IRA FLATOW: This Science Friday. I’m Ira Flatow. When they do Large Hadron Collider opened in 2010, physicists had high hopes for what it might help us discover. By 2012, the world’s most powerful particle accelerator had already proven the existence of the Higgs boson.

But physicists were hoping it might also detect other particles, help determine the nature of dark matter, or explain how gravity might fit in a unified model of physics. It’s 2018, and we are still waiting for all or some of those answers.

My next guest, a physicist herself, reports that it’s getting harder to justify the work, not because the answers aren’t out there, she says, but because we’re not chasing the best theories, just the most mathematically beautiful, elegant, and simple ones. She says the real answers may not to conform to mathematical standards of beauty, and we won’t find them until we let go a bit and embrace some messier ideas.

Sabine Hossenfelder is a research fellow at the Frankfurt Institute for Advanced Studies in Germany and author of the new book, Lost in Math, How Beauty Leads Physics Astray. She joins us by Skype, and you can read an excerpt of a book on our website at sciencefriday.com/beauty. Welcome to Science Friday.

SABINE HOSSENFELDER: Hi, thanks for having me.

IRA FLATOW: You start the book with a pretty bleak picture of physics as it stands. Give us a play by play of the discoveries that you think are missing right now.

SABINE HOSSENFELDER: Yes. So this is a story which has been going on, basically, since 40 years. We have been searching for an explanation for what dark matter is made of, some kind of particle for which we have built detectors, but we haven’t found anything. You just mentioned that we have also had high hopes that the Large Hadron Collider would see new particles.

This has not happened. Actually, we hoped that we would see them already at previous colliders. People have also hoped that we would find evidence of some new unified force that would have the effect of protons decay, and we’ve looked for this, but we haven’t seen that.

We have also tried to find for some evidence that dark energy is some kind of field. That hasn’t happened. We have been discussing for a long time about the foundations of quantum mechanics that a lot of people are unsatisfied with, but nothing really has changed there. So I really have this feeling that we’re stuck there.

IRA FLATOW: Let me get out the number, because a lot of tweets have come in. I want to get our phone audience in 844-72408255. 844-724-8255. You can tweet us @scifri. One big example, as you mention, is the Large Hadron Collider. Physicists are still waiting for these particles. And you say the problem is the beautiful math. What do you mean by that? What constitutes beauty in physics and math? And why is that getting in the way, the need to have to have that?

SABINE HOSSENFELDER: Yes, well, so actually peculiar, as I found out when I was interviewing people for the book, the theoretical physicists more or less agree on what they mean by beauty. So it has typically three ingredients. The first one is probably the ones that most people are familiar with is simplicity. So a good example for this is string theory, which pretty much everyone has heard of these days. So it’s idea that everything is made of strings.

So, you know, that’s an idea that is so simple that I can formulate it in a few words. But, of course, it doesn’t stop there. You know, because this assumption, even though simple, has a lot of consequences that lead to very surprising insights. That’s why people are so convinced of string theory. And this discovery of surprising insight is something that is often referred to as elegance.

And that’s something that is not only specific to string theory, but it’s also something that theoretical physicists admire about general relativity, which is simple in its formulation, but it has a lot of interesting consequences, like it leads to black holes, and gravitational waves, and maybe worm holes. Who knows?

So we have simplicity and elegance, and then there is a third criterion that is called naturalness, which is something that most people are not so familiar with. It’s basically a sense of decent proportion. You know, you don’t want things that don’t really fit together in size, roughly speaking.

So concretely, this means if you write down a theory in a mathematical form, you do not want it to contain numbers that are either much smaller or much larger than 1.

IRA FLATOW: Do you think, for example, in string theory that– I mean, we haven’t gotten any– you talk about the need for evidence in science. And in your book, you talk about scientists sort of pooh poohing evidence as the necessary ingredient to do science these days.

Is string theory– should we let it go? Has it become more of a religion now since we don’t have all that evidence we need?

SABINE HOSSENFELDER: It kind of depends on exactly what you’re talking about. So string theory is a big field where a lot of different things are going on. So the reason that string theory originally attracted so much attention was that theoretical physicists thought it would be a candidate for a theory of everything, that it would unify all of the four now fundamental forces that we know. And

On that account, things aren’t going well. Let me put it that way. But it turns out that string theory has other uses in other areas of physics. Like, for example, in condensed metaphysics. And that’s really a different thing entirely that, really, I’m not touching on in the book. I’m concerned with this search for more fundamental laws of nature, for the theory of everything, for the grand unification. You know, that kind of thing.

IRA FLATOW: If we did not require– excuse me, if we didn’t required the beauty that you talk about, what other alternative ideas could we come up with that would be worth investigating?

SABINE HOSSENFELDER: [LAUGHING] That’s the interesting question, of course. You know, I want to know. I want to know, what would they come up with if they gave up on this insistence that the laws of nature have to be beautiful in this specific way? So you know, I’m not a seer. I can’t tell you. But I think that it’s problematic that so much of the effort in these fields is focused on recovering in the specific sense of beauty.

You see, these theorists are basically dictating nature, what it’s supposed to do. And I think that just doesn’t make sense from a scientific perspective. We should look at what the evidence tells us, and then try to describe it.

IRA FLATOW: Let me go to the phones. 844-724-8255. Monica in Michigan. Hi, welcome to Science Friday.

MONICA: Hi. Thank you for taking my call. You guys have actually kind of touched on my question already. I’m a biologist, and it just sounds like you’re implying that we should move forward the notion that the most parsimonious answer is the most correct. And if that is the case, if that is what you are saying, I wonder how us as scientists, how we should move forward and continue to try to answer the questions that we have in science. If parsimony has gotten us this far and, you know, the most simple answer being, or the beautiful answer, has gotten this far, how do we move forward from parsimony no longer being as valuable as we thought it was?

IRA FLATOW: Good question. Dr. Hossenfelder?

SABINE HOSSENFELDER: So first, I want to be clear here that when I talk about beauty or parsimony, I don’t mean this in a comparative way. So if you have two theories that explain the same, you pick the one that is simpler, you know, the one that doesn’t require as many assumption. That is a perfectly good scientific procedure.

What I think is going wrong is that theorists try to construct theories that are simple, period. You know, have as little axioms as possible, and there’s just no good rationale for why this should be the case. You know, why should a theory with a few axioms describe nature any better than a more complicated theory?

It’s not something that we know should be the case about the fundamental laws of nature. We don’t know that they should be getting simpler. But your question was, what else could we do? Well, I think that we should focus on what are good scientific problems. You know, if you have a theory and you don’t like it because it’s not pretty enough, that’s not a scientific problem. You know?

I mean, I understand this perfectly on a personal basis, that people would like to work with theories that are beautiful. But from a scientific perspective, that’s the kind of problem that you should be focusing on, is if there is some kind of inconsistency, either in the theory itself, so that it has internal contradiction, or it’s actually inconsistent with data.

IRA FLATOW: Here’s a tweet from Nathan, who says this reminds me of something Steven Weinberg once wrote, that if you want to actually make progress in science, you go where things are messy.

SABINE HOSSENFELDER: [LAUGHING] Did he really say that? Well, it’s interesting. So Steven Weinberg’s one of the people who I interviewed for the book. And he has an interesting point of view in that he’s trying to make an argument that our reliance on beauty is actually based on experience, because arguments from beauty have been useful in the past.

So this is why, I think, at least that was my impression, that he doesn’t see a problem with relying on the sense of beauty. That in particle physics, for example, is very strongly built on using unification and symmetries. And this is certainly something which Weinberg has excelled him in himself. Right? So now, I’m not sure what you might mean with, you should go where things are messy.

IRA FLATOW: Well, we’re not quite sure of the quote either. Sometimes people hear things, and it might not be exactly like it was said. But you never know. You even say, though, that Einstein used beauty to guide him. Was he wrong in that case?

SABINE HOSSENFELDER: No. I mean, beauty, searching for beauty, is certainly a strong personal motivator. And you see this documented in a lot of the scientific history, that it was very important for people to proceed in their work.

But you also have to see that the actual reason– we know this in hindsight– that Einstein made progress with that was that he had a good problem to work with to begin with. Like, for example, think of general relativity, we already spoke about this. He had his theory of special relativity. And that theory just is not compatible with Newtonian gravity.

So he had an actual strong contradiction that he was trying to solve. And yes, if you look at his lectures and the interviews he gave, he was talking a lot about the beauty of that, and it’s also a theory that we still consider beautiful. But he was also really working on solving a god problem to begin with. And that’s just currently no longer the case.

IRA FLATOW: So what area of physics do you think would be right, the most right, for using theories that are not beautiful, pretty, satisfying those?

SABINE HOSSENFELDER: I’m not sure what you mean what.

IRA FLATOW: I’m trying to narrow down a wide field, where you’re talking about all of physics. Is there one area of physics, either cosmology, particle physics, where it would be most ripe– there are a lot of interesting ideas that are not so beautiful, but might be useful to look into?

SABINE HOSSENFELDER: I’m not talking about all of physics. You know, I’m talking about the foundations of physics in particular, where we’re trying to find, really, new laws of nature. So in other areas of physics, this reliance on beauty is not as pronounced, basically because people don’t have the need. They have close contact to experiment. And that guides the theory development in what I think is a healthy way.

But in the foundations of physics, you already mentioned this earlier, data has not really been coming in that has been of much use in the guidance of the development of new theories. And then, theorists start to rely on lofty ideas, like beauty.

IRA FLATOW: I’m Ira Flatow. This is Science Friday from WNYC Studios, talking with Sabine Hossenfelder, author of Lost in Math, How Beauty Leads Physics Astray. Let’s go to the phones, to Alexander in San Antonio. Hi, welcome to Science Friday.

ANDREW: Hello. I wanted to ask Dr. Hossenfelder, in my experience as a physics students at university, largely, all my professors in the community that I’ve encountered often have very similar opinions on string theory, and similar theories centered around beauty. They’re very opposed to them, and they feel that a lot of them are dead ends. So why do you feel that this is so prominent in the community still, if there’s so much backlash against it?

SABINE HOSSENFELDER: [LAUGHING] Well, probably because there’s not enough backlash against it. So it’s curious that you would be saying this. Actually, most of the feedback that I’ve gotten from physicists did not come from the communities that I was writing about, but from physicists in other communities who basically said, yeah, I meant to say this for a long time, and I’m glad you said it.

So, you know, in hindsight, it’s good to know that I’m not the only one who has this perspective. But the way that science is organized right now, it is possible– I mean, the evidence shows it– that if you have a community of a certain size, like it is the case with string theory, that basically becomes self-supported, it keeps on continuing to work, because there are sufficiently many people, so it attracts sufficiently much interest, and it attracts a sufficient amount of funding. And there’s just no reason to stop it, so it just keeps going.

IRA FLATOW: You also mentioned that, in reading in your book, that you were sort of a new generation of physicist who has had to just adopt the old ways, and you’re not happy with that.

SABINE HOSSENFELDER: Yes. So there’s certainly this aspect of experience that I was mentioning that Weinberg talks about. There’s certainly truth to this. I mean the generation before me of physicists who have seen the completion of the standard model of particle physics, they have seen that these criteria of beauty actually work. You know, they are realized in the standard model. The standard model has a lot of symmetries. It is natural. General relativity is elegant.

So, it’s there. So, it’s perfectly reasonable that they would try to continue using the success, and try the same thing again. And that’s exactly what they did starting in the ’80s. OK. But that was then, so now we’re not in the 1980s. There’s a lot of time that has passed, a lot bridge under the water. And I think that at some point, you have to reconsider these criteria and ask if they are actually working. And I think the answer to this is clearly no. We tried to use them for 30, almost 40 years, and it’s not working.

IRA FLATOW: Yeah, That’s interesting. And do you think that, make way for the younger physicists might be an answer?

SABINE HOSSENFELDER: Well, actually, yes. So I do think that, at least in my sample of young physicists that I have spoken with, there is more– well, I should say, maybe a less romantic sense. People are much more pragmatic. And part of the reason, interestingly, is also because they have grown up being used to using numerical calculations. You know, they’re very good with putting things on a computer.

And I have this impression that, for them, beauty is not so relevant anymore. And I think that’s a good development. But still, it will take a long time until these people will really be able to set research directions. So if we rely on this, we might have to wait another 20 years to see some progress in the foundations of physics. So I’m kind of hoping we could get there a little bit earlier.

IRA FLATOW: All right. We’ll come back and conclude our interview with Sabine Hossenfelder. Maybe we’ll talk about one of the continuing reasons why this research goes, is because you go where the money is. Right? We’ll talk about that.

Sabine Hossenfelder is author of Lost in Math, How Beauty Leads Physics Astray. She’ll join us after the break, and hopefully, you will too. Our number, 844-724-8255. You can also tweet us @scifri. Stay with us. We’ll be right back.

This is Science Friday. I’m Ira Flatow. We’re talking this hour about the big questions in physics that still remain unanswered, and whether this is a realm of science that needs new ideas and a new approach. Sabine Hossenfelder there is author of Lost in Math, How Beauty Leads Physics Astray. Let’s go to the phones. A lot of people still want to talk about it. Let’s go to Jack in Fort Lauderdale. Hi, Jack.

JACK: Hi, how are you doing?

IRA FLATOW: Hi, there, go ahead.

JACK: Now I have a new book I have to read, apparently. So I’m just going to say this, and then I’ll go away and listen to the response. So I think human nature plays a part of this. An elegant solution– obviously, if you’re a physicist, you have to be published. An elegant solution is easily defensible. A complex solution or a theory that has lots of variables and degrees of freedom is very difficult to defend, and people sometimes, you know, need a defensible argument. And the more complex it is, the uglier it is– so to speak, in this context– the more averse they are going to be to produce something and [INAUDIBLE]. Thank you.

IRA FLATOW: OK. Dr. Hossenfelder, what do you think?

SABINE HOSSENFELDER: I totally agree with that. Couldn’t have said it any better.

IRA FLATOW: But so that, he he’s sort of noodling around the idea that it’s about the money. Isn’t it? To get money to do the research, you need a more elegant, more beautiful theory.

SABINE HOSSENFELDER: Well, someone joked to me some while ago that any discussion about any topic in academia eventually turns to a discussion about funding. So I think there’s probably some truth to this. Because the reason is that, of course, funding is important. You know, because without money, we can’t continue to do our research.

And it is certainly true that some theories are just easier to defend than others. They are more popular. If you have a theory that is beautiful, that appeals to others, that’s something that attracts more attention. And now, the way that academia is organized right now, the more attention to your research gets, the more citations your papers get, the better it looks, because that’s the criterion that is used to decide whether your work is important. It’s how popular it is, how many people use it in their own work.

IRA FLATOW: So if you have a simple, elegant idea, people are going to point to it. And it’s been published. And isn’t it getting more difficult because of the kinds of theories we have and the questions we have to ask to actually make the devices?

I know there’s always a great divide between the theorists and the people who have to make the experiments to prove those theories. Isn’t it getting wider, because we have to spend a lot more money to find out whether it’s true or not?

SABINE HOSSENFELDER: Yes. That’s certainly the case. I mean, it’s just that the simple things have been done already, so it becomes increasingly harder to prove new theories. This is why we now have to build huge telescopes, or large accelerators. And of course, it takes a lot of time to build them, and it takes a lot of money

So, yes, you would expect progress to slow down. So that’s a natural expectation. But still, I think you have to ask the question, are we doing the best we can? And I think the answer to this is clearly no, because either way you churn it, relying on beauty is not a scientific approach.

IRA FLATOW: So what keeps you going? If you’ve written a book about beauty and physics, and it’s getting pushed back, and you think this is not the approach that we should be taking, what joy do you find in doing this?

SABINE HOSSENFELDER: Well I generally derive joy from the prospect of discovery. You know, I want to know more about nature, and I don’t really care all that much if the theory is mathematically beautiful in a specific way. I really think this is a very misleading and bad criterion.

One of the reasons, for example, that it has been the case in various circumstances in the history that a theory that was originally ugly, or was considered ugly, was later considered beautiful, sometimes just because people’s perception of beauty changed, but sometimes also because we learned to reformulate the mathematics.

IRA FLATOW: Interesting. This is a great book, Dr. Hossenfelder, and thank you for taking time to be with us today.

SABINE HOSSENFELDER: Thank you.

IRA FLATOW: Sabine Hossenfelder, author of Lost in Math, How Beauty Leads Physics Astray.

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