- If like most other people you’re stuck at home, and having trouble concentrating on the projects you thought the current situation would cause you to finally find the time to complete, one thing you could do is watch a lot of talks about mathematics online. As far as I can tell, mathematicians are doing much better than any other field right now in dealing with this, since they have a wonderful site developed at MIT called mathseminars.org. It contains a fairly comprehensive set of listings of Math seminars now being run online.
If there’s anything similar in the physics community, I’d be interested to hear about it.

- A new book about the problems of fundamental physics has recently appeared, David Lindley’s The Dream Universe: How Fundamental Physics Lost its Way. I’ve been thinking for a while about whether to write about it here, have held off mainly because I felt I didn’t have much interesting to say. Today I see that Sabine Hossenfelder has written a review of the book which I mostly agree with, so you should read what she has to say.
There are a couple places where I significantly disagree with her. For one thing, unlike Hossenfelder, I’m a great fan of Lindley’s much earlier book on this topic, his 1993 The End of Physics. This was written a very long time ago, at a time when writing for the public about fundamental physics was uniformly positive about the glories of string theory. Unlike all those books, this one has held up well. Reading it at the time it came out, it was remarkable to me to find someone else seeing the same problems with the field that seemed to me obvious, providing a very helpful indication that “no, I’m not crazy, there really is something wrong going on here.”

It’s interesting to read Hossenfelder’s take on the way Lindley makes “mathematical abstraction” the villain in this story:

The problem in modern physics is not the abundance of mathematical abstraction per se, but that physicists have forgotten mathematical abstraction is a means to an end, not an end unto itself. They may have lost sight of the goal, alright, but that doesn’t mean the goal has ceased existing.

Here is where I definitely part company with Lindley, and to some extent with Hossenfelder. The current problems with fundamental physics have nothing to do with mathematical abstraction, but with the refusal to give up on bad physical ideas that don’t work. Thirty-six years ago Witten and many other leaders of the field fell in love not with a mathematical abstraction, but with a bad physical idea: replace fundamental particles with fundamental strings. One reason they fell in love with this idea was that it could be fit together with two other bad ideas they had been dallying with at the time, that there are new forces mixing leptons and quarks (GUTs), and that you can relate bosons and fermions with the square root of translation symmetry (SUSY).

Unfortunately it seems to me that many theorists have now drawn the wrong conclusion from the sorry story of the last forty-some years, deciding that what they need to do is to stay away from unwholesome mathematics, and stick to the wholesome experimentally observable and testable. But what if the underlying reason you got in a bad relationship with a seriously flawed love interest was that there weren’t (and aren’t) any experimentally testable ones to be found? Maybe what you need to do is to work on yourself and why you stay in bad relationships: the mathematically abstract love of your life might still be out there.

- Witten yesterday posted a definitely not mathematically abstract paper on the arXiv, Searching for a Black Hole in the Outer Solar System. It’s basically a proposal for finding a physical black hole we could then go and get into a relationship with. I can’t help thinking the probabilities are that getting into a healthy relationship with a new mathematical abstraction is more likely to work out than this.

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https://virtualscienceforum.org/#/long_range_colloquium

for particle pheno talks, https://sites.google.com/site/lhcresultsforumtalks/ seems to be pretty thorough

Hi Peter,

Thanks for the link. You quoted the one paragraph with a typo! Can you make the “end to a means” a “means to an end”? I didn’t read the “End of Physics” when it came out but only a few years ago, which may have had an influence on my impression. Yours and Lee’s and Jim Baggott’s books are all considerably more informative and provide more solid arguments. Lindley’s in comparison is rather superficial. But I admit it’s somewhat unfair to compare his to books that appeared much later. Best,

Sabine

Hi Sabine,

Fixed.

This site aggregates calendars of known physics webinars:

https://sites.google.com/site/onlinephysicsseminars

If something is missing, contact organisers (indico or google format only). Furthermore, physics is going to be included here (https://researchseminars.org) and InSpire is starting an analogous initiative. However these do not aggregate automatically.

Hi Peter,

The ‘mathseminars.org’ website has now been expanded to include all of physics and mathematics. It is officially live, as of this afternoon, at:

http://researchseminars.org

The site has good coverage of talks in high-energy theory, but we hope that word will spread quickly to the rest of physics.

Best,

Jamie

Peter,

Is it possible that your conception of what has gone wrong in terms of “bad physical ideas” is just another way of framing Sabine’s conception in terms of “forgetting that mathematics is a means to an end”?

After all,

1. most of mathematics is not at this time relevant to physics, and is not expected to be.

2. This implies there are plenty of opportunities for physicists to be inspired by pieces of math which entail “bad physical ideas”.

3. But then, falling in love with, and consequently overlooking any red flags as one develops those ideas seems pretty accurately describable as Sabine does.

Armin,

Mathematics is the language of physics, so you can blame any bad idea on “mathematics”. My disagreement with Hossenfelder is that I dislike her use of that framing of the problem, when what she mainly has in mind are certain specific failed ideas, which I think are more properly thought of as failed physical ideas, nothing to do with the fact that they are formulated in certain mathematical terms.

There is and always has been a strong tradition among physicists of skepticism about use of any type of mathematics beyond what they were trained in. If you go back to the early days of quantum mechanics you can find people complaining about matrices, a little later complaining about group theory (the “gruppenpest”). The failure of string theory has led such people to blame this failure on the use of such mathematics. But what if, absent help from experiment, what is needed for progress is a new idea coming out of mathematics, not out of experiment? Fundamental theoretical physics may be in the process of turning against exactly the tools it needs to get anywhere.

There’s a huge universe of mathematical ideas, most of which won’t be helpful in finding new physics. Those skeptical of the value of abstract math for physics have plenty of good examples to point to where mathematical structures are being invoked that are not of any help in physics. My reading of the history that I’ve seen over the course of my career though is not that the main problem is people getting lost down blind alleys of mathematics, but getting lost down blind alleys of bad ideas about physics. As an example, consider the multiverse. Claiming to explain things with “everything happens” is an awful idea for how to do physics and how to do science, and that’s the problem with it, not whatever mathematical language you choose to dress it up in.

Or, put differently, the problem isn’t with people falling in love with ideas because they find the math attractive. This may be our best hope for new ideas. The problem is not giving up on one’s ideas when they fail.

Thank you, Peter. I think I understand your perspective better now.

A propos history of physics: One richly informative website with accounts literally from the mouths of those physicists who lived it is https://www.webofstories.com/

Is it me or is that black hole article a bit at odds to Witten’s typical interests?

Bernhard,

Yes, although Witten has always had wide interests, and his interests fundamentally are more about physics than mathematics. If you want to find a reason for him getting interested in this particular topic, it’s hard to overemphasize how central a topic black holes have become to theorists. Also, Witten has been involved with the Breakthrough Prize organization, which is a Milner/Zuckerberg operation, and they’re the ones behind the Breakthrough Starshot idea.

Bernhard and Peter,

there are a lot of comments on different internet forums that state that Witten has basically given up on trying to find a TOE, and now has focused his attention more on the famous It from Qubit idea.

But he’s not the only one. If you look closely, many top theoretical physicists are directing their research and energies towards the high-tech world. His involvement with the Breakthrough Starshot idea is one of the clues.

DB,

I don’t think it’s Witten in particular who has given up on trying to find a TOE, this is the attitude of most influential particle theorists. Among string theorists, the majority opinion now appears to be that the “landscape of string vacua” that predicts nothing at all is an indefensible position at the end of a blind alley, and that continued focus on string theory requires other arguments.

Peter,

thanks for the info.

For many of us, it was pretty clear a long time ago that pursuing the search of a final TOE was a complete waste of time, for the simple reason that… it does not exist.

Witten probably saw the light a couple of years ago, as proved in the interview he gave to Graham Farmelo in Princeton. He accepted the landscape idea, which is the dominant position nowadays.

Only a couple of fanatic radical defenders of string theory being the TOE carry on saying that ST will come up with the final, unique solution to the Laws of Nature.

I happen to know a couple of them, one from a small country in Central Europe and the other from the Sates.

I don’t know what other arguments string theorists are thinking of focusing on and pursuing, but I’ll be very interested if you could tell me what they are.

Thanks!!

DB,

I don’t think that it it’s clear that a TOE doesn’t exist, although it is clear string theory as currently understood cannot give you one. String theory defenders have the following options:

1. Claim that string theory has succeeded, but because of the landscape can’t predict anything. The problem with this is that most other physicists will not take you seriously. At one point I linked here to discussion at a Simons Center talk where Vafa explained just how damaging this has been to the perception of string theory among the public and among other scientists.

2. Claim that there is a problem with the landscape, that string theory as currently understood may be able to make some sort of prediction of something. This is the “swampland” program favored by Vafa. For reasons explained in many places here I don’t think this will work. I see no evidence this point of view is getting much traction in the physics community.

3. Claim that the problem is that string theory is too poorly understood to be able to tell if it makes predictions or not, but that it is our “best hope for a TOE”, justifying continued work on it. My impression is that this is currently the most common point of view among theorists who call themselves “string theorists”. Since there are no viable ideas out there for how to move string theory in the direction of giving a predictive TOE, in practice people in this camp have stopped work on the problem and taken up other things to work on (e.g. it from qubit ideas).

Thanks for your reply Peter.

This will be my last email on this thread, otherwise I will almost monopolize it.

I know about Vafa’s swampland idea. As you say, it’s going nowhere. Even though it’s been out for years now, no top theoretical physicist has followed that road. Just him and his team. It doesn’t look promising at all.

On one of the conferences organized to talk about it, I remember Arkani-Hamed said the following:

“QM forces us to split the world into two parts: infinite “observers” and finite “systems”, but… neither Gravity nor Cosmology likes this!!!”

And two minutes later, the following:

“This raises the possibility that we are misinterpreting string landscape-

the different regions aren´t “out there”, but are different approximate “system/observer” splits of a single object”.

I can send you the link of the conference if you want.

So it seems to me that Nima has a hunch that all that swampland and landscape ideas have no traction at all.

I fully agree with what you say that the majority of string theorists now tend to defend point number 3. Actually, the phrase you’ve noted was said by Witten himself. No wonder the rest follows suit.

The most probable future for string theory, IMO, is going to be that it will be studied as a branch in mathematics.

Is it useful? Yes it is.

Can we fully discard it? No ways.

Has it got future? You bet.

But it does not describe Nature. It is not a unique theory of reality, but maybe something deeper -a set of mathematical principles that can be used to relate all physical theories. A new kind of Calculus, if you like.

Finally, when it comes to a possible TOE, that’s where we part our ways.

I don’t believe one exists at all. I think it’s too much to hope for. And if it does exist, I tend to believe that it will always stay out of reach.

DB,

There are lots of problems with solving the problem of string theory by announcing that it is just “mathematics”, beginning with the problem that one doesn’t know what “string theory” actually is. To the extent the words have any meaning, they are as a program to develop a specific sort of fundamental physical theory, not as a specific mathematical construction.

What you quote from Arkani-Hamed seems to me just the kind of off the top of his head speculation about some unknown possible new revolutionary fundamentals of physics replacing quantum mechanics that he likes to indulge in. He and others have gotten pushed into this by the (unacknowledged) failure of their previous research programs. A few years ago, pre-LHC results, in all his talks he put up a slide showing a fork in the road, arguing that in a few years the LHC would tell us whether there was weak-scale new physics providing naturalness or else it was the landscape.

The results are now in: no weak-scale new physics. But instead of now giving talks about how the LHC has proved the landscape picture (which he knows would cause his audience to laugh him out of the lecture hall), instead he is promoting speculation about replacing space, time and QM with something completely different.

Thanks Peter.

To be honest, I never understood Nima’s quote very well…

Hi Peter. I was struck by the starkness of your comment that the idea of there being new forces mixing leptons and quarks is a bad idea. It’s long seemed to me unlikely, purely from a prejudice towards the simplicity of things (and perhaps this is just one more example of a prejudice that might lead a physicist astray), that the number of protons at the beginning of time would be the same very large number that it is now. Are you saying that this is a bad idea? or are there other ways to avoid proton number conservation besides having a mixing of leptons and quarks? (Similarly, where do you stand on Sakharov’s conditions to explain prevalence of matter over antimatter?)

David Hillman,

I don’t see any point to trying to guess based on our prejudices about what the world should be like whether quarks can turn into leptons. Given that we don’t see protons decay quickly, that’s strong evidence that quarks don’t turn into leptons. It makes perfectly good sense to speculate that maybe they do, just at a very low rate, and build experiments underground to look. We did this and found that, at the lowest rate we can probe, doesn’t happen. Quarks turning into leptons is not an idea about mathematics, it’s an idea about physics, a “bad idea” in the sense that all evidence is that it doesn’t work.

I was really trying to make a point about the failure of GUT models. Some people like to point to that failure as a failure driven by mathematics: theorists wrote down a theory based on a large Lie group (SU(5)) that was supposed to be “mathematically beautiful” and that theory failed, so the problem was the use of the Lie group and obsession with mathematical beauty.

But the underlying problem with GUT models is not the mathematics. There are an infinity of different ways you can dress up in mathematical language (eg. an infinite number of choices of groups and representation) a GUT hypothesis which postulates new physics at a new energy scale that allows quarks to turn into leptons. In all of them the “mathematical beauty” of a large symmetry group is cancelled by having to introduce a new complicated and ugly Higgs sector to break the symmetry and explain why we don’t see it. What drove the GUT hypothesis was not mathematics but physics (ask Georgi and Glashow…), and its failure is a failure of a physical idea, not of the idea of pursuing mathematical beauty as inspiration for new ideas about fundamental physics.