Into the Impossible With Brian Keating - Dan Green Physics is NOT In Crisis! (#296)

Episode Date: February 5, 2023

Please support the podcast by taking our short listener survey: https://www.surveymonkey.com/r/intotheimpossible Is fundamental physics in trouble as past guests like Lee Smolin, Lawrence Krauss, Eric Weinstein, Sabine Hossenfelder, and Neil Turok have suggested? Dan Green is a theoretical physicist focusing on the intersection of cosmology and high energy particle physics. He's a professor at UC San Diego, where Into The Impossible's new studio is located. Dan discusses his career progression, his research, and some of the most significant, though possibly underappreciated, results in fundamental physics for the last several decades. Enjoy a great discussion and learn some new physics in our very first in-person episode at our new studio! https://twitter.com/nu_phases 00:00 Introduction 02:01 Dan's Origin Story 04:16 Theory vs Experiment 06:56 Significant Results Thread 14:12 How Emergent Ideas Form from Research 16:16 Sara Seager's Atmosphere Models, for Exoplanets 17:53 Is Physics In Crisis? 22:54 Science Psychology: The Ikea Effect 24:37 A Defense of String Theory 27:26 Physics, a Cutthroat Career 34:08 What is Supersymmetry? 40:36 Future Topics Connect with Professor Keating: 🏄‍♂️ Twitter: https://twitter.com/DrBrianKeating 📸 Instagram: https://instagram.com/DrBrianKeating  🔔 Subscribe https://www.youtube.com/DrBrianKeating?sub_confirmation=1 📝 Join my mailing list; just click here http://briankeating.com/list ✍️ Detailed Blog posts here: https://briankeating.com/blog.php 🎙️ Listen on audio-only platforms: https://briankeating.com/podcast Subscribe to the Jordan Harbinger Show for amazing content from Apple’s best podcast of 2018! https://www.jordanharbinger.com/podcasts  🎧 On Apple devices, click here, https://apple.co/39UaHlB scroll down to the ratings and leave a 5 star rating and review The INTO THE IMPOSSIBLE Podcast. Other ways to rate here: https://briankeating.com/podcast Support the podcast on Patreon https://www.patreon.com/drbriankeating  or become a Member on YouTube- https://www.youtube.com/channel/UCmXH_moPhfkqCk6S3b9RWuw/join Learn more about your ad choices. Visit megaphone.fm/adchoices

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GoogleFi Wireless is not subject to data traffic deprioritization during times of high network usage. These research is very complex. There's people doing all kinds of different things. And so to say, physics is not making progress is often just completely ignoring huge swaths of the community that are making real progress. In other fields, like one person's working on a subject like, oh, someone's got that covered, I should go do something else. Whereas in particle physics, it tends to be, oh, everyone's thinking about dark matter.

That's the thing I should be working on, dark matter. And it's like, yeah, that's a strategy for research that I find can be problematic when The motivation is just to be part of the crowd. Welcome everyone to this physics insider edition of Into the Impossible. For the first time since the pandemic, your host Brian Keating goes live in our new University of California San Diego studio with theoretical physicist and fellow UC San Diego professor, Dan Green. Dan addresses the so-called crisis and physics head-on.

His fundamental physics in a problematic echo chamber, as has been suggested by past guests including Lee Smolin, Lawrence Krauss, Eric Weinstein, Sabine Hassenfelder, and Neil Turok. Dan's Twitter exploded as he tweeted his picks for the most significant fundamental physics results of the last 40 years that did not win a Nobel Prize, arguing that physics is doing just fine. Decide for yourself as you enjoy a great discussion and learn some new physics in our very first in-person episode at our new studio. Any sufficiently advanced technology is indistinguishable from magic.

Open the bud bay doors, please help. And I'm joined today with a renowned cosmologist, a collaborator, a colleague, Professor Dan Green. Welcome, Daniel, to The Into the Impossible Podcast. Hi, Ryan. Great to see you. Good to see you, too. Today we're talking about Nobel dreams

or maybe not Nobel dreams. We're talking about things that aren't necessarily Nobel recipients, but are potentially Nobel worthy. And it's really prompted by Daniel's amazing tweet storm of the month of December, which caused him to really gain a tremendous amount of well-deserved attention for his perspicacity and everything that he does. He's an amazing colleague, and I'm so glad that we poached him away. And I want to give him an introduction, but I want him to do it so I don't get anything wrong. And that will commence right now. So, Dan, where do you come from? What's your origin story? We're cosmologists.

You're a theorist. I'm an experimentalist. We work together on many projects, including the Simon's Observatory. And what's your origin story? Tell the audience, where did you come from? So, yeah, I grew up in Vancouver, British Columbia, Canada. I was science fair and enthusiast and amateur astronomer as a kid and stayed in Vancouver to go to the University of British Columbia for undergrad. And there I interacted with a bunch of the local famous people like Bill Unruh, who's famous for the Unru radiation. And after spending four years there, I was ready to make the big move to the United States for graduate school.

And I went to Stanford, where I studied with Eva Silverstein, who's well known in part because she's a MacArthur Award winner. But she is one of these interesting people who bridges the boundary between many fields. She's a string theorist by training, but's really interested in cosmology. And while it was there, many other things like condensed matter physics,

And so she was kind of a very broad person who liked to investigate different interesting things. And so that rubbed off on me in a certain way. And so after graduate school, I moved to Princeton at the Institute for Advanced Study. And I tried a bunch of different fields out. And in part because of the presence of David Spurgel and Matisse Aldiaga, who were just some of the most brilliant people I'd ever met, that kind of their unique style of just kind of doing everything in cosmology was really entomical. And I kind of became a cosmologist from that point forward. And so from there, I went back to

Stanford and then eventually to the University to Toronto at the Canadian Institute for Theoretical Astrophysics. Where we poached. Yes, indeed. And so I was there, I also got to meet Dick Bond, who's another just incredible cosmologist with great stories about the history of the subject that I had never been exposed to. So a lot of, even in my list, a lot of the sort of what I was thinking of, you know, what were big things. I would think back to conversations with Dick, where he you've kind of been like, oh, at this time, it was really, this thing is really what moves the field. And so that was a very useful perspective for me.

And then I moved here in 2017 and I've been here ever since. You've been here ever since. And you're now. Associate Professor, which means you're tenured, which means you could speculate on all sorts of crazy stuff like I like to do. Maybe have your own podcast someday. And certainly, you're a must follow on Twitter. And I recommend everybody do that because Daniel is, he, I think you're unique in a lot

always. You have a very high command of experimental results in the history of the experimental field. And I always say, and tell me what you teach your students, but I always say that experimental is my students should understand theory as well as your graduate students do, but they're not required to create new theories. Do you feel, well, first of all, how do you react to that? Do you think theorists should have to understand experiments, but not do experiments? I think, I mean, it's different people have different styles. So for me, there's always, like, I don't think there's one right way to do it, But, you know, what drew me to the subject of cosmology is the ability to go. So I can distinctly remember a meeting in Princeton where in the span of one meeting,

David Spurgel had kind of brought up why a telescope they were designing was going to have slinging mirrors. And then at the same time, was talking about topological defects in the early universe from a theoretical point of view. And for me, that the idea that a single conversation could cover all of that ground and that one person could be in command of all of those things at the same time, that was amazing. And I think it's not for every subject, right? If you're in particle physics, like, there's a very hard line between really doing experiment and doing theory because if you join the experiment, there's like rules. You can't publish certain things if you're part of the experiment. And so I actually just, that seems problematic to me. It would be nice if everyone could find the balance between how much theory, how much experiment work for them. But to your point on the coming from the experimental side, I do remember there's like experimentalists, sometimes they hate it when theorists say, oh, we need theorists to calculate things.

And they're like, I can calculate just fine. Like, don't tell me I don't know how to do math. It's more the like, it's the new ideas. And that the health of the field requires an influx of new ideas, not just new calculations for testing experiments. So I think that a blend is great. And I think cosmology, that's the great thing about our field, is that that blend is very alive and well in a way that maybe other fields have become really

split into theory and experiment. Yeah. And I think that is something that has drawn me to, you know, remain in the field, dabble in theory, you know, to whatever extent I'm capable of doing it. I'm always trying to have one of my students who is more theoretically inclined, so to speak, and, you know, thankfully I've had a bunch of phenomenal students and help to, you know, kind of shepherd their careers through through all the different hoops they have to jump through, and thankfully they're back off their strike.

We broke the picket line. But I want to talk about this epic, you know, tweet thread that you had. I mean, you've got millions of impressions and just tremendous feedback and a lot of attention. And I want to have you explain the predicate for it. What was the sort of impetus? Why did you choose to present it in this way? And how did you maintain your sanity and strength or the month of the same? I can hardly post stuff that other people write from not. Everybody writes my tweets. But what was the impetus of it? How did you come? So, you know, it was one of these things. I think a lot about what's important research just for myself. And I tell my students to as well.

I think it's valuable as an exercise as a researcher to know sort of what is something that would rise to the level of the best result of a year, the best result of five years, the best result of 10 years. And I tell them this in the same way that you would think about, like, what's your best movie of this year? Imagine you're a filmmaker, you know, you want to know what makes a good movie. We don't have to agree on what the best movie is at all time or even the best movie of the year, but we can probably agree that certain movies are good and certain movies are not so good. Obviously, it's nice to aim to make movies that are good if you're a filmmaker. And for me, it's the same with research. Like, I think everyone knows that Einstein's contributions to physics were important. But, like, even if you aspire to be Einstein, like, no one just jumps into being Einstein.

You have to, like, have some more modest goals to tick along the way. And so I think that's what's often missing for me in the conversation around what's good and bad research is, like, it's either there's Einstein or there's nothing else. And it's like, and I was just. you know, I'm inspired all the time, be like, well, what's the middle? What was the best paper of the past 10 years? And then, I don't know, just suddenly there's something my kids have Advent calendars. And so the month of December is a time where there's a kind of thing every day. And I was just like, you know what?

Maybe it would be just fun to every day of this month just put one of these kind of ideas out there. For people to digest and whether they like it or not, I felt like I could do that. It'll be fun. And, you know, it wasn't hard to get 25 interesting papers because I was. wasn't ordering them. To be, to be honest, if it was like, I was going to do the best paper, then the second best paper, I would have agonized way more. But it's just like, here's 31 papers I like. You know, that's not, that's not so difficult. Right. And so we'll go through a couple of the highlights. And some of them I just really could not agree with you more. And some of them I felt like, oh, why didn't you leave this one off?

And so we'll talk about the ones that were orphaned, the great results that you did. But there was one criterion, which was it could not have been appeared in this book or this book, Nobel Dreams, or Into the Impossible Mind. And why was that? What was that choice? So it might, like, it aligns with your missions pretty well. But actually, like, the reason was just to make an interesting list. Like, I thought it was like, you know, it's like saying your favorite thing is poppies.

Like, no one's going to disagree with that. Like, I thought to be an interesting list. to be a list of things that hadn't had the kind of like obvious acclaim that everyone can agree on. Because I'm like, yeah, this thing that won the Nobel Prize was a good result. It's like, yeah, great. Right. No duh. But I thought, you know, just had, and again, I didn't just, Nobel Prize was the easiest line to

drew, but I drew some other ones where I was like, you know, that it's so obvious that everyone would have that on their list because it's so well popularized. And the fun of making a list is to give some light onto things that are sort of less well-known, the same way that if you're a movie critic, like, that's why they tend to be less likely to put the blockbuster that made a billion dollars on the list because like, yeah, everyone knows that movies out there. And that's why they'll throw in that, like, weird foreign film that no one's heard of. It was like, this is my opportunity to sort of cast some light on something I really appreciate it.

So that was the idea, not because I had any sort of thing against Nobel Prize winners or one or the other, but just an easy way to exclude them. You know, I'm a vendetta. So where did you start up? What was the first tweet and then the last tweet? And then we'll get to some of that, the ones that we've, that we've, can debate. So I started with heavy cork effective theory. So heavy cork effective theory was this idea that when you're thinking about, when you're thinking about states of matter, or particularly

particles that are made out of lots of quarks or made out of corks that include one whose mass is very large, there's a secret trick to understand what's going on, which is to kind of treat that one cork like it's infinitely heavy. And And this trick has a way of explaining why a bunch of these sort of barionic states tend to have similar properties, even though they're made out of different combinations of quarks. And this idea was like, this was the first example where someone had taken a theory that's written down. And by kind of expanding it in a non-obvious way made new properties emerge that were not

obvious from the beginning. So there's kind of secret symmetries that related different states of particles in a way that was, you couldn't have just said, oh, well, we knew that from the beginning, and you just made it obvious in some other way. And that's the kind of, that was sort of the first example, at least in my knowledge of the history of the subject, of sort of effective field theory, which is this great thing that has really transformed the field in the past 30 years, where effective field theory wasn't just a way of saying a result that people already knew, but really was a way of rethinking about what physics is about, where by focusing in on the, the scale of the problem you care about, what is the right way to think about the theory, you really make, you know, you really make things obvious that were not obvious before. And so that has happened. There's been many, many further examples since. And that was, I picked that one because I was like, this is the thing that kind of started at all.

And our colleague, Anish Manahar was one of the people who really pushed that forward in the early 90s and has since discovered many other great examples of this kind of like mysterious things that come out of thinking about what the right way to organize physics problems is. And so that was one where I picked that one as the first one, because it was the kind of thing where I feel like people who really know the subject, know that heavy core effective theory was important. But like, it's kind of niche. Like, not very many people know it,

and it deserves much more credit as kind of spawning a lot of development of the field. And then the last one, which will be close to your heart, I imagine, was the age of the universe. This was sort of a measurement. And this was feeding back to our kind of. comment about Dick Bond, I really, this was the one that drove me crazy because the history is that it was really first definitively pinned down by cosmic microwave background measurements. But Dick would have would tell me that it was the boomerang experiment and the analysis that they did around boomerang, which was, which was before the satellite W map, which usually gets the credit for the measurement.

That was, that was a big deal. But the part three is I put it on my list is that when I was in Canada, I worked on a space telemet, which was. called Most. And the proposal for most, which was made in the 90s, was that they were going to measure the age of the universe by doing astro seismology to measure the age of stars in our galaxies. And when the proposal was made in the mid to late 90s, the age of the universe was so uncertain that that was a compelling thing to do. Like we literally didn't know, is it 8 billion years or 20 billion years? And so peeing down how old stars was seemed like a really important problem. And while they were building that telescope, C&B came along and determine the age of the universe to basically 1%. And that suddenly became overnight, not an interesting question. It's just obliterate. Yeah. Now, to be their, to their good luck, though, at the same time that they were, you know,

the fields were evolving, exoplanets came along. And a telescope that's really good at measuring very small changes in light of stars, really excellent for exoplanets. So while their age of the universe, science target disappeared, exoplanets emerged. And so that was like, you know, it's the give and take of science. But that one for me is very personally resonant because I was coming along right at that moment. That was right when you were kind of hitting maturity and really coming into your own as a scientist and thinking about projects that could then take your interest. So my first project on most was to do exoplanes.

I was the first person who thought about exoplanes for most. And it was like literally as an undergrad, they put me on this because it was like, this was not part of our proposal at all. But it's obviously very important science. And so it's the example of how new targets emerge in the middle of a project. You don't just do what the project set out to do. And so serendipity exactly is a great. That project never... So it launched in 2003, I think, on a Russian satellite, I run Russian rocket.

It was one of these converted ICBMs. I think at the time it was the rocket that had put the most satellites into independent orbits that had ever been done using that great ICBM technology to hit multiple U.S. targets. Words into plush. And so they had a couple of high-profile papers around Astrocysmology, but they did, and they put some upper limits on exoplanets. But the thing that's really challenging with exoplanets is to see a light curve. You need to see the light reflected up planet.

It depends on the exact atmosphere. And so actually at the time, as an undergrad, I got to work with Sarah Seeger because she was the one who was making these. Two-time past guests on the end of the past. And so she had these atmosphere models. And so we are using her atmosphere models to, to predict what it might look like. And they were so uncertain at the time.

It was totally possible that most could detect it. And they ended up setting some interesting upper limits, but we're unable to actually see. Oh, that fascinating. Okay. Well, let's get back to the tweets in just a minute. But I did want to take a detour into a subject that's very, very prominently featured on this channel, which is the crisis in physics.

So I've had, probably, you said this place was steps from the water. We just haven't found the steps yet. How much did we save? enough. Enough to get lost. Or you could book a stay with Hilton. Welcome to your ocean front room. Just steps from the water. The Hilton sale is on now. Book on Hilton.com or the Hilton app and save up to 20% to get the stay you expected.

When you want savings, not surprises. It matters where you stay. Hilton for the stay. Three dozen podcasts or interviews or webinars with my friends at PBS FaceTime and others. saying basically is physics in crisis. We've had on guests like the Savine Hassanfelder and Neil Turrock. The episode is called Physics is in Crisis. We've had on Eric Weinstein.

We've had on many, many kind of iconoclastic people. But we've also had on many, many, you know, kind of supporters that physics is doing just fine. And we should stop the histrionics amount about what's wrong with physics. But let's talk about that. How do you react to these claims that, you know, physics is suffering, not to crisis, of tensions, those are healthy. We'll talk about those.

And we'll talk about some unhealthy, you know, maybe corollaries to those tensions that people use a tension or research direction or a lacuna in the Big Bang, you know, CDM model to kind of call doubt, cast doubt upon all of physics or something stupid like that. But we'll talk about, I shouldn't say stupid. Strike that. Strike that from the right. But, but click baby, you know, I've been guilty of itself. But anyway,

but let's talk about physics. Is physics in crisis? What is this notion that people seem to want to believe almost that we as physicists are chasing angels dancing and pinnets? Well, I think what I would say is that my, as I try to emphasize, my thought process around what's good and bad science, I try to have a very nuanced view because it's important for me as a research. And so I would say the thing that I, so I will first say the thing I agree with, which in this context, it's always, it's typically around are we crisis, zero. zeroing in on really one field. It's usually like there's a group of people working on this one thing. Is this one thing going to lead for progress? And the reality is research is very complex.

There's people doing all kinds of different things. And so to say physics is not making progress is often just completely ignoring huge swaths of the community that are making real progress. But the part where I would agree with, I would say that I at least agree with the spirit of it is that particle physics in particular as a phenomena where people tend to kind of, I describe them in physics terms. They're like bosons. They all like to do the same thing, right?

They don't like whereas fermions like to not be in the same state. So if one person's working on a subject, in other fields, like one person's working on a subject, like, oh, someone's got that covered. I should go do something else. Whereas in particle physics, it tends to be, oh, everyone's thinking about dark matter. That's the thing I should be working on, dark matter. And it's like, yeah, that's a strategy for research that I find can be problematic when the motivation is just to be part of the crowd, right? And if we don't have good checks on, are we making progress? And again, we could be making progress, but the question is, is the progress worth the number of people working on it? And so

I think in a new one, you know, typically hear about the string theory. Yeah, so string theory is exactly the same, but I want to spread it because string theory, the criticism is also that it doesn't make contact with experiment. And I would say, I don't see it necessarily as just as being an issue of contact with experiment. There's great results that didn't intend to be in contact with experiment when they started, they made contact later. And there's some of those on my list on purpose for that reason. But it's more just a number of people, right? It's like, is this subject so, in making so much progress that it warrants the attention

to it, or ignoring subjects that are making real progress and need more people? And is that healthy for the field? And so I would say my point of view is at times I'm frustrated that there's not more people working on inflationary cosmology, a subject close to my heart, and that there's perhaps more emphasis on dark matter than maybe I find is warranted. But dark matter, I also think is the correct theory of cosmology. All the data and my point of view is that is absolutely correct and we should definitely look for it.

And there's just some, you know, it's around the edges, you know, how much attention doesn't warrant, are setting bounds on models of dark matter that no one in their right mind thinks that the model of nature a worthy use of time or should they be exploring more generally. And okay, those are, I think, legitimate things to work. worry about is the health of any field is this, you know, how does sociology affect what people feel they can and cannot spend their time on? So I think from that point of view, I agree that there's a reason to worry, but there's a reason to worry all the time, right? Like the, the health I mean, people would say inflation gets away more attention than bouncing cosmological models.

We've had an antieges and also. So I would say in that example, I know the field in that case, and I would say, you know, I don't, I think there's a lot in this sort of clickbaity way, which is like people, and I think this is true to most of the criticism, which I've come to, which is the criticism also tends to paint researchers as not thinking about why they spend their time on what they do. And again, they think about it, but in this complicated way. They think about it both from like, if I choose to work on this thing, like, and not like, is it going to ruin my career? And that's just being like looking at the job prospects and saying like, hey, there's not a job ad that says, you know, to work on this weird topic and that might influence what they do. But within any area that you're working on, you're not oblivious to why you pick one model over the other.

So the reason people to work on dark matter is not because they're not aware that it could have been explained by something that's not dark matter. It's because you can look at the, they've thought about the ways in which something is not dark matter might manifest. And the data doesn't support those kinds of ideas. And the same is true with bouncing cosmology. So all of the people, so for my point of view, I actually think the debate between bouncing cosmologies and inflation isn't the most exciting.

thing to me because to me they both solve the same problem in more or less the same way. Like I don't see bouncing as really that big a deviation from inflation. It just slightly different. And I honestly don't care which one it is. I happen to think the data is easier to make a model of inflation. And so I work on inflation, but actually a lot of the tools I use would apply equally well to balancing cosmologies. So it's not, so I would say like the idea that I have some, I am absolutely, you know,

I religiously against bouncing cosmologists first, that have some deep, seat of prejudice. I would be totally fine with the balance of cosmology. If someone wrote a model that worked better than inflation, I'd be like, yeah, that's totally fine. I kind of see it like, are you familiar with something called the IKEA effect? No, no. It's where you, they take people and they give them a piece of

high-quality furniture like this, which and they give them from IKEA, and they say, build this table, and they build it. And then they have another group or they even the same group and basically the same table, but they just give it to them. And the people that built the table themselves value it, ten

What the people who got it from a, you know, so I feel like people are so invested in whatever power. And this is true, you know, power law, independent of what field we're in. But it just so happens that you and I are both cosmologists that we see it, that people are really entrenched in it. And so that's why people like Paul Steinhart, who did have a lot of, you know, so called sunk cost, you know, into inflation. It's so impressive to me that he can pivot, you know, people that come up and just, you know,

their whole career have been entrenched and, oh, the Big Bang never happened and all these other things. But so let's dwell a little bit more on string theory. A lot of the claims that I had on Kamran Bafa and I've had on Avi Loeb and Eric Kwanza and Sabina. And the claims that I always hear is that they don't make, you know, testable predictions. They make a lot of retradictions.

And actually, to be fair, Kamran, you know, he had a wonderful appearance in one of my most popular episodes of the book links somewhere up there. And he said, no, no, no, Brian, you're wrong. You know, street theory does make predictions. It predicts that the mass of the electron is, you know, between, you know, a 10 to the minus, you know, one plank masses to, you know, 10 to minus 30 plaque masses. You know, it's in a range. It makes prediction. It could be, you know, 10 to the 80th. That would be inconsistent. What do you make, I mean, that was, and I asked him, I said,

what's like, give me something that is a concrete, you know, answer the skeptics. We have a saying in Judaism, you know, know what to say to a heretic. So tell me, you know, like, how do you react to that? I mean, is that what would you use? Oh, so actually, I, okay, I am, I am not going to, I am not going to, my PhD advisor will be very upset. If I, if I, if I, if I were just to not defend string theory very, very strongly. But to be honest, like, I don't see the value of string theory in terms of whether it makes experimental predictions or not. Like, I think the attempt to put it into the does it predict particle physics or not,

you know, hasn't been very successful. And I know that there's, you know, lots. I read all the papers when I was a grad student and people trying to make models of the standard model. And like, I just, I don't find that to be particularly useful as a scientific. who now does not spend most of my time doing string theory. However, I find many results in string theory useful to what I do. And a lot of what's called string theory is, you know, now, you know, the impact is sort of as laying the foundation for the laws of physics that we then use.

So one of the examples I brought up in this, I brought up in this list was the, what's called the conformal bootstrap. And it's sort of, you know, one of the applications is to try to make sense of, you know, what are the restrictions on? on theories of quantum gravity are inspired by what we know about string theory. But the exact technique that is being used in that one case to understand quantum gravity in anti-desider space, which is what lots of string theories do, is actually also the best way we have to predict what will happen to helium four at this particular critical point. Yes.

It's been measured. And it's one of these things that's like, yeah, they didn't set out when they were thinking about quantum gravity to predict what helium does. That was not what anyone thought they were doing when they were thinking about black holes, But at the same time, like, it is making a real experimental prediction there. And, like, it's really useful in that regard. And so for me, it's more, like, the value of string theory as a research endeavor is more in that regard. Like, I, as a person trained in string theory, I, so as an undergrad, I worked on loop chronic gravity with Bill Unru and, you know, at UBC.

And then I went to grad school and worked on string theory. And I used neither one in my, like, directly in my day-to-day work now. But the things I learned by learning string theory inform a lot of what I do. Like there's a lot of just ideas that came out of string theory that you can remove the string theory are super useful ideas. And they really change how I think about physics. The stuff I learned about loop quantum gravity has not been useful at all. And so for my point of view, it's like, well, okay. And again, this is the attention thing, right?

Like you could say, you know, given how many people work on string theory, has it delivered enough? And I think that's a fair question to ask. But I wouldn't go so far as to say strength theory is not useful because there are many, many results in string theory that have really helped me understand the universe and come up with tests that we can do in cosmology to understand how, you know, how structure was created in you know. Good question. When you're looking at and you and I serve a lot of committees, you know, we have, as I say, we have the hardest three hour a week job in the world. There's no way around it, Dan, right? I mean, we have these committees that mean, you know, every quarter, but sometimes hiring committees and we have to look forward to faculty and we get 400 applications. for a single position.

It's so much more cutthroat than when you joined, let alone when I joined, you know, the ranks of faculty 19 years ago. I can't believe it. But the point being, do you have like a goal? Is there a rub, like string theorists want it and loop quantum gravity, you know, obviously you're going to say no. Like we don't, we don't exclude anybody. It's basic merit.

But talk about like, because people say, well, there's too much effort going into it. But I can't tell my student. I can't force my student. You have to work on the Simon's Observatory or Simon's Array, polar bear. I can't force it. If they don't want to work, don't they go to a different group? They join your group or do something else.

So to what extent do we really have anything to the people that say, like, there's too much going into this field? What do you answer that? In a practical sense. I mean, again, this is where for me, like, that's part of taste, right? Like, if you ask someone what their favorite movies are and they're all terrible movies, probably not going to give them money to make their next movie, right? Because you kind of know what they're doing. And so if we hire someone who I feel has just a nose for interesting ideas,

is. And through that process, it leads them to loop quantum gravity or leads them to string theory. Like, I will trust that they have good taste and they know why they're doing it. But I also think that being dogmatic about it, like we will hire someone because we need someone who knows how to calculate some process and stringer. We don't even need people to calculate anything as establish a force. The new ideas that we care about. So, you know, I think to what the great thing about our institution is that our theory group is very diverse in the topics they work on. But I think we all have both a common language of effective field theory. So I think that's usually the thing.

If you don't understand effective field theory, it's hard to know what's an interesting problem and not an interesting problem. So what that subject has done for the world is it took the space of problems and it really organized them in a way where hard problems were obvious and easy problems were obvious and interesting problems were obvious. And so within our group, we all have a collective understanding of that. And so we can all communicate to each other. Some people were trained to string theory. Some of them not. Some of them very critical string theory. Some of them very supportive of the string theory.

But if you put us all in a room and you say, why are you working on this problem, they can instantly communicate to everyone else in the room why that's an interesting problem. And everyone will come away and going, yeah, that's a really interesting problem. And if you can hire people like that, like, that's fantastic. Like what they work on. Like, they'll tell you why it's interesting after they figure something out. And that's, I think what's important. Now, talk about, let's get back to your tweet storm.

So any controversial choices, You get feedback from your vast audience. Hopefully it'll grow, but anything controversial. So I actually got less feedback that I was expecting. I was expecting to get a little bit more pushback on some of the choices. I would say the one obvious omission that I had, which was very intentional, was ADS-C-FT, which is this idea that quantum gravity and anti-Dissiter space, which is some space that's not our universe, is equal mathematically to

conventional quantum field theory. And this was a, it's like the most cited paper of, I think it is like the most cited paper in theoretical physics at this point. And, you know, I left it off. It was written in, what was in 97. And I left it off for the same reason I left up Nobel Prize. It's not because I, also because, you know, it, again, it evokes so many emotions when you bring up that paper because it's so well known.

And for me, I thought, you know, that's, it's so, it's been incredibly useful for things that ended up being connected to experiment, but I'd rather zoom in on the things that ended up being, that came after, that ended up being really useful and clearly progress, because everyone already knows about it is. Yeah. And then Supernova 1987A, back up my eye. Talk about that. What would that sense?

So I put that, I, so I'm glad you caught that one because I, that was one I was, I was proud of to have on the list. And again, to connect back to your many, many written documents about the Nobel Prize, like, I like separating science from the people that do science. Like, those people that do science are important, but what I was trying to get out with the list is like, I don't care about who did it. I care about like the thing that was important. And so putting an event and not a paper or not a thing was useful because Superdome 1987A,

a core collapse supernova in the large magillanic cloud. It's the closest supernova we've been able to observe in the modern era where we have technology, particularly neutrino detectors. And so it was this unique event that a lot of people point to is like the moment when particle physics and astronomy kind of merged into this particle astrophysics because we had the direct observations with light, but we also had these neutrinos that came out of the supernova and showed up in our detectors. And like to this day, like there are many, many papers in particle physics every year. that are like, this new person had this idea, but the observation of the supernova in 1987 rules it out because, like, are, it gives us a window into what happened at extremely high densities that we can't make an earth. And like, it's just luck, right?

Like we have, it's not like, nobody wrote a proposal for that neutrino thing. I mean, they might have said, oh, if we're lucky enough that a supernova happens nearby, then we could do something with it. But the actual impact on the field has been enormous and long lasting because we don't get supernova like that all the time. And so that was the one where I thought it was the most obvious, the scientific value of the event where there's no, like, person you point to and you say, this was important because this person had this idea. It was like just important because it happened. Right. Fun fact that supernova indirectly led to me being here because it was discovered when I was in the middle of high school or late high school, early high school. And it was really, you know, kind of surprising.

I thought, oh, there's a supernova every century and every galaxy. No, we haven't had a supernova in a long time. And maybe that's a good thing. But it was discovered by, I think, Robert Sandalik, who's an astronomer at Case Western Reserve University, which, as you know, for my interview with Stacey McGa and Glenn Starkman, that's where the main alma mater. So talk about, you know, so next after kind of CMB, which so happened, such a direct A lot of places on their list.

Honorable mentions, yeah, although that could mean, you know, we're due for more and more Nobel prizes, right? Talk about the, talk about the appearance of, you know, Susie. I mean, to some people, they'd say, oh, Susie's ruled out. right? So at what extent is Susie rolled out and why did a feature so, you know, I did a histogram, you know, in the head of your tweets, and Susie appears pretty frequently. So I think the main tool in the use of supersymmetry in the instances on my list is as a tool to solve quantum field theories. And the reason I like to sort of put it in that perspective is that toy models are very valuable in physics, right? And not even just in physics, like I think the Icing model, which is this model, which we use. to understand magnetism is now used to understand machine learning. Like, it's like, there are like these toy models that we can solve

and we can understand all the dynamics of are incredibly powerful in every domain of physics. So I'll give you a quote of this story as Steve Kippleson, who's a very famous condensed matter theorist at Stanford. I took a class of a fitness matter of physics during when I was in grad school. And at the beginning of the class, like we've really done anything. He said, if you want to be a successful condensed matter physicists, you just pick one of these models. It doesn't even matter what the model is.

And you study literally everything about it. You study what happens when it's a strong coupling, a weak coupling at high temperature, low temperature. You just do literally everything. And then the rest of your career, whenever anyone comes up to you with a new idea, you say, oh, that's just like an icing model when it blah, blah, blah, this happens. And it was like, it was a very useful comment because that that is the use of these toy models is that they just give you a way to sort of in a way that you can solve, understand what complicated systems do.

And so a lot of the use of supersymmetry, whether or not it's true in the real world, is it allows us to solve for quantum field theories, like what happens in them that we literally can't solve in the ones that are closer to the real world. So we can understand nuclear physics in a super symmetric world mathematically improve all kinds of very important results that help us understand what real world nuclear physics could do or real world strongly coupled systems

where it's hard to solve the equations ourselves. And so as a tool, it's been incredibly powerful just as a way to think about dynamics of complicated systems. Absolutely. So in the next subject that I want to turn to, just in a couple of minutes we have, before we have to get over to the Faculty Club for our Friday afternoon scotches, is our topics that didn't make the list. So sometimes that's even more revelatory than, obviously, you only had 31 days to make these epic tweet storms possible.

But tell me a couple that you, if you had to go into, you know, February, the shortest month. By the way, do you know which month has 28 days in it? All of them all. Your summer starts now with Memorial Day deals at the Home Depot. It's time to fire up summer cookouts with the next grill, four-burner gas grill on special buy for only $199. And entertain all season with the Hampton Bay West Grove seven-piece outdoor dining set for only $49.

This Memorial Day get low prices guaranteed at the Home Depot. While supplies last, price invalid May 14th or May 27th. U.S. only exclusions apply. see homedipo.com slash price match for details. All right. That's one of my dad jokes. What didn't make the list? What did you put on?

Do you want things that didn't make the list because of my rules or things I would add to the list so I had more time? Yeah, let's do one of each. Okay. So I would say if I had more, so one of them that probably qualifies that I didn't add to my list, not for any good reason, was the study of proton decay. So proton decay is, like, we have all these really interesting things. that predict that protons should decay. And we really don't have a good reason for thinking that protons are stable.

And the study of proton decay was inspired by these grand unified theories that predicted it should be there. And it really took off in the 80s. And in the 80s, it really killed a lot of ideas that were at the time very considered, very realistic to be how the world worked. Yes, ISO5. Yes. I think the sort of early like SU5 models that are not super symmetric or dead, the super symmetric ones are still alive. we could do better in proton decay, we could really just either find or rule out some of our most exciting ideas for grand unified theories. But it was this example of something that, you know,

like it came out of theory, but it's a great test to do. And theory kind of motivated doing a thing we should have done anyway. And I think that would have made my list because it was very influential about how people thought about particle physics. It kind of like people thought they were really going to see it at the level predicted by these early grand unified models. And it was kind of the first thing that didn't go according to plan. Like the standard model kind of came along and everything that it predicted was seen. And I think a lot of people in the 80s thought, okay, you know, we saw the W boson, we're now going to see proton decay and everything's going to go according to plan. And that was the first thing that kind of didn't go as we thought it might. And I think in that

regard, you might to say like it was very influential both in a good and bad way. But that was like, I mean, it's hard to overstate the kind of sense in which like both if we ever saw anything, that would be incredible. But just that the. bounds that exists now or some of our most sensitive tests of physics that we can't see directly. So that was one. I think it would qualify under my rules, but I didn't want to dig into. The history is very complicated of where do you draw the line? Yeah, exactly.

And then one that didn't meet it because it failed my rules that I really love is this prediction that the absence of seeing temperature fluctuations in the C&B in the 1980s meant that there had to be dark matter. So there's this great argument. So if you go back in time to when they first saw the C&B, they said, it looks really smooth. Temperature in every direction is the same. But the universe we see is very not smooth. There's lots of stuff everywhere, planet, stars, galaxies. And this had to come out of that smooth starting point. And in a universe that only has the kind of matter that we experience, you can say, okay, well, there's big fluctuations today. There's Planet Earth here, not over there. That's a big change in the density. And from what we know,

given when we observe the CMB in the history of the universe and where we are today, the temperature fluctuations should be one part in a thousand. It can't be any smaller than that or there's just no way it could have worked. And they didn't see it up one part in a thousand. They didn't even see it at one part in 10,000. So by 1980, they knew that there was no fluctuation on one part in 10,000. And people wrote this paper in 1982 that's like, that means there's dark matter. right like that's the only thing that I can obvious thing I can think of that we have some kind of evidence for already but like that's that's what's going on

because otherwise we thought we were supposed to see at what part of a thousand we're definitely not finding it and that paper so it fails my rule because I had said I was only going to take papers after 1983 so but then the second thing is it's technically cited in the Nobel Prize for people's but people I mean it's kind of unfair because people got to like a career you can't say every paper that people ever wrote it doesn't count for the list.

But the other thing about it is, like, if you look at the citation history, it was getting like 10 citations a year for, you know, 40-ish years, that just, I think that's criminal. It's such a beautiful idea that it really, like, I just feel bad that it's not going to, I didn't get more attention. Well, speaking of Professor Dimm Peebles, invited on the show, he had a great book came out last year. He also had two years ago now.

He had a wonderful paper called anomalies in cosmology, which came out late at the end of last year, which in which he goes through all these tensions, and kind of crises, but from a real, obviously the highest caliber of physicists on the Earth right now. I hope we can talk about that in a part two, and other things. The crises, the Hubble tension, dark matter crisis, other phenomena that we have as well as, you know, how can we get more and better students around the world to come into physics and what you're optimistic about in physics and what you're kind of hoping will change in our physics,

both from the depth, the breadth, the diversity of who we can appeal to and bring in under the tent. But I want to thank you for spending this little hour with us in my audience. And you're going to be definitely an audience favorite. I hope you'll come back and get soon. And we'll talk many, many more times. And I hope I can call upon you whenever there's a calculation. I don't understand. I'm actually not that good at it.

I still have to sing the alphabet song to know what comes after R. It's embarrassing. Danone Green, Professor Dan and Green, one of the brightest people I know, bluest flame thinker, you know, in this, in this neck of the universe. Thank you so much, Richard. Thanks, Brian. This is awesome. Any sufficiently advanced technology is indistinguishable from magic.

Thanks for listening. Let us know what you think about the state of physics. In review, include your suggestions. Professor Keating reads them all. And if you enjoy this thought-provoking content, consider awarding us a five-star rating. For a chance to win your very own macro particle from, the cosmos in the form of a meteorite fragment, subscribe to Brian's mailing list at briankeetting.com slash list. And remember, always be curious.

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