondence, we've revolutionized our understanding of quantum information and black holes. We've developed holographic dualities that are now used in condensed matter physics. And sure, that latter case is not string-inspired, but it's not string-contingent, okay, still, there are tools that we've developed, that pure mathematicians used, and so on.

So is this not evidence that we're on the correct track? What is your response to that? Well, there's never evidence that one is on the right track. If there was such a thing, then one could move further along the track. I'm not qualified to judge mathematics. So there might be very beautiful mathematics, which in string theory, which sets up alternate realities that are like ours in some way and unlike ours in another way. And I can't prove to you that when they keep fiddling with it, it won't eventually resemble our one or be our one.

But to get an answer without first having the problem to which that is the answer is, is, I think, very rare. Even when you cite examples like Alexander Fleming working on bacteria and he found penicillin and it really wasn't like that. He had an idea which was, which had finding a therapeutic chemical in the landscape of what he was looking for. He wasn't specifically trying to find penicillin, and it was because he was in that landscape that he recognized the accidental discovery as being relevant.

so it was because the he recognized the now if somebody had said to him the let's say two or three years before here's a petri dish what do you see he might well have said i don't know they're just some bacterial colonies on there what am i supposed to what am i supposed to look for and then somebody might have said well look there's a patch here where the bacteria aren't going and then then he might have made further progress but that idea

is an idea of that kind a proposed solution to a problem first a conception

of a problem and then a proposed solution to that problem come before a viable theory that solves it

or that addresses it partly solves it it. And so in the case of string theory, I don't see that it has solved any existing problem. What they're hoping for is that some mathematics that resembles the existing mathematics will come out of it and will have desired properties. But I don't know, maybe the right theory of contagravity has infinities.

Maybe they're a good thing. Maybe we ought to have more of them. or whatever. Okay, so I imagine the rejoinder from the string theorist is, okay, you say that we haven't solved any problems, but look, string theory is the only framework that's been developed where quantum mechanics and gravity coexist without mathematical contradictions and every other approach either breaks fundamental symmetries

or has these contradictions. So is that not progress to you, David? Well, it is a mathematical progress. but that it might solve the conceptual problems is a hope and I keep saying I can't prove that that's not going to be fulfilled maybe it'll be fulfilled tomorrow and also it's not up to me to tell other people what to work on so they should work on it for whatever reason they like

and the funding entities should fund it for whatever reason they like. So getting back to committees, I imagine that the Manhattan Project had a committee. I'm not a historian, and I haven't looked into that, so I'm nowhere near an expert in the Manhattan Project other than watching Oppenheimer. So what was different about their committee? Yeah, I'm not well up on. the history either, though I have seen Oppenheimer. So I don't know how accurate that.

We're in the same boat. Right. I think that was a very unusual organization, and it did not run on this kind of committee theorem, a pattern. What happened? So for a start, nobody applied to be on the Manhattan Project. Ah, they were picked. They were picked.

So somebody would come and see you. and say, do you want to work on work of national importance? Right. And it will involve a lot of sacrifice on your part, and we can't tell you what it is, but it is of national importance. And this was like during the war. So a lot of people said yes.

And a lot of people then went there and never found out what it was about because they were not employed at the center of the research. They were just supporting researchers. And they were just told, you know, get this machine to work, never mind why. And then there were the lab assistant level people who were just told, keep that dial between this number and this number and turn this knob and press this button all day every day and don't tell anyone what you're doing

and they did except a few who were Soviet spies fortunately Stalin didn't have the wherewithal to make use of the knowledge himself before the end of the war If there had been Nazi spies, it would have been a much bigger catastrophe. I mean, it was a catastrophe as it was, but Nazis had an atom bomb project underway with Heisenberg at their head. And if he'd been told a few of the secrets of the Manhattan Project, he could have done it. He later said he didn't want to. but I don't believe him.

You mentioned in your interview with Sam Altman that you keep a list on your computer of progress in fields where there's been significant progress but you thought you couldn't have achieved that progress. And I believe you said the World Wide Web was one and AGI, sorry, not AGI, but being able to converse generally in natural language

with something. So I want to know more about this list. Tell me about this list. Well, shall I bring it up on my computer screen and tell you a couple of the other things on it? Please. Well, obviously I was wrong, and being wrong could be a spur to inventing something. So another one was, I've got the list up here in front of me, so another one was Mathematica, Stephen Wilfrum's program, because I thought there could never be a general purpose.

application interface that would allow you to define your own mathematical notation. Ah, interesting. Most serious uses of mathematics depend on making your own notation as you go along. But Mathematica can. I didn't think it was possible. Just a moment. To linger on this notation aspect, what are you referring to? do you mean to say like Leibniz invented the little S that's squished together for an integral and that would be, I imagine, trivial to program anything back in the, even when early computers came out to display whatever notation you like?

No, I mean things like, well, so when working on quantum computers, I wanted to go over to the Heisenberg picture, which was an unusual thing to do. and I wanted a notation that was very suitable for the Heisenberg picture. So instead of using sigma matrices, I wanted to say a Q matrix where Q was a function of T, function of time. And then I wanted to have an automated thing to say, take the commutator of two Qs, to take the commutator of two cues at the same time would be zero unless they were the same cue

in which case they'd be the powerly algebra and then at different times it would be the commutator would depend on how much the Hamiltonian had evolved the two of them sorry how much it had evolved

one of them compared with the other one at an earlier time so I did have a computer at the time it was a home computer and I had to write my own software for doing that for me and so I wrote a little program to do to manipulate these Q quantities

with Mathematica I could just define the Q quantities and Mathematica couldn't do it And I didn't see how a general purpose thing of that kind could exist. I see. But Mathematica did. So after getting Mathematica, I didn't have to write my own program to manipulate things anymore. Okay.

Tell me more about what's on this list. Okay. Okay. So another important one was... When I was first told about the laser guide star technique for allowing telescopes to see through shifting atmosphere, I didn't think that that could make much difference. I thought the difference that that could make was very marginal because the, the atmosphere affects the laser beam going up as well as coming down.

So you don't know what to correct for. And the people, I was in Dennis Sharma's department as well in the early days of people doing this and they were making the hardware and they were explained to me how it worked. And I was saying, I don't see how. that can be, and they were trying to explain it to me. Perhaps they weren't trying to explain it very well, but I came away with the idea that this wasn't going to make much difference, and it makes a lot of difference. So that was a piece of hardware or experimental physics that

I underestimated the power of an idea. What's the latest on this list? community notes. Okay, all right, tell me about that. Well, so a previous one was Wikipedia, which I didn't think could work because it would get filled up with spam edits. Yeah, I don't know who thought that would work. It's remarkable. Well, it worked for several years, and that's so that's why it's on the list, but it's

now on the list but crossed out. because now it no longer works. So this failure mode has actually happened, but several years later. So I don't know why it worked. I still don't know why it worked when it did work, but I now know why it isn't working anymore. And it was my original objection.

And now the, and I thought that the community notes thing would suffer from the same problem. that the error correction mechanism would itself get taken over, a bit like AIDS infecting the immune system, so that the immune system was not capable of combating AIDS, you know, that kind of phenomenon. So I thought that the trolls and the bad actors on X

would find ways of infiltrating the or sorry not infiltrating because it's it's now completely automated

as far as I understand it so not they'd find a way of gaming it okay maybe they still will but again

I thought it wouldn't work at all I thought it would make matters worse but it didn't it has made matters better the issues you're referring to regarding Wikipedia, are they of spam or of bias? Bias, except I don't think bias exists. It's error, either intentional or unintentional. Interesting. Okay, let's talk about Everett. I heard that you had a restaurant conversation

with Everett. Is that story true, and do you mind me telling it if it is? Yes, I, Bryce DeWitt contrived to let me sit next to Everett when he visited Austin, I forget when it was sometime in the 70s, and the group of us, postdocs, graduate students and professors often did go out to one of the rest of the rest of, restaurants in Austin and have lunch together. And on that occasion, Everett joined us and I had a long conversation with him over lunch. What happened during that conversation? Did Everett say something that convinced you of many worlds? No, no, I was already, this is why Bryce DeWitt sat me there. I was already convinced long before. But I was curious about whatever it thought about various of the issues that came up. and the most important thing perhaps for historians, any historians watching this,

there's a sort of myth growing up about Everett or two myths. One was that he didn't think in terms of parallel universes that he thought in terms of relative states. but he was the most enthusiastic person about parallel universe is that I had met up to that point he was very enthusiastic

the relative states were a thing that was imposed on him by his supervisor Wheeler so that was one thing and another thing is that the sort of folklore in physics at the time I think people have realized that this is now this is false

was that he left physics because of the lack of reception of his ideas. But that's not the case. He left physics because he wanted to make a fortune. Interesting. And he did make one. So he, I mean, he didn't say this, but presumably he didn't, you know, he didn't have any problems that he thought he could solve by remaining in academia.

So he went into the consultancy business and worked for the Pentagon. Wait, was it so that he could be rich or because he didn't have problems to be solved? Yeah, sorry, I was speaking too glibly. Okay. It's because he wanted interesting problems and he found interesting problems

in a different way, and optimization, I don't know what it was exactly. what was he like personally very intense um uh very very smart i mean very quick quick on the uptake and quick and in jumping from stepping stone to stepping stone um chain smoker that upset everybody even then, even in the 70s, like, you know, people smoked, but not the whole time like that. He was a chain smoker. Do you think he understood his many-worlds theory

beyond just unitary evolution? Yes, yes, yes. So for a start, he'd thought deeply about the problem of probability. He got that wrong, and Bryce DeWitt had a better theory, which was also wrong, and my theory, which is right, I developed that because Bryce DeWitt told me that his version was wrong, and he explained it to me, and I have told this story many

times. I used to go and see him in his office in Texas, and whatever we were talking about, he would say, at some point, he would say, well, there's this problem of probability, and he would write on the board, you know, what the problem was, and then I would say, Okay, I see the problem. I'll think about it. By the time I got home, I'd forgotten what the problem was. And this happened several times until finally, I have it in mind as about the fifth time, but maybe it was only the second time or something. Sure.

Anyway, finally I went home, and I still remembered what the problem was when I was at home. And then I worked on it, and then I solved it. So this is now called the decision-theoretic approach to probability and quantum theory. I see. Okay. What were Wheeler's and Do-It's and Graham's role when developing or promoting Everettianism? Oh, well, this is a very complicated historian. You need to ask a historian, but as far as I know, in short, Wheeler hated the many world's interpretation, as it was called then, but Wheeler was a good supervisor and wanted to give his student every possible opportunity to get his work seen as far as possible.

It was Wheeler who sent Everett's paper to do it, and do it. and DeWitt wrote a scathing response saying, you know, there's a problem with this, there's a problem with that, there's a problem with that, there's a problem with that, and he ended up saying, and finally, I don't feel myself split. And Everett wrote back his famous reply saying, Galileo didn't feel the earth move, but it does. and that persuaded DeWitt and he then became for several years the major backer of Everett of Everett in Quantum Mechanics

and he got together this book of the many world's interpretation of quantum mechanics Princeton University Press which contains every paper even remotely relevant to Everett in not a very thick book at the time. And he is

responsible for me and many other people getting interested and taking the theory forward. So DeWitt, as I said,

he had a theory of Everettian probability which didn't quite work and he knew it didn't quite work and he wanted to fix it. I don't know why he didn't fix it himself. He was doing some highly mathematical things above my head at the time. Yes, the way it had an kind of attitude that it was kind of obvious that this was the right interpretation and he didn't have any interest in working on it. It's like backwards

looking. And that was true of Everettian quantum theory for many years, that everything was focused on trying to explain again and again and again to reluctant people, why the prevailing view is untenable, why the Everettian view is illuminating, and it's the only possible one that will work. And the trouble is that that attitude, as I have often said, that's a bit like as if biologists had spent all their time proving and reproving that creationism doesn't work and that you should have Darwinism. You know, it's, yes, you can keep doing that, but what was needed was to improve Darwinism.

and make further progress. And they wouldn't have made further progress if they'd kept on just engaging with this problem of why the creationists are wrong. So Everettians tended to, by the way, I think no one was a full-time Everettian. They were all working on a lot of things as well. So they did spend

a lot of intellectual effort on killing and re-killing and re-killing these zombie theories that were already dead until

relatively recently a lot of progress has been made on Everett and after the probability thing there's also the question of the structure of the multiverse which I think

is still an unsolved problem that we don't have an equivalent geometry of the multiverse, in the sense that we do for spacetime. We can say space time is a four-dimensional pseudo-Romanian manifold with metric. So we can say what it is mathematically, which is different from saying it obeys Einstein's equations, here you are, here the equation it obeys, that's a different thing. Right, right. With Everett, we only have, not only,

that's an exaggeration, but we do not have that statement, the multiverse is, we don't have that yet. We only know it in special cases like measurement and quantum teleportation and so on. have a general theory of what the multibus is in general.

Speaking of people who are skeptical and then you constantly have to disprove or correct their misunderstanding of many worlds, I was speaking to Leonard Suskind on this podcast. I asked him about many worlds and he said, there are several technical questions that people who are believers in many worlds have, that I mean, sorry, that I have toward them, that they aren't able to answer. And he listed two that I recall. One was that branches in quantum theory can recombine. He said this whole notion of completely separate branches is, well, he questions that. We'll get to that. And then number two, he said, well, what about if you have, sure, you can have half a branch here, half a branch there, and the Bourne rule says 50%, 50%, but what if it's two branches

and then one is one third and the other is two thirds? Does the universe split into three and then irrational numbers and so on? So I know that these issues have been solved or at least have answers and have had answers for decades. Yes.

So my question is two parts. One, I would like you to actually answer those questions for people who are in the audience who are like, yeah, those sound like reasonable objections. But then number two, someone like Suskind, who's in the field of fundamental physics, he said they've never been able to answer this. So it's either that he's asking people who are

rudimentary in many worlds theories, or he's not asking them, or he's not listening to them, or something like that. I don't know what's going on there. And I don't know if you see that as well with many of these people who are skeptics saying, look, they're never able to answer this. And you're like, I've had answers to these. You're just not listening. I guess that's a psychological question, which you perhaps don't want to go down. But yeah, I, I, Either way, what is the answer to those two critical questions? We'll get to the psychoanalyzing question later. So the, that was the one about probability.

Recombination of branches. So, yes, recombination of branches. Well, this is going right back to Everett. One of the things that was kind of mistaken in Everett's view is that it regarded the, although he made the enormous bit of progress of, regarding a measurement as a quantum process, instead of regarding it as a structuralist classical process that gets an answer.

So the measurement process is a process like any other, and then you see that there are superpositions of the observer as well as the system. And then you can see how the correlations happen and so on. However, although he analyzed the measurement, measurements that way, he analyzed measurements in terms of what happened at the beginning and what happened at the end. He didn't actually ask what happens during the measurement at the time when the branches are forming. And people later did that in the 1980s. I had to go at doing it in the

late 70s and early 80s, and my proposal was rubbish, but at least it kept me interested in the subject, and then some philosophers actually were the people that persuaded me of what the right answer is, which is that the branches are emergent properties. There's no, branches don't appear in the fundamental theory. Instead of, like in Everett's way of doing it, you had one world and then three worlds, let's say, or one world and a million worlds. Whereas what really happens is that there isn't really one world. Even when you have a single pure state of a system, it's still the state of its being, of a particle being at a particular place also includes within that unity there is a diversity

that the more the particle is in one place, the more its momentum is different. So there is no such thing as there being one world at the beginning. There's always a continuum of universes or worlds but they're only worth calling universes when they subsequently evolve independently of each other and typically that happens when there's been a measurement in a measurement process so before there's a measurement when there's just a particle of a wave packet sitting there yes there's lots of momentum there's lots of positions all happening at once nothing is ever sharp but you can't say that there are different momenta in different universes

because all those universes are interacting with each other. So you should only call something the universe when it is causally autonomous. In other words, it's behaving exactly as it would if the others were not there. And that's what happens after a measurement.

So, it's been a bit long-winded, but the answer is that the the rejoining of universes is what happens in an interference experiment and during the interference experiment you can't speak of universes

because the different branches are affecting each other. Precisely, the interference is precisely the fact that the different parts of a single photon around a interferometer they're not behaving as if the other were not there. So when they come together, they do something completely different if the other one is there

from what they would do if the other one weren't there. That's the whole interference phenomenon. So the picture you can have in mind is that there's a continuum in some kind of entity that's a bit like space-time but in Hilbert's space or something in the multiverse, which we don't know how to classify mathematically yet. And then that continuum just differentiates itself into two.

And as it's differentiating, there is no moment of split. what happens is that branch A is affecting branch B less and less. And when they have separated enough, like when you have made the measurement and you've copied it or something, then they're hardly affecting each other at all. They're affecting each other only to the level of 10 to the minus 10 to the 100 or something. So then you can speak of them that those things as different universes. So that happens after a measurement, and during interference, and also in the general case,

you can't speak of universes. You can only speak of the multiverse and the multiplicity of values of things within the multiverse. And now briefly speaking, probabilities. Probability is so, whoops, basically, why do we need probabilities at all? And the answer, well, within physics, the answer, is basically because we need to know when we have refuted a theory

if the theory says that there's a probability of 10 to the minus 10 to the 100 of X happening and the rest of the probability is all about Y happening why can we be confident

that Y will happen and that we will never see X even though we know that in the multiverse we will some of us will see X, but why should we expect Y to happen and not X? So then you only have to give an account that kind of synthesizes probability in certain special cases like when there's a thing to expect.

and that only happens after a measurement at the time when the universes have decohered. And in fact, we know that when this should have been obvious. We know that when the universes have not decohered, they don't even obey the probability calculus. Or rather, the physical world does not obey the probability calculus when you're in the middle of an interference phenomenon. there's a probability of a half that this will happen and probability of a half that that will happen, and at the end there's a probability of one quarter, one quarter, one quarter, one quarter, when they pass through another beam splitter,

and that's simply not true. The probabilities do not add up in the way that the probability calculus says relative probabilities ought to behave. But you want to have relative probabilities behaving properly when there has been a measurement and you're actually looking at what happens rather than thinking about it theoretically what is the particle doing

and if you look at it that way then it turns out that quantum theory with the born rule removed just having no reference to probability just quantum theory sort of stripped down quantum theory without probability

and then you take classical decision theory which is about things like if you prefer A to B and you prefer B to C then you prefer A to C that sort of thing if you take classical decision theory and take the probability rule out of that the rule being

that you should prefer the thing that has the highest expectation value of your utility so you take that out because there's no you take that out because you've taken probability out and therefore there's no such thing as an expectation value then you put the two together

quantum theory without probability and decision theory without probability put them together and they tell you what a rational person would decide in the case in the case where there is where there is some substantial amplitude for two or more things

to happen and it gives, in those cases it gives the born rule, but you don't have to postulate it. So when you were developing early quantum computing, was ever its interpretation

important to you, or was it a driving force behind the idea of quantum advantage? Completely. crucial. Yeah. Yeah, I couldn't have done it if I'd been thinking in the old way. Does that prove to you in your mind that research in quantum foundations or philosophy of quantum mechanics actually drive scientific breakthroughs? Well, it did in this case, but I don't think that's a proof of anything. As I said some time ago, it very often happens that fundamental

things cause practical improvements as well eventually. But I don't think it's tenable to say that that's why one should think about the fundamental things. It's a thing that can happen sometimes, a thing that often happens, perhaps even very often. I don't know. I don't know how to characterize it. But it certainly happened to me in this case. If I thought of quantum theory in the in the wave-function collapse way, I wouldn't have thought of quantum computation. And in fact, at the time when I was persuading people of quantum computation and that it's a thing and they ought to think that way,

a lot of them didn't want to make this change in their conceptualization. I remember talking to Landauer in his office. when I, I think I was either just about to publish my first paper on that or just after. And I gave a talk, he very kindly invited me to give a talk, even though he very much disapproved of this theory at the time. And he was saying to me, no, this is just something you write down on paper. This can never work because when the wave function evolves in this, way and then there are two systems. And then the door was partly open in his office. He had

quite a small office for such an eminent man. And so he grabbed the door and he said, so when you shut the door, slam, and he slammed the door. And he said, you see, it's not coming back. If this was quantum, it would bounce back. And so he was explaining why basically in modern terms, he was explaining why quantum error correction is impossible. But it isn't impossible. And then I infuriated him by saying, that's a problem that will be solved. And you said this behind the closed door? No, no, I didn't.

That would have been a good joke, yes. No, I said that. And he, in his mind, it was a fundamental problem. that will never work. And Asher Perez made the same objection to me at the Broadway conference. He said, you know, I was writing stuff up on the blackboard, and he said, yeah, but that won't work in real life because it will be more effort to correct those errors than to

than what you're correcting. Ah, okay. And again, I said technical problem, that is going to be solved and indeed it was solved by Peter Shaw very soon afterwards.

Now, the reason I thought it was a technical problem and they didn't is because I was thinking Everett and they were thinking collapse. Yes. Is the universal function as physically real to you as the camera or your laptop that's in front of you and the microphone? Is it more real?

What are David Deutsch's ontological commitments? So I try not to have commitments like WW Bartley said. We should retreat from commitment. And I also try not to have beliefs either. But it is, let me put it this way around. my theory that this computer that I'm talking into now exists has the same status in my mind as the theory that many copies of it exists in other universes

and in both cases that status is that there are no rivals to that theory that I know of that aren't nonsense. I mean, there are only nonsense rivals. So you could call that belief, but that suggests that I wanted to be true or that I would resist it not being true if an argument were presented,

but I hope and expect that that is not the case. But it's, it's, whereas the opponents of everything, do have beliefs and that that I think is what is well again I said I wouldn't be psychic so I'll try not to be psychic let me be psychic it seems like beliefs to you is synonymous with dogmatic beliefs yes although so dogmatic belief is absolutely a belief that nothing could persuade you otherwise so that's absolute dog dogmatic belief but I'm I'm a against having a 10% dogmatic beliefs saying that, you know, I'm pretty sure that it would take a lot to

persuade me that that's true. I don't have anything on that scale, and I don't think that stuff on that scale really exists. It's a misconception about how thinking works. The way thinking works is to have a problem and then solve it, attempt to solve it, and then criticize the attempted solutions. And if you're lucky enough to come to a place where there are no criticisms left that you can think of, then you don't accept the theory. You just are in the position of not being able to think of another criticism. So you go and work on something else. So when David Deutsch has a interpretation of Everettian quantum mechanics and Sean Carroll has an Everettian quantum mechanics and David Wallace has an Everettian quantum mechanics, are these different theories? Like, are there disagreements between you and Sean Carroll and David Wallace?

There certainly are disagreements, but the things we're disagreeing on are very, very minor compared with the difference between. Everettian theory and all the other theories. So, for example, David Wallace thinks that there are substantive assumptions behind my proof of the equivalent of the born rule in decision theoretic approach to quantum probability. and I don't think there are substantive assumptions. So he naturally works on trying to make clear what those assumptions are, to analyze them, to see what the arguments for and against those assumptions are. I don't think such assumptions are needed, so that's the difference between me and David Wallace.

And assumptions in this case, is that just axioms or something else? Okay, so is there a rigorous list of axioms of your species? specific Everettian approach somewhere? So I don't believe in axioms, but David Wallace has written down how he characterizes my approach. So in his book, he has what he thinks are the axioms behind my approach. I don't think physics should work that way. Axioms are a bit like definitions.

There's something you can come back to after you've got a theory. but working forward from them so the axiom is never completely captures the theory anyway we know that from girdle and so on we know that Pia knows axioms don't tell you everything

that's possible to know about the integers but you can have a conception of the integers and you can say oh this new axiom someone's proposed makes that conception, brings the theory closer to my conception of the integers. Well, I was going to ask you what the axioms of constructor theory are. Well, so the basic axiom of constructor theory, if you can call it an axiom, is that the laws of physics can be characterized by specifying a dichotomy

between physical processes that can be brought about by something else which is a constructor but we needn't say that that can be brought about and those that cannot be brought about once you've stated that dichotomy

with all possible all conceivable physical transformations you've stated the laws of physics and so then the constructive theory research program is on the one hand to reformulate all existing laws of physics in those terms of saying what is possible to bring about and what is impossible to bring about and then to formulate purely constructive theoretic laws that are over and above that

which are a bit like the laws of quantum theory are at a level above the dynamics of particular systems. Quantum theory doesn't refer to any particular system. It just says, it just has a theory of what laws of physics can say. They have to have a space of states and they have to have a Hamiltonian. I mean, whatever, or Lagrangian, whatever you say, however you phrase it. So, constructed theory is a level of body. that. It's a law about laws, but also a law about laws about laws.

Hmm, okay. And that's actually how I first thought of it, because I first thought of it as an extension of the theory of quantum computation. In a way, the theory of quantum computers contains the whole of the rest of physics, since the universal quantum computer can simulate any other physical system. So the set of all motions of the universal quantum computer is a one-to-one correspondence with the set of all possible motions of anything. So in a way, the study of physics is the study of the possible motions of the universal quantum computer. Well, then I realized that that wasn't right because you still have to have a theory of which program of the universal quantum computer

correspond to which physical systems and that is not contained in the abstract theory of the universal quantum computer so I wanted to have an extended theory of the universal quantum computer that included saying which program corresponds to which physical system and then I generally built on that

and so on and eventually got down to the to the core of the issue, which was the dichotomy between things that can be brought about and those that can't. Speaking about interpretational splits as a framework or theory develops, for constructor theory, has it developed, since I think, almost more than a decade now, has it developed in a manner that you're largely happy with, you agree with, or are there, no, other people who are, you're on the wrong constructor branch? Yeah. So you're right to say that the development of constructive theory since I first thought of the idea has been mainly the correction of errors in it, mainly the correction of ways that I thought were viable, which turned out not to be viable. And in fact, Kiara Marletto first came to me, say, after I'd given a talk at the clarinet laboratory about my ideas of constructor theory. So she came up to me at the end of the lecture and said, that thing you said can't be true because so-and-so.

And I said, oh, yeah, right, okay, thanks. And then I invited her, and eventually we end up working together on the theory, we ended up solving that and many other things. and the first thing that resulted in was the constructor theory of information which is the only constructor theory construct a theory of something

that we've completed so far and you could say that we've also got a constructor theory version of quantum theory but you know you may and may not think that But for information, we made real progress, and we unified classical and ponton information via constructive theory. It couldn't have been done otherwise.

And as for how it's developed with other people involved in constructor theory, there's now a, quote, unquote, program of constructor theory. Largely speaking, do you look at that field with pride and happiness, or are there some child that you kick out of the house? I like being baffled and we're still at the so I haven't really worked on quantum computers ever since I stopped being baffled by the field

there's still plenty of things to be baffled with in the experimental side on the experimental side but I'm useless at experimental physics so there's nothing I can really contribute there's nothing I can really contribute to on the theoretical side nowadays.

In constructive theory, no, it's not satisfactory yet. But I don't think that there are crass errors in it anymore. Okay, now before my last question of what advice do you have for people who are watching, and as I mentioned, they comprise professors, researchers, graduate students, but also lay people. So before I get to that question, I have a question from Scott Aronson here about free will. So Scott said to me, David once remarked that he's certain that free will exists and equally certain that it has nothing to do with

quantum mechanics while he wants you to expound on that, what could possibly be the source of such certainty on either account. So, rather like with belief, I certainly don't want to be certain of anything, and I want to think, you know, on introspection, I think if I was presented with a good argument on either of those points, I would be open to it. But in both cases, I think the idea that consciousness doesn't. doesn't exist, free will, sorry, that free will doesn't exist, or that free will requires quantum theory, are both in the status that there is no such position. You can say maybe it has something to do with quantum theory, but there is no actual theory, or even in principle of how, apart from pen roses, which I think is wrong for other reasons, there's no actual

theory of how quantum theory could produce free will or philosophical theory about how free will could not exist. And I think that the philosophical problem that people have with free will is that they have a conception of free will which by definition violates the laws of physics. It's basically, although they don't often say it like this, but it's basically free will is the human capacity to override the laws of physics. And I don't think anything overrides the laws of physics. We might be wrong about what the laws of physics are, again, like Penrose thinks, but I don't see, in that case, I don't see a proposal for different laws that would help with the problem of consciousness. sorry, free will.

Now, I think that free will has to do with knowledge. The problem that does make sense about free will is that we have an intuition and it's in all our explanations of human behavior and so on that when we make a choice, not a random choice, but a choice that we have thought about. We have brought something new into the world. So, for example, when Einstein was inventing general relativity,

he was bringing that into the world. It didn't exist before. The theory of general relativity did not exist before Einstein thought of it. And ultimately, if you think it did, then you've got to say it was in the Big Bang. Okay, so I don't think it's tenable view philosophically or physically that all the knowledge that's ever going to be created in the world was in the Big Bang, and that all that happens is that it's being made real in some sense,

although why one time should be more real than another time. I don't know either because that seems to violate relativity as well. But I think there is such a thing as bringing something new into the world, and the thing that you're bringing into the world is knowledge or explanatory knowledge. So Einstein, the thing that didn't exist before, even if the equations of general relativity existed, like apparently Hilbert had the equations before Einstein,

but he didn't know what they were about. He didn't understand the physics problem, which is, again, touches on a thing we were talking about earlier. Einstein was seized of the physical problem and he eventually came up with the equations and I think that the discovery of general relativity was discovery of the explanations of what the equations mean

which actually came before the equations so and it's the same with everything when you decide that you want to have a curry for dinner tonight and if it was possible that you would have chosen something else that decision is something new you have brought into the world when children learn their native language the language which they learn is different from everyone else's and it has been an act of creativity to bring that language

which is unique to them into the world you seem to be puzzled but you know if if I make a list of 20 words and ask you to define them, you will not produce the same list of 20 definitions as anyone else on the planet. So everyone has a different language in mind, and it's a bit of a miracle that we can communicate with each other. The reason we can is basically error correction and again creativity, because we need not mechanical error correction,

but creative error correction. so creativity brings something new into the world and then there is no problem with how come you're violating the laws of physics because it's not new trajectories of the electrons that you'll bring into the world it's new knowledge which can only be understood at an emergent level

so that's my answer I think to both questions I've forgotten what they were now well one was about advice to perspective of students and researchers and so on. Oh, yeah, advice. Right. Okay. Again, I don't know because I, I'd have to be psychic to be able to second guess someone else's decisions about their own life. But in the most general setting, in the most general scale, at the most general scale, I would say,

go for the thing that is fun rather than the thing that you think will lead to fun or lead to some other benefit heaven forbid some other benefit that isn't fun that is extremely dangerous but the more prophecy you have to make to justify your present choice

the more error prone it's going to be and the more different from the reality that is going to happen. What do you mean the more prophecy you have to make? What do you mean? Well, so if I decide to work on LLMs, because I think that LLMs are going to give rise to AGI, and I want to do that because I think that AGI is going to be terribly

dangerous and that we have to understand it well. And so that I'm prophesying various things in the future, according to some theory that I have now. But that theory is going to change. If that theory doesn't change over the period we're talking about, you know, 10, 20 years, then I won't have discovered anything, or nobody will have discovered anything if that landscape of ideas doesn't change. Okay.

So it's better to make decisions according to the shortest possible time scale of prophecy. I see. So in the case of someone predicting about AGI, thinking it's an important issue, let me attempt to solve that now, that would be different if they were passionate about trying to solve the issue of AGI. Exactly. I imagine you would say, yeah, that's your curiosity, that's your, that's the fun you refer to, go after that. Don't try to leapfrog ahead two decades, let alone one decade, well, sorry, one decade, let alone two decades, and then think backward from there, because you could be incorrect, most likely

it would be. When working on, if you have an idea for AGI, you can work on it today. You can drop what you're doing and work on that instead. That's the sort of thing you should be doing. Professor, it's an honor to speak with you. It's something I've wanted to do for years, and I'm, I'm. I'm honored that, like, more than honored to have spent a couple hours with you, and I appreciate that you took some time out of your day to spend with me.

Well, it's been fun to say it oppositely. And hopefully next time we speak, I would like to talk about consciousness, as that got brought up toward the end, and also the philosophy of science. Mm-hmm. Thank you. You're welcome. Fun chatting. Hi there. Kurt here. If you'd like more content from theories of everything and the very best listening experience,

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