Kind of like the last posting, but this time you get two worthwhile items to make up for one that’s not.

- Dan Garisto has a very good article here examining the present state of high energy experimental particle physics and phenomenology. He also summarizes current thoughts about the future. The CERN FCC-ee proposal is still in feasibility study mode, with the big problem its high cost. Numbers like \$15 – \$20 billion have shown up in press reports, and Garisto has “tens of billions”. The feasibility study is supposed to be finished late next year, and presumably a big part of it is people at CERN crunching numbers trying to figure out some plausible way this could work financially.
- There’s a very good article at Quanta about efforts to put together version 3 of the very influential “Kirby List” of open problems in topology. For version 1, see here, version 2 here, and as far as I can tell, version 3 still not finished (but discussed here).
- Brian Keating has a video asking “What would It take for String Theory to move beyond the realm of pure math, Into verifiable territory”? The answer obviously is a conventional substantive scientific prediction of anything. By describing the problem with string theory as being that it is now in “the realm of pure math”, I think Keating is missing the point. The problem with “string theory” is not that it’s pure math, but that it’s not a theory. “String theory” is now a 50 year old set of failed hopes and dreams that a theory might exist, see for instance Theorists Without a Theory. Every so often I try to figure out what people still pursuing this are up to, most recently today taking a quick look at KITP talks by Liam McAllister here and here.
The problem shows up clearly at 10:23 of the first talk where he’s talking about his goal, which gives up on studying all or even representative string theory solutions and tries just to find any “valid solutions”. But what is a “valid solution”?

And by valid solutions, we should say what equations are we trying to solve? And, it’s not the case that we can currently think about finding cosmological solutions of the exact theory in any non-perturbative sense.

McAllister artfully avoids saying what everyone at the talk knows (after all, the talk is part of a program entitled “What is String Theory?”): you can’t look for solutions to the theory because there is no theory. More specifically, no “exact” theory, just a long list of possible theories that one hopes might be in some sense approximations to a real theory. He then goes on to specify the extremely complex approximate theory he wants to work in, chosen by the “look under the lamppost” method as something you could actually imagine calculating. Whenever I look at things of this kind I’m completely mystified why anyone thinks it make sense to embark on insanely complicated calculations like these with essentially zero credible scientific motivation. Somehow though, he has a whole group of people doing this. By the end of the second talk he’s giving his vision of the future, which features an old photo of a room of hundreds of men in suits and ties calculating with pencil, paper and slide rules.

I was mystified twenty years ago why anyone thought this was a good idea, and the whole thing has just gotten stranger and stranger…

The FCC cost estimate numbers I have seen or heard is something like USD 12 billion for the first stage, USD 20 billion for the first & second, and the “tens of billions” that includes the operation cost which is (conservatively) another billion per year. Even if these numbers are somewhat off, I think it’s realistic that in total it’ll be $40 billion at least.

I find it interesting how graphic designers can’t seem to resist the temptation to arrange the standard model particles in some sort of symmetrical configuration even if that doesn’t make any sense. The infographic in the MIT Tech Review article is another example of that. If you Google it, you’ll find many more examples. All with symmetries that have nothing to do with the physics.

Everyone who thinks that SUSY “explains” the Higgs mass misunderstands what it means to “explain” something in scientific terms. The Higgs mass is a free parameter with and without SUSY. It’s about time this naturalness nonsense stops.

@Sabine:

If you want a visualization of the Standard Model particles that makes an attempt to group things according to their actual physical properties, see this one: https://www.quantamagazine.org/a-new-map-of-the-standard-model-of-particle-physics-20201022/

Peter, I assume you’re aware of the recent use of machine learning to estimate physical yukawa couplings in various string compactifications, using simpler ones for which analytical results exist, as a way to benchmark the AI estimates? e.g. https://arxiv.org/abs/2402.01615

Mitchell Porter,

Doesn’t matter how you do these calculations, they’re still meaningless.

Since people are throwing their money at AI, I assume this is both a great way to attract funding, as well as generate papers with minimal effort.

@suomynona sorry I don’t know what you mean, the ones I see on that page make as little sense as all others I have seen

Hi Peter,

Any plans for the eclipse next month? Going to this one won’t involve an exotic trip around the world – although some parts of Ohio may seem like a third world country when traveling from Columbia.

David Yager,

Will definitely go to somewhere on the eclipse track. I’m canceling my class for that day, and a couple days before will head up to Boston first then Burlington area day of eclipse if weather there looks good. Otherwise will head west looking for clearer skies. My 93 year old mother is very enthusiastic about coming along.

@Sabine: Are there any good infographics out there, to your mind? Or is the point that there is no “natural” way of grouping the standard model particles in a visual representation? If that’s the case, then it seems any arbitrary viz would be as good (or bad) as any other… Blindfolded people touching the elephant and all that…

If people are going to discuss this, I’d like to advertise the graphic for SM fermions from my book, see

https://www.math.columbia.edu/~woit/fermions.pdf

Is anybody even still trying to turn the conjectured M-Theory (or its successors) into an actual concrete theory with specific principles & equations?

To use General Relativity as an analogy, if string theorists don’t have the Einstein tensor or Field Equations yet do they at least know that the equation they’re looking for will relate matter & energy distributions to warped space-time geometries? Do they at least know they need a tensor equation, or that it must satisfy the strong equivalence principle?

I ask because it isn’t clear that even the “string” theorists are still working that problem. About the closest thing to it that I’m aware of is that “Swampland” project trying to find non-trivial consistency conditions that all the ‘string vacua’ must honor. Sort of meta-conditions on any such equation and its solution space. But even that effort appears to have produced little of substance, beyond the vaguest possibility that a positive cosmological constant is incompatible with string theory.

@maxstroke I’ve never seen one that made sense. I thought about this a lot for my first book and came up with something that made sense (at least it’s what I thought) but it was so complicated I realized it wouldn’t do any good. I have my own infographic (it’s the one I keep using in my videos) but it’s omitting a lot of information about the gauge groups. Though at least I do have 8 gluons.

Just to give you an idea it was kind of similar to this:

https://static.scientificamerican.com/blogs/cache/file/65C0B45B-606B-44AF-83F80189256EB5D6_source.jpg?w=590&h=800&29A6937B-1463-45E9-823B3D940BC2F532

Kinda messy, but I think it’s actually a pretty good summary of the SM Lagrangian. (Leaving aside that it has only 1 gluon…)

My point is just that humans seem to have a tendency to want things to be nicely symmetric and sorted and fit into easily understandable categories, and the standard model just isn’t to their liking. I understand of course why graphic designers want pretty graphics, but I’m not at all sure that the message these graphics convey is helpful.

Zachary Yezek,

As far as I can tell, no one has ever had a viable idea about M-theory of this kind. In particular, if you look at Witten’s papers from the 90s, this is something he was very much looking for. But at some point he seems to have given up.

One goal of the KITP “What is String Theory?” program seemed to be to attract interest to this problem, but looking at the talks, I see no one even trying to address it.

Twenty years ago I attended a theory summer school where a very personable professor would make remarks such as (while arriving at the solution of a long example on the whiteboard) “and now we’ll do what string theorists have not been able to do for twenty years, we’ll write down the lagrangian”.

I wonder if there has been any progress with that.

tulpoeid,

No.

The thing I like most about the Association for Mathematical Research, the new politically-neutral alternative to the American Mathematical Society, is that it has the most comprehensive list of problem lists I have ever seen:

https://amathr.org/problems/

@Zachary

I don’t follow the research field actively, but given the proximity of the work of my one-time coauthor Urs Schreiber to my own interests in geometry, I watch what he is doing with Hisham Sati. They are slowly chipping away at a very principled approach to finding core principles of M-theory using contemporary mathematical tools and showing how scattered observations derived in special cases are consequences of them. It’s not throwing up ones hands and blaming the swampland, but trying to get to a point of rigorously proving things posited in the 90s (like, for example, Witten’s idea that brane charges are quantised in K-theory) from a central underlying principle.

I’m not sold on string/M-theory as The One True Theory, but from the point of view of mathematical physics it’s much better than all the alternatives I see Peter pointing to. The fact it requires heavy formalism from mathematics developed in the past 20 years and even the past 5-10 years means that I suspect a lot of people in the physics world prefer to stick to claiming an mathematical model of a quantum system on a chip using linear algebra is really telling us about real-world cosmological wormholes, since it’s a lot less effort to understand and explain, especially to the popular press.

David Roberts,

The problem with Sati/Schreiber is that the answer to “what is M-theory” that they are pursuing has no connection to actual physics. The string theorists gathered at the KITP to discuss “what is string theory?” don’t think of what Sati/Schreiber are doing as relevant to the question they are asking. For most physicists, the math apparatus Sati/Schreiber are using is a barrier to them getting interested, but there are physicists (Witten most notably) who can follow this and they show no signs of interest, exactly because there’s no connection to physics.

This kind of thing has always been to me the main problem with string theory, more than the lack of connection to experiment. When string theory research finds a direction that is mathematically fruitful (take mirror symmetry as an example), it is a direction orthogonal to any connection to physics. When string theory research finds a direction that tries to connect to physics (any “string phenomenology”), it is mathematically hideous, orthogonal to interesting mathematics. This has always seemed to me conclusive evidence that whatever “string theory” is, it’s a wrong idea about unification, that a right idea will not be orthogonal to good mathematics.

I can’t get over the picture of hundreds of people in suits and ties in a room calculating with slide rules. I laughed so hard I cried.

@Peter

apologies for the slow reply, but what I posted was in response to the question by Zachary

Regardless if one thinks that M-Theory is even a theory with connection to physics or not, one can attempt to build a more principled theory that is based on some specific principles, as opposed to a bunch of ad-hoc conjectures and suppositions. It is a stretch to my imagination deny that Schreiber and Sati are trying to “turn the conjectured M-Theory into an actual concrete theory with specific principles”. This is their literal stated goal. Whether these principles are physical or not is a separate question. They are certainly building up a mathematical theory and proving it gives rise to effects conjectured in the literature.

I repeat also: I’m not sold on it being a physical theory either (with the caveat that I’m not a physicist), but I certainly admire the intention to sort out the mathematics that lies behind a bunch of things in the M-theory literature.

(All this comes of course with the usual disclosures that I know Urs reasonably well, and I admire the mathematics he works on.)