For much of the past week, I’ve been attending off and on (on Zoom) the Strings 2023 conference. This year it’s in a hybrid format, with 200 participants in person at the Perimeter Institute, and another 1200 or so on Zoom. These yearly conferences give a good idea of what some of the most influential string theorists think is currently important, and I’ve been writing about them for twenty years. Videos of the talks are being posted here.

As in many of these Strings conferences in recent years, there was very little discussion of strings at Strings 2023. Of the 24 standard research talks, only 4 appeared to have anything to do with strings. A new innovation this year was to schedule in addition four “challenge talks”, conceived of as talks explicitly about material outside of string theory that might interest string theorists. In particular Edward Frenkel gave a nice survey of a wide range of ideas from quantum integrable systems and ending up with geometric Langlands. He motivated this with reference to what Feynman was working on very late in life and the problem of solving QCD. His slides are here, video here.

In addition there were four morning “Discussion Sessions”, which I attended most of, and at which string theory put in little to no appearance. Today’s discussion featured Nati Seiberg and Anton Kapustin and was about lattice versions of QFT, especially in their topological and geometrical aspects, a very non-stringy topic dear to my heart. Yesterday was It From Qubit, which had Geoff Penington discussing topics related to black holes. The conventional wisdom now seems to be that the information paradox is gone, solved semi-classically, so giving no insight into true quantum gravity dynamics. While this means you can’t see anything interesting at large distances from the black hole, Penington had some new ideas about something that might in principle be observable at atomic-scale distances from a super-massive black hole. Maldacena started off the session with slides promoting the way forward as quantum computer simulations involving 7000 qubits, a variant on the wormhole publicity stunt. The only time string theory made an appearance was in a suggestion by Dan Harlow that perhaps by doing quantum computer simulations theorists could solve the the problem of what “string theory” really is. It’s pretty clear what the leading direction is now for continuing the long tradition in string theory of outrageous hype.

After this week, I’m even more mystified about why the conference was called “Strings 2023” And how does one decide these days what “string theory” is and who is a “string theorist”? Oddly, two of the things that now distinguish this yearly conference from others are a pretty rigid exclusion of both real world physics (Frenkel comments on this here) as well as of what got people excited about string theory, superstring unification and its implications for seeing low energy SUSY at colliders. People still interested in that have split off to other conferences, especially String Phenomenology 2023 and SUSY 2023.

Those conference have their own kinds of mysteries (why do people keep working on ideas that failed long ago?). In particular, the closing talk on the Status and Future of Supersymmetry at SUSY 2023 was all about the great prospects for SUSY at the LHC, and included a Conclusion written (no joke) by ChatGPT:

The future of supersymmetry as a research program holds both exciting challenges and potential breakthroughs. While the LHC experiments have yet to observe direct evidence of supersymmetric particles, ongoing theoretical advancements and reﬁned experimental techniques oﬀer renewed hope. The future of supersymmetry research lies in two key directions. Firstly, novel theoretical models are being explored, including new variants of supersymmetry that incorporate dark matter candidates or non-linear realizations. These approaches push the boundaries of our understanding and allow for further exploration of the particle zoo. Secondly, upcoming experiments, such as the High-Luminosity LHC and future colliders, aim to explore higher energy scales and increase the sensitivity to supersymmetric signals. With these advancements, the quest for supersymmetry will continue to shape the ﬁeld of particle physics, inspiring new theoretical insights and propelling experimental discoveries.

Things just get stranger and stranger…

**Update**: Speaking of stranger and stranger, you can listen here to Sean Carroll talking by himself for four hours and twenty-two minutes about why there really is no crisis in physics, the whole supersymmetry/string theory thing is going just fine.

**Update**: I hadn’t realized just how accurate Joe Conlon’s description of the conference as “IAS-centric” was. For the four discussion sections, no IAS in one of them (“strings, QFT and mathematics”, the other 3 sessions were all IAS (two IAS faculty, the rest an assortment of ex or current members).

ChatGPT requires very large volumes of text of a given type to train well for it. It’s not too surprising that it can write good string theory hype.

Maybe they will rebrand themselves to X-theory

As a (serious) string theorist I must fully agree on this post.

Interestingly in the past there were a vision and summary talk in particular saying

how well and prosper string theory is doing. It seems that all this enthusiasm is gone: no vision anymore, nothing to conclude.

Nanopolous gave a plenary talk about this

https://arxiv.org/abs/2303.04814

Very nice and interesting. An experimental detection proposal for something predicted by both the standard model of particle physics and cosmology, about which string theory says nothing.

There’s a comment from Joe Conlon here that is interesting

https://twitter.com/JosephPConlon/status/1685222041249587200

His diagnosis is that this series of conferences is “IAS-centric”, features mainly discussion of topics of interest to the Princeton IAS faculty.

Looking at the backgrounds of the speakers, I think Harvard plays as big a role as the IAS, so this should be “Harvard and IAS-centric”, with most speakers having a student/postdoc/faculty background at Harvard and/or Princeton.

F.T.,

Yes, one change in this latest version is elimination of the “vision talk” category. This is turning into a subject with no plausible vision of a way forward.

Sabine Hossenfelder,

There is already “M-theory”, where the “M” could stand for “Mystery”, “Magic”, or “Mediocre”. About as apt of a name as any for the current state of string theory.

Kurt Schmidt,

The problem is “M-theory” refers to a certain sort of unified theory, one that appears even less at Strings 2023 than “string theory”.

A correct name would be something like “topics that people at Harvard and Princeton who used to work on string theory are working on this year instead, since the string theory stuff didn’t pan out.”

Sabine Hossenfelder,

The pun inside the joke is extremely clever. I missed it the first time. Bravo.

I read the entire transcript of the of whole Sean Carroll thingie. I can’t imagine the boredom one must endure to listen to the whole of it.

The most striking thing about it is the lack of phenomenological calculations or even phenomenological suggestions about what dark matter is (concrete suggestions of a rest mass, not just “axions would be really light”).

It also over-attacks MOND by not seriously treating more recent theories than straight original TeVeS.

Other than that, it would actually be convincing. That’s why most pros are seriously completely convinced.

“… the information paradox is gone, solved semi-classically”: ? Can we please learn more about this?

From Frenkel’s tweets: “… never lost sight of the big prize: understanding the physics of THIS Universe. And I think that’s still a good guiding principle for today’s physicists.” Just stating the obvious, but to me this is one of the most concise meta-comments on the state of the field ever written: in 2023 prominent theorists have to timidly suggest that the definition of physics might be a good guiding principle for physics.

Of course “a pretty rigid exclusion of real world physics” does seem to be the defining feature of the field. Even more, it’s a lifestyle. If one appeared at a similar setting talking of real world connections, one would appear like the backwards relative visiting from the countryside.

tulpoeid,

This has gotten a huge amount of attention at Quanta and elsewhere, see for example

https://www.quantamagazine.org/the-most-famous-paradox-in-physics-nears-its-end-20201029/

https://www.quantamagazine.org/netta-engelhardt-has-escaped-hawkings-black-hole-paradox-20210823/

also

https://iopscience.iop.org/journal/0264-9381/page/Focus-Issue-on-Reproducing-the-Page-Curve-in-Black-Hole-Evaporation

I don’t think the problem with the current state of “string theory” is lack of connection to real world physics. The huge criticism of “string theorists” of this kind is what is causing them to head in absurd “quantum gravity in the lab” directions. There is no way to solve their problems by just redirecting them to the real world. I’ve gone on endlessly here and elsewhere about what those problems are (e.g., not actually having a theory…), it’s a complex topic, not reducible to sound bites.

tulpoeid,

Quanta today has a new article about exactly this:

https://www.quantamagazine.org/new-calculations-show-how-to-escape-hawkings-black-hole-paradox-20230802/

What I’d be curious to see is a story about the implications of this. The main reason much of the “string theory community” abandoned everything else to become focused on toy models of the information paradox was the hope that solving this paradox would tell us something about the nature of quantum gravity. Instead, the solution they found says that solving the paradox can be done within the semi-classical framework, so you learn nothing new about quantum gravity this way. Given that, what do you do now? If your answer is to keep working on the details of the toy models (lots of work to be done!!), why are you doing this?

*Supposing* Harlow et al. are right with their non-isometric codes account of the black hole information paradox (the subject of the new Quanta article), I’d say that you unequivocally DO learn something new about quantum gravity. Namely, you learn that a key to QG is that there’s a “fundamental Hilbert space” that perfectly obeys QM, but that our (3+1)-dimensional experience is described by an “effective Hilbert space” that has an apparently much larger number of qubits, but in which most of the “exponentially complex” quantum states don’t actually exist. And you learn that the way this gets implemented is via a linear map between the fundamental and effective Hilbert spaces, which acts like an isometry (or nearly one) on all “low-complexity” effective states, with the illusion breaking down only for “high-complexity” states like those that arise in the firewall paradox, or in decoding the Hawking radiation from an old black hole.

There’s still the obvious difficulty, that as far as known, the only way to test these ideas experimentally might involve waiting ~exp(10^67) years and THEN jumping into a black hole — and having learned the answer, you couldn’t tell anyone outside the black hole! But I don’t think one can argue that there’s not a new proposal here about quantum gravity to chew on.

Scott Aaronson,

Thanks for the explanation. From what I can tell, if the proposal right, the information paradox gets resolved generically in the class of theories people are considering (some day I’d like to see a precise definition of that class, but it looks like whatever it is, it’s very large). How this happens is perfectly interesting, but if it doesn’t help pin down a more specific theory, isn’t this approach to quantum gravity just more definitively lost in an infinite landscape of theories with no way forward?

Yeah, you could imagine a huge space of possible theories implementing these ideas, just like a huge space of theories all implement the ideas of QM or SR. That’s a bug insofar as none of this seems to helps you pin down (e.g.) the specific particle content of our universe, but also a feature insofar as it doesn’t stand or fall with the fortunes of a particular proposal like string theory.

Simple question: do the new understanding mean that a black hole made of 10^10 kg of hydrogen emits this energy in photons (and other light particles)?

Alessandro Strumia:

I don’t think anybody has questioned that black holes emit most of their energy in photons since Hawking discovered Hawking radiation. The new understanding does nothing to change this.