This Week’s Hype

This morning Quanta Magazine informs us that Physicists Create a Wormhole Using a Quantum Computer, promoting the article on Twitter with BREAKING: Physicists have built a wormhole and successfully sent information from one end to the other and Physicists have used Google’s quantum computer to send a signal through a wormhole, a shortcut in space-time first theorized by Einstein and Rosen in 1935.

This work is getting the full-press promotional package: no preprint on the arXiv (unless I’m missing something?), embargoed info to journalists, with reveal at a press conference, a cover story in Nature, accompanied by a barrage of press releases (see here, here, here, with Harvard, MIT and Google to come). This is the kind of PR effort for a physics result I’ve only seen before for things like the Higgs and LIGO gravitational wave discoveries (OK, and the primordial gravitational wave non-discovery). It would be appropriate I suppose if someone actually had built a wormhole in a lab and teleported information through it, as advertised.

An additional part of the package is the Quanta coverage, with a very long article by Natalie Wolchover and an over-the-top seventeen minute film How Physicists Created a Wormhole in a Quantum Computer, with abstract

Almost a century ago, Albert Einstein realized that the equations of general relativity could produce wormholes. But it would take a number of theoretical leaps and a “crazy” team of experimentalists to build one on Google’s quantum computer.

The two senior physicists behind this, Joe Lykken and Maria Spiropulu, have histories that go way back of successfully promoting to the press nonsense about exotic space-time structures appearing in experiments that have nothing to do with them. Back in 1999, the New York Times published Physicists Finally Find a Way to Test Superstring theory, which featured Joe Lykken. In 2003, they featured Maria Spiropulu explaining how she was going to find extra dimensions (or “something just as ‘crazy””) at the Tevatron, or failing that, the LHC.

I just saw that the New York Times also has a big story about this: Physicists Create ‘the Smallest, Crummiest Wormhole You Can Imagine’. At least this article has some sensible skeptical quotes, including:

“The most important thing I’d want New York Times readers to understand is this,” Scott Aaronson, a quantum computing expert at the University of Texas in Austin, wrote in an email. “If this experiment has brought a wormhole into actual physical existence, then a strong case could be made that you, too, bring a wormhole into actual physical existence every time you sketch one with pen and paper.”

An odd thing about the Quanta article is that it contains a couple quotes from me, that aren’t at all about the wormhole business. They’re about the attempt to use AdS/CFT to either solve QCD or get a viable theory of quantum gravity. Back in June Wolchover contacted me with some questions about AdS/CFT. It seems that she was planning a long piece on AdS/CFT, one which somehow many months later got amalgamated with the wormhole nonsense. I had forgotten that I was thinking of turning what I sent her back then into a blog posting but never got around to it, so just earlier today posted it here.

On the substance of what is really going on here, it’s exactly the same as what was discussed extensively a month ago in this posting and in its comment section. The claim that “Physicists Create a Wormhole” is just complete bullshit, with the huge campaign to mislead the public about this a disgrace, highly unhelpful for the credibility of physics research in particular and science in general.

Update: Here’s the promotional piece from Google, and Will Kinney’s reaction.

Update: Physics World has Quantum teleportation opens a ‘wormhole in spacetime’ with a quote from Witten saying positive things about this experiment (“a ‘milestone’ in developing control over microscopic quantum systems”), nothing about the wormholes.

Update: I tried reading the paper in some more detail. Almost all the calculations in the paper were done on paper or on a classical computer. As far as I can tell, all they did was perform elaborate SYK calculations on a classical computer, together with simulations of noise on the Google quantum computer, trying to find a possible calculation on the quantum computer that would have signal, not just noise. Once such an N=7 SYK calculation was identified, they used a 9 qubit quantum computer and the noisy result matched the simulation result from the classical computer, exactly as expected. Seeing the completely expected match between results from a 9 bit noisy quantum computer and the results of the simulation of this on a classical computer caused Maria Spiropulu to say that “I was shaken” and “It was nuts. It was nuts”, while Joe Lykken felt that the moment was on a par with discovery of the Higgs particle.

I hadn’t noticed that the Nature issue comes with an article by Brown and Susskind, A holographic wormhole traversed in a quantum computer. Amidst the hype, they do at least point out:

because nine qubits can be easily simulated on a classical computer, the results of this experiment cannot teach us anything that could not be learnt from a classical computation, and will not teach us anything new about quantum gravity.

New Scientist is the sober one here, with their headline the relatively reasonable A quantum computer has simulated a wormhole for the first time

Update: MSN is going for the larger context: physicists didn’t just create a wormhole in a lab, also This tiny 2D wormhole could finally solve the biggest problem in physics

Update: Andreas Karch on Twitter I think has an accurate characterization of this “mostly a publicity stunt”:

Experimentally it’s of course cool they can do SYK – as a demonstration they have control over their device. They can couple 9 qbits in a pre-specified way. But I guess we knew they could do this before. Going after SYK in particular, in my mind, is mostly a publicity stunt.

Update: Quanta has changed the title of their article from “Physicists Create a Wormhole” to “Physicists Create a Holographic Wormhole”.

The MIT press release is out, and it’s comical in the other direction, explaining the huge breakthrough as MIT researchers use quantum computing to observe entanglement.

Chad Orzel is getting flashbacks to 2006, which I can well understand. Many of the worst offenders in this hype campaign were hard at work doing the same thing back then (and earlier), and I was, as now, ineffectually trying to do something about it (the first edition of “This Week’s Hype” dates back to that year).

Update: Quanta has also deleted the original “BREAKING: Physicists have built a wormhole and successfully sent information from one end to the other” tweet. Davide Castelvecchi at Nature as a more sober story, ending with

The theory tested at the Google lab “only has a very tangential relationship to any possible theories of quantum gravity in our Universe”, says Peter Shor, a mathematician at the Massachusetts Institute of Technology in Cambridge.

Update: More coverage of this here, here, here and here. Quanta and Wolchover are, quite appropriately, blaming the “some of the best-respected physicists in the world” who sold them this nonsense, see here, here and here.

This is something I wrote back in June, for context see the next posting.

First of all, there’s the following, which is not strictly scientific, but very relevant to how one decides to evaluate progress in a subject.

• The Maldacena AdS/CFT paper is almost 25 years old and has nearly 18,000 citations. Trying to exploit ideas based on AdS/CFT has been the main goal of thousands of the best theorists in the world for decades. Questions like “what about getting this to work in the more physical case of dS?” are not new but very old and have been the subject of tens of thousands of person-years of unsuccessful effort. This doesn’t mean it can’t be done, I think it does mean that what’s needed are some quite different ideas, there’s little point in further banging away at ones that haven’t worked for this long, after this much effort.
• Some of the hype surrounding AdS/CFT has been outrageous. One example is the claim that AdS/CFT gives a good way to calculate things about heavy-ion physics. This is just not true, and the people saying things like this should know better. Seeing people do things like this make me question their arguments about whether other ideas work or not (or have good prospects for working).
• As time goes on, people start using “AdS/CFT” to mean a wider and wider array of things. It often now denotes very general and vague conjectures about duality relations between gauge theory and gravity systems, or holography, or entanglement. It becomes impossible at some point to have a coherent discussion about the subject since there is no well-defined thing to talk about.

Sticking to the specific meaning of a duality between a specific superstring theory on AdS_5 x S^5 and N=4 super Yang-Mills on the conformal boundary, back in 1997 there were two reasons to get excited about this:

• Reading the duality as telling you about gauge theory in terms of string theory, you could hope that the duality could be extended to non-supersymmetric Yang-Mills, providing the long-sought string dual to QCD, allowing reliable strong-coupling QCD calculations. After a few years post 1997, it started to become clear this wasn’t working, and why. N=4 SYM has zero beta-function and is conformally invariant, so the effective coupling and physics are the same at all scales. QCD has a running coupling constant, with weak-coupling and strong-coupling physics very different. AdS/CFT allows strong-coupling calculations on the gauge theory side using weakly-coupled strings, but this has the same problems that we’ve always had with QCD: there are ways to write down strong-coupling expansions, but no way to match those to weak coupling physics, no way to capture the way physics changes from strong to weak coupling.

By the way, I noticed the Simons Foundation has just announced a collaboration to study QCD and strings
https://www.simonsfoundation.org/2022/06/09/foundation-announces-the-simons-collaboration-on-confinement-and-qcd-strings/
and this doesn’t even mention AdS/CFT. People have tried really, really hard over decades to use AdS/CFT to say something about QCD, with very limited results.

• Reading the duality as telling you about strings and quantum gravity in terms of gauge theory, the hope is to understand quantum gravity this way. There are a bunch of problems with this:

There’s the gravity in AdS rather than dS problem that you mention. As noted above, back in 1997 it was reasonable to expect a useful extension to dS. After 25 years of failed efforts, if there is such a thing it has to be something very different.

You want gravity in 4d, not 5d. This may not be a serious issue since you can take 5d with one small dimension, or brane or whatever to get rid of a dimension.

There’s a fundamental problem with doing gravity this way: string theory-based quantum gravity uses weakly coupled strings with the graviton a weakly-coupled mode. But this theory is dual to strongly-coupled gauge theory where you can’t calculate anything. So, AdS/CFT is telling you nothing about the usual picture of how gravity arises from string theory. What it supposedly tells you about are strongly coupled strings (using weakly coupled gauge theory), but then the connection to gravity is something very different than what was originally advertised for string theory.

Put together, the problem is that, to the extent AdS/CFT is telling you something about strings and quantum gravity, it’s telling you about the wrong kind of space-time (AdS) in the wrong dimension (5) with the wrong kind of strings (strongly-coupled). The general philosophy seems to be that at least it’s telling us about some kind of quantum gravity, which is a reasonable motivation, but leaves one far from real physics, in the land of general issues like resolving the black hole information paradox. But 20 years ago we were being told that it was resolved by AdS/CFT, then ten years later we were being told it wasn’t (the “Firewall”). Again, given the level of hype people operate with, it’s hard to evaluate any of this kind of thing with no relation to anything measurable.

I’m all in favor of good toy models, and from what I can see the main activity in AdS/CFT these days is trying to understand lower dimensional toy models. This leads to lots of interesting things to study, but you seem to end up with very complicated things happening even in much lower dimensions (0+1 SYK models, 1+1 JT gravity models), far from the 3+1 dimensions one wants. There are no physical gravity degrees of freedom below 3+1 dimensions, so it’s all too possible that what one is studying in these lower dimensional models is exactly the things of no physical relevance to the real problem.

Finally, my feeling has always been that the difficulty of measuring purely quantum gravitational effects means that the only convincing quantum gravity will be one unified with the rest of physics, fitting together well with what we can observe. The danger with studying pure quantum gravity is that you’ll end up with not one theory, but an infinite number of them, empty of any predictive value. The landscape is a realization of that danger.

Update: By the way, this is roughly the 25th anniversary of AdS/CFT, Scientific American has a piece by Anil Ananthaswamy.

Posted in Uncategorized | 5 Comments

The Mystery of Spin

Scientific American has a new article today about the supposedly mysterious fact that electrons have “spin” even though they aren’t classical spinning material objects. The article doesn’t link to it, but it appears that it is discussing this paper by Charles Sebens. There are some big mysteries here (why is Scientific American publishing nonsense like this? why does Sean Carroll say “Sebens is very much on the right track”?, why did a journal publish this?????).

These mysteries are deep, hard to understand, and not worth the effort, but the actual story is worth understanding. Despite what Sebens and Carroll claim, it has nothing to do with quantum field theory. The spin phenomenon is already there in the single particle theory, with the free QFT just providing a consistent multi-particle theory. In addition, while relativity and four-dimensional space-time geometry introduce new aspects to the spin phenomenon, it’s already there in the non-relativistic theory with its three-dimensional spatial geometry.

When one talks about “spin” in physics, it’s a special case of the general story of angular momentum. Angular momentum is by definition the “infinitesimal generator” of the action of spatial rotations on the theory, both classically and quantum mechanically. Classically, the function $q_1p_2-q_2p_1$ is the component $L_3$ of the angular momentum in the $3$-direction because it generates the action of rotations about the $3$-axis on the theory in the sense that
$$\{q_1p_2-q_2p_1, F(\mathbf q,\mathbf p)\}=\frac{d}{d\theta}_{|\theta=0}(g(\theta)\cdot F(\mathbf q,\mathbf p))$$
for any function $F$ of the phase space coordinates. Here $\{\cdot,\cdot\}$ is the Poisson bracket and $g(\theta)\cdot$ is the induced action on functions from the action of a rotation $g(\theta)$ by an angle $\theta$ about the $3$-axis. In a bit more detail
$$g(\theta)\cdot F(\mathbf q,\mathbf p)=F(g^{-1}(\theta)\mathbf q, g^{-1}(\theta)\mathbf p)$$
(the inverses are there to make the action work correctly under composition of not necessarily commutative transformations) and
$$g(\theta)=\begin{pmatrix}\cos\theta&-\sin\theta&0\\ \sin\theta &\cos\theta &0\\ 0&0&1\end{pmatrix}$$

In quantum mechanics you get much same story, changing functions of position and momentum coordinates to operators, and Poisson bracket to commutator. There are confusing factors of $i$ to keep track of since you get unitary transformations by exponentiating skew-adjoint operators, but the convention for observables is to use self-adjoint operators (which have real eigenvalues). The function $L_3$ becomes the self-adjoint operator (using units where $\hbar=1$)
$$\widehat L_3=Q_1P_2-Q_2P_1$$
which infinitesimally generates not only the rotation action on other operators, but also on states. In the Schrödinger representation this means that the action on wave-functions is that induced from an infinitesimal rotation of the space coordinates:
$$-i\widehat L_3\psi(\mathbf q)=\frac{d}{d\theta}_{|\theta=0}\psi(g^{-1}(\theta)\mathbf q)$$

The above is about the classical or quantum theory of a scalar particle, but one might also want to describe objects with a 3d-vector or tensor degree of freedom. For a vector degree of freedom, in quantum mechanics one could take 3-component wave functions $\vec{\psi}$ which would transform under rotations as
$$\vec{\psi}(\mathbf q)\rightarrow g(\theta)\vec{\psi}(g^{-1}(\theta)\mathbf q)$$
Since $g(\theta)=e^{\theta X_3}$ where
$$X_3=\begin{pmatrix}0&-1&0\\ 1&0&0\\0&0&0\end{pmatrix}$$
when one computes the infinitesimal action of rotations on wave-functions one gets $\widehat L_3 + iX_3$ instead of $\widehat L_3$. $S_3=iX_3$ is called the “spin angular momentum” and the sum is the total angular momentum $J_3=L_3 + S_3$. $S_3$ has eigenvalues $-1,0,1$ so one says that that one has “spin $1$”.

There’s no mystery here about what the spin angular momentum $S_3$ is: all one has done is used the proper definition of the angular momentum as infinitesimal generator of rotations and taken into account the fact that in this case rotations also act on the vector values, not just on space. One can easily generalize this to tensor-valued wave-functions by using the matrices for rotations on them, getting higher integral values of the spin.

Where there’s a bit more of a mystery is for half-integral values of the spin, in particular spin $\frac{1}{2}$, where the wave-function takes values in $\mathbf C^2$, transforming under rotations as a spinor. Things work exactly the same as above, except now one finds that one has to think of 3d-geometry in a new way, involving not just vectors and tensors, but also spinors. The group of rotations in this new spinor geometry is $Spin(3)=SU(2)$, a non-trivial double cover of the usual $SO(3)$ rotation group.

For details of this, see my book, and for some ideas about the four-dimensional significance of spinor geometry for fundamental physics, see here.

Update: I realized that I blogged about much this same topic a couple years ago, with more detail, see here. One thing I didn’t write down explicitly either there or here, is the definition of spin in terms of the action of rotations on the theory. It’s very simple: angular momentum is the infinitesimal generator of the action of rotations on the wave-function, spin angular momentum is the part coming from the point-wise action on the values of the wave-function (orbital angular momentum is the part coming from rotating the argument). Using a formula from my older posting, for a rotation about the z-axis, the total angular momentum operator $\widehat J_z$ is by definition
$$\frac{d}{d\theta}\ket{\psi(\theta)}=-i\widehat J_z \ket{\psi(\theta)}$$
The spin operator $\widehat S_z$ is what you get for $\widehat J_z$ when you act just on the wave-function values. For a spin n/2 state particle, the wave-function will take values in $\mathbf C^{n+1}$. For the spin 1/2 case the action of rotations is by 2 x 2 unitary matrices of determinant one (the spinor representation). For a rotation by an angle $\theta$ about the z-axis, this is
$$e^{-i\theta\frac{\sigma_3}{2}}$$
so the spin operator is
$$\widehat S_3=\frac{1}{2}\sigma_3$$

Posted in Quantum Mechanics | 45 Comments

Math Job Rumors

I noticed yesterday a website named Math Job Rumors that has been operating for a couple months. No idea what the story behind it is other than that it’s clearly a descendant of Economics Job Market Rumors, which had some small participation by mathematicians, but is somewhat of a dumpster fire of misinformation, trolling, misogyny and various sorts of juvenile behavior. It looks like someone is trying to provide something similar aimed specifically at mathematicians, with some improvement over the EJMR environment.

One aspect of the site are threads devoted to rumors about tenure track and postdoc hiring in pure math, I don’t know if there has been something like this before. In theoretical physics there’s the venerable Theoretical Particle Physics Jobs Rumor Mill and the HEP Theory Postdoc Rumor Mill, but these are run in a very different way, with all information posted coming from one or more people who run the site, based on information sent to him/her/them.

The problem with the EJMR or Math Job Rumors model is that anonymity is needed for the whole thing to work, but once you start allowing people to post things anonymously, if you don’t moderate what is posted, you’ll quickly get overrun by idiots, trolls and other sorts of bad actors. Some kind of moderation is going on at the new site, but it’s unclear who is doing it or on what basis.

After starting with the Official Peter Woit blog hate thread, I moved on to reading a few other threads. Lots of dumb stuff, lots of inside jokes, lots and lots of trolling. I confess though that in one case the trolling was clever enough to make me laugh out loud, but it’s aimed at a really small audience. I did learn one piece of information that appears to be true, that prominent string theorist Shamit Kachru has gone on leave from his position at Stanford to work as a consultant in the finance industry.

In summary, for those mathematicians who read this blog and feel that they are not wasting enough time on mostly dumb internet stuff, you might want to take a look…

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Career Prospects for HEP-TH Students

Guangyu Xu, a student just finishing his Ph.D. at the Centre for Particle Physics at Durham University, recently sent me a public letter he wrote, explaining the story of his job search, in hopes that it might be useful to others in a similar situation. As he acknowledges, his research record has been rather weak, so not surprising that his postdoc applications were not successful.

Back when I was writing Not Even Wrong, I did some detailed research into whatever information I could find about the HEP-TH job market, but I haven’t tried to do this more recently. Erich Poppitz did some analysis of data from the Theoretical Particle Physics Jobs Rumor Mill (available here), but only up to 2017. Given the large investment of various government agencies in the support of Ph.D. students, I would think that there would be data on career outcomes gathered by such agencies, but haven’t tried to look. Any pointers to this kind of data from anyone who has been looking into it would be appreciated.

Also of interest would be any up-to-date job search advice from those like Guangyu Xu who have been going through this recently.

Posted in Uncategorized | 21 Comments

No Landau-Siegel zeros?

A couple weeks ago rumors were circulating that Yitang Zhang was claiming a proof of a longstanding open conjecture in number theory, the “no Landau-Siegel zeros” conjecture. Such a proof would be a very major new result. Zhang was a little-known mathematician back in 2013 when he announced a proof of another very major result, on the twin prime conjecture. Before that, he had a 2007 arXiv preprint claiming a proof of the Landau-Siegel zeros conjecture, but this was never published and known to experts to have problems such that at best the argument was incomplete.

Zhang now has a new paper on the arXiv, claiming a complete proof. The strategy of the proof is the same as in the earlier paper, but he now believes that he has a complete argument. At 110 pages the argument in the paper is quite long and intricate. It may take experts a while to go through it carefully and check it. Note that this is a very different story than the Mochizuki/abc conjecture story: Zhang’s argument use conventional methods and is written out carefully in a manner that should allow experts to readily follow it and check it.

For an explanation of what the conjecture says and what its significance is, I’m not competent to do much more than refer you to the relevant Wikipedia article. For a MathOverflow discussion of the problems with the earlier proof, see here, for consequences of the new proof, see here.

Update: I’m hearing that the above is not quite right, that what Zhang proves is weaker than the conjecture, although strong enough for many of its interesting implications. Perhaps someone better informed can explain the difference…

Update: Davide Castelvecchi at Nature has a news story here.

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Physical Mathematics c. 2022

The arXiv today has a very comprehensive survey of a conventional point of view on where “Physical Mathematics” is in 2022 and where it is going, written by a group of six authors. “Physical Mathematics” is a term popularized by one of them, Greg Moore (see here and here, with some commentary here), and it’s an expansion of a Snowmass white paper. A separate paper by Nikita Nekrasov covering the material listed in Section 10 is advertised as forthcoming with the title “The Ghosts of Past and Future Ideas and Inspirations on Interface of Physics and Mathematics”.

The term “Physical Mathematics” is a play on the more conventional name of “Mathematical Physics” to describe work being done at the intersection of math and physics. In its usage by Moore et al. it refers to a point of view on the relation of math and physics which heavily emphasizes certain specific topics that have been worked on intensively during the last four decades. These topics mostly have roots in seminal ideas of Witten and his collaborators, and involve calculational methods developed in quantum field theory and string theory research. The huge volume of this research is reflected in the fact that the survey reference section contains 62 pages giving 1276 separate references. A major problem for anyone taking up an interest in this field has been the sheer scale and complexity of all this work, and this survey should be helpful in providing an overview.

While some of these 1276 papers could equally well be simply characterized as “Mathematics”, it’s hard to describe exactly what makes a lot of the rest “Physical Mathematics” rather than “Physics”. Part of the answer is that these are not physics papers because they don’t answer a question about physics. A striking aspect of the survey is that while a lot of it is about QFT, the only mention at all of the QFT that governs fundamental physics (the standard model) is in a mention of one paper relevant to some supersymmetric extensions of the SM. The only other possible connection to fundamental physics I noticed was about the landscape/swampland, something only a vanishingly small number of people take seriously.

Also striking is the description of the relation of this field to string theory: while much of it was motivated by attempts to understand what string/M-theory really is, section 3.1 asks “What Is The Definition Of String Theory And M-Theory?” and answers with a doubly-boxed

We don’t know.

with commentary:

This is a fundamental question on which relatively little work is currently being done, presumably because nobody has any good new ideas.

In the background of this entire subject is the 1995 conjecture that there is a unique M-theory which explains various dualities as well as providing a unified fundamental theory. After nearly 30 years of fruitless looking for this, the evidence is now that there is no such thing, and maybe the way forward is to abandon the M-theory conjecture and focus on other ways of understanding the patterns that have been found.

I share a faith in the existence of deep connections between math and physics with those doing this kind of research. But the sorts of directions I find promising are very different than the ones being advertised in this survey. More specifically, I’m referring to:

• the very special chiral twistor geometry of four-dimensions (no twistors in the survey)
• the subtle relation of Euclidean and Minkowski signature (only a mention of the recent Kontsevich-Segal paper in the survey)
• the central nature of representation theory in quantum physics and number theory (very little representation theory in the survey)

Looking back at Greg Moore’s similar 2014 survey, I find that significantly more congenial, with a more promising take on future directions (in particular he emphasizes the role of geometric representation theory).

Posted in Uncategorized | 8 Comments

This Week’s Hype

CERN on Wednesday is hosting a colloquium talk by Joseph Lykken, who supposedly will discuss Prospects for experimental quantum gravity. There’s by now a long tradition of string theorists dealing with criticism that their research program is inherently immune from experimental test by making bogus claims about experimental testability. Lykken has been at it for at least twenty years (see here), and this sort of misleading claim about testability is the latest in a long campaign.

If you read the abstract, it looks like what Lykken is actually talking about is numerical simulations of an SYK model with of order 100 Majorana fermions on a quantum computer. Ignoring the quantum computer hype (unclear how long it will really be before such simulations are feasible), keep in mind that the SYK model is a quantum mechanical toy model, not a model of quantum gravity in a physical dimension. The only thing a quantum computer could test would be the validity of certain approximations schemes in such a toy model. For comments by David E. Kaplan about similar testability claims, see the interview discussed in the previous posting, which includes:

That there are actual people who are deciding string theory’s important, wanting to do string theory, and they’re even protecting the field. And some of those people are talking about how entropy now of a black hole can be described as a geometric thing, an entanglement, and that Hawking’s paradox about evaporating black holes is really wormholes, virtual wormholes coming from the inside to the outside, and all kinds of language. And you could test information theory of black holes using atomic physics experiments. And it’s literally bullshit.

There are people—prominent people—in physics who say, “I’m applying for this money from the DOE, but I know it’s bullshit.” And then there are experimental atomic physicists who don’t know and are shocked to learn that “What? String theorists don’t have a Hamiltonian? They don’t actually have a [laugh] description? What am I testing?”

Update: Lykken was giving Colloquium talks on Experimental String Theory nearly a quarter century ago. He was also one of the main sources for the embarrassing NYT 2000 article Physicists Finally Find a Way to Test String Theory.

“For the first 25 years, the thinking has been that superstring theory is so difficult to see experimentally that you have to figure it out by its own mathematical consistency and beauty,” Dr. Lykken said. “Now that’s completely changed. If this new picture is true, it makes everything we’ve been talking about testable.”

Hopefully science journalists have learned something and we won’t see a forthcoming NYT article on how “Physicists Finally Find a Way to Test Quantum Gravity”.

Update: Lykken’s slides are here. His proposal for an experimental test of quantum gravity is explicitly acknowledged as the same as one made by Lenny Susskind here in 2017. At the time that made no sense to me and I wrote about it here. It still makes no sense.

David E. Kaplan interview

There’s a long interview with David E. Kaplan (not the same person as David B. Kaplan…) by David Zierler at the AIP Oral Histories site. The whole thing is quite interesting and I recommend reading it, but I do want to point out that it shows that I’m a voice of moderation on the string theory issue. Some extracts follow:

About Ann Nelson and string theory in the 1990s:

She was extremely dismissive of string theory, and thought it was—you know, there was—my impression from her and from other people of that generation that weren’t doing string theory was that the string theorists were colluding in a sense, or were dismissing anything but string theory, and deciding that if you did string theory then you’re much smarter than the people who are not doing string theory. There was some unhappiness in the theoretical field. And the cancellation of the SSC probably added to that tension between the two.

But I don’t think she came of it from taking a side. I think she looked at the situation and said, “String theory is total bullshit.” In the mid-’80s, there were some realizations—there were some consistency checks that kind of worked in string theory, and people got super excited. Oh, my god, string—yeah, it could be the, you know, underlying thing to particle physics. But that was it.

The successes after that were few and far between. But there was an obsessive—like we’re studying the theory of quantum gravity. And it was deridingly called the theory of everything. And then they took that on, you know. We’re studying the theory of everything. And then the young people who want to do the greatest stuff would go to string theory. And there was a concern and some upset by the people not doing string theory that they’re absorbing a lot of people to do this crap, which is not very physics like. “It’s I believe the theory, and so I’m going to study all aspects of it, and maybe one day we’ll connect it with the physical world.” As opposed to I believe in the phenomenon, and I’m trying to explain that and more, and so I’m going to try out different theories and see what they’re consequences are.

And now I look back, and it’s obvious that string theory was bullshit in the sense of there were so many people working on it, and they were not manifesting any real progress externally. It was all internal consistency checks and things like that. And so at the time, you know, whenever it came up—and it didn’t come up much because there were no string theorists in Seattle—she was just very dismissive, like, you know, “What are those people doing? I don’t know what they’re doing.” [laugh]

About being a postdoc at SLAC:

There were a lot of string theorists at Stanford. I didn’t understand any of those talks. Or sometimes when the talks were not in strings, Lenny Susskind would yell at the speaker that this is bullshit or whatever, da, da, da, da—you know, abusive at some level. So Stanford was weird in that way.

About realizing what was going on in string theory, his evaluation of past (Strominger-Vafa) and current claims about string theory and black holes:

But—so I don’t—and it’s part of probably why I didn’t understand—I didn’t think of myself as a physicist because there’s a lot of physicists working very hard on what? I don’t know what they’re working on. It’s not—you know, I used to just think I’m too stupid to understand what they’re working on. And finally reading some of those papers, they’re not what—it’s stupid. There’s a lot of stupid stuff in there. String theory really is just stupid. It’s unbelievably stupid. There’s so many people who are working on it that don’t actually know physics that they can’t even describe a physical characteristic of the thing they’re calculating. They’re missing the whole thing.

So that’s when I realized string theory is like a video game. There are people just addicted to it. That’s all that’s happening. And it’s couched in the theory of everything and da, da, da, da.

So that’s all. I just kind of—I learned quite a bit about these things. And then I saw the people like Lenny Susskind, who was terrorizing people who work on regular physics, as just a plain asshole. That there are actual people who are deciding string theory’s important, wanting to do string theory, and they’re even protecting the field. And some of those people are talking about how entropy now of a black hole can be described as a geometric thing, an entanglement, and that Hawking’s paradox about evaporating black holes is really wormholes, virtual wormholes coming from the inside to the outside, and all kinds of language. And you could test information theory of black holes using atomic physics experiments. And it’s literally bullshit.

There are people—prominent people—in physics who say, “I’m applying for this money from the DOE, but I know it’s bullshit.” And then there are experimental atomic physicists who don’t know and are shocked to learn that “What? String theorists don’t have a Hamiltonian? They don’t actually have a [laugh] description? What am I testing?”

So I have converted a little bit to the opinions of my predecessors, only because I’ve actually done the work. I’ve actually tried to understand black holes of late, and I’ve gone back to those papers which are the breakthrough, celebrated, amazing papers about black holes, and there’s nothing in them. It’s really—it’s just a very simplistic picture where, look, if you take this hyper-simplistic picture, these numbers match these numbers, which means thinking about a black hole having entropy is correct, da, da, da, da, da.

No matter that the black hole they’re talking about is extremal. It doesn’t actually Hawking radiate. It’s a totally hyper-supersymmetric, multiple charges, free parameters. So now that I’ve finally dug into it, I realize that—not that all humanities fields are bad. But it’s much more like a humanities field where there are the prominent people in the field, and they decide what’s interesting. And that if you impress those people, you can get ahead. But that dictates then what research is done. And they’re not going to discover anything in that context. They’re not going to get anywhere. There’s not a lot of people doing—you know—thinking outside the box or just thinking diff…you know, doing different things, you know.

About the argument that string theory must be worthwhile because lots of people are doing it:

Zierler:

What is your response to a string theorist who would say, and I know this because one has said this to me, “Look, four people were doing this in 1968, 20 people were doing it in 1984, 1,000 people were doing it in 2000, and now there’s 6,000 people who are doing string theory all over the world. And that’s proof that there’s something here that’s worthwhile”? What is your response to that line of reasoning?

Kaplan:

[laugh] Take those numbers, continue the exponential, and apply it to Christianity—

Zierler:

[laugh]

Kaplan:

—and Islam and Judaism and Buddhism. Give me a fucking break. They’re describing a religion that can attract and addict people. That is exactly the kind of statement that shows it’s bullshit and non-scientific. They’ve proven it for me that they are not about discovering something. They’re about dominating the field for the purpose of what? That’s proof? Give me a break. Give me a fucking break. Slavery was very popular, and became widely used. Nazism. Come on. You can take extreme examples and show that that is so non-scientific and sick that the progress they have made is to get more people to work on something that isn’t producing anything. Oh, man, I wish you didn’t tell me that. [laugh]

About the current state of the field:

There are so many things to think about. I don’t know what narrowed our field. I don’t see it as we’re dying because we’re coming to the limits of what we can do, the limits of what we can calculate in string theory, and the limits of how big of a ring we can build. I think most people are just doing useless stuff.

And so that’s why I—the whole depression or whatever, that’s a product of the non-willingness to feel stupid by the majority of our field. Expertise is more important to them than discovery. And that’s what I think is happening. And so what we’re seeing is not the death of the field, but the death of a direction that is being committed to by 98% of them.

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Will Machines Have Good Mathematical Taste?

A question that has always fascinated me about mathematics is that of how the field manages to stay healthy and not degenerate in the way I’ve seen theoretical physics do as it lost new input from experiment. On Twitter, Ash Joglekar gave a wonderful quote from von Neumann that addresses this question. The quote was from a 1947 essay “The Mathematician” (available here and here). von Neumann argues that:

…mathematical ideas originate in empirics, although the genealogy is sometimes long and obscure. But, once they are so conceived, the subject begins to live a peculiar life of its own and is better compared to a creative one, governed by almost entirely aesthetical motivations, than to anything else and, in particular, to an empirical science.

but warns

As a mathematical discipline travels far from its empirical source, or still more, if it is a second and third generation only indirectly inspired by ideas coming from “reality” it is beset with very grave dangers. It becomes more and more purely aestheticizing, more and more purely l’art pour l’art. This need not be bad, if the field is surrounded by correlated subjects, which still have closer empirical connections, or if the discipline is under the influence of men with an exceptionally well-developed taste. But there is a grave danger that the subject will develop along the line of least resistance, that the stream, so far from its source, will separate into a multitude of insignificant branches, and that the discipline will become a disorganized mass of details and complexities.

which describes all too well what has happened to string theory. What saves a field from this? “Men with an exceptionally well-developed taste”? He poses the general question this way:

What is the mathematician’s normal relationship to his subject? What are his criteria of success, of desirability? What influences, what considerations, control and direct his effort?

Normally mathematicians are loath to debate this kind of “soft” topic, but the rise of computer software capable of producing proofs has recently led several first-rate mathematicians to take an interest. Each year the Fields Institute in Toronto organizes a Fields Medal Symposium, structured around the interests of a recent Fields Medalist. This year it’s Akshay Venkatesh, and the symposium will be devoted to questions about the changing nature of mathematical research, specifically the implications of this kind of computer software. Last year Venkatesh wrote an essay exploring the possible significance of the development of what he called “Alephzero” (denoted $\aleph(0)$):

Our starting point is to imagine that $\aleph(0)$ teaches itself high school and college mathematics and works its way through all of the exercises in the Springer-Verlag Graduate Texts in Mathematics series. The next morning, it is let loose upon the world – mathematicians download its children and run them with our own computing resources. What happens next – in the subsequent decade, say?

Among the organizers of the conference is Michael Harris, who has written extensively about mathematical research and issues of value in mathematics. Recently he has been writing about the computer program question at his substack Silicon Reckoner, with the most recent entry focusing on Venkatesh’s essay and the upcoming symposium.

One of the speakers at the symposium will be Fields medalist Tim Gowers, who will be addressing the “taste” issue with Is mathematical interest just a matter of taste?. Gowers is now at the Collège de France, where he is running a seminar on La philosophie de la pratique des mathématiques.

I’ve tried asking some of my colleagues what they think of all this activity, most common response so far is “why aren’t they proving theorems instead of spending their time talking about this?”

Update: For yet more about this happening at the same time, there’s a talk this afternoon by Michael Douglas on “How will we do mathematics in 2030?”.

Update: The talks from the Fields Institute program are now available online.

Terry Tao is one of the organizers of a planned February workshop at UCLA involving many of the same people, much the same topic.

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