The story of string theory as a theory of everything has settled into a rather bizarre steady-state, with these three recent links providing a look at where we are now:
- At his podcast site, Sean Carroll has an interview with string theorist Clifford Johnson. It’s accurately entitled What’s So Great About Superstring Theory, since it’s an hour of unrelenting propaganda about the glories of string theory, save for a short mention that there had been some criticism from (unnamed) sources a decade or so ago.
The truly odd thing about the discussion though was the way it seemed frozen in time back in 1998 just after the advent of AdS/CFT duality, with almost no discussion of developments of the last twenty years. Nothing about the string theory landscape and the controversy over it, nothing about the negative SUSY results from the LHC. The attitude of Carroll and Johnson towards the failure of string theory unification seems to be to simply refuse to talk about it, and try to keep alive the glory days just after the publication of The Elegant Universe. They’ve taken to heart the post-fact environment we now live in, one where if you keep insisting something is true (string theory unification is a great idea) despite all evidence, then for all practical purposes it is true. Johnson has famously admitted that he refuses to read my book or Lee Smolin’s. As far as he’s concerned our arguments do not exist, and Carroll goes along with this by not even mentioning them.
- For the latest on the Swampland (for background, see here), there’s String Theorists’ Heads Bobble Over Potential Dark Energy Wobble, where we’re told that string theorists are claiming “huge excitement” over the possibility that string theory might make a “prediction” about dark energy. Over the years there have been endless claims about “predictions” of string theory, none of which have ever turned out to actually exist, and this is just one more in that long line. The rather odd aspect of this latest prediction is indicated by how it is described in the last paragraph of the article:
The real excitement comes from how soon we might know whether Vafa’s work has produced a testable prediction of string theory—which would be a first. Experiments like the Dark Energy Survey or the upcoming WFIRST telescope could possibly detect whether dark energy is constant or changing over time, and could perhaps do so within the next few years.
Reading this, one gets the impression that we’ll know what string theory “predicts” about dark energy just when there’s a measurement. This actually does describe what’s going on here: for some, string theory is a theory of everything as a matter of faith, so to them any new measurement tells us more about string theory, in particular that string theory “predicts” that measurement.
- Finally, there’s an article out by Thomas Hertog, which contains more about his work with Hawking that was widely advertised after Hawking’s death (see here). Hertog claims another sort of “prediction” of string theory:
String theory predicts that our universe is fundamentally a hologram that reveals itself only in the most extreme conditions, such as those at the Big Bang.
For the implications of this prediction, see String Theory Summarized.
I heard about Vafa’s “prediction” from another article(https://www.sciencedaily.com/releases/2018/10/181009102431.htm) the other day, where the impression I received was that if Vafa was correct then String Theory was essentially being ruled out based on current observations of dark energy: “String theory is said to be fundamentally incompatible with our current understanding of “dark energy” — but only with “dark energy” can we explain the accelerated expansion of our current universe”. So the “excitement” seemed to arise just from the fact that a testable prediction was finally at hand!
My questions are does this prediction really count against String theory based on our current understanding of dark energy? And if not, or if more observations are needed to test the prediction, what are those observations, and when might they be made?
“Science advances one funeral at a time.” This century-old meme is no longer relevant, methinks. I believe it was Sabine who pointed out that the easiest way for a financially strapped department to give itself some cachet is to hire a string theorist. It’s self-perpetuating. It’s alive. It is not enough that it fail; something else must succeed.
Paul in Tacoma,
I’ve added an answer to this as an FAQ, see
If you really want to know what’s behind the misleading hype, see the more recent postings in this category
Hiring a string theorist is no longer an obvious move for a physics department trying to get some cachet and show it is on the leading edge. Most physicists, grant officers and university officers have by now noticed that string theory has been promising breakthroughs for over thirty years, but nothing much has come of it, and skepticism is now widespread. It’s exactly because of this worsening environment for string theory hires that those invested in it are involved in publicity efforts to try and prop it up.
Unfortunately I think you’re right though that the fad won’t just die off naturally, absent something else that comes along to replace it. It has become oddly institutionalized, with a large and powerful group of “string theorists” of a wide variety of ages, most of whom have stopped working on string theory, but still retain “string theory” as a tribal affiliation.
Paul in Tacoma,
My best attempt to understand that sciencedaily article…
Vafa group says assumptions that lead to Landscape are incompatible with constant dark energy because of other assumptions. Prediction: other assumptions are correct and thus Landscape/Multiverse assumptions are incorrect. Vindicates: A future “String Theory” that no one knows how to write down minus the Landscape/Multiverse ie., the hope that someone will find a pearl in the Swampland.
Stanford group says assumptions that lead to Landscape are correct and Swampland are incorrect, but hedging bets by saying dark energy might not be constant. Prediction: that dark energy will be constant and Swampland assumptions incorrect OR dark energy is inconstant and while Swampland assumptions are incorrect, they are based on other faulty assumptions ie, constancy of dark energy. Vindication: Anthropic Landscape with no need for finding a future “String Theory” cuz why bother since the multiverse did it.
Own prediction: no matter what happens experimentally neither side will rule out “String Theory” and claim vindication in some way meanwhile the rest of physics will move on ignoring them.
Thanks for the references.
I think it’s different to say ‘we can’t predict anything because we don’t have a paradigm’ than to say ‘we can’t predict anything because we have a paradigm and that’s what it predicts’.
You seem to be often scandalized that person X calls oneself a “string theorists” while not working on “string theory”. First, who defines what string theory is? Second, who cares? The kind of research discussed at Strings conferences is not discussed at any other major series of conferences. So that series of conferences serves its intellectual purpose. And much of it is valid and great research by any measure (e.g. work on strongly coupled QFT).
Feynman said it clearly 30 years ago: “String theorists don’t make predictions, they make excuses .” Sometimes the excuse is “we don’t understand the theory well enough”, sometimes it’s “we understand the theory and it is of a nature that makes no testable predictions”. These are really all the same thing though, excuses for a failed idea about fundamental physics.
I don’t think “string theorists” calling themselves whatever they want is scandalous, what’s scandalous is misleading the public about “string theory”, the way Carroll and Johnson are doing.
I do think though that people interested in solving problems of strongly coupled QFTs are making a big mistake by deciding to adopt an inappropriate name for themselves and what they’re doing. Why organize yourself in a tribal manner, branded with the name of a failed idea, and end up getting associated with very prominent ridiculous pseudoscience like the Landscape? Why not disown the failed ideas? In particular, why not change the name of your yearly conference?
It’s because what you brand as “failed idea” has not failed. It’s an existence proof that the problem of quantum gravity has a weakly coupled solution. Even if we don’t know yet which solution was chosen by Nature, an existence proof is better than nothing. Some discussed ideas may have some questionable parts here and there, and you choose to emphasize them as a sign that the whole field is rotten. That’s wrong – the bulk of string theory is here to stay. It’s based on actual correct and highly nontrivial calculations, related to properties of 2d CFTs and to moduli spaces of (super)Riemann surfaces. When I do strongly coupled QFT I use the results about CFTs obtained by string theorists. If they invite me to their conference, which they decide, for sentimental historical reasons or whatever, to call “Strings”, I go. I love to speak to the audience of people whom I respect intellectually, and this is the case for that crowd. There are other conferences out there with sentimental historical names, who cares. You call this tribal as a pejorative, but there is also a good sense of tribalness. There is simply no other community devoted to think hard and steady about tough nonperturbative QFT questions, and having necessary mathematical background for that.
Sorry, string theory as an idea about unification has failed, conclusively. Those who promote it to the public without acknowledging that “the stuff we told you about all particles and forces being vibrations of strings doesn’t work, now we just mean an untestable idea about gravitational degrees of freedom at unobservable scales which doesn’t really quite work either, but sucks less than the competition”.
Sure, there are now often quite interesting talks about QFT (perturbative and non-perturbative) being given at “string theory” conferences. I disagree with you though that the tribe of “string theorists” have a monopoly on being willing to think hard about non-perturbative QFT.
As Peter W. says, a minority who work on nonperturbative aspects of field theory make a point of not calling themselves string theorists (I avoid the label and I know others who do, from private discussions). Their reason for shunning the label is not just that it is a misnomer, but that it gives the impression to non-field-theorists that their work is connected to the better-publicized aspects of string theory (the landscape, etc.).
Axions nor magnetic monopoles nor proton decay have not been found yet, but this does not mean all those ideas have failed conclusively. They may still be revealed experimentally one day. Supersymmetry is no different. Perturbative string theory is no different. It’s just an idea about how high-scale physics can be made. It’s mathematically consistent, but as yet experimentally untested.
Perturbative string theory (1od, remember) is not just “experimentally untested” (and, by the way, it’s not completely mathematically consistent either…). Describing string theory’s problem as “not yet experimentally tested” is extremely misleading, since it implies you’re talking about some well-defined predictive theory that just happens to be hard to test. One needs to figure out how to get 4d known physics out of the theory, and all attempts to do that have failed. One can argue about how many decades of failed work by thousands of people need to go by before you can describe the failure as “conclusive”, but I think we passed that point a while ago.