A paper on Monday: The first paper was posted in the initial second of the day (showing their pride) by a Munich triplet. They develop a machine learning technique to guess correlations in the string landscape and look for viable vacua. With clever techniques, it could even be possible to find the right vacuum in a googol-like set. Anti-string simpletons don't get such things because their extremely modest brains can only understand brute force (which must be done by others because they don't possess it, either).David B. specifically asked me to rewatch this video
especially the part between 20:45 and 48:35 (in the first 20 minutes, both Green and Schwarz mostly review their important work around the 1970s). It is a discussion of selected string theory big shots at the end of "String 2021" which formally took place in Sao Paolo but which followed the format of an "online conference" of the Coronazi era. I don't think that Jair Bolsonaro would agree with this kind of a "conference in Brazil". Participating in the discussion were Gentlemen such as Seiberg, Witten, Green, Schwarz, Strominger, Vafa, Yin, Harlow, Berkovits, Ooguri, and a few more.
Witten started by a current version of his thoughts about the emergent spacetime, emergent quantum mechanics, and "what is string theory" – as he is ready to talk about these things in mid 2021. These comments rather similar to the comments he has said many times in the past and I have agreed with them to a similar extent. But I think that he hasn't really updated his conclusions about (and deep research into) all these deep topics in the light of the newest developments in string theory and adjacent fields – and what became important in them. It is my feeling that he hasn't really thought about these things much in recent years.
Concerning the updates, he said that holography and similar "spacetime developments" has superseded the idea of looking for the best formulation of a theory of everything in the form of an "extension of topological string theory". The latter may be too linked to perturbative string theory, we used to say, and that made it obsolete in the 1990s when strongly coupled string theory started to be understood. But I actually tend to think that this elimination was premature.
Witten seemed worried about a particular technicality, namely the "non-unitarity of world sheet CFTs" in the presence of a time coordinate, if I summarize it by a well-defined specific version of the trait of these theories. This (spacetime) time coordinate existing on the world sheet makes the dimensions "not bounded from below" which makes it possible to create near-zero-dimensional world sheet operators out of \(\exp(i\omega t)\) times an arbitrarily high excitation of the other degrees of freedom. That corresponds to the relevance of operators with arbitrarily many derivatives in the spacetime and that implies nonlocality and – as he slightly carefully says, but he does say it in between the lines – the death of a very general Ansatz for a final theory.
OK, I don't believe that any of these things are a "problem" in the sense of Witten's negatively sounding judgement. Indeed, string theory produces actions that look nonlocal in the spacetime and the existence of the time coordinate is a factor that makes it unavoidable. But as some basic string theory textbooks correctly pointed out, string theory still manages to remain free of ghosts – despite these nonlocal traits that would generically imply ghosts, an infinite increase of the degrees of freedom, and other pathologies in quantum field theories. I think that this is a purely positive news describing some special structure beneath string theory.
When you formulate string theory in the explicit Minkowskian spacetime and you think about the result in the language that tries to mimic quantum field theories, you will see "problems". But they're really problems of your way of thinking about the structure (and the QFT paradigm that you are implicitly using), not disadvantages of string theory itself. Instead, you could choose to think in terms of the Euclidean spacetime. And I think it's right to think about the continuation to the Euclidean spacetime where things simply look less pathological. And in the Euclideanized spacetime, many of the "pathologies" just cannot arise. The real, Minkowski spacetime dynamics is just the Wick continuation of "something more constrained, manifestly less pathological" that you can construct in the Euclidean spacetime. Maybe other signatures are relevant, too.
Daniel Harlow – a young man in front of fake mountains – pointed out that you can be professionally hired in "things like string theory" even though you don't really know string theory, supersymmetry, and other things. Well, he may have been talking about himself, too. I have been warning about these things since 1998 or so – it became increasingly "normal" to do undemanding things and the AdS/CFT correspondence was already misinterpreted as an invitation of "people who have no real clue about string theory" into "string theory".
While the AdS/CFT correspondence is very important and its main father is damn reasonable about all these matters, AdS/CFT just is very far from everything, as Cumrun Vafa was emphasizing. Back in the 1990s, I used to think that Vafa had to have rather different thoughts, more mathematical-physics-like thoughts, about all these matters than I had. After all, he was a big shot in topological string theory that looked (and, to some extent, still looks) rather unphysical to me. But I was completely wrong. My thinking about these matters may be more aligned with Vafa's than with the thinking by any other Gentleman in this conversation.
Aside from more amazing things, the AdS/CFT correspondence became just a recipe for people to do rather uninspiring copies of the same work, in some \(AdS_5/CFT_4\) map, and what they were actually thinking was always a quantum field theory, typically in \(D=4\) (and it was likely to be lower, not higher, if it were a different dimension!) whose final answers admit some interpretation organized as a calculation in \(AdS_5\). But as Vafa correctly emphasized, this is just a tiny portion of the miracle of string/M-theory – and even the whole AdS/CFT correspondence is a tiny fraction of the string dualities.
This superficial approach – in which people reduced their understanding of string theory and its amazing properties to some mundane, constantly repetitive ideas about AdS/CFT, especially those that are just small superconstructions added on top of 4D quantum field theories – got even worse in the recent decade when the "quantum information" began to be treated as a part of "our field". Quantum information is a legitimate set of ideas and laws but I think that in general, this field adds nothing to the fundamental physics so far which would go beyond the basic postulates of quantum mechanics.
"Quantum information" (including "quantum computers", "quantum error correction", and all stuff of this kind) is really just an engineering-like application of the basic postulates of quantum mechanics. It follows from them – plus the application of pure mathematics that is in principle perfectly understood. For this reason, you just can't learn "something new" about the quantum foundations (and even the foundations of quantum gravity) if you start to intensely work on "quantum information". In practice, "quantum information" has only provided us with some toy models that are neither realistic nor terrible deep.
When Cumrun correctly mentioned that the real depth of string theory is really being abandoned, Harlow responded by saying that there were some links of quantum information to AdS/CFT, the latter was a duality, and that was important. But that is a completely idiotic way of thinking, as Vafa politely pointed out, because string theory (and even string duality) is so much more than the AdS/CFT. In fact, even AdS/CFT is much more than the repetitive rituals that most people are doing 99% of their time when they are combining the methods and buzzwords of "AdS/CFT" and "quantum information". Many people are really not getting deeper under the surface; they are remaining on the surface and I would say that they are getting more superficial every day.
There is a sociological problem – coming from the terrifying ideological developments in the whole society – that is responsible for this evolution. I have been saying this for a decade or two as well – and now some key folks at Princeton and elsewhere told me that they agreed. The new generation that entered the field remains on the surface because it really lacks the desire to arrive with new, deep, stunning, revolutionary ideas that will show that everyone else was blind. Instead, the Millennials are a generation that prefers to hide in a herd of stupid sheep and remain at the surface that is increasingly superficial.
A real problem is that folks like Harlow openly talk about "being able to stay in the field while not being interesting in XYZ". This is not how my generation or the older generations thought about it at all. We (or at least the great among us) didn't join theoretical physics because we wanted to have comfortable chairs from which we could easily attack everyone who doesn't parrot insane SWJ-like lies which is what the members of the "Particles for Justice" are doing. We joined the field because we were and we still mostly are passionate about finding the deepest truths about the Universe. This is almost completely lost in the younger generation that sees "being in theoretical physics" as an entitlement, not a result of their deepest dreams that have nothing to do with careers.
So most of the stuff that is done in "quantum information within quantum gravity" is just the work of mediocre people who want to keep their entitlements but who don't really have any more profound ambitions. As the aforementioned anonymous Princeton big shot told me, their standards have simply dropped significantly. The toy models in the "quantum information" only display a very superficial resemblance to the theories describing Nature. That big shot correctly told me that in the early 1980s, Witten was ready to abandon string theory because it had some technical problems with getting chiral fermions and their interactions correctly.
Harlow says that many of the people – who may be speakers at the annual Strings conference and who may call themselves "string theorists" when they are asked – don't really know even the basics of string theory. And they can get away with it. Just like there is the "grade inflation" and the "inflation of degrees", there is "inflation in the usage of the term string theorist". Tons of people are using it who just shouldn't because they are not experts in the field at all. Harlow said that many of those don't understand supersymmetry, string theory etc. but it's worse. I think that many of them don't really understand things like chiral fermions, either. It's implicitly clear from the direction of the "quantum information in quantum gravity" papers and their progress, or the absence of this progress to be more precise. They just don't think it's important to get their models to a level that would be competitive with the previous candidates for a theory of everything – like the perturbative heterotic string theory, M-theory on \(G_2\) manifolds, braneworlds, and a few more. They are OK with writing a toy model having "something that superficially resembles a spacetime" and they want to be satisfied with that forever.
There are lots of questions and possible hypotheses that remain unanswered and that are tremendously exciting. But most of the people who should have a high probability to think about these matters don't think about it at all. They are increasingly repeating buzzwords – and repetitively applying well-known, not very important, methods in contexts that are increasingly similar to the previous ones – and they don't really do better because they are not the people who are passionate in getting the deepest ideas (or who are good at getting them, for that matter).
For example, it is totally possible (my ideas) that the correct interpretation of the "quantum information", starting with the ER/EPR correspondence, is that the topological string/field theory may be extended to contain the full dynamics of string/M-theory that we need to describe everything in the world. Why? Because ER/EPR may map a wormhole configuration into an entangled state of "states of matter" at two places and vice versa. In one of the directions, this map increases the fraction of the quantum information that is stored in the "information about the spacetime topology". It is totally possible that all microstates of matter may be parameterized in purely topological data in an appropriate space that isn't necessarily the same thing as the spacetime. There could be a basis of the black hole microstates (for a finite black hole mass, a finite-dimensional space) in which all the basis vectors describe objects that topologically differ from each other. The real task is either to prove that this picture is incorrect; or to prove that it is correct and then find particular realizations of this Ansatz.
None of these things (and hundreds of other important things) are really taking place, despite those 2500 people who were registered for the online Strings 2021, and it's mainly because an overwhelming majority of the 2500 people aren't really interested in deep questions, the most accurate statements and the most universally valid ideas, in the ideas that really encapsulate everything that has been learned. They are OK with "remaining a part of a comfortable enough herd of sheep" that uses fancy names for itself that it shouldn't be using.
I think that this general negative development must be seen by many others who no longer belong to the youngest generation (although I do remember some of them when they belonged there LOL). So Shiraz Minwalla was answering a question of Daniel Harlow's. Shiraz's answer was that some question about M2-branes and M5-branes was basically answered by the uniqueness of string theory. This important concept, the uniqueness of string theory, is the kind of thing that the likes of Harlow simply don't get. They are not even interested. You could have seen the intrinsically unscientific thinking of Harlow's at another place. He said that in AdS/CFT, there are qualitatively different CFTs for every AdS background of string theory or quantum gravity. Those "used to be" thought to be different solutions in the same theory and "this AdS/CFT work" therefore makes this picture of a unified theory with many solutions obsolete or incorrect or politically incorrect or whatever his adjective is exactly supposed to be – it is surely an adjective that means that "he won't do research on that".
Well, the problem with this thinking is that it is completely wrong and idiotic. Those vacua are still demonstrably related by dualities and they demonstrably are solutions to the same theory. The AdS/CFT description obscures this unity but it doesn't make the unity go away because there are other ways to see that the unity exists. But the likes of Harlow don't want to see any other ideas that give them "inconvenient" truths such as the truth that string theory unifies all the vacua. They don't really have the passion for the truth and they choose the "convenient lies" that allow them to call themselves string theorists, although they are not, and to terrrorize all sane people with their radical and criminally dishonest SJW organizations.
So sorry, Mr Harlow, but if you hide your head into the sand because you find the unity of the string theory vacua inconvenient for an easy job which is really why you arrived, that says something bad about you, not about string theory. If your whole herd adopts this strategy which really denies the important truth by spinning some superficial, distorted, and narrow-minded parts of the research, it only shows that the herd itself sucks. You may find it enough but it is enough for the actual science and actual scientists – and for the people who have some value. String theory does unify all the consistent quantum gravitational vacua and with a couple of extra conditions added (e.g. a 11D flat vacuum), it produces unique theories. That is the truth and you can't turn it into a non-truth just by joining a herd of dishonest sheep that decided to "research" only things that confirm your convenient lies.
I don't plan to proofread this text because the benefits would seem to exceed the costs.