Two recent interviews with founders of string theory are out there. A recent CERN Courier published Matthew Chalmers' interview with the founder number zero, Gabriele Veneziano:
In Veneziano's presentation, it was all very systematic. The strong force was seen, its precise theory wasn't known, but some properties seemed experimentally known as well and researchers employed some reverse engineering. From that proper historical perspective, it isn't even true that string theory was discovered by an accident. They systematically looked at many properties of the strong force and the existence of the string-like fluxtubes is simply a fact. That's why they investigated a possible string-like description of the nuclear effects, amplitudes with lots of resonances, and why they had to try the amplitudes and Lagrangians describing the string itself.
In that enterprise, the Veneziano amplitude had to be found at some moment. At a later moment, the connection to the string had to be found. And when one analyzes perturbative string theory, they couldn't avoid gravity and general relativity, of course.
In the interview, Veneziano also mentions his pre-big-bang string cosmology – which is far from the stringy picture of cosmology as believed by a majority of string theorists. He says that young people should study more ambitious questions and the huge hierarchy between the short Planck scale and the long Hubble scale is the greatest challenge.
Veneziano also reiterates the point that all the claims that string theory is untestable or unfalsifiable are just completely wrong. The difference between the 1960s and the present is that we don't have any major experimental anomaly, a crisis that requires some explanation.
Meanwhile, two days ago, Craig Cannon interviewed Leonard Susskind:
The transcript of this 66-minute interview is available at the Ycombinator server.
Leonard Susskind, an ex-plumber who noticed – along with Nielsen and perhaps Nambu – that strings could produce the Veneziano amplitude starts with saying that he is not a contrarian at all and the claims to the contrary are a misconception.
I find these claims by Susskind about his being the "most mainstream physicist in the world" rather implausible. His very work on the Veneziano-like business placed him somewhat out of the mainstream in the early 1970s. But I think that Susskind's contribution was less systematic than e.g. Veneziano's at that time. It turned out to be correct and important – strings were behind formulae with these nice properties.
And indeed, string theory has grown to a super-mainstream framework, although it's questionable whether we should still say it is true in the environment flooded with assorted postmodern crackpots and non-physicists pretending to be physicists. But string theory's later mainstream status says very little about Susskind's alleged contrarian traits. Those should be judged according to the apparent "normality" and reception of the ideas at the very moment when they were presented, not in the subsequent 50 years, right? The interviewer understands this point well, Susskind doesn't. The holographic principle by Susskind and 't Hooft was also far from mainstream when published (and in fact, 't Hooft's thinking about the holographic principle remained extremely out-of-mainstream if not away-from-experts even by now, 2018). It did gain power in the next two decades but because of the chronology, that outcome cannot be used to quantify Susskind's contrarian traits.
Susskind has done lots of things that are quickly seen to be right and that work – that could be said to be mainstream – after a shorter or longer delay. But you know, he has also written an extremely above-the-average number of speculative paper and even an unusually high number of super speculative papers that are not just wrong but stupidly so. Hundreds of TRF blog posts contain Susskind's name – it's not shocking given his status as a physics titan, and my natural top 5 role model at some important times.
But those texts may remind you of some weirder and weird papers by Susskind. Just to be sure, the BFSS Matrix Model is a mainstream thing – but because it doesn't encourage people to reuse their 4D QFT toolkit all the time, it's unfortunately less mainstream than the AdS/CFT. ER-EPR is also mainstream, a new duality relevant for quantum gravity, but I grew almost certain that Juan Maldacena gave it all the things that work and Lenny Susskind mainly gave it the tendency to expand in provocative directions. Maybe such an inspiring idea was needed at the beginning as well but Juan was essential to turn it into a paper that makes sense (almost the same is true in the case of the holographic principle).
Some subsequent, ER-EPR-related papers by Susskind only are unequivalent to the propositions of the first ER-EPR correspondence paper and they promote crazy concepts such as the anti-quantum zeal, AQZs' nonlocality claims, classical simulations instead of the genuine quantum mechanical theory, and wrong things that are in no way related to the ER-EPR correspondence itself because they're just efforts to abuse the ER-EPR context to promote some standard misconceptions about quantum mechanics.
A similarly crazy was a Bousso-Susskind "hypermultiverse" paper promoting the many worlds interpretation of quantum mechanics along with some parallel worlds in cosmology and – insanely – claiming that those were the same thing. On its title page, that paper had famous enough authors who had been known for some very serious work but this classification notwithstanding, it was a full-blown crackpot paper.
Most recently, Susskind is being associated with the complexity in cosmology and quantum gravity – click to read the newest Quanta Magazine article about it. That's provocative and numerous people have joined this fad, numerous papers have acquired 100-200 citations but the Quanta Magazine rightfully quotes Aron Wall (Stanford, moving to Cambridge) who says that it's very speculative and may be wrong. I am convinced that most physicists from such elite productive corners would agree with Aron Wall. Complexity surely isn't mainstream within theoretical high-energy physics.
A spatial volume found inside the black hole is claimed to be "equal" to the computational complexity and those people seem excited because it's a more "algorithmic" cousin of the second law of thermodynamics – some complexity "grows" which they believe to be "good". But what complexity? In which programming language? What is the numerical coefficient? Which precise surface? And why should the law take one form or another? Susskind et al. don't even seem to ask these questions – and especially the "why" questions which is what I find very annoying and I am convinced that my view is the majority view among the professionals.
If there is a link between spatial volumes inside black holes (or even cosmology) and some computational complexity, it must be a "derived law" that is waiting for a clarification or a proof. They don't even seem to accept this statement and deal with the "computational complexity" as if it were an elementary concept in theoretical physics – which it simply isn't. And people in this complexity realm also add lots of things that look like pure hype – e.g. that the expansion of the Universe is due to some growing complexity. Well, given the identification of complexity and volumes, this statement would be self-evident. What is unclear is any added value, any evidence for that statement, or any useful implications. It sounds like pure hype that just "sounds" interesting.
Susskind continued to be extremely productive, even in very recent years. But much of this production is an industry of provocations. Especially in these recent papers where he combines many worlds, simulations of quantum mechanics, computational complexity, and lots of other things, it seems clear that his "comparative advantage" is that without too much evidence, he is not afraid of combining lots of somewhat random things that other physicists wouldn't combine so casually. And Susskind also says lots of big things that seem completely unbacked and that even seem easy to disprove, e.g. that "gravity and quantum mechanics are the same thing and make each other unavoidable. For this reason, I think that Susskind is a classic example of a contrarian – who enjoys saying provocative things for the provocation's sake. That doesn't mean that his papers end up being as overwhelmingly wrong as e.g. Lee Smolin's. But Lee Smolin isn't a contrarian, he is just a hopeless crank. That's a different level.
An incredibly strong extra piece of evidence to debunk Susskind's claims that "he is not a contrarian" is his bizarre monologue about the validity of string theory. He says that it is a consistent theory of quantum mechanics and gravity and a valuable playground to test ideas. But it doesn't describe "particles" or "the real world" – string theory needs to be modified or deformed to describe the real Universe. WTF? Would you please provide us with a paper to support your extraordinary statements? How can string theory fail to describe "particles"? They're there – e.g. perturbatively, they are the eigenstates of vibrating string, right?
A very important, more or less established property of string theory is that it cannot be deformed. Every truly "mainstream" string theorist who has gone through the material that is believed to be standard and important knows it (it's included in the first chapters of some rudimentary textbooks) – and can reconstruct a partial proof of a sort to show that the non-deformability isn't just some faith. Perhaps one may ignore some knowledge or lore – but that's surely only how contrarians approach it. The statement that the real world theory should be just "inspired by the mathematically precise" theory known as string theory, but that theory needs to be "deformed", seems like a crazy statement not backed by any persuasive scientific work. Susskind starts by describing that statement as "his guess" but a few sentences later, he even says that "we know it". Sorry, we surely don't.
The interview continues with an enjoyable but mixed baggage of comments about GUT, cosmological constant, holography, simulations, Feynman (I agree with Susskind that Feynman was actually a deep philosopher and a deep mathematician – he just hated the formal crap and unnecessary complexity in the presentation that is spread in both of these disciplines), the bomb (Susskind says that physicists should naturally try to discover everything and politicians – someone else – should regulate them if there are immoral or dangerous implications), quantum computers (Susskind says that they may be built but have no applications – which just shows that he isn't an expert), teaching (to teach is a great way to learn; Susskind believes that if he could go back in time and teach something to his father, the father would stop being a crackpot – because of some experience, I greatly doubt it, I even greatly doubt that Lenny would be listened to at all), and many other things. It's all very interesting but it's also a mixture of scientific results, scientific beliefs that are supported by some good reasons, beliefs that aren't supported by good reasons, and some plain incorrect assertions.
Susskind is and has been a brilliant and prolific fountain of ideas but physics has absolutely depended on the existence of other people who can deal with the "half-baked stuff" coming out of Susskind's mind and turn it into physical insights that make sense.