How Politics And Beauty Leads Physics Astray | Sabine Hossenfelder

1. 0:00 – 3:54

   Why foundational physics feels stuck despite ongoing discoveries

   1. CWChris Williamson0:00

      (wind blowing) Hi, friends. This week, I am talking to a theoretical physicist.

   2. NANarrator0:10

      (music)

   3. CWChris Williamson0:10

      Bit of a departure from my usual sort of guests, which is very interesting. Sabine Hossenfelder is a theoretical physicist, blogger, and author. Her most recent book, Lost in Math: How Beauty Leads Physics Astray, talks about physicists' obsession with beautiful theories, and how this is potentially leading to a restriction in progress for physics overall. (laughs) Now, it sounds like quite a nebulous and difficult to define area, and it turns out that it actually is, but we do a pretty good job of working out just what is happening in the physics world at the moment. What I found to be particularly interesting was discovering just how much politics influences physics to get your research funded, what the hurdles are that you need to jump through, and who, uh, whose rings you need to kiss (laughs) in order to be supported. It- it- it seems very contradictory to think that a scientific subject area requires people to play a game akin to what you would presume in Wall Street, where you're sticking to the right kinds of rhetorics, and you're pushing the correct narrative coming from the right educational background, coming from the right conceptual, theoretical background. Really, really interesting, and it was, um, a whole world that I didn't even know (laughs) existed. So, here we go.

   4. NANarrator2:07

      (music)

   5. CWChris Williamson2:10

      Sabine Hossenfelder, how are you today?

   6. SHSabine Hossenfelder2:14

      I'm doing fine. How are you?

   7. CWChris Williamson2:15

      Very good. Thank you. Where are you in the world at the moment?

   8. SHSabine Hossenfelder2:18

      I'm in Heidelberg. That's like 100 kilometers south of Frankfurt.

   9. CWChris Williamson2:24

      Oh, very nice indeed. Very nice. So, I wanna get straight into it. You will be the first physicist which we've featured on the podcast.

   10. SHSabine Hossenfelder2:34

       (laughs)

   11. CWChris Williamson2:34

       Uh, so you- the- the weight of the entire world of physics is resting on your- (laughs)

   12. SHSabine Hossenfelder2:38

       (laughs)

   13. CWChris Williamson2:38

       ... shoulders at the moment. Um, I wanna ask a really fundamental question. It's been a really long time since we've seen major breakthroughs in physics, you know, global, newsworthy breakthroughs. I- is there a reason why that's the case?

   14. SHSabine Hossenfelder2:56

       Well, one of the reasons is probably that you're reading the wrong news. (laughs)

   15. CWChris Williamson3:01

       (laughs)

   16. SHSabine Hossenfelder3:01

       Um, there have been a- there have been a lot of breakthroughs in physics. Uh, what I'm mo- mostly concerned with are really the foundations of physics. So, uh, the biggest breakthroughs in physics are the ones that the Nobel Prizes are getting handed out for, and you find a list of that on the website of the Nobel, uh, Prize Academy. Um, but I'm- I'm really talking about the foundations of physics, and there, you are right, it has been a really long time since there has been a breakthrough where we have discovered something really new. I mean, the stuff that has made headlines, like say the- the direct detection of gravitational waves, or, um, you know, neutrino masses, neutrino oscillation and so on and so forth, these are all ideas that go back at least 30, 40, in some cases 100 years.

   17. CWChris Williamson3:46

       So, this is physical proof of something which theoretically has been around for a little while?

   18. SHSabine Hossenfelder3:53

       Yes.

2. 3:54 – 6:15

   Low-hanging fruit is gone: why progress is harder now

   1. CWChris Williamson3:54

      Okay. So, uh, is it a case at all that there's less stuff "to discover," in quotation marks? Are we mapping so much of physics that the remaining dark spots on the map are, uh, are limited? Or is it something to do with the approach that physicists have got at the moment, or is there a- a sticking block or a glass ceiling that we've hit?

   2. SHSabine Hossenfelder4:17

      Well, that's a very good question, but how would I know? (laughs)

   3. CWChris Williamson4:20

      (laughs)

   4. SHSabine Hossenfelder4:20

      How would I know what- what is still left to discover? What I can tell you is that, um, we have already discovered a lot, and that just means that the easy things have been done, uh, you know, the stuff that you can m- measure in your little laboratory with, uh, your handheld equipment and so on and so forth, that's all been done. Um, that's the case in experiment. It's also the case in theory development, you know, the easy things have been tried. So, it's kind of natural to expect that it will become more difficult. Um, then on balance to that, though, we also now have a lot of m- more people working on it, uh, so that should help. Uh, but apparently it doesn't.

   5. CWChris Williamson5:00

      (laughs)

   6. SHSabine Hossenfelder5:00

      So, we have, uh, at least in the foundations of physics, um, we have had the mathematical structure of the theories that we're using right now since the mid-1970s.

   7. CWChris Williamson5:12

      Okay. So, the low-hanging fruit, to one degree or another, as- as low-hanging as physi- physics can get, I suppose, has been- has been gathered to a large degree. Would you say that's fair?

   8. SHSabine Hossenfelder5:23

      Yeah, certainly.

   9. CWChris Williamson5:25

      Okay. So, what- what's the- what is the current sticking point that we've got at the moment? Is it technological? Is it that the instrumentation that we're using? Is it the minds? As you say, there's more- more people than ever are dedicating their efforts towards physics. Are they looking in the wrong place?

   10. SHSabine Hossenfelder5:47

       Well, I- I do think that they are looking in the wrong place. But, uh, of course, I don't know, you know? I- I don't know what's the right thing to do. Uh, but the question that we can reasonably look at and try to answer is, uh, whether they are using good scientific methods that would give them the highest probability of making progress, and I think that's just currently not the case.

   11. CWChris Williamson6:09

       Okay. Well, let's expand on that then. Why- why is that not the case?

3. 6:15 – 7:13

   A decades-long pattern of null results (dark matter, proton decay, new particles)

   1. SHSabine Hossenfelder6:15

      Well, um, we have seen a lot of null results in the foundations of physics in the last four decades. Um, for example, in the search for dark matter, um, this has been going on since the mid 1980s-

   2. CWChris Williamson6:30

      Mm-hmm.

   3. SHSabine Hossenfelder6:30

      ... um, that people have looked for the rare interaction of the hypothetical dark matter particles with normal matter. Y- you can do this basically by building large tanks of some stuff, and then you put detectors around the stuff and, um, try to measure these interactions. And people have tried, but they haven't seen anything. Um, they have also looked for proton decay. That's a prediction of a certain, um, new hypothesis. Um, they have also, of course, looked for new particles in particle colliders. Um, the most popular ones are probably supersymmetric partners of the already known particles, and that hasn't worked out either.

   4. CWChris Williamson7:13

      Is that-

   5. SHSabine Hossenfelder7:13

      That-

4. 7:13 – 8:15

   Supersymmetry’s moving goalposts: modifying theories to evade data

   1. CWChris Williamson7:13

      ... is that coming out with the LHC?

   2. SHSabine Hossenfelder7:16

      Well, that's actually a long story. I mean, supersymmetry is an idea that also dates back to (laughs) , uh, hang on, the late 1960s or something. (laughs)

   3. CWChris Williamson7:26

      Okay. Can you- can you- can you briefly-

   4. SHSabine Hossenfelder7:27

      So I'm not too sure about the date, but-

   5. CWChris Williamson7:29

      (laughs)

   6. SHSabine Hossenfelder7:30

      ... uh, peop- people have... Uh, you know, I'm not a historian, but people have, uh, looked for supersymmetry, for evidence of supersymmetry, um, since at least the 1990s, and that didn't work out. Uh, uh, in- indeed, um, they should have seen it already in the 1990s, so they actually had data that was just in conflict with the idea that, uh, supersymmetry is obeyed by- by the laws of nature. And what then, what they did was not to say, "Well, we've ruled out supersymmetry," but they said, "Well, we will just modify the theory," and so they added a new symmetry on top of it, which is called R parity. So now we have supersymmetric models that obey this additional symmetry called R parity, and that's compatible with observations so far.

   7. CWChris Williamson8:12

      Okay. So how long-

   8. SHSabine Hossenfelder8:14

      Okay. (laughs)

5. 8:15 – 9:16

   When do you stop? Funding, community size, and inertia

   1. CWChris Williamson8:15

      ... how long, how long do you pursue down a route of trying to find a physical manifestation that proves a theory-

   2. SHSabine Hossenfelder8:24

      Ah.

   3. CWChris Williamson8:25

      ... before you actually-

   4. SHSabine Hossenfelder8:26

      Yeah. Well... (laughs)

   5. CWChris Williamson8:26

      ... before you actually say, "Well, maybe the theory is just wrong completely"?

   6. SHSabine Hossenfelder8:29

      Well, you do it until you come up with something better.

   7. CWChris Williamson8:33

      (laughs)

   8. SHSabine Hossenfelder8:33

      Uh, but- but that- that's the rub, uh, because it's really, really hard right now to come up with something better in the sense that you can get funding for it and collect sufficiently many people so that sufficiently many people agree it's better.

   9. CWChris Williamson8:48

      (laughs)

   10. SHSabine Hossenfelder8:49

       Um, and that, the- the problem is you have a community like supersymmetry, which, um, for the foundations of physics, is a really, really large community, you know? You have something like, I don't know, 1,000 or 2,000 people of that order of magnitude. Uh, and if you try to say, "Well, maybe that's not the right path," that's really hard to get people to listen to. And accordingly, it's also hard to get funding for it.

6. 9:16 – 10:16

   Physics vs politics: selling research and beauty as a magnet

   1. CWChris Williamson9:16

      Yeah. I can imagine. So how much of physics is about physics, and how much of physics is about politics?

   2. SHSabine Hossenfelder9:23

      (laughs)

   3. CWChris Williamson9:24

      (laughs)

   4. SHSabine Hossenfelder9:24

      There, there is unfortunately, a lot of politics, uh, not only in physics but in science generally, or maybe you could call it psychology.

   5. CWChris Williamson9:32

      Mm-hmm.

   6. SHSabine Hossenfelder9:33

      You know, you always have to think about, "How do I, how do I sell my research, uh, to get other people to listen to it? How do I get other people to like it?" And of course, the easiest way to get other people to like what you're doing is to work on something that they like already.

   7. CWChris Williamson9:47

      Yeah.

   8. SHSabine Hossenfelder9:47

      And that you clearly see this trend that people work on stuff that other people like for sometimes not entirely scientific reasons, you know? Supersymmetry has a reputation of being a particularly pretty theory. It has a lot of, um, aesthetic appeal to it. That's something that you hear physicists who work in these areas talk about very, very frequently. And that's certainly one of the reason why it attracts so many followers, because people just like working with it.

7. 10:16 – 14:44

   What supersymmetry is (and why it predicts unseen partner particles)

   1. CWChris Williamson10:16

      Mm. Can you briefly explain to us what supersymmetry is, please?

   2. SHSabine Hossenfelder10:21

      Supersymmetry is an extension of the theories that we currently use. Um, we have something that's called the standard model of particle physics in which we have 25 particles that, for all we currently know, make up all matter in the universe. And, uh, in this standard model, we have two different types of particles. They are called fermions and bosons, and they are just different things. Now, supersymmetry is a symmetry that relates the fermions with the bosons so that they actually belong together. Now, the problem is that from the particles that we already have observed that are in the standard model, they do not pair up into the, um, proper supersymmetric pairs. So, um, what you have to do if you believe in supersymmetry is that you just postulate there are new particles to find that pair up with the ones that we have already. And then there's the question, "Well, where are they?" (laughs) Because we haven't seen them. And the answer to this is that they are so heavy that we have not yet been able to produce them in particle colliders.

   3. CWChris Williamson11:23

      Okay. Well, it's, um... (sighs) it- it- from a basical logical standpoint, it does seem a little bit like making the, making the foot fit the shoe as opposed to the other way around.

   4. SHSabine Hossenfelder11:37

      (laughs)

   5. CWChris Williamson11:37

      And I guess it- it sounds like you, for all that physics and physicists have got unbelievably logical brains, there's a lot of probably ego and dogma and, uh, patriotism to particular approaches. Do you think that that's restricting physics in moving forwards, this lack of ability to let go of existing models and potentially look elsewhere?

   6. SHSabine Hossenfelder12:05

      Yes, sure. But I should add that, of course, these ideas do have certain scientific motivations that got them started in the first point. Uh-

   7. CWChris Williamson12:14

      They're not just plucked out of the air, right?

   8. SHSabine Hossenfelder12:16

      (laughs) Uh, no. I mean, supersymmetry was, um, something that, uh-... um, attracted a lot of attention, for example, because it comes out of string theory. So you, if you believe in string theory, you actually need supersymmetry. Um, the opposite is not necessarily true. You know, if you, if you have s- supersymmetry, you don't necessarily also need strings. Um, but since there are a lot of people who like string theory, um, they are kind of forced to also have the supersymmetry. So, that's one thing. But supersymmetry is also, um, something that people like to work with because it solves some mathematical problems with the theories, um, and, um, n- that's just something that they find appealing.

   9. CWChris Williamson13:01

      Mm-hmm.

   10. SHSabine Hossenfelder13:02

       It's, it's also, it turned out that, um, if you have the supersymmetry and you add R-parity to it, then you get particles that can also make up dark matter, so that fit very nicely with the story.

   11. CWChris Williamson13:16

       Mm-hmm.

   12. SHSabine Hossenfelder13:17

       Um, but that was, as I said, it was something like 30 years ago. And since then, the situation has just changed, you know? And, um, I think that the appeal of super- symmetry has dramatically fallen since, because we haven't seen it in the data.

   13. CWChris Williamson13:32

       Yeah.

   14. SHSabine Hossenfelder13:32

       Um, but people keep adjusting their models so they become more and more complicated to, um, address the lack of evidence that we have.

   15. CWChris Williamson13:43

       Yeah.

   16. SHSabine Hossenfelder13:44

       And then, th- then at some point, you come (laughs) to the question that you ask, like, when do, when do you stop, you know? (laughs) When, uh, when do you just conclude that physicists are not able to let go of their ideas because they have invested too much time and effort into it?

   17. CWChris Williamson14:00

       Does it feel a little bit like flogging a dead horse sometimes?

   18. SHSabine Hossenfelder14:05

       Uh... (laughs)

   19. CWChris Williamson14:05

       (laughs)

   20. SHSabine Hossenfelder14:06

       I'm sorry, that, that, that's an idiom that I don't know.

   21. CWChris Williamson14:08

       (laughs) That's fantastic. So it's, um-

   22. SHSabine Hossenfelder14:11

       Uh, I'm not sure-

   23. CWChris Williamson14:12

       (laughs)

   24. SHSabine Hossenfelder14:12

       ... that's fantastic.

   25. CWChris Williamson14:13

       Oh, uh, okay. So, it's, um, what it means is, you are, um... (smacks lips) You've taken every opportunity that you can, you've taken every route that you can to try and, um, distill from one thing something else, and that something else hasn't worked. Therefore, it's time to move on. It's, uh, (laughs) it's interesting that that hasn't, that hasn't crossed over into, uh, into your vernacular. That's really cool.

   26. SHSabine Hossenfelder14:37

       (laughs)

   27. CWChris Williamson14:38

       Um-

   28. SHSabine Hossenfelder14:38

       I actually, I actually once read a whole book, uh, with idioms, but, uh, I can't recall this.

   29. CWChris Williamson14:43

       (laughs)

8. 14:44 – 16:32

   Naturalness: the hidden assumption that steered decades of theory

   1. SHSabine Hossenfelder14:44

      Uh, in any case, um, so that, that's an interesting question because, um, if supersymmetry is not the right thing, then it means that, that physicists have made some wrong decision pretty early on that-

   2. CWChris Williamson14:56

      Fundamentally.

   3. SHSabine Hossenfelder14:57

      So we actually... Yeah, so we have to go back and ask if one of the assumptions that entered all these arguments that led them to work on supersymmetry to begin with was maybe the wrong path to take.

   4. CWChris Williamson15:11

      Wow, so that's potentially a- an awfully big upheaval in the physics community, I'm gonna guess.

   5. SHSabine Hossenfelder15:17

      Well, you see people discussing this right now. So the argument that I make in my book is that this, uh, belief in naturalness is an issue, um, and that's a problem that needs to be rethought right now. So naturalness is this idea that the theories of physics should only contain numbers without units that are close to one, not much larger than one or not much smaller than one. Th- there are more complicated versions of this, but that's, that's the one- the easy case. (laughs)

   6. CWChris Williamson15:48

      Yeah, yeah.

   7. SHSabine Hossenfelder15:49

      Um, and, um, that's something that they use to construct theories. And now, it, um, just happens that supersymmetry, um, obeys this idea of naturalness. It actually helps to make the standard model natural. So the standard model, by itself, is not natural, but if you add supersymmetry to it, it works. And, uh, a lot of theoretical physicists take that as strong evidence that there's something true about supersymmetry, that it has power to describe nature. And I just think that that's a wrong conclusion, you know? I see no reason why the theories of nature should have this property that they call naturalness.

9. 16:32 – 19:10

   Defining ‘beautiful’ physics: simplicity, naturalness, elegance

   1. CWChris Williamson16:32

      Okay. So, in your book, uh, Lost in Math: How Beauty Leads Physics Astray, you talk about this, um, this desire within the physics community to have beautiful theories. Can you describe what, what is considered to make a theory beautiful?

   2. SHSabine Hossenfelder16:52

      Y- yes. So it's interesting that if you ask theoretical physicists what they mean by beauty, they all more or less say the same thing. (laughs) Um, so I, I think this is not, um, an idea of beauty that you find, uh, find among non-physicists, um, but for what physicists are concerned, uh, beauty has three major ingredients. The one is simplicity, and by this I mean that the theory should be simple in absolute terms. I don't mean in, in relative terms where you say, "Well, I take the theory that is simpler than some other theory-

   3. CWChris Williamson17:25

      Yeah.

   4. SHSabine Hossenfelder17:25

      ... but achieves the same." But it, but just that the, the theory should have simple laws, like it should have... Unified force, for example, is simpler than four different forces. Um, if you add symmetry to a model, that usually, um, combines two different concepts to one or several different concepts. Like with supersymmetry, we already talked about this, where you have the fermions and the bosons, they actually belong together.

   5. CWChris Williamson17:51

      Mm-hmm.

   6. SHSabine Hossenfelder17:51

      So that, that's a simplification in terms of the axioms of your theory. So simplification is one aspect of beauty. Then there's naturalness. I already told you about naturalness, the thing with the parameters that have no units, that should be of ￰.

   7. CWChris Williamson18:07

      Yup.

   8. SHSabine Hossenfelder18:08

      And then the, the third aspect is something that's usually referred to as elegance, and that's, uh, kind of a fluffy criterion- (laughs)

   9. CWChris Williamson18:16

      (laughs) Ve- very much so. It's not something I heard, I expected to hear coming out of physics.

   10. SHSabine Hossenfelder18:20

       (laughs) Well, it's, it's something that they, uh, talk about a lot, and you actually find this also in a lot of, um, older literature. Like there's, uh, there's a book by Chandrasekhar where he- where he goes on about this already.... but, um, so, what they mean with elegance is that the theory should be simple, but it shouldn't be too simple. So, it should lead to some interesting insights. You should, you should have some aha effect here and there, you know? It, it should have unexpected connections. It, um, should give you some surprises. So, that's this idea, um, of, of elegance. And you also find these three aspects in a lot of artworks, uh, by the way. I mean, um, simplicity is all well and fine, but if it's too simple, it's just boring. (laughs)

   11. CWChris Williamson19:04

       Mm-hmm.

   12. SHSabine Hossenfelder19:05

       And, and so, I think it's the same sense, um, that y- you find here.

10. 19:10 – 21:47

    Beauty changes with history—and can mislead selection of experiments

    1. CWChris Williamson19:10

       That's really interesting. It sounds like reducing the theory down to its simplest, simplest possible terms is, is, um... (sighs) Does this cause people to... Does this cause physicists to look in the wrong places sometimes when they're trying to develop theories? Is this a- an artifact of E equals MC squared and other very, very short, very, very simple theories like that?

    2. SHSabine Hossenfelder19:36

       (laughs) You know, I would actually say that E equals MC squared is too simple. You know, it's not elegant enough. (laughs)

    3. CWChris Williamson19:41

       That's gone... That's o- that's, that's overshot it. Okay, so that's interesting.

    4. SHSabine Hossenfelder19:43

       Yeah, yeah. But, but that makes an interesting point because th- this sense of what is elegant, um, you know, what is surprising, what, what gives you some, uh, new insights and so on depends, of course, on how much you know already. So, the sense of what counts as elegant and what counts as beautiful changes, um, throughout the history of science. Y- you find evidence for this in the literature.

    5. CWChris Williamson20:05

       Mm-hmm.

    6. SHSabine Hossenfelder20:06

       You know? When y- you look back, uh, several hundred years, they thought that planets on circular orbits, well, that's a beautiful idea, also turns out to be wrong.

    7. CWChris Williamson20:13

       (laughs)

    8. SHSabine Hossenfelder20:14

       (laughs) But, uh, that- that's an ideal of beauty that you just wouldn't find today among physicists.

    9. CWChris Williamson20:20

       Yeah.

    10. SHSabine Hossenfelder20:20

        It's, it's something that no one would, uh, pull upon. Uh, now they have other ideas of beauty and, well, maybe these work or maybe that these don't work. We just don't know. So, generally, I think it's a bad idea to impose, um, our current ideals of beauty on the laws of nature in the sense that we use it to construct new theories. Because the problem is, you know, we were talking about these experiments earlier where they look for dark matter and, and the particle colliders and, uh, I don't know, some telescopes and so on and so forth. These are really costly experiments, and we just can't test all theories that, uh, theoretical physicists come up with. So, we have to make a selection. Uh, and of course, we try to select those theories that we consider to be the most promising. Now, if we make a bad choice, we go and test theories, um, that are wrong, then the only thing we get are null results. Now, the null results are also results, of course, um, but they are not very useful results when you try to develop a new theory.

    11. CWChris Williamson21:25

        Mm-hmm.

    12. SHSabine Hossenfelder21:27

        So, that, that gets you stuck in a cycle where looking at the wrong theories (laughs) gives you null results that gets you stuck at the wrong theories and so on and so forth.

    13. CWChris Williamson21:37

        Yeah. Well, it's-

    14. SHSabine Hossenfelder21:37

        And, and-

    15. CWChris Williamson21:38

        I- i- it's just crossing one thing off the board as opposed to directing you on towards the right direction on the board.

    16. SHSabine Hossenfelder21:45

        Yes, exactly.

11. 21:47 – 23:39

    Echo chambers in academia: incentives to work on fashionable topics

    1. CWChris Williamson21:47

       Yeah. I mean, (laughs) it sounds... In between the, uh, potential for dogma, this dogmatic and, um, patriotic, uh, holding onto existing bodies of knowledge or existing directions within theories, plus this desire for beautiful theories to come out, it must lead to a little bit of an echo chamber and a lot of theories that are similar. And as you say, you add a, add a section onto something which already exists, and now this works despite the experiments not showing anything that supports it.

    2. SHSabine Hossenfelder22:22

       Yes, that's certainly true. Uh, and I think that's an organizational problem with the academic system in general. You know, if you want to get something funded, if you wanna get something published, it's much easier if you work on something that people already work on. Uh, and, and of course, people know this, so that's, that's what they do. I- it's, you know, in some sense, it's not particularly (laughs) surprising. What, what is surprising is that they accept this and play along with it.

    3. CWChris Williamson22:52

       Mm-hmm. Yeah, I understand. So, where do we go from here? Do you have a... Do you have a suggestion for how physicists can look at the, the field in a different way?

    4. SHSabine Hossenfelder23:05

       Well, sure. I think, uh, the first step is that they, they become aware of what they are doing so that they actually understand where they are using assumptions from beauty that are not scientific. In some cases, I think people know this, but in other cases, I'm pretty sure they don't. Like, this, this idea of naturalness, for example, um, I, I would say, like, half of the people, um, know that, that it's not a scientific criterion, um, but the other half thinks it is. So, there's, uh, clearly there's something at odds there.

    5. CWChris Williamson23:38

       Mm-hmm.

12. 23:39 – 26:49

    Theory of everything and unification: attractive idea, weak justification

    1. SHSabine Hossenfelder23:39

       Uh, and there's also this idea, for example, of, uh, unification or the theory of everything. I mean, these are all nice ideas, um, but there isn't really any good logical reason for why there should be a unified force or for why there should be a theory of everything. It's just something that people work on because they like the idea. And so, at some point, we should draw the conclusion that maybe that's not the right path to work on. And, uh, I think it would help if they would just, you know, uh, take into account the arguments for and against it, uh, when they write a paper, say, or, or give a talk. It's... Unfortunately, it's very common that they only list the arguments that speak for their theory.

    2. CWChris Williamson24:25

       Mm-hmm. Yeah. I c- I, I can totally see that you want to hear people. It's a, a very, very educated version of yes-men, isn't it? Having someone who just-... says yes and agrees with what it is that your, your particular stance. You, you've touched on something there that I did want to discuss. Um, there was once upon a time a dream of a theory of everything or a grand unification theory. Um, (laughs) is that, is that a lost cause now? Does it seem to... Do, do the current state of theoretical physics suggest that that's not the direction that we're going to end up in?

    3. SHSabine Hossenfelder25:05

       Who knows? Um, I mean, um, personally, I think that this whole idea of a theory of everything doesn't make a lot of sense, because, I mean, suppose I tell you, "Here's the theory of everything and it explains everything that we see." How do you know that it will still be a theory of everything tomorrow?

    4. CWChris Williamson25:21

       Mm-hmm.

    5. SHSabine Hossenfelder25:21

       You know, that, that we will not, at some point, uh, measure something that does not fit into this theory. So, so I, I think that this is... you know, it just doesn't make a lot of sense conceptually. Then, of course, there is this, uh, issue that what, uh, people in the foundations of physics mean when they say theory of everything does not actually explain everything (laughs) . Um, that's just a way to say, "Well, we have combined all the four known forces into one." So, so, so that's what they mean, just, just to get the terminology (laughs) sorted out.

    6. CWChris Williamson25:55

       Yep. Yeah.

    7. SHSabine Hossenfelder25:56

       Um, and that might still work out at some point, uh, or it might not. Uh, I mean, presently, I think we just really don't know. Um, personally, I have, um, (laughs) developed an interest in an approach that is called asymptotically safe gravity. It basically solves the problem that we have with the quantum properties of space and time, um, but it does not also include a unification of the interactions. You know, they... You kind of have a framework in which they all fit, but they are not unified in the way that physicists usually speak about, uh, unification. But the theory seems to be working just fine, so, uh, presently, I don't see any urgent reason for why these forces should be unified. You know, maybe our universe just has four different forces, and that's that.

13. 26:49 – 28:56

    Where unification stands: four forces and the gravity problem

    1. CWChris Williamson26:49

       Yeah. What are the four forces, please?

    2. SHSabine Hossenfelder26:52

       Well, one of the forces is gravity. You all know gravity. There's electromagnetism, and then there's the strong and the weak nuclear force.

    3. CWChris Williamson27:00

       And the odds are... How much of that has been pulled together? Because there's obviously still conflict between certain areas of that. Have you managed to unify certain areas, and others are still out on a limb?

    4. SHSabine Hossenfelder27:16

       It kinda depends on what you mean by, uh, unification. So, the, um, electromagnetic and the strong and the weak nuclear force are kind of of the same type.

    5. CWChris Williamson27:25

       Mm-hmm.

    6. SHSabine Hossenfelder27:26

       And we describe them all with the same mathematics, basically, in what we call the standard model of particle physics. But they are not unified in the sense that they are still three separate forces.

    7. CWChris Williamson27:37

       Yeah.

    8. SHSabine Hossenfelder27:38

       Uh, and then there's gravity, which is described by a different mathematical framework, so it doesn't really fit together with the other three forces. Um, usually, that doesn't really bother us because in the circumstances where we use the standard model, so we describe, uh, collisions that happen at particle colliders, then, um, we are dealing with elementary particles. And the gravitational force is so weak that we don't have to worry about what to do with gravity. But there are certain circumstances where it would be necessary to take both of these, um, theories into account, like, for example, close to the center of a black hole or something like that. And for these cases, we just don't have a theory.

    9. CWChris Williamson28:23

       Right. Okay. So, to a degree, gravity is the... It's the black sheep of the bunch, which is, is it the most difficult to make fit? You said recently that we've discovered, um, uh, experiments have managed to detect gravitational waves. Is that correct?

    10. SHSabine Hossenfelder28:39

        Yes. Well, it's not so recent. It was in 2015. (laughs)

    11. CWChris Williamson28:43

        Okay. I guess-

    12. SHSabine Hossenfelder28:44

        But, yeah. I mean-

    13. CWChris Williamson28:44

        ... I guess in physics, in physics terms, that's, that's a long time ago.

    14. SHSabine Hossenfelder28:48

        (laughs)

    15. CWChris Williamson28:49

        (laughs)

    16. SHSabine Hossenfelder28:49

        Uh, well, yeah. I mean, the prediction, uh, dates back, uh, you know, eight years or something.

14. 28:56 – 32:25

    LHC realities: lots of measurements, but only one new fundamental particle

    1. CWChris Williamson28:56

       Okay. So, going back, you'd mentioned there about, uh, particle colliders, and the LHC was... during the, the buildup to it, was, uh, hailed as, by sensationalist press, as something (laughs) that was going to create a black hole in the middle of Europe and absorb the entire world. And then it didn't, and then what came out of it was the Higgs boson was detected. But since then, this huge 23-mile round trip, um, experiment doesn't really seem to have elicited much else. Is that correct?

    2. SHSabine Hossenfelder29:34

       No. That's not correct. (laughs)

    3. CWChris Williamson29:35

       Oh, no.

    4. SHSabine Hossenfelder29:36

       No. Again, as I said, I think you're reading the wrong news. (laughs)

    5. CWChris Williamson29:40

       So-

    6. SHSabine Hossenfelder29:41

       Uh, probably because you're not a physicist.

    7. CWChris Williamson29:43

       Yeah, maybe.

    8. SHSabine Hossenfelder29:43

       So, the, the LHC has detected the Higgs boson. That's the news that everyone has heard of.

    9. CWChris Williamson29:49

       Mm-hmm.

    10. SHSabine Hossenfelder29:50

        But it has also done a lot of other things. It's just that these did not make so big headlines. You know? It has, for ex- example, um, probed the structure of the proton in much, much better details than was previously known and found a few surprises there. People are working on it. It has also been able to measure a lot of the constants in the standard model of particle physics to much higher precision than what was previously possible. It has also measured a lot of composite particles, um, that are made of, uh, several quarks and measured their properties. So, it, it's not like nothing hasn't been going on besides the Higgs boson. (laughs)

    11. CWChris Williamson30:31

        Yep.

    12. SHSabine Hossenfelder30:31

        Uh, uh, it's just that the other stuff has not been quite as exciting as producing a tiny black hole that eats up Europe.

    13. CWChris Williamson30:38

        (laughs) Yeah. Well, I mean, that would have made the news if it had happened. It would have definitely-

    14. SHSabine Hossenfelder30:45

        If, if, if there would have been still news then, yeah.

    15. CWChris Williamson30:47

        Y- yeah, exactly. News in America, perhaps. Um, but that is... I am right in saying that that's the only new particle which it found. That's correct, right?

    16. SHSabine Hossenfelder30:54

        The only new fundamental particle, yes.

    17. CWChris Williamson30:57

        Okay. Um, is there a likelihood or is, uh, uh, people still holding out hope that it's going to find more, or again, have we hit a, a little bit of a glass ceiling with, with that particular, uh, that-

    18. SHSabine Hossenfelder31:08

        Oh, yes. Oh, yes, definitely. Um, there are still people who think that, uh, supersymmetric particles will eventually show up. Um, so the thing is that this assumption of naturalness that I was talking about earlier would have put the supersymmetric particles in the regime, um, of fairly low energies close by the Higgs, basically. So, we should have seen them already.

    19. CWChris Williamson31:32

        Okay.

    20. SHSabine Hossenfelder31:32

        So, we know that this idea of naturalness was just wrong-

    21. CWChris Williamson31:36

        Mm-hmm.

    22. SHSabine Hossenfelder31:36

        ... and it's gone out of the window, but nothing has replaced it. And this means that, um, people who work on supersymmetry basically now have no particular reason to think that the particle should be at any particular mass scale. So, it, it could be there in the data or it could not be there. There are definitely people who think that it will be there, and the LHC has not, um, totally, um, analyzed all the data that they have. They're still collecting data and, um, uh, you know, getting better statistics from which they try to extract more details and so on and so forth. So, there's, there are still hope that they will find something new.

    23. CWChris Williamson32:16

        But the early evidence would suggest not?

    24. SHSabine Hossenfelder32:21

        Y- yes. I mean, so far, they haven't found anything besides Higgs.

15. 32:25 – 35:19

    Dark energy vs dark matter: what’s unknown, and what’s testable

    1. CWChris Williamson32:25

       Okay. Okay. So, moving on, I wanted to talk about dark matter or dark energy, and discuss why that's so important to physicists to find that. Could you, could you explain just why it's such an important, uh, concept within physics?

    2. SHSabine Hossenfelder32:45

       Well, let me start with saying that dark matte- matter and dark energy are totally different things. So, dark energy is whatever is causing the accelerated expansion of the universe. You know, that's just the name that we give to it. We call it dark energy. And, uh, f- personally, I think there's really nothing to explain because this, this acceleration of the universe can just be described by the constant. That thing is called the cosmological constant, and you can just go and measure it, and it has a value, and that's it.

    3. CWChris Williamson33:17

       Mm-hmm.

    4. SHSabine Hossenfelder33:18

       You know? Um, there are people who think that, um, it should have some kind of, um, microscopic explanation, you know. It should be made up of something, basically, and then there is something to explain. But I see no reason f- for why this shouldn't be so.

    5. CWChris Williamson33:34

       So, the, the line's, the line's drawn underneath dark energy as far as you're concerned?

    6. SHSabine Hossenfelder33:39

       Uh, yes, unless you sh- really show me some data that cannot be fitted with that constant.

    7. CWChris Williamson33:44

       Okay.

    8. SHSabine Hossenfelder33:45

       You know? But so far, there isn't any, and so far, the constant ju- does a good job. So then, there's the thing with dark matter. Um, dark matter is stuff, you know, basically similar to the stuff that we are made of, um, except that it does not interact with light in any form. So, it does not absorb it, it does not emit it, it doesn't scatter it. And, um, it's believed to sit around galaxies, you know, hover around them in clouds, um, and it plays a, uh, big role in the formatio- formation of structures in the universe. Uh, that's for what the simulations are concerned. Now, the problem with dark matter is that if you believe it's made up of particle, you want to actually measure the particle (laughs) , and that has not happened.

    9. CWChris Williamson34:34

       Ah.

    10. SHSabine Hossenfelder34:35

        Um, then the other option is that, uh, we actually do not need any additional stuff, but that we should change the law of gravity so that it, gravity does not work the way that Einstein envisioned it as with his theory of general relativity, you know, curvature of space-time and the rubber sheet and so on and so forth-

    11. CWChris Williamson34:54

        Mm-hmm.

    12. SHSabine Hossenfelder34:55

        ... um, about that we need a different theory for gravity, and that's what's called modified gravity. Maybe not the greatest term ever-

    13. CWChris Williamson35:02

        (laughs)

    14. SHSabine Hossenfelder35:02

        ... but that's what it's called. And, uh, ever since, uh, people came up with this idea of modified gravity, we have had two camps. The one who's the big camp, that's the particle dark matter camp, uh, and then there's the smaller camp of modified gravity, and the case still is not settled.

16. 35:19 – 37:09

    Why dark matter is hard to rule out—and how funding locks in paths

    1. CWChris Williamson35:19

       I see. But I'm right in thinking that if it was proven that dark matter didn't exist, if, or, I guess, I guess it's gonna be very difficult to prove that it doesn't exist because there's al- always the potential to continue, uh, detecting up until the point at which you do detect it. Is that right?

    2. SHSabine Hossenfelder35:38

       Yeah.

    3. CWChris Williamson35:38

       Is it difficult to disprove a theory like that? Are- some people are always going to hold onto the hope that we finally do detect it?

    4. SHSabine Hossenfelder35:44

       Yeah, so it's basically impossible to rule out because as you say, you can always... I- I mean, you build a detector, and the detector has a certain sensitivity, uh, to some interaction, uh, probability and so on and so forth. And then you can always just say, well, may the particle, maybe the particle just had a lower probability of interaction than what we have been able to prove so far, so we need to build a bigger detector.

    5. CWChris Williamson36:06

       Turn the sensitivity up.

    6. SHSabine Hossenfelder36:08

       Yeah, yeah, right, and that's been going on, um, since the mid-1980s, and the sensitivity has increased by at least a factor of 100,000 since.

    7. CWChris Williamson36:17

       Oh, my God. (laughs)

    8. SHSabine Hossenfelder36:18

       Yeah. And I, and I mean, you can continue to play this game as long as you want, as long as you can get money for it. (laughs)

    9. CWChris Williamson36:26

       (laughs)

    10. SHSabine Hossenfelder36:27

        Um, so but, but again, you know, um, the thing is that the theories that, um, we think are plausible direct the efforts that we make in testing the theories. So, if we invest money in building more detectors for dark matter, we will, we cannot invest the same money into, I don't know, building, um, some telescope, uh, put it on a satellite and measure, I don't know, gravitational lensing better or what have you, something that would allow us to test modified gravity. So, we have, we have decisions to make, and I think we have to be really, really careful as theoretical physicists in, um, how we rate the promise of a theory.

17. 37:09 – 46:08

    Groupthink, denial of bias, and proposed institutional fixes

    1. CWChris Williamson37:09

       It's very interesting how theoretical physicists and the relative weight behind each of their theories, across all, all of the, the different subject areas, uh, sub-disciplines within physics, is having such an impact on the experimenters and what they get to do, and where they can direct their efforts. That you guys are kind of like the roots of the tree, and from that determines what can grow out of it, to a degree.

    2. SHSabine Hossenfelder37:38

       Well, yes, it's, it's interesting, but it's not really surprising, is it?

    3. CWChris Williamson37:41

       Mm-hmm.

    4. SHSabine Hossenfelder37:42

       I mean, look, you have a lot of people in a community and they basically only talk to each other. Uh, and they constantly tell each other that what they are doing is interesting-

    5. CWChris Williamson37:51

       (laughs)

    6. SHSabine Hossenfelder37:51

       ... and it's probably the right thing. Then, then they believe it's the right thing, and of course, there are a lot of people they will be able to convince other people that probably what they're doing is the right thing. And then you have this small group of people who work on, you know, just to pick this example, uh, modified gravity or something. You know, there are maybe a few dozen people who work on this, and they are full of self-doubt. Not so surprisingly, because a huge number of really smart people is working on something else-

    7. CWChris Williamson38:18

       The opposite side of the scale, yeah. (laughs)

    8. SHSabine Hossenfelder38:20

       ... and they're constantly saying... Right. And they are constantly saying that modified gravity is a joke, um, and so the people who work on it are like, "Mm, yeah, um, pfft." You know, they're really, really, um, reluctant to make those big proclamations that the other people have no problem making.

    9. CWChris Williamson38:36

       Yeah. It's, um-

    10. SHSabine Hossenfelder38:37

        So there's just ... You, you have this backup, you know, behind your back, you have a, a large group of people who support you-

    11. CWChris Williamson38:43

        Yeah.

    12. SHSabine Hossenfelder38:43

        ... that makes big psychological difference.

    13. CWChris Williamson38:46

        Oh, 100%. It, it must be ... I don't know. As, as someone from the outside looking in, I would ... M- my goal or my, my aim would be to have to expedite the discovery of whichever theory is correct, not to dogmatically stick to whichever one is most popular. And it seems that it's definitely not for the benefit of physics for anyone who's looking at alternative theories to be ostracized or to, you know, be ridiculed, or whatever it might be. Because if, if that research is the right direction, and these people are being reluctant or they're, y- you know, someone's in, in the camp of the existing model of, of gravity and is thinking that they, they might not be right, but they're terrified of moving over because of what their peers are going to say to them. That's not a tremendously holistic view of, or a holistic direction for physics to take overall, is it?

    14. SHSabine Hossenfelder39:44

        Yeah, well, that's certainly true. Um, the thing is, of course, that if you would go and ask physicists, they would deny that this is what's going on.

    15. CWChris Williamson39:52

        Ah, okay.

    16. SHSabine Hossenfelder39:53

        You know, because they, they are too smart to fall for mistakes like this, and of course, they have good reasons to work on what they work on, and, and so on and so forth. So, so they, they think that they are, they are not biased. They cannot-

    17. CWChris Williamson40:05

        Mm-hmm.

    18. SHSabine Hossenfelder40:05

        ... possibly be biased by the size of the group that they work on. It's just, that's just a possibility that's not on their radar.

    19. CWChris Williamson40:13

        (laughs)

    20. SHSabine Hossenfelder40:13

        You know, for, for its ... For, for the physicists, sociology and psychology are not real sciences. It's not something that they pay attention to. They think it's not necessary.

    21. CWChris Williamson40:21

        Which is crazy because it's, it would appear that an obvious, uh, an obvious example of groupthink is going on here. You have-

    22. SHSabine Hossenfelder40:32

        (laughs) Yes.

    23. CWChris Williamson40:32

        You have this echo, you have this echo chamber, you have people that support theories that it would appear have more and more experiments proving nothing to support them, and no one being prepared to move in a different direction. It's so interesting how y- as you say, the, the ... m- guy, the people that are in the field of physics are so clever, and yet fundamentally appear to perhaps be unable to see the wood for the trees a little bit here.

    24. SHSabine Hossenfelder41:02

        (laughs) Yeah, maybe. Well, you say that it's an obvious example for groupthink, um, but, uh, I would be more careful there. I would say there's a possibility that it is groupthink-

    25. CWChris Williamson41:15

        Yeah.

    26. SHSabine Hossenfelder41:15

        ... which cannot be ruled out because the current organization of the research does not guard scientists for falling for it. There just are no measures, uh, against it. Uh, it's, indeed, it's actually the opposite, that the current organization of research supports this groupthink. Because as I said earlier, it's easier for people to get funding and to get positions if they work in what is already a large, uh, group. So, um, you know, I, I don't really know what's going on.

    27. CWChris Williamson41:47

        (laughs)

    28. SHSabine Hossenfelder41:47

        Maybe there's nothing wrong whatsoever, but, uh, either way, I think that we should institutionalize some measures that prevent people from, uh, falling into this, uh, groupthink trap.

    29. CWChris Williamson42:00

        That's interesting. So, how do you suggest that you institutionalize that?

    30. SHSabine Hossenfelder42:07

        Well, uh, one of the things I alread- already said, uh, briefly previously is that, uh, I think that scientists generally, not just physicists, need an awareness for these, uh, cognitive and social biases that you develop when you work in large groups. It's just something that people should know of, you know, so that they can recognize what's going on. Like this wishful thi- thinking or loss of awareness that we already talked about, you know? That's this reluctance to abandon a research project that you have been working on for a long time just because you have invested a lot of effort into it.
18. 46:08 – 49:46

    Talent drain and closing reflections: ‘physicists are humans’

    1. SHSabine Hossenfelder46:08

       Yes, sure. A lot of them just leave. You know, I've, I've seen people leave. Uh, I mean, it's... Uh, you see, th- these are people who figure out that, uh, they will not be able to get money to work on the research that they think is most promising, and then they just com- conclude then it's not worth their time. So, they just leave academia and do something else. And, you know, there is life outside of academia too (laughs) .

    2. CWChris Williamson46:33

       There is, but it's-

    3. SHSabine Hossenfelder46:34

       But, so-

    4. CWChris Williamson46:34

       ... it seems like a terrible shame to lose fantastic talent in the, in the field of academia because of this sort of systemic, uh, dogma.

    5. SHSabine Hossenfelder46:45

       Yes, it's a shame, but it's also just a problem for science. Because of course, uh, the people that are left are the ones who, who don't have the big problems with, uh, joining these large research programs and just producing papers. You know, if they had a large problem with it, then they would be leaving (laughs) .

    6. CWChris Williamson47:01

       Yeah, yeah, for sure. But it's not necessarily the best for the subject, this, the body of knowledge as a whole, right? People could be doing something a lot more productive if, if it was a little bit more free flowing.

    7. SHSabine Hossenfelder47:12

       Um, I, I think so. You know, this is why I hope that, uh, making some organizational changes, uh, to academic research would, um, help overcome this impasse.

    8. CWChris Williamson47:24

       For sure. For sure. So, Sabine, I really appreciate your time. Would you be able to tell the listeners where they can find you online? I'll make sure that I put a link to Lost in Math: How Beauty Leads Physics Astray, your book, in the show notes below. But where can they find you online? I really like your blog, so you need to put that in.

    9. SHSabine Hossenfelder47:43

       (laughs) Well, it's not complicated, you know? For all I know, there's only one person with my name. You type it into Google-

    10. CWChris Williamson47:49

        (laughs)

    11. SHSabine Hossenfelder47:49

        ... and, like, the first 100 hits will actually direct you to my websites. I have a website that's called sabinehossenfelder.com. It's not hard to remember if you can remember my name. Um, I have a blog that's called BackReaction, and that's at blogspot.com.

    12. CWChris Williamson48:07

        Mm-hmm.

    13. SHSabine Hossenfelder48:07

        Uh, and I'm also on Facebook, and I'm on Twitter. And I w- write for a lot of, um, websites every now and then, so you will find all this, uh, by help of Google or your search engine of choice.

    14. CWChris Williamson48:21

        (laughs) Fantastic. Sabine, I really appreciate your time. Uh, I, I hope that we've opened some people's eyes to what the physics community's like at the moment. Uh, I, I hope this doesn't sound like a, a disparaging criticism of what's going on within there. Uh, you know, it's, it's obviously a very difficult subject for, for, um, everybody to wrap their heads around, even the best minds in the world. But I do think it's so interesting what you've said about these social influences and cognitive biases influencing, uh, who we consider to be the, some of the cleverest people on the planet. And in a weird way, I think it's actually a little bit, um, it's a little bit reassuring that for us normal (laughs) , normal people who perhaps aren't, uh, aren't at the level of a theoretical physicist, that they are still subject to these, uh, these psychological and sociological influences.

    15. SHSabine Hossenfelder49:15

        Oh my God, you just found out that physicists are humans.

    16. CWChris Williamson49:19

        (laughs) Yeah, I did. And do you know what it is? Sometimes, like, sometimes I'm not sure. But, uh-

    17. SHSabine Hossenfelder49:24

        (laughs)

    18. CWChris Williamson49:24

        ... (laughs) I think I did. So, thank you very much for your time, Sabine. I'll make sure everything's in the show notes below. Thank you very much.

    19. SHSabine Hossenfelder49:31

        Uh, thank you. You're welcome.

    20. NANarrator49:35

        (instrumental music)

Episode duration: 49:46