- Concerning the “no dS string vacua” conjecture, a new preprint begins by explaining why the existence or non-existence of such vacua is a question that has not been resolved (and, it seems likely to me, can’t be resolved):

classical no-go theorems such as [12] indicate that realizing de Sitter vacua in string theory requires quantum and/or stringy ingredients. The fact that corrections to classical 10d low energy supergravity are qualitatively important implies that dS compactifications, in contrast to AdS or Minkowski compactifictions, must live in a regime in which these corrections cannot be made arbitrarily small [13], hence perturbation theory cannot be made arbitrarily accurate. Moreover the absence of supersymmetry in dS, and perhaps more fundamentally the lack of a complete, nonperturbative formulation of string theory, make it hard to obtain exact results beyond perturbation theory. Thus a completely rigorous, parametrically controlled construction of individual de Sitter vacua in string theory has remained out of reach.

The paper also explains why if you try and get known physics with a quintessence field rather than a CC, you immediately run into serious problems with coupling to the Standard Model.

- Slides and video of the talks at this year’s PiTP summer school on “From Qubits to Spacetime” have started to appear. Once I get back from vacation I’ll try and watch some of the talks and hope to figure out how one is supposed to get our spacetime and its physics out of qubits.

Recently people have contacted me suggesting I blog about two physics-related topics likely to lead to vigorous debate. I’d begged off in both cases, since engaging in such a debate or moderating it would be on a short list of things I’d most like to avoid doing. This afternoon though, it struck me that there is an excellent, if cowardly, way to deal with this. I’ll mention the two topics briefly here, then shut off comments on the blog and leave town. So, some may find interesting and want to argue elsewhere about:

- One of the PiTP lecturers, Aron Wall, has a blog on physics and theology, called Undivided Looking. Wall’s theological views include thinking he has a pretty good idea about how God wants people to behave, in particular he’s pretty sure that God doesn’t want them having homosexual relations. He wrote extensively about this in a blog entry (now deleted) back in 2015. He’ll be soon taking up a faculty position at Cambridge University, and some people are not happy about this, see for example this statement from the Cambridge University Student’s Union.
- If you’d like to attend an early universe conference this September, one place you could do so is in the Israeli-occupied West Bank settlement of Ariel, where Ariel University is hosting a workshop on Inflation, Alternatives and Gravitational Waves.

The last couple months I’ve heard reports from several people claiming that arithmetic geometers Peter Scholze and Jakob Stix had identified a serious problem with Mochizuki’s claimed proof of the abc conjecture. These reports indicated that Scholze and Stix had traveled to Kyoto to discuss this with Mochizuki, and that they were writing a manuscript, to appear sometime this summer. It seemed best then to not publicize this here, better to give Mochizuki, Scholze and Stix the time to sort out the mathematics and wait for them to have something to say publicly.

Today though I saw that Ivan Fesenko has put out a document entitled Remarks on Aspects of Modern Pioneering Mathematical Research. It refers in footnote 18 to:

two recent texts by Sh. Mochizuki, ‘Report on discussions, held during the period March 15–20, 2018, concerning inter-universal Teichmüller theory (IUTCH)’and ‘Comments on the manuscript by Scholze–Stix concerning inter-universal Teichmüller theory (IUTCH)’, July 2018

I haven’t seen these two texts, or the Scholze-Stix manuscript. What I have heard about them is that Scholze-Stix identify what they see as a specific, serious flaw in the proof, and that Mochizuki denies that this is a problem or that his manuscript needs to be revised. Presumably, after the two sides try and sort this out amongst themselves, at some point we’ll see something publicly available describing the details of their disagreement.

Fesenko’s document has a lot of unpleasant things to say about those who have written anything at all skeptical concerning Mochizuki’s claimed proof, mostly without naming names. He refers to journalists and “US bloggers” as having produced “ignorant absurd articles and posts”, presumably has someone other than me in mind since the information posted here about this I believe has been quite accurate and of reasonably high quality. The one negative reference to identified mathematicians is in the text with footnote 18 pointing to Scholze and Stix, which says:

Several researchers, who could have become potential learners of IUT and then progressed to become experts, declined invitations to participate in the IUT workshops. Some, affected by negative emotions, broke professional rules of conduct and made public their ignorant and sometimes intolerant opinions. Tellingly, the only questions produced were shallow and misplaced and they were communicated only after several years of requests to do so.

Peter Scholze is by far the most talented arithmetic geometer of his generation, a sure thing to receive a Fields Medal at the ICM in a couple weeks. That his questions about Mochizuki’s proof were “shallow” seems highly unlikely, to me at least.

Much of Fesenko’s article concerns the question of whether contemporary mathematical research is too narrow and unambitious, devoted to minor improvements and producing lots of publications. This is a serious issue, one though where other fields than arithmetic geometry (e.g. fundamental physics) are in a much worse state. Fesenko tries to make the difficulties mathematicians have had with Mochizuki’s claims about his IUT research an exemplar of this problem, but this seems to me misguided. There are quite good reasons for why experts have been skeptical about IUT and the supposed abc proof, reasons which will be conclusively vindicated if Scholze and Stix turn out to be right. Ironically, an excellent example of the kind of fundamental breakthrough that Fesenko is asking for is Scholze’s own ground-breaking work over the past few years.

]]>- New videos from the IHES include new interviews, and talks from the recent Ofer Gabber conference. If you want to know more about prisms than what you can get from the video here, I hear rumors that Bhargav Bhatt will be our Eilenberg lecturer this fall at Columbia.
- Another talk at the Gabber conference was the latest on local (quantum) geometric Langlands from Gaitsgory. Also on this topic, there’s a July 4 preprint from Arakawa and Frenkel (advertised here).
- John Horgan has an interview with Jim Holt, headlined Why Does Jim Holt Exist?. For reviews of Holt’s two most recent books, see here and here.
- For two interesting blog posts from HEP experimenters about news from their field, see Jonathan Link at SciAm on neutrinos, and Tommaso Dorigo on the Higgs self-coupling. Dorigo’s posting is the more technical one, explaining a new CMS result bounding the Higgs self-coupling.
The LHC experiments still seem to be a long ways away from actually measuring the Higgs self-coupling, but may be able to do so in future higher-luminosity stages of the LHC program. The Higgs remains the least understood part of the SM, responsible for most of the undetermined parameters of the theory. Any measurement of its self-interactions is an important goal.

While it often seems that experimental results relevant to going beyond the Standard Model are inaccessible due to the necessity of higher energies, these two blog posts point to important open questions about the SM that are hard to study not because of fundamental limits on collision energies, but because of small event rates and high backgrounds.

- The question recently came up here (see this posting) of how good the SUSY GUT coupling constant unification prediction is. At a recent summer school lecture, Ben Allanach says the prediction is off by 5 sigma, i.e. that if you try and predict the strong coupling at the Z mass this way, you get 0.129 +/- 0.002, whereas the measured value is 0.119 +/- 0.002. Someone should tell Frank Wilczek…

**Update**: For more on the dS vacua issue, see this blog posting by Ulf Danielsson. Danielsson refers to criticism of the landscape at my blog, but ignores the point I’ve often made that string theory is in just as much trouble if the advertised dS vacua don’t exist, since then it has no known way to connect to the real world and its positive CC. Somehow he sees this as a virtue, that “These are exciting times”, which I find mystifying.

He also claims that, all is well, since:

By studying the mathematics of the theory we will find out what it predicts, and by comparing with observations we will learn whether it has anything to do with reality.

But the underlying problem here is that the mathematics of the theory is unknown. Read the responses above from two experts to the question of why this issue has not been conclusively determined. Neither of them present any possibility of a conclusive determination. For both of them, this is about weighing the plausibility of various conjectures about possible solutions to unknown conjectural equations. At this point I seriously doubt it is possible for this to be resolved one way or the other.

**Update**: ICHEP 2018 is winding up, talks available here. There was one plenary summary talk on “Formal Theory Developments”, by Tadashi Takayanagi. It begins by promoting string theory, then goes on to address the problem of how it relates to fundamental physics with:

However, please do not ask me questions like:

How to derive Standard Model from string theory?

Why do we live in 4 dimensions?

How to realize de-Sitter spacetimes in a well-reliable way?String theory is still too infant to give complete answers to them.

The “complete” is intentionally misleading, since string theory now gives no answers at all to these questions. While celebrating the 50th anniversary of string this year, it seems that “string theory is too new an idea to evaluate” is the standard answer to anyone who points out its failures.

]]>**David Gross**: The plurality of questions had to do with the connections of string theory to real-world experiment. Some of these were raised by the panelists already. Let me just give you a sense of those questions, and see if you would like to briefly address them:

How long can string theory survive without experimental verification? At what point does it become mathematics?

Can string theory survive as a theory of the physical world if de Sitter space can’t be accommodated and supersymmetry ruled out?

In the next fifty years do you expect any physically relevant result (i.e. worthy of a Nobel Prize) to come out of string theory?

Has string theory given up on particle physics? [Gross:”no names attached” (laughter)]

When and where do you foresee a real confirmation of string theory in particle physics or cosmology (other than the existence of gravitons)?

In what area of physics do you expect the first observation of string theory?

Do you think string theory is closer to phenomenology than 50 years ago?

What could be a prediction of stringy models that can be verified in the lab and it cannot be an effective field theory model that gives you the same prediction?

How much of the string community has given up on the goal of connecting string theory to the standard model and observational cosmology?

Susy isn’t observed, what should we do? Is it okay to believe that string theory is still the theory of everything?

**David Gross**: So, this is symptomatic of this community. I imagine [for] the younger members of the community perhaps a bit worrisome.

**Eva Silverstein**: My answer is yes. (laughter) To the very last question you posed.

**Juan Maldacena**: I think the main virtue of string theory is to be a consistent theory of quantum gravity and maybe we shouldn’t be… I mean of course it would be wonderful to have a comparison to experiment but it’s a complicated theory and it might take many years until we understand how to compare it to experiment. I think an important thing is to understand the theory, understand basic things like the singularity because it might be that we’ll understand that experimental connection by understanding the Big Bang singularity and some predictions from there, or something in this direction.

**John Schwarz**: One of those questions had to do with “is string theory just mathematics?” I’ve heard this question many times and I find it puzzling that someone would consider mathematics to be a pejorative term. Where would physics be without it?

**David Gross**: I don’t think that was the question. The question was “if string theory without experimental verification goes on and on is it indistinguishable”. There was nothing pejorative.

**John Schwarz**: I’m sure the person in this audience who raised that question didn’t mean it that way but I’ve heard it used by others in that way.

**Dan Harlow**: I just want to give a sociological data point so I mean I won’t repeat what I said in my talk but it’s a true fact that you know every every month or two I am contacted by an experimentalist. Usually this or that atomic physics experimentalist who is looking for things to do in their lab and somehow thinks that talking to me will help. I’m not sure if it will or not, but I think that there’s this fantasy that you find on the blogs that string theory is something that exists independent of the rest of physics and I think really nothing could be further from the truth. I mean I feel we’re really part of physics I talk to physicists all the time and not just string theorists. (laughter)

**David Gross**: There were a few other versions of this question that perhaps reflected the anxiety of some of you here, which had to do with funding and and having to defend yourselves in your academic departments and universities and that I think is a real issue. I think Daniel addressed that but let me give you some other points of advice to defend string theory or what we call the activities of this crowd, with respect the funding agencies or department chairmen. String theory was attacked bitterly in the eighties for being not even science and but now it’s truly impossible to make that argument. It is continuously connected to the standard model after all through our dualities and the standard model is certainly part of nature and verified experimentally. So string theory and field theory are not distinguishable and certainly not the standard model. String theory has given us many insights into the standard model, condensed matter theory, information theory, mathematics etc. It is easy to defend it intellectually, aside from the fact that it’s addressing these deep conceptual problems of unifying quantum gravity with the other interactions, or just understanding gravity. So you should feel no shame in defending this field and arguing for both funding and positions.

**Gabriele Veneziano**: One mistake we made in the early days of the atomic theory was to think that the hadrons were elementary and to which we had to find a string idea. One of the big assumptions of the new 80s interpretation is that the particles we consider elementary today are indeed so. Maybe the fact that we so far failed to find a model is that we try to find a string theory for the wrong thing.

**David Gross**: There are also many questions about de Sitter space:

The existence of dS solutions appears to be controversial. What are the technical obstacles to resolving that controversy?

Is de Sitter space in the swampland? Can we get de Sitter in string theory? If yes why haven’t we succeeded? If no, why not?

**David Gross**: Igor [Klebanov] (sorry Igor) asked an even broader question:

Is there a stable non-supersymmetric compactification of superstring theory whose existence has been established using known controlled approximations? Should have Poincaré or dS or AdS symmetry corresponding to the two or more non-compact dimensions?

**David Gross**: This is an interesting topic where there’s clearly controversy. I’ve been unable to find a strong statement on the negative side. Juan has offered to defend it or at least he has been put forward to defend the existence of dS solutions.

**Juan Maldacena**: There are constructions that I think are reasonable, there are scenarios for how the solutions should work. They involve complexity in an essential way in the sense that you have to invoke complexity to find this fine-tuning that [?] was talking about, and they are reasonable so if you’re going to say that they don’t exist you also should argue with comparably strong arguments. Also no one guarantees us that the physical theory will have very simple solutions, so if you want to solve for the oxygen atom you can decide whether it will exist or not. Even in QCD if you try to decide what’s the last stable nucleus you will not beable to predict it probably from pure theory.

I’ll say one more thing, but this is more speculative. So our understanding of the vacuum in string theory many times relies on having an asymptotically simple situation: asymptotically flat space, asymptotically AdS, and if we ask “where does AdS arises from?” then “Oh well it’s a brane embedded in a bigger space and so on”. So we have this kind of “turtles upon turtles upon turtles” picture of the theory, so everything is defined by a bigger simpler asymptotic space. But where did this asymptotic space come from? de Sitter is different, de Sitter is a bit like a sphere, so it has no edge or anything and we need to think now “We’re theorists, how to describe that?” So maybe we’ll understand another framework where we understand the fact that it has no boundary is more crucial and essential and we’ll see that those equations might have a different nature than the types of equations we think about.

**David Gross**: That’s a defense of KKLT. Trivedi isn’t here, I was going to ask him to defend it. There are many people who are confused as to whether this is a crisis for string theory or not, and Hiroshi volunteered to give some criticism of these compactifications.

**Hirosi Ooguri**: I was asked to say something about it probably because I posted a paper with Cumrun earlier this week about this which Cumrun talked about. So, the last 20 years or so, especially after dark energy was identified, there have been enormous attempts to construct de Sitter space and other accelerated universes, with various degrees of rigor, and this is really a very important part of string theory research. So, many of the things we do is to look at a set of these constructions and try to deduce lessons from these data. This is like experimental science where we are given a set of this data and then try to understand it. But of course depending on how much rigor you ask, how much sort of control you would like, the set of data you look at can be different. Just like experimenters look at the different sigmas and then select reliable data. I should say in the case of string theory it’s particularly difficult because string theory doesn’t have parameters so all the low-energy parameters are the vacuum expectation value of some field. So if you successfully stabilize all the scalar fields then by definition these are numbers and not controlled. This is in contrast to the case of say, QED, where we have the fine structure constant which you can dial in a given theory, in our world a given number you can dial, so we can trust it, so the situation seems to be different. When the KKLT compactification first appeared I was hoping that maybe since there are so many ends around the flux that you can actually find a series of models where you have control over that, which we have not seen. I think this is difficult and so you can draw different lessons from this and I think it’s very important to sort of develop tools to make more sort of finer predictions out of this existing situation.

How to think about… The multiverseThe idea of an infinite multitude of universes is forced on us by physics.

It starts off quoting Sean Carroll:

“One of the most common misconceptions is that the multiverse is a hypothesis,” says Sean Carroll at the California Institute of Technology in Pasadena. In fact, it is forced upon us.”It is a prediction of theories we have good reason to think are correct.”

The problem with this claim is that it’s simply not true. There is no model that “we have good reason to think [is] correct” that predicts a multiverse of universes with different physics (i.e. fundamental constants). I’ve written about this many times, see for instance Theorists Without a Theory. In case you were thinking of interpreting Carroll’s claim in some other way, the article goes on to invoke Alexander Vilenkin:

“The so-called constants of nature, like the mass of the electron or Newton’s gravitational constant, will have different values in different bubbles,”

To be fair to New Scientist, I haven’t read beyond the headline and first few paragraphs of this article, since the rest is behind a paywall. Maybe the later part of the article (which most people can’t read) explains what is wrong with the Carroll and Vilenkin claims.

For the latest on the models supposed to give us different physics in different parts of the multiverse, you might want to take a look at this new paper on the arXiv, and Cumrun Vafa’s talk about it this week at Strings 2018. The paper and talk conjecture that the supposed metastable dS solutions of the string landscape don’t really exist (they are in the “swampland” of things that aren’t solutions of string theory). If this is true and you want to save string theory, as Vafa explains, you need to invoke different sorts of supposed solutions to string theory, with the CC replaced by a “quintessence” mechanism.

At the end of the talk (1:01), Eva Silverstein tries to explain what is wrong with Vafa’s arguments. He responds “I’m not saying you’re wrong, you might be right, this might be also be right”. This shows clearly the fundamental problem of the subject: there is no well-defined theory here, just a bunch of conjectures about what one might be, with no way to tell whether Vafa or Silverstein is right, and no way to extract well-defined predictions from the mass of possible conjectures.

**Update**: Thanks to those who sent me a copy of the full New Scientist article. It’s short, and the part behind the paywall is even worse than the part publicly available, just adding to the confusion by invoking “many-worlds”, with more from Sean Carroll. Our doppelgangers doing exciting stuff in other universes make an appearance, although Carroll expresses a lack of interest in what they’re up to.

**Update**: The Strings 2018 talks and videos are available here or at this Youtube channel, and 4 gravitons has a blog posting. As usual with Strings 20XX conferences, very little about actual string theory there. For an overview of the state of the field, you might want to watch this video of the 50 years of string theory session, moderated by David Gross. Dan Harlow was the only speaker raising the elephant in the room question: “is string theory still a useful candidate as a theory of HEP physics?” (and also asked whether they should finally rename the conference series). Gross read off submitted questions for the panel, most of which were asking about the elephant in the room. The panelists each found a different way of avoiding dealing with the question. Other questions asked about the hot “is there a dS string vacuum?” issue, responses were “maybe yes, maybe no”, with no indication of any way to resolve this.

The trouble is that it’s not clear when to give up on supersymmetry. True, as more data arrives from the LHC with no sign of superpartners, the heavier they would have to be if they existed, and the less they solve the problem. But there’s no obvious point at which one says ‘ah well, that’s it – now supersymmetry is dead’. Everyone has their own biased point in time at which they stop believing, at least enough to stop working on it. The LHC is still going and there’s still plenty of effort going into the search for superpartners, but many of my colleagues have moved on to new research topics. For the first 20 years of my scientific career, I cut my teeth on figuring out ways to detect the presence of superpartners in LHC data. Now I’ve all but dropped it as a research topic.

While most HEP physicists still try and end their talks with some sort of optimistic expression of hope that things will change soon, I was struck by a recent talk by John Iliopoulos, which was more somber and more realistic:

No coherent picture emerges

We were expecting new physics to be around the corner…..

But we see no cornerThe easy answer: We need more data

Two problems: (i) We do not know what kind of data

(ii) They will not come for quite a long timeA rather frustrating problem!

and he ends with

The Future of Particle Physics will undoubtedly be bright, but

I will not learn the answer

While thinking about this I happened to look at an old posting of mine, a review of Lisa Randall’s Knocking on Heaven’s Door written back in 2011. There I wrote

One odd thing about the book is the title, which for Randall carries a positive meaning that she acknowledges doesn’t correspond to the very dark one of the Bob Dylan song from the soundtrack of the Sam Peckinpah film. It’s a beautiful song, but one not about finding truth, but about getting shot in the gut and facing death, hopefully not relevant to particle physics in the LHC era:

Mama, put my guns in the ground

I can’t shoot them anymore.

That long black cloud is comin’ down

I feel like I’m knockin’ on heaven’s door.

It does seem like much of the last 40 years of HEP theory is now “knockin’ on heaven’s door”, deeply wounded by negative results from the LHC. What this means for the future is still up in the air: what story about what has happened will become the conventional wisdom?

]]>The predicted (median) value is 50–60 times larger than the observed value. The probability of observing a value as small as our cosmological constant Λ

_{0}is ∼2 per cent.

If your theory only makes one prediction, and that prediction is off by a factor of 50, that’s the end of it for your theory. I’m very glad that this has now been sorted out, the multiverse hypothesis has been falsified, and theorists who have been working on this can move on to more fruitful topics.

**Update**: As David Appell realized, the last sentence here was sarcasm (or maybe black humor). Those promoting the multiverse are doing Fake Physics™, not Physics. This is ideology, not science, and there is no chance that they will stop referring to the “successful multiverse prediction of the CC”, no matter what analysis shows a seriously incorrect prediction.

As Blake Stacey points out, this paper was on the arXiv back in January (see here), and has just been ignored by multiverse proponents. Part of doing Fake Physics™ is ignoring any information that contradicts what you want to believe. Another commenter points to this 2014 argument from Sesh Nadathur, which similarly as far as I know has just been ignored.

After appearing on the arXiv in January, this latest work was promoted by press release from Durham University back in May, which led to lots of media stories (e.g. here). For some reason, the press release didn’t really explain that this work falsifies the usual claim that the value of the CC is evidence of a multiverse. Instead, the work was promoted as showing that the multiverse is “more hospitable to life” than thought, which sounds good I guess, but seems like a bizarre way to explain the significance of this work.

For various sensible explanations of what is really going on here, see Jim Baggott, Philip Ball, and Sabine Hossenfelder. I’ve often repeated my own version of how to see there’s a problem with trying to explain the CC this way. There is no actual multiverse theory, so proponents assume a “flat measure over the anthropically allowed region” and then calculate. This is exactly the same input as my theory of the CC, which is that I have no idea what is going on, so any value is equally likely. The bottom line from the latest work on this is that, even if for some reason you believe you can get a sensible “prediction” this way, the prediction comes out wrong.

]]>Hossenfelder’s main concern is the difficult current state of theoretical fundamental physics, sometimes referred to as a “crisis” or “nightmare scenario”. She is writing at what is likely to be a decisive moment for the subject: the negative LHC results for popular speculative models are now in. What effect will these have on those who have devoted decades to studying such models?

Back in 2006 Lee Smolin and I published books concerned about where fundamental physics was heading, and five years ago Jim Baggott’s Farewell to Reality appeared with another take on these issues. Hossenfelder’s is the first book on this topic to appear since the LHC results showing a vanilla Standard Model Higgs and no evidence of supersymmetry or other speculative BSM physics. The remarkable thing she has done is to address this in a characteristically direct manner: go talk to those responsible and ask them what they have to say for themselves.

Four of the people that Hossenfelder interviews would be on any short list of the most influential figures in theoretical particle physics, both responsible for where we are now by their past actions, and looked to by others for a vision of where the field is going next. They are Nima Arkani-Hamed, Steven Weinberg, Frank Wilczek, and Joe Polchinski.

Arkani-Hamed is introduced with:

He’s won loads of awards, including the inaugural 2012 Breakthrough Prize for “original approaches to outstanding problems in particle physics.” The problems are still outstanding. So is Nima.

and here’s an extract from the interview

“Has the LHC changed your perspective on naturalness?” I ask.

“It’s interesting–there is this popular narrative now that theorists before the LHC were totally sure that susy will show up, but now there’s a big blow. I think that the people who are professional model builders, the people I consider to be the best people in the field, they were worried already after LEP… The good people, they were not at all sure susy would show up at the LHC. And nothing has changed qualitatively since 2000. Some loopholes have been closed, but nothing has changed qualitatively…”

As with many of the interviews, Hossenfelder intersperses her own internal response to what she’s hearing:

But not one of those “best people” spoke up and called bullshit on the widely circulated story that the LHC had a good chance of seeing supersymmetry or dark matter particles.

She doesn’t mention, but surely is aware, that many prominent theorists pre-LHC had made public bets that the LHC would find SUSY, and that those wagering this way included Arkani-Hamed himself. For accounts of the 2016 Copenhagen event where the bet was paid off, see here and here. You can read there what Arkani-Hamed had to say then about losing the bet, and the quote:

“I think Winston Churchill said that in victory you should be magnanimous,” Damgaard said after Arkani-Hamed’s talk. “I know also he said that in defeat you should be defiant. And that’s certainly Nima.”

In the interview with Hossenfelder, Arkani-Hamed goes on to say:

The people who were sure it would be there are now positive it’s not there. There are people now who speak out about being depressed or worried or scared. It drives me nuts. It’s ludicrously narcissistic. Who the fuck cares about you and your little life?

There’s a lot more in the interview and you should get the book and read the whole thing. Hossenfelder does a wonderful job of portraying both Arkani-Hamed’s serious arguments and his aggressive “Damn the torpedoes” self-confident attitude. This is not someone who is going to admit that, whatever bet he lost, some failure has occurred that indicates this is a time for reflection on mistakes made and reevaluation of the path forward.

Hossenfelder travels to Austin, Texas to talk to Steven Weinberg, who it appears may not realize she is a physicist, just has been told he is supposed to talk to a “writer”. She notes that:

Weinberg doesn’t talk with you, they told me, he talks

atyou. Now I know what they mean. And let me tell you, he talks like a book, almost print-ready.

I won’t try and reproduce much of her conversation with Weinberg, the multiverse is a main topic (she thinks it’s an empty idea, Weinberg is willing to go along with it). About where particle theory is headed, Weinberg says:

I don’t know how much elementary particle physics can improve over what we have now. I just don’t know. I think it’s important to try and continue to do experiments, to continue to build large facilities… But where it will end up I don’t know. I hope it doesn’t just stop where it is now. Because I don’t find this entirely satisfying…

I don’t take seriously any negative conclusion that the fact that the LHC hasn’t seen anything beyond the standard model shows that there isn’t anything that will solve the naturalness problem… Supersymmetry hasn’t been ruled out because it’s too vague about what it predicts.

Her next interviewee is Frank Wilczek, who she finds in Tempe, Arizona. His take on string theory unification is rather negative:

… it’s not clear what the theory is. It’s kind of miasma of ideas that hasn’t yet taken shape, and it’s too early to say whether it’s simple or not–or even if it’s right or not. Right now it definitely doesn’t appear simple.

Asked about the argument that string theory could reproduce gravity, Wilczek responds:

If your standards are low enough, yes. But I don’t think we should compromise on this idea of post-empirical physics. I think that’s appalling, really appalling… If there was any bit of experimental evidence that was decisive and in favor of the theory, you wouldn’t be hearing these arguments. You wouldn’t. Nobody would care. It’s just a fallback. It’s giving up and declaring victory. I don’t like that at all.

Wilczek is still unwilling to give up on SUSY and the idea of a SUSY GUT, with his main argument the coupling constant unification calculation he did with Dimopoulos and Raby back in 1981:

“They haven’t found susy partners, though,” I say. “Is this something that worries you?”

“I am starting to get worried, yes. I never thought it would be easy. There have been bounds from [the LEP experiments] and proton decay for a long time, and this indicated that a lot of the superpartners have to be heavy. But we have another good shot with the [LHC] energy upgrade. Hope springs eternal… I would definitely not believe in supersymmetry if it wasn’t for the unification of gauge couplings, which I find very impressive. I can’t believe that’s a coincidence.”

~~It’s not mentioned in this book~~ [actually, she does mention this], but Wilczek has already paid off one bet about SUSY (with Garrett Lisi) and likely will have to pay off another next year. I don’t know if by “energy upgrade” he’s thinking of the HE-LHC, or the 100 km much bigger proposed ring, but in any case those won’t happen before at least 2040. No matter what happens, I don’t think Wilczek will ever change his mind about the SUSY-GUT paradigm he has found attractive since the 1980s.

In January 2016 Hossenfelder traveled to Santa Barbara to talk to Joe Polchinski, who was already sick with the brain cancer that ultimately would take his life two years later. Unlike Wilczek, Polchinski was a fan of string theory and of evaluating it by “post-empirical” criteria. He at one point published a “Bayesian” calculation arguing that string theory is correct with probability “over 3 sigma” (i.e. over 99.7%). Asked about prospects for a unified theory, Polchinski says:

I think string theory is incomplete. It needs new ideas… But string theory has been so successful that the people who are going to make progress are the people who will be building on this idea.

Arkani-Hamed, Weinberg, Wilczek and Polchinski reflect a range of points of view about the current situation and what it means. Unfortunately it seems to me that they share an unwillingness to face up to failure, and this doesn’t bode well for the future of particle theory, with “more of the same” the agenda that is being set.

Besides these four interviews, the book also contains accounts of meeting and discussions with quite a few other physicists, all well worth reading, and often written with a sly humor. The description of visiting Garrett Lisi on Maui is not to be missed, and he has a lot of sensible things to say (“For a surf bum, he’s surprisingly intellectual” the author writes). He tells the story of how Jacques Distler and others threatened (unsuccessfully) to organize a boycott of Scientific American if it published an article by him. In addition to the interviews there’s a great deal of valuable discussion of the problems with the way research is organized and the reward structures scientists operate under (for instance, publicly admitting failure is definitely on the “not encouraged” list).

So far I’ve ignored the main framing device that Hossenfelder uses throughout the book, that of her questioning the idea of “beauty” as a motivation for evaluating ideas about physics. This is not because I disagree all that much with what she writes, but instead that I fear a complex set of issues is likely to get over-simplified, and this over-simplified version of the book’s argument is all that much of the public is ever going to hear about it. Hossenfelder explains that the concept of “beauty” she is challenging is a specific set of ideas about “symmetry, unification and naturalness” that she sees as dominating physics research. I agree that there’s a problem with this specific set of ideas and how they have been used, but I’d keep them separate and don’t see putting them together as “beauty” to be helpful. At various points she makes it clear that her worry is that we are getting stuck due to outdated notions of “beauty”, while still believing that successful new ideas will come with a new form of “beauty”.

The book ends with

We know that the laws of nature we presently have are incomplete. To complete them, we have to understand the quantum behavior of space and time, overhauling either gravity or quantum physics, or maybe both. An the answer to this will without doubt raise new questions…

…There’s much work to do. The next breakthrough in physics will occur in this century.

It will be beautiful.

**Update**: Science magazine has a review. For some reason they seem to have decided it was a good idea to have the book reviewed by a postdoc doing exactly the sort of work the book is most critical of. The review starts off by quoting nasty anonymous criticism of Hossenfelder from someone the reviewer knows on Facebook. Ugh.

**Update**: I’ve written a similar but somewhat different version of this review for MAA Reviews, one aimed more at mathematicians.

**
Update**: More reviews here and here, as well as a posting from Hossenfelder where she explains her current professional situation in the context of deciding to write the book.

**Update**: I’m glad to see that Science has edited the review there to remove the use of an unattributed quote.

- Inference has a review of my book, Woit’s Way, by Andrew Jordan. I like the way it starts out:

*Quantum Theory, Groups and Representations*is based on a series of lectures that he gave at Columbia University.And it is excellent.

The review gives a very good explanation of what’s in the book, what level it’s at, and what I’m trying to accomplish. Besides getting all this right, he also gets right some of the things that could have been done better (I did the indexing and I’m kind of lazy, it should have at least twice as many entries).

A reminder: the book is available either in my version at my website, or from Springer here.

By the way, when I was in Cambridge I spent a couple days at the conference in honor of Bert Kostant, who was a major figure in the study of the relation of representation theory and quantization. Among the talks there, David Vogan gave a survey talk on Quantization, the orbit method, and unitary representations. He explains clearly the fundamental relationship between representation theory and quantum theory that is central to my book. Roughly the first half of the talk corresponds to topics discussed in the book. I decided to not write about the topic of the second half of Vogan’s lecture, the representation theory of reductive groups and the orbit method, since that would take the book in a different direction, one currently of more interest to mathematicians than physicists (and Vogan has already done a better job of writing about this topic than I ever could).

- Also in the new issue of Inference are several pieces commissioned as responses to Natalie Paquette’s wonderful survey article A View from the Bridge about topological QFT and influences running from physics to mathematics. These pieces include takes on the relation of math and physics from Édouard Brezin, John Iliopoulos, Hirosi Ooguri and Martin Krieger, as well as a rather odd one from string theorist Xi Yin.
Yin’s piece is entitled An Ode to Ugly Physics, and he argues that:

the deepest and most far-reaching ideas of physics are not the most elegant or beautiful, but the ideas that are confusing, not rigorous, improperly formulated, or, in fact, utterly incomprehensible to mathematicians.

One problem is that many of the examples he gives of “ugly” physical ideas (for instance, spontaneous symmetry breaking) are ones that I think most mathematicians would describe as rather beautiful. He’s right that some of the examples he gives (e.g. complex string theory calculations) are ones that mathematicians wouldn’t find that beautiful, but often these are calculations that have been unsuccessful in their goal of making contact with reality. Yin ends with:

I believe that part of the job of a theoretical physicist is to make the lives of mathematicians miserable. There are, incidentally, few things I can think of that could make a mathematician more miserable than reading Leonard Susskind’s papers.

This includes a footnote to this recent paper by Susskind, and he’s right that this is not one mathematicians would think highly of. For good reason though, with Yin’s implication that this is an important idea in theoretical physics something I find rather dubious (but then again, some would say I’m a mathematician…).

Truly bizarre is Yin’s response to the fact that string theory has failed to make any connection to observable physical reality:

I couldn’t help but notice a striking parallel with the way mathematics became detached from physics during the nineteenth century and, in particular, the outrage that accompanied Cantor’s transfinite set theory and Hilbert’s non-constructive proofs. Was the kind of mathematics that could never be exhibited with real objects actual mathematics, or was it theology? With the benefit of hindsight, we now know that the mathematics flourished like never before during the twentieth century. One can only hope the same thing happens with string theory in the decades to come.

So, having no connection to experiment and observation is not a bug, but a feature, exhibiting a radical new advance in how to do physics? This takes the “post-empirical” thing even further than I’ve seen anywhere else.

Finally, also in the same issue of Inference is the final part of a series of articles by Sheldon Glashow, this one dealing with the Standard Model. Glashow ends the essay with some comments on string theory, quoting someone I have to agree with.

- On the neutrino front, there’s a new result out from MiniBooNE that has gotten a lot of attention. As usual, good sources for clear explanations and informed evaluations are Tommaso Dorigo and The Mad Hatter.
For much more of the latest results on neutrinos, Neutrino 2018 is happening this week in Heidelberg, slides of presentation appearing here.

- The Perimeter Insitute earlier this year hosted a workshop on geometric Langlands and QFT, talks available here. Dan Falk has an article about this subject here. He also has a piece about Why some scientists say physics has gone off the rails, partly based on Sabine Hossenfelder’s new book, which I’ll write about here very soon.
- Michael Harris at his book’s blog tells the story of how he was commissioned by New Scientist to write something about Peter Scholze’s ideas. His draft ended up not getting used, luckily for us he includes it in the blog posting. New Scientist did however end up publishing a story about this, under the headline The Theorem of Everything (non-paywalled version here).
- The Simons Foundation has just put out its 2017 annual report. To get some idea of their increasingly large influence on mathematics and physics research, here are some numbers:
Assets, end 2017: \$3.298 billion

2017 income: \$646 million

2017 expenses: \$409 million

2017 grants: \$273 millionMathematics and physical sciences receive 31.77% of the grant money. To get a sense of the scale of this, one could compare the fraction of expenses corresponding to math and physical sciences (31.77% x \$409 million= $130 million) to the FY 2017 NSF budget numbers

Mathematical sciences: \$234 million

Physics: \$281 million

Astronomical sciences: \$252 millionIn the areas of math, physics and astronomy where the Simons Foundation is concentrating its resources, I suspect that the amounts they’re spending are getting up to the NSF level.

**Update**: For a take on the Copenhagen interpretation that I very much agree with, see Philip Ball’s Myths of Copenhagen.

Zeh is the physicist most responsible for first identifying and studying the crucial role of decoherence in the measurement problem. As Becker explains, he encountered a quite hostile reaction to his early work from defenders of Copenhagen orthodoxy. He finally managed to get his paper On the Interpretation of Measurement in Quantum Theory published in 1970, and then started to explore what came to be known later by the term “decoherence”. In later years he wrote many articles explaining these ideas, for one that includes some historical context, see here. Zeh maintained a website with links to his writings, at www.decoherence.de or www.zeh-hd.de, which seems to be down at the moment, hopefully only a temporary situation (a recent Wayback Machine capture is here).

I was pleased that every so often Zeh contributed insightful comments here, most recently just three weeks before his death. Here’s a list of the ones I found in a quick search:

During the past few years I also had some email exchanges with Zeh. For details of his latest thinking about issues like the multiverse, he pointed me to this paper, which he every so often updated. A few months ago I was quite sorry to realize (when someone told me that Zeh lived in Heidelberg) that I had missed an opportunity to try to meet him in person when I was there a couple years ago. I’m even sorrier about this now that such a meeting will no longer be possible.

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