Graham Farmelo has posted a very interesting interview he did with Witten last year, as part of his promotion of his forthcoming book The Universe Speaks in Numbers.
One surprising thing I learned from the interview is that Witten learned Calculus when he was 11 (this would have been 1962). He quite liked that, but then lost interest in math for many years, since no one gave him more advanced material to study. After years of studying non math/physics subjects and doing things like working on the 1972 McGovern campaign, he finally realized physics and math were where his talents lay. He ended up doing a Ph.D. at Princeton with David Gross, starting work with him just months after the huge breakthrough of asymptotic freedom, which put in place the final main piece of the Standard Model.
If only back in 1962 someone had told Witten about linear algebra and quantum mechanics, the entire history of the subject could have been quite different. It seems quite possible that within 5 years he would have picked up quantum field theory and maybe started thinking about Yang-Mills generalizations of QED, perhaps, at 16, beating Weinberg and Salam to the electroweak theory. Surely he could have figured out how to do one loop calculations in gauge theory, beating Gross/Wilczek/Politzer to asymptotic freedom and a Nobel prize, possibly a few years early. If he had done this at Princeton, he would have overlapped with John Schwarz, who surely would have then been more interested in pursuing gauge theory than string theory. So, no superstring theory or 1984 “revolution”, and who knows what different sort of path the history of the field would have taken.
A lesson for all parents: if your child is an off-the-scale genius, learning Calculus at age 11, don’t even think about trying to give them a normal childhood. Push them, hard, to skip grades, get to college/grad school early. Do whatever it takes.
I did though find some of the later parts of the interview quite depressing. While acknowledging that neither he nor anyone else has been able to figure out what string theory actually is, this hasn’t shaken Witten’s faith that it’s the only viable path towards a unified theory. Most disturbing, on the topic of the landscape he says that he has gone from finding it upsetting to reconciling himself to the idea. For years, whenever asked about how evidence could be found for string theory, he would point to the naturalness arguments indicating that something like SUSY had to happen at the electroweak scale. Now that the LHC has falsified this and there’s nothing to point to as any sort of “test of string theory”, he shows no signs that this falsification has in any way shaken his faith.
Looking to the near future, he’s most optimistic about the “It from Qubit” business. Maybe he’s right and something will come of this, but I’ve seen no indication of a path to a unified theory in this direction (how do you get the Standard Model? Or has he just completely given up on that?).
I don’t have time right now to transcribe the most relevant portions of the interview, might find time later, or maybe Farmelo will make available a transcription.
Update: As explained in the comments, the advice to parents was not meant to be taken seriously. No, your child is not going to grow up to be Edward Witten, and they do not need to hurry up to revolutionize physics before it is too late.
Sabine Hossenfelder had posted a transcript of the interview here. I’ll add some extracts and some more comments about the interview.
About the landscape:
These two puzzles although primarily the one about gravity which was discovered first are perhaps the main motivation for discussions of a cosmic landscape of vacua. Which is an idea that used to make me extremely uncomfortable and unhappy. I guess because of the challenge it poses to trying to understand the universe and the possibly unfortunate implications for our distant descendants tens of billions of years from now. I guess I ultimately made my peace with it recognizing that the universe hadn’t been created for our convenience.
GF [00:20:43] So you come to terms with it.
EW [00:20:45] I’ve come to terms with the landscape idea and the sense of not being upset about it. As I was for many years.
GF [00:20:49] Really upset?
EW [00:20:50] I still would prefer to have a different explanation but it doesn’t upset me personally to the extent it used to.
GF [00:20:56] So just to conclude what would you say the principal challenge is all down to people looking at fundamental physics.
EW [00:21:01] I think it’s quite possible that new observations either in astronomy or accelerators will turn up new and more down to earth challenges. But with what we have now and also with my own personal inclinations it’s hard to avoid answering new terms of cosmic challenges. I actually believe that string slash M theory is on the right track toward a more deeper explanation. But at a very fundamental level it’s not well understood. And I’m not even confident that we have a good concept of what sort of thing is missing or where to find it.
If you theory is not well understood, you don’t even know what sort of thing is missing, and a multiverse is being invoked to explain away why it can’t be tested, the situation seems clear: you have a failed theory. Yes, failure may be personally upsetting to you, but, that’s science.
GF [00:23:20] There’s a famous book about night thoughts of a quantum physics. are there night thoughts of a string theorists is where you have a wonderful theory list developing you know unable to test it. Does that ever bother you.
EW [00:23:31] Of course it bothers us but we have to live with our existential condition. But let’s backtrack 34 years. So in the early 80s there were a lot of hints that something important was happening in string theory but once Green and Schwarz discovered the anomaly cancellation and it became possible to make models of elementary particle physics unified with gravity. From then I thought the direction was clear. But some senior physicists rejected it completely on the grounds that it would supposedly be untestable. Or even have cracked it would be too hard to understand. My view at the time was that when we reached the energies of the W, Z and the Higgs particle we’d get all kinds of fantastic new clues.
EW [00:24:11] So. I found it very very surprising that any colleagues would be so convinced that you wouldn’t be able to get important clues that would shed light on the validity of a fundamental new theory that might in fact be valid. Now if you analyze that 34 years later I’m tempted to say we were both a little bit wrong. So the scale of clues that I thought would materialize from accelerators has not come. In fact the most important clue possibly is that we’ve confirmed the standard model without getting what we fully expected would come with him. And as I told you earlier that might be a clue concerning the landscape. I think the flaw in the thinking of the critics though is that while it’s a shame that the period of incredible turmoil and constant experiment and discovery that existed until roughly when I started graduate school hasn’t continued. I think that the progress which has been made in physics since 1984 is much greater than it would have been if the naysayers had been heeded and string theory hadn’t been done in that period.
“34 years later I’m tempted to say we were both a little bit wrong”??? No, others had good arguments and were right about this (string theory is untestable and has nothing to do with LHC-scale physics), and you had bad arguments and were quite wrong. That this clear result is not being acknowledged and is having no effect on faith in string theory is disturbing.
Update: For another interview with an influential theorist, Sean Carroll has an interview with Leonard Susskind. I don’t think this is a good thing, but Susskind has been very influential in blazing the path that Witten now seems headed down (invoke the multiverse to justify giving up on unifying particle physics, hope very general “it from qubit” considerations will explain gravity). The interview explains in detail Susskind’s point of view.
Update: Farmelo has another interview with a string theorist up, this time it’s Michael Green. When asked if he’s troubled by string theory not being experimentally testable, Green says (19:20):
I don’t think at the moment there’s anything directly to test, because we don’t know what its predictions are.
and says that string theory should really be called “string (not yet a) theory”. Earlier (16:40), he explains
The ingredients of something are there, but it’s clearly not formulated in the right language, and because it’s not formulated in the right language, we don’t really know how to even make sense of its predictions. It doesn’t have any really genuine rigorously derived predictions yet.
Green has been working on string theory for forty years, an entire professional lifetime during which string theory has gone from a relatively simple “(not yet a) theory”, with a true theory seeming not far away, to a much more complicated “(not yet a) theory”, with no progress towards an actual theory in sight. Farmelo doesn’t ask the obvious question of why people shouldn’t interpret this story straightforwardly as the story of a failed speculative idea that never worked out.