B Sabine Hossenfelder and Beauty in Physics

[Dr. Courtney]

This question is in the same category as whether people should stop taking part in the lottery.
The scientific answer was the one my mentor used to give: "Lottery is a special tax for idiots."
My friend had the economic reply: "The chances are low but so is the fee, so the small amount of costs justifies the risk."

Why is this the same? Because problems with expected solutions in a reasonable amount of time won't bring you the Nobel prize!

This is well put. I would add that all the physicists I know tend to have had some past successes with their aesthetic preferences on past problems, so we tend to have confidence that the same aesthetic preferences will work on future problems.

I also think I've learned to pick problems well suited to my aesthetic preferences, but this requires self-awareness both in what my preferences are and what kinds of problems they are well suited to. Hint: I don't pick problems where others with similar preferences and greater abilities have already been working hard and long and coming up empty. I pick problems where my preferences and approach are considerably different from what's been done and is not working well.

 

[Dr. Courtney]

The title doesn't quite mesh with the content of the review. Siegel isn't really saying that what the various unsuccessful programs--string theory, GUTs, supersymmetry, etc.---are nonsense. He's just saying (I think) that they haven't produced anything, and so maybe it's time to give up on them.

I wouldn't say that it's a matter of beauty considerations leading people astray, though. It seems more like that there are some mysteries about the universe that may never be solved, or may even not have a solution. You have a real-valued parameter in your model that could presumably be any real number, but it turns out that it is $10^{17}$. That's a mystery: why is it so big? But it might not have any answer at all, beyond: that's just what it is.

Given the 400+ year track record of mysteries having mathematical models, I think less than 50 years is a bit early to conclude that some mysteries relating to physical laws may never be solved. Perhaps more of a time to change tactics. We trained a generation of physicists with a narrow conception of beauty and naturalness that had worked pretty well for QED and the Standard Model. It may not be that beauty considerations are the problem. It may be that the same beauty considerations in which this generation of physicists were trained and guided is the problem.

 

[fresh_42]

Given the 400+ year track record of mysteries having mathematical models, I think less than 50 years is a bit early to conclude that some mysteries relating to physical laws may never be solved. Perhaps more of a time to change tactics. We trained a generation of physicists with a narrow conception of beauty and naturalness that had worked pretty well for QED and the Standard Model. It may not be that beauty considerations are the problem. It may be that the same beauty considerations in which this generation of physicists were trained and guided is the problem.

Sounds a bit like the patient who consulted a couple specialist and came back with as many diagnosis as there have been specialists - each one diagnosing along his lines of interest.

Unfortunately this concept of beauty is pretty simple and straight forward: Describe the system by differential equations and determine the symmetries aka invariants. That's it. In return this makes it difficult to get a foot into the door: there is simply not much place for what could be changed. I've recently read that there is a physicists who suggested to forget about Noether and symmetries. But how can you disregard such a fundamental concept? Not that he offered alternatives. (I made a thread about it then, but have forgotten what to search for now.)

SUSY is an (are) example(s) which always sounds to me as if it is basically the standard model plus some rather arbitrary generalizations: grade the algebra, increase dimensions, consider bigger groups, etc. I guess latest in $SL(1,000\,;\,\mathbb{C})$ you can find embedded whatever you want. To me as an absolute layman it always looks like shots in the dark hoping to hear something cry. Not very convincing.

 

[Vanadium 50]

Sorry for the slow response. Been out of the country and wanted to be complete.

For example, I suspect that we will never be able to resolve which QM interpretation is correct

We won't. The math is still the same in every interpretation, so there is no experiment that can - even in principle - tell us which interpretation is right. Indeed, "which interpretation is right" isn't a well-defined question. Interpretations are stories we tell ourselves as computational mnemonics, and we use them all the time in other subfields without thinking about them. ("Image charges", "heat flows", "virtual image", etc.)

Figuratively speaking, 10² MWI researchers, but not 10⁴ (edit: add the words "supported by public money.")

It's nowhere near this many. US-DOE supports maybe 200-300 theorists in total. The number supported to work primarily on quantum interpretations is, as far as I can tell, zero. If someone is funded to do some other thing and they write a paper on interpretations nobody is going to complain, but if that's all they are doing? No way.

Are you saying the Standard Model is more beautiful with the Higgs mechanism than without

I would say so. Spontaneous Symmetry Breaking is clever, and it happens in many different systems as well, e.g. ferromagnets.

That [the Higgs boson] was just a confirmation of the Standard Model. It did not provide support for any of the "beyond the standard model" ideas that have been proposed over the last 40 years.

I am old enough to remember when the Higgs boson was not part of the Standard Model. What is in the SM and is not in the SM has been retconned several times: I remember when massive neutrinos were in, but as soon as oscillations were discovered, out then went. Then oscillations become "the first sign of BSM physics". So that's not an argument I find convincing. Or even well defined.

But that wasn't quite the point I was making. One can't argue that billions spent to verify the Higgs mechanism is OK but billions spent to search for SUSY is not because it's the very same instrument so it's the very same billions. Similarly, if it's OK to have 50 years between proposal and discovery for the Higgs, shouldn't SUSY have until 2024? (I'm taking Wess and Zumino's paper as the starting point, although it's probably too early)

 

[PeterDonis]

What is in the SM and is not in the SM has been retconned several times

Yes, that's true; models develop over time so this is actually to be expected. My point was that when the Higgs was actually observed in the LHC, it had already been part of the SM for quite some time, so it wasn't "new evidence" that required changing any models, and it wasn't a sign of anything beyond the SM as the SM had been understood for quite some time. If the LHC had discovered the Higgs in, say, the 1970s, that would have been a different story.

I remember when massive neutrinos were in, but as soon as oscillations were discovered, out then went.

Do you mean "massless" neutrinos were in but then out? I thought the original SM had massless neutrinos, and the discovery of oscillations forced the change to massive ones.

One can't argue that billions spent to verify the Higgs mechanism is OK but billions spent to search for SUSY is not because it's the very same instrument so it's the very same billions.

I agree with this. I also don't think Hossenfelder was making the argument that it was OK to fund the LHC to find the Higgs but not OK for SUSY. I think she was just making the point that no predictions of SUSY have been confirmed thus far.

if it's OK to have 50 years between proposal and discovery for the Higgs, shouldn't SUSY have until 2024?

It's not a question of how much time passes, but whether experiments can probe the regime where the hypothesis being considered (such as SUSY) predicts that something new should be found. SUSY, or at least the versions of it that everyone seemed to be favoring, predicted that the LHC, operating at the energy regime it's currently in, should have found some supersymmetric particles. But it hasn't found any.

 

[Vanadium 50]

I thought the original SM had massless neutrinos, and the discovery of oscillations forced the change to massive ones.

That's the retcon. In the 80's and early 90's, most people would have said neutrinos probably have a small [Dirac] mass. Then as soon as neutrino oscillations were discovered, the SM was retconned to require massless neutrinos. (By the way, it was 41 years between the prediction of neutrino oscillations and their discovery)

, but whether experiments can probe the regime where the hypothesis being considered (such as SUSY) predicts that something new should be found

I don't disagree with this, but it's a bit unfair of Hossenfelder to limit herself to predictions intended to give large signals in early LHC running, and then declaring failure when they don't come to pass. I am no fan of SUSY, but it is not difficult to come up with models that stabilize the Higgs mass, yet need more data to produce a visible signal at the LHC.

I also think the very premise is unfair. If Hossenfelder has a better approach, she should publish it. But "you're doing it wrong! You're doing it wrong!" is not helpful.

 

[PeterDonis]

In the 80's and early 90's, most people would have said neutrinos probably have a small [Dirac] mass. Then as soon as neutrino oscillations were discovered, the SM was retconned to require massless neutrinos.

So by "massless" you mean "zero Dirac mass", so that neutrino mass is generated by a different mechanism?

 

[gmax137]

retconned

Well I learned a new word today. At first I thought this was a typo. [/tangent]

 

[Vanadium 50]

o by "massless" you mean "zero Dirac mass", so that neutrino mass is generated by a different mechanism?

No, I mean that masslessness of the neutrinos did not become part of the SM until late in the game - near or after when they were discovered to be massive.

 

[PeterDonis]

I mean that masslessness of the neutrinos did not become part of the SM until late in the game

I'm not sure that's true. As I understand it, the original SM only had the left-handed neutrino, and it was massless (you need both left-handed and right-handed to have a Dirac mass term, and there was no other mass mechanism for the neutrino).

 

[stevendaryl]

Well I learned a new word today. At first I thought this was a typo. [/tangent]

It's from comic books (or similar long-running fictional stories, such as TV series of movie series). At some point, there is a plot development that contradicts what was previously said about the fictitious characters or their fictitious history, so the history is just changed to accommodate the new plot development. Sometimes in the comics, the authors explain the contradiction by invoking a parallel world where things happened differently. Other times, they just hope readers won't notice, or at least, won't complain too much.

 

[Vanadium 50]

I'm not sure that's true. As I understand it, the original SM only had the left-handed neutrino

And what I am saying is that nobody in 1990 was saying that.

 

[PeterDonis]

nobody in 1990 was saying that

The original Standard Model dates from the 1970s. What particular significance does 1990 have?

 

[PeterDonis]

The original Standard Model dates from the 1970s. What particular significance does 1990 have?

To expand on this a bit: when I say the original SM, to the best of my understanding, had massless neutrinos, I am talking about the 1970s SM, the one that combined original quantum chromodynamics with the Weinberg-Salam electroweak theory. As I understand it, this model gave masses to the W and Z bosons via the Higgs mechanism, and to the quarks and electron-series leptons by having both left-handed and right-handed spinor fields for them with a Dirac mass term put in by hand. But there were no right-handed neutrinos so neutrinos were massless in this model.

When experimental evidence for neutrino masses appeared, as I understand it, this SM was extended by adding right-handed neutrinos in order to allow the neutrinos to have masses; but other mechanisms were also proposed.

 

[stevendaryl]

To expand on this a bit: when I say the original SM, to the best of my understanding, had massless neutrinos, I am talking about the 1970s SM, the one that combined original quantum chromodynamics with the Weinberg-Salam electroweak theory. As I understand it, this model gave masses to the W and Z bosons via the Higgs mechanism, and to the quarks and electron-series leptons by having both left-handed and right-handed spinor fields for them with a Dirac mass term put in by hand. But there were no right-handed neutrinos so neutrinos were massless in this model.

When experimental evidence for neutrino masses appeared, as I understand it, this SM was extended by adding right-handed neutrinos in order to allow the neutrinos to have masses; but other mechanisms were also proposed.

I thought that in the electroweak model, the only mass that electrons had was via the Higgs mechanism. So there is no Dirac mass (what takes its place is the coupling term between the electron and the Higgs, which is nonzero after symmetry-breaking). (Or is that term still considered a "Dirac mass"?)

 

[PeterDonis]

I thought that in the electroweak model, the only mass that electrons had was via the Higgs mechanism.

I think that in the original model, the electron and quark masses were actually Yukawa mass terms from the interaction with the Higgs. But they look just like Dirac mass terms once you give the Higgs a nonzero constant vacuum expectation value.

 

[Vanadium 50]

In the 80's and early 90's, most people would have said neutrinos probably have a small [Dirac] mass.

The original Standard Model dates from the 1970s. What particular significance does 1990 have?

It was before the discovery of neutrino oscillations. Other than that, it's a description of a period in time. If I said "bell bottoms and hot pants were popular in the 70's", there is no answer to "why the 70's" other than that's when it happened. (And, of course, there is no rational explanation why they were popular at all)

If you look at textbooks at the time describing the SM, say Halzen and Martin or Griffiths, you will not see statements like "neutrinos are massless". You will instead see statements like "neutrinos are ultrarelativistic". If you look at the SN1987a papers, like Arnett and Rosner, same story. If you go back to Weinberg's "A Model of Leptons", arguably the birth of the SM, he barely discusses neutrinos, but he most certainly does not claim they are massless. The 1978 review article of Bilenky and Pontecorvo jumps right into what is known about neutrino masses and mixing without so much as a nod at the supposed masslessness of the neutrinos in the SM. If you go earlier, say Perkin's 1972 text, he actually comes right out and writes that neutrino velocities are approximately c - not exactly c as one would have for a massive particle.

It wasn't until after neutrino oscillations were seen that people started saying "Neutrinos are massless in the SM" about the time that neutrino masses were discovered.

 

[PeterDonis]

If you look at textbooks at the time describing the SM, say Halzen and Martin or Griffiths, you will not see statements like "neutrinos are massless". You will instead see statements like "neutrinos are ultrarelativistic". If you look at the SN1987a papers, like Arnett and Rosner, same story. If you go back to Weinberg's "A Model of Leptons", arguably the birth of the SM, he barely discusses neutrinos, but he most certainly does not claim they are massless. The 1978 review article of Bilenky and Pontecorvo jumps right into what is known about neutrino masses and mixing without so much as a nod at the supposed masslessness of the neutrinos in the SM. If you go earlier, say Perkin's 1972 text, he actually comes right out and writes that neutrino velocities are approximately c - not exactly c as one would have for a massive particle.

Hm, interesting. I'm curious whether any of the textbooks or review articles actually write down the fields they are using, or a Lagrangian, and if so, whether the fields or the Lagrangian they write down allow a nonzero mass for neutrinos.

I was able to find a copy of Weinberg's 1967 paper online. He specifically writes down a left-handed doublet (neutrino and electron) and one right-handed singlet (electron), and says those are the only lepton fields he's using. That means he is using a model in which the neutrino has to be massless, because you need both left- and right-handed fields (as the electron has in his model) for a nonzero mass. He doesn't explicitly say that the neutrino in his model is massless, but I don't see how the math he gives can lead to any other conclusion.

In short, I'm trying to understand whether the apparent failure you describe of many references to say that the neutrino in the original SM was massless was because the original SM actually allowed a nonzero neutrino mass, or simply because the references were sloppy and didn't actually take the time to explore or discuss the actual consequences of the underlying math for neutrino mass.

 

[TeethWhitener]

It's nowhere near this many. US-DOE supports maybe 200-300 theorists in total. The number supported to work primarily on quantum interpretations is, as far as I can tell, zero. If someone is funded to do some other thing and they write a paper on interpretations nobody is going to complain, but if that's all they are doing? No way.

This is really important to keep in mind. There's a significant misconception as to what gets funded. It's like the surveys where people estimate NASA's annual budget as ~20% of the total federal budget.

I'm looking, and I can't find a pie chart breaking down the number of researchers in the various fields of physics, but I do know that nobody at my university worked on interpretations of quantum mechanics.

[edit] I should say, rather, that nobody was funded to work on interpretations of quantum mechanics. Some people (such as me, actually) worked on it in our spare time.

Here's a (somewhat) detailed breakdown: https://www.aip.org/fyi/federal-science-budget-tracker/FY2018
See, in particular, the DOD breakdown. All basic research (denoted 6.1, or technology readiness level 1--see here for a definition of DOD technology readiness levels) done by DOD totals to ~$2B, versus the total R&D budget at ~$88B.

 

[Vanadium 50]

I'm trying to understand whether the apparent failure you describe of many references to say that the neutrino in the original SM was massless was because the original SM actually allowed a nonzero neutrino mass, or simply because the references were sloppy and didn't actually take the time to explore or discuss the actual consequences of the underlying math for neutrino mass.

Neither, I think. The modern language of Weyl fields wasn't popular back then (Griffiths specifically warns against it) and the (1+γ₅) terms were viewed as projection operators rather than fields in their own right. That is, the W coupled to the left-handed components of fields rather than left-handed fields. In this view, there is (or at least can be) a non-interacting right-handed component to the neutrino.

 

[PeterDonis]

Neither, I think. The modern language of Weyl fields wasn't popular back then (Griffiths specifically warns against it) and the (1+γ5) terms were viewed as projection operators rather than fields in their own right. That is, the W coupled to the left-handed components of fields rather than left-handed fields. In this view, there is (or at least can be) a non-interacting right-handed component to the neutrino.

Ok, thanks, this is good background that I wasn't aware of.

 

[martinbn]

I tried to read her book but I couldn't. It was a bit boring and I had the constant impression that she tries a bit too hard to be witty all the time, which seemed to me forced and was very tiring. I am not saying that the book isn't worth it, it's just not for me. I also still don't know what the main thesis is.

 

[Android Neox]

From the article:https://motherboard.vice.com/en_us/...ists-are-misled-by-outdated-notions-of-beauty

I wouldn't call multiverse interpretation "beautiful". Everett was kicked out of physics for proposing Many Worlds. The only reason multiverse models exist is because they are the only models that are consistent with quantum entanglement, Bell's Inequality, and non-simultaneity.

 

[Lish Lash]

I would argue that "beauty" is such a culturally loaded term that it is inappropriate to apply it to a field as rigorously objective as physics. Beauty is not only an intrinsically subjective term, it is entangled with intimately personal associations of pleasure and sexual attraction, activities often dismissed as inessential. It seems covertly provocative to apply a term with such connotations to intellectual pursuits of knowledge. I think "elegance" is a more genuine characterization of the esthetic inclinations of scientific intuition.

 

[fresh_42]

I would argue that "beauty" is such a culturally loaded term that it is inappropriate to apply it to a field as rigorously objective as physics. Beauty is not only an intrinsically subjective term, it is entangled with intimately personal associations of pleasure and sexual attraction, activities often dismissed as inessential. It seems covertly provocative to apply a term with such connotations to intellectual pursuits of knowledge. I think "elegance" is a more genuine characterization of the esthetic inclinations of scientific intuition.

This is quibbling. I don't think that beauty is a subjective term. There is such a thing as classic beauty, and you know it if you see it. The point is that uneducated people use this term as well, and for them it is highly subjective and emotional, but this is not the beauty scientists speak of. Why does Beethoven's 9-th work on the entire globe, or Chopin? Why are Michelangelo's sculptures beautiful? These are in the category which is meant here, not someone's favorite color, food or body shape.

Whether you call this elegance is just a workaround of the fact, that many people simply don't have a sense of beauty. You may call this sad, but I think it is true. If scientists speak of beauty, they usually mean the incredible simplicity of many natural phenomenons, or how slim some proofs are, or how a few equations reveal deep insights. There is an inherent beauty in most theories and it can neither be discussed, nor is it a matter of opinion. Galois' theory is beautiful. The only question about it is whether people are able to see it or not. If they don't, then the reason is a lack of understanding, not a lack of beauty.

 

[PeterDonis]

I don't think that beauty is a subjective term. There is such a thing as classic beauty, and you know it if you see it.

I think you're on very shaky ground here. First, "you know it if you see it" is pretty much the classic definition of "subjective". Second, I'm not sure how much agreement there is among scientists and mathematicians about what specific theories, models, proofs, etc. count as "beautiful".

The only question about it is whether people are able to see it or not.

But if they can't see it, and it's defined as "you know it if you see it", how can it possibly be objective?

 

[fresh_42]

Yes, 'You know it if you see it' might have been too bold, as my definition constraints the set of people I mean by 'you'. It is a rather snobbish and certainly political incorrect way to see it, because I couple it to education. However, it is not shaky ground, as I don't want to defend it, neither make it mass compatible. It is my personal opinion, and I declared it as such. It doesn't demand to be 'provable' as I don't have the desire to convince people.

I cannot run the 100 meter under, say 20 seconds, so I am not an athlete. The beauty of science can't be seen by the majority of people, but this doesn't mean there wasn't athletes who can run the 100 meter under 10 seconds.

 

[Lish Lash]

If scientists speak of beauty, they usually mean the incredible simplicity of many natural phenomenons, or how slim some proofs are, or how a few equations reveal deep insights.

While I agree with your characterization of scientists, those are examples of what I (and I believe most dictionaries) would describe as "elegance". You may insist on conflating that term with more fashionably publicized forms of "beauty", but it's a distinction I think we do recognize when we see it.

 

[PeterDonis]

'You know it if you see it' might have been too bold

My issue isn't that it is "too bold", it's that it is subjective, when you specifically tried to claim it wasn't.

If, for example, you argued that General Relativity is "beautiful" because it takes a very simple field equation derived from a very simple Lagrangian and extracts from it a huge variety of detailed quantitative predictions that have been confirmed experimentally to many decimal places, that would be an objective criterion for "beauty" (and one I would tend to agree with). But that criterion, or anything like it, is very different from "you know it when you see it".

For the criterion I just described, I would agree with @Lish Lash that "elegance" is a better word for it than "beauty", but that's a matter of personal preference; the criterion itself is objective. The problem with "you know it when you see it" is that it isn't.

The beauty of science can't be seen by the majority of people, but this doesn't mean there wasn't athletes who can run the 100 meter under 10 seconds.

And if the criterion of "beauty in science" is something like what I described above, there is no problem. Certainly the fraction of people who can understand why GR is beautiful in the above sense is small, just as the fraction of people who can run 100 meters in under 10 seconds is small, but that doesn't make either one any less true or objective.

The problem with "you know it when you see it" is that if you then turn around and say that, well, some people just can't see it, you are undermining your own criterion; it becomes useless.

 

[fresh_42]

The problem with "you know it when you see it" is that if you then turn around and say that, well, some people just can't see it, you are undermining your own criterion; it becomes useless.

Maybe "bold" was the wrong word. It was what the dictionary gave me for the word I was looking for. "You know it if you see it" shouldn't be the definition, rather emphasizing that people who can see it will recognize it as such, in the same sense as people around the world apparently agree that the final chorus in Bethoven's 9-th is beautiful. There is no objective criterion either, nevertheless there are dozens of flash mob videos from around the world which support this point of view.

And to find GR (or my example Galois' theory) beautiful, you first have to understand it. I don't think that this sense of beauty can be measured in bytes as in CS: the shorter the more beautiful. This would be too short in either meaning. And that's my difficulty here and why I only expressed my personal point of view: there is no objective scale, but this does not automatically make it subjective. It depends on whether you're able to see it, i.e. whether you really understood GR. GR is beautiful despite the fact that the rubber sheet isn't accurate. It's beauty doesn't come from the numbers 21 or 18 (I don't remember the exact number of equations, resp. free parameters, which is why I've chosen Galois theory as example).