Interview with a Theoretical Physicist: Sabine Hossenfelder - Comments

[Greg Bernhardt]

TheAdmin submitted a new PF Insights post

Interview with a Theoretical Physicist: Sabine Hossenfelder

Continue reading the Original PF Insights Post.

 

[martinbn]

I am surprised that she has never heard that the models are commonly regarded as simple and beautiful. Aren't they?

 

[Greg Bernhardt]

Martin, where have you seen such comments on the models?

 

[Charles Link]

Very good article. @Greg Bernhardt I wanted to give my vote and give it a "5", but I don't see anywhere I can click on to vote...

 

[kodama]

What are your views on Loop quantum gravity, and should top Universities like Princeton, Harvard, MIT, Stanford sponsor a loop quantum gravity research group and faculty?

Loop quantum gravity is even more detached from physics than is string theory, and the math is less interesting on its own right. No, I wouldn’t recommend to any university to set up a research group on loop quantum gravity. If some department is interested in quantum gravity, they should set up a research group on quantum gravity phenomenology, and hire people to take on the question how to find experimental evidence that gravity is even quantized. (And, at some point, find out which theory of quantum gravity is the correct one.)

Reference https://www.physicsforums.com/insights/interview-theoretical-physicist-sabine-hossenfelder/

i'm glad you asked the question I've asked.

i'm sure abhay ashketar or smolin or rovelli would disagree.

given sabine's answer

what about loop quantum cosmology's contact with observation in CMB and other observable?

what about loop quantum gravity reproducing hawking entropy and radiation?

what about asymptotically safe gravity, noncommutative geometry, causal dynamic triangulation etc?

should universities that do have LQG research groups and LQG researchers like penn state shut down their LQG research group and fire abhay ashketar et al?

since the LHC found no evidence of SUSY, and proton decay has found no evidence of proton decay as predicted by GUT's

Should universities that do not currently have a string theory research group, set one up in light of current LHC SUSY results?

 

[UsableThought]

Martin, where have you seen such comments on the models?

Even as a layperson reading pop-sci accounts, I retain a strong impression that over the years, some inside physics have complained of the un-tidyness of various modern models; that smacks of an aesthetic argument.

Beyond that, mathematics famously has aesthetic appeal; and since physics relies so heavily on math, it wouldn't be surprising that some researchers and authors inside physics would say the same, at least in pop-sci presentations. I did a quick Google and "symmetry" seems particularly mentioned. Here are just a few hits out of many:

- A PBS-related article: Symmetry: How Beautiful Math Makes Elegant Physics

- A particular physicist's pop-sci book: https://www.amazon.com/dp/080187971X/?tag=pfamazon01-20 (re: the standard model)

- Another book, with a Penrose forward: https://www.amazon.com/dp/0691173265/?tag=pfamazon01-20

Feynman too seems, in his recorded remarks and interviews, to hint here & there at aesthetics; the difference is, I doubt he would have insisted on it in relation to usefulness. Indeed, in his lecture on harmonics, he says this:

In this one discovery [by Pythagoras], there are the three aspects: experiment, mathematical relationships, and aesthetics. Physics has made great progress on only the first two parts.

 

[martinbn]

Martin, where have you seen such comments on the models?

I didn't mean the latest speculative models, I mean mathematical models in general and throughout history. For example Dirac (and many others) has always maintained such a view.

 

[UsableThought]

For example Dirac (and many others) has always maintained such a view.

Following up on this - Wikiquote has some particularly toothsome remarks by Dirac along these lines; they are taken from a 1963 article by him in Scientific American. The article was reprinted in 2010 and can be found here; the title is "The Evolution of the Physicist's Picture of Nature". These quotes are pulled directly from the article; bold is mine:

. . . There is one other line along which one can still proceed by theoretical means. It seems to be one of the fundamental features of nature that fundamental physical laws are described in terms of a mathematical theory of great beauty and power, needing quite a high standard of mathematics for one to understand it. You may wonder: Why is nature constructed along these lines? One can only answer that our present knowledge seems to show that nature is so constructed. We simply have to accept it.​

. . . It seems that if one is working from the point of view of getting beauty in one's equations, and if one has really a sound insight, one is on a sure line of progress. If there is not complete agreement between the results of one's work and experiment, one should not allow oneself to be too discouraged, because the discrepancy may well be due to minor features that are not properly taken into account and that will get cleared up with further developments of the theory.​

Clearly Dirac was expressing a preference only; his argument goes no deeper than that. So even in his time others might have dismissed such a view as irrelevant, just as they might today. This is besides the fact that beauty is subjective.

 

[UsableThought]

A related question might be whether Occam's razor (which I would argue is rooted in aesthetics) has any real utility; this blog piece presents a good argument against its over-use in physics and other branches of science: Why The Simplest Theory Is Never The Right One: Occam’s Razor Has A Double Edge. Here's a quote; the bold is mine and highlights the relevance to this thread:

Theories with the fewest assumptions are often preferred to those positing more, a heuristic often called “Occam’s razor.” . . . But there are numerous reasons to suspect that this simple “theory of theories” is itself fundamentally misguided. Nowhere is this more apparent than in physics, the science attempting to uncover the fundamental laws giving rise to reality. The history of physics is like a trip down the rabbit hole: the elegance and simplicity of Newtonian physics has been incrementally replaced by more and more complex theories. At the time of writing, this has culminated in M-Theory, positing no less than 10 dimensions of space and the existence of unobservably small “strings” as the fundamental building block of reality. It seems safe to assume that the fundamental laws of reality will be even more complex, if we can even discover them.​

 

[Lapidus]

Nice overall interview. But this must probably the dumbest thing she ever said:

I have never heard of the fact that “physical models are commonly regarded as beautiful and in a sense minimal” and even if that was so I don’t know why it would matter. Yes, quite possibly it’s a pretty bad idea to rely on the aesthetic sense of humans to find a good theory to describe nature.

 

[Denis]

i'm sure abhay ashketar or smolin or rovelli would disagree.

Why should one care?

what about loop quantum gravity reproducing hawking entropy and radiation?

That's more of a counterargument, given the trans-Planckian problem with Hawking radiation. Ok, to have some Hawking-like radiation you don't need much, all you need is that you have to prevent stability (stable stars do not Hawking-radiate), while everything else somehow radiates. So, it is not really a counterargument. But it is nothing which should somehow count as positive.

 

[Denis]

A related question might be whether Occam's razor (which I would argue is rooted in aesthetics) has any real utility;

It has. There is Popper's criterion of empirical content: We should prefer theories which make more falsifiable predictions.

A theory with more free parameters to fit with observation has typically less predictive power.

 

[kodama]

Why should one care?That's more of a counterargument, given the trans-Planckian problem with Hawking radiation. Ok, to have some Hawking-like radiation you don't need much, all you need is that you have to prevent stability (stable stars do not Hawking-radiate), while everything else somehow radiates. So, it is not really a counterargument. But it is nothing which should somehow count as positive.

i was replying to this claim

Loop quantum gravity is even more detached from physics than is string theory, and the math is less interesting on its own right. No, I wouldn’t recommend to any university to set up a research group on loop quantum gravity. If some department is interested in quantum gravity, they should set up a research group on quantum gravity phenomenology, and hire people to take on the question how to find experimental evidence that gravity is even quantized. (And, at some point, find out which theory of quantum gravity is the correct one.).

 

[UsableThought]

It has. There is Popper's criterion of empirical content: We should prefer theories which make more falsifiable predictions. A theory with more free parameters to fit with observation has typically less predictive power.

Can you give a couple of examples? That would be helpful.

Meanwhile I recently started reading Philosophy of Science: A Very Short Introduction, a primer by Samir Okasha; and he happens to raise a similar point to the one I was groping for; he doesn't use the phrase "Occam's razor" but to say "parsimony" is to say essentially the same thing:

The idea that simplicity or parsimony is the mark of a good explanation is quite appealing, and helps flesh out the abstract idea of IBE [inference to the best explanation]. But if scientists use simplicity as a guide to inference, this raises a deep question. Do we have reason to think that the universe is simple rather than complex? Preferring a theory which explains the data in terms of the fewest number of causes seems sensible. But are there any objective grounds for thinking that such a theory is more likely to be true than a less simple rival? Or is simplicity something that scientists value because it makes their theories easier to formulate and to understand? Philosophers of science do not agree on the answer to this difficult question.​

All of which echoes something that Hossenfelder says in the interview that this thread is about - here is that quote:

I have never heard of the fact that “physical models are commonly regarded as beautiful and in a sense minimal” and even if that was so I don’t know why it would matter. Yes, quite possibly it’s a pretty bad idea to rely on the aesthetic sense of humans to find a good theory to describe nature.​

We might like the "feel" of parsimony (I certainly do); we might like Popper's argument that theories ought to be falsifiable (despite criticisms by some of that argument); but these sorts of things are preferences on our part. Hossenfelder seems to be implying what might be an interesting caution though she doesn't go into detail.

 

[Denis]

Can you give a couple of examples? That would be helpful.

Simply add a parameter to a theory. Say, instead of $G=T$ use $G=T+c T_1$ with some constant c. The original theory is simpler, by Occam's razor "Don't add entities without necessity", which includes such additional terms. Now let's look at the empirical content. An observation which falsified the new equation falsifies the old equation too, given that it is a particular case, with $c=0$. On the other hand, it is possible that observation fits with the second equation for some $c >0$, but not for $c=0$. In this case, the first equation would be falsified, the second not. So, the simpler equation is more falsifiable, thus, has more empirical content, and should be preferred by Popper's criterion.

Of course, one can invent examples in the other direction too, the ultimate most simple theory would be "we know nothing", with zero empirical content. But the case where the more complex theory has more parameters to fit, and therefore less empirical content is, I think, quite typical. It goes back to Popper himself, and is, therefore, part of established standard scientific methodology.

How to give a meaningful explanation of aesthetic feelings like beauty of a theory is much less clear. And beauty can be very misleading. A lot of mysticism has some beauty, so that beauty can lead us into mysticism.