Fantastic Realities

Frank Wilczek has a new book out, it’s called Fantastic Realities: 49 Mind Journeys and a Trip to Stockholm, and is published by World Scientific. It’s a great read by one of the best in the business for anyone interested in physics and should be accessible to people with a wide variety of backgrounds. The book consists of a collection of 43 short pieces, most of which have been published elsewhere (often as “Reference Frame” columns in Physics Today), broken into 11 sections, each with a short introduction. The writing is exceptionally well-informed, elegant, lucid, and thought-provoking.

There’s also a section of 6 original poems, which I’ll not comment on since I’m not a literary critic, as well as a final section of extracts from Wilczek’s wife Betsy Devine’s blog Funny Ha-Ha or Funny Peculiar?. The blog entries explain exactly what it’s like to be a family member of a Nobel prize winner, and contain lots of useful tips for you and your fellow family members should you ever win a Nobel prize and need to know exactly how to prepare for your trip to Stockholm. I hope I won’t be damaging sales of the book by noting that they’re available on-line.

Wilczek started out his career with a bang, discovering the asymptotic freedom of Yang-Mills theory in joint work with his advisor David Gross. He was thinking of this work in terms of perhaps showing that the SU(2) part of the new electro-weak gauge theory of Weinberg and Salam might not have the same problem that QED had (effective coupling growing at short distances, invalidating perturbation theory), but Gross was thinking more about the strong interactions and the short-distance scaling behavior recently observed at SLAC. If it could be shown that Yang-Mills theories also had effective couplings that grew at short distances like all other known QFTs, that would rule out QFT as a theory of the strong interactions. The discovery of asymptotic freedom made it clear that Yang-Mills theories might provide a successful strong interaction theory, and there was one obvious choice for the right theory: QCD.

Many of Wilczek’s pieces deal with QCD in one way or another, from explaining his original work with Gross, to more recent developments concerning high temperature (relevant to heavy-ion collider experiments) and high density versions of the theory. He also explains some of the beautiful data that has accumulated over the past more than thirty years since its discovery that give us impressive evidence for the validity of QCD. Wilczek puts QCD into a more general context, explaining how logarithmic running of coupling constants can explain the small size of the strong interaction scale when compared to the scale of a putative GUT or even the Planck scale. Besides QCD, he provides excellent discussions of the rest of the standard model, the electroweak theory.

In several different pieces about beyond the standard model physics, Wilczek emphasizes two pieces of evidence that we have for some sort of GUT scenario. One is the fact that if you take the 16 dimensional half-spinor representation of SO(10), under the SU(5) subgroup it decomposes as 1 + 5 + 10, giving all the standard model fields of one generation (including a right-handed neutrino), but in a single irreducible representation. The second is the calculation (that he did in 1981 with Dimopoulos and Raby) of the running coupling constants for the supersymmetric SU(5) GUT (see here, although I’m not sure I agree that this falsifies Popper), which show much closer unification of the three couplings at a single energy than in the non-supersymmetric case.

These two facts are definitely the strongest evidence around for the idea of a supersymmetric GUT, an idea which has dominated thinking about beyond the standard model physics for nearly 30 years, but they are far from convincing. Wilczek deals with the other main idea that has dominated the field, string theory, by essentially ignoring it. I only noticed one or two mentions of string theory in passing in the book. He’s not taking a position pro or con on the subject, just deciding that other things are more worth writing about.

The longer pieces in the book are among the best, including a piece on the Dirac equation, written for a book on the most beautiful equations, and pieces on fractional charge quantization and quantum field theory in general, which are a bit more technical than the others. Wilczek brings in interesting historical context to most of the things he writes about, often in an original way.

Perhaps my favorite piece is one entitled “What is Quantum Theory?”, which deals with one of my obsessions. Wilczek claims that perhaps we still don’t properly understand the significance of quantum theory, especially what it has to do with symmetries. He notes that Hermann Weyl, soon after the discovery of quantum mechanics, realized that the Heisenberg commutation relations are the relations of a Lie algebra (called the Heisenberg Lie algebra), and that this exponentiates to a symmetry group (the Heisenberg group to mathematicians, Weyl group to physicists). Wilczek goes on to speculate that:

The next level in understanding may come when an overarching symmetry is found, melding the conventional symmetries and Weyl’s symmetry of quantum kinematics (made more specific, and possibly modified) into an organic whole.

Wilczek is still at it; last week he had a new preprint with Brian Patt which I wish I had time to look at more carefully. In this month’s Physics Today, he has another Reference Frame article, now about the anthropic principle, and I’ll write about that soon and separately.

There’s also a podcast of an interview with Wilczek and his wife conducted at a party in Brooklyn held last month to celebrate the release of the book. If you listen closely maybe you can hear me and others chatting in the next room, despite being told to keep it down because of the recording session…

Posted in Book Reviews | 4 Comments

Comment on Comments

Over the last week or so I’ve heard privately from several very different parties with complaints about the comment section here. The general feeling is that it would be more useful and attract more serious contributions if the level of uncivil, disrespectful ad hominem attacks was much lower. One contributing factor mentioned is that anonymity allows people to behave in uncivil behavior that they would not engage in if their names were publicly attached to their words. On the other hand, the worst offender in this is someone who is not anonymous.

I’d be curious to hear thoughtful comments by others about this. My own feeling at the moment is that the criticism is accurate: the uncivil atmosphere here keeps many serious people who would have something interesting to contribute from doing so. The anonymity is probably part of this problem, although given the current unhealthy situation in particle theory, some people have very legitimate reasons for keeping their comments anonymous.

In many ways I think the comment section has been a success, but it could stand a lot of improvement. Unfortunately I don’t know of any really successful models out there to follow. Among the more active blogs by physicists, Cosmic Variance does a good job of keeping a civil discussion going, but it is rarely about physics these days. Jacques Distler’s Musings has high-level content in its postings, but no one has submitted a single comment about physics there in over a month and a half. The comments at Lubos Motl’s Reference Frame are as uneven as the blog’s proprietor.

I already delete quite a few comments on grounds of lack of civility, but tentatively plan on trying to raise that standard by deleting a larger fraction of uncivil comments, especially if they are posted anonymously. It would help if people could keep the following in mind when posting comments:

1. Please consider abandoning anonymity and posting under your real name, unless you have a good reason for not doing so.

2. Please take much greater care to keep comments civil and respectful. Ad hominem argument about the ignorance and lack of intelligence of people you disagree with has no place here.

3. Please ignore silly comments when they appear. Maybe I’ll also think they are silly and just adding to the noise and will get around to deleting them, maybe not. But in any case you’re not adding anything by submitting a comment criticizing the silliness, but instead are adding to the hostility level.

Constructive comments are welcomed. One thing to keep in mind is that I already am spending more time on this than I should, suggestions that involve a lot more work on my part are non-starters.

Posted in Uncategorized | 35 Comments

Priority for the Landscape

The string theory anthropic landscape point of view has now become so widely accepted and entrenched in the particle theory community that various people are making their claims about having had the idea first. The standard first paper that people generally reference is Leonard Susskind’s February 2003 The Anthropic landscape of string theory, which now has 243 citations. Susskind claims credit at least for the “Landscape” terminology in his recent book.

Last month Dutch string theorist Bert Schellekens posted a paper on the arXiv entitled The Landscape “avant la lettre”, in which he claims credit to some extent for the idea. He is quite enthusiastic about the Landscape as a paradigm shift and a new way of doing physics:

… I think even today we are only in an intermediate stage of a very slow shift of opinions regarding the objectives of our field. Although landscape ideas and even the anthropic principle are now at least discussed, it seems to me that the importance of the landscape is still severely underrated. I have tried to express my enthusiasm about the recent progress during seminars, but apparently with little success.

Schellekens claims that:

My own thoughts in this direction started around 1987. The year before I had published a paper with Wolfgang Lerche and Dieter Lust. Like other authors at the time, we found large numbers of four-dimensional chiral string theories, but much more than others we made a point of strongly emphasizing the non-uniqueness of the result.

He goes on to say that already back then it was clear to him that string theory was sending the message “if we find one vacuum we are going to find a huge number of them.” He recalls that when he was working at CERN in the years before 1992 he was promoting the anthropic string theory landscape idea and encountering a lot of resistance, often from people who now tell him that they had always been saying this kind of thing.

In 1998, at the occasion of his inauguration at the University of Nijmegen he gave a speech on this subject in Dutch. In the arXiv preprint Schellekens reproduces the Dutch text of his speech, together with an English translation. He notes that he used the Dutch word “landschap” in the text, although he mostly referred to the landscape using the Dutch word for a “mountain range”.

Schellekens admits that string theory may not be correct, but he says that string theory implies the landscape, so for string theory to be correct the landscape must exist. His only comment indicating that this might be a problem for string theory is that

…the unexpectedly huge size of the landscape is making it a lot harder to convince ourselves of that.[e.g. the correctness of string theory]

He does admit that back in 1998 he expected the size of the landscape to be much smaller than it now appears to be, smaller than the 1080 vacua that, uniformly distributed, could cover all possible values of the standard model parameters to the accuracy that we can measure them. So he expected that one would be able to somehow check string theory by seeing if one of the vacua agreed with the real world. Now that the number of vacua seems to be vastly greater than this, eliminating any reasonable hope of checking string theory this way, for some unfathomable reason his enthusiasm for the idea is undiminished if not intensified.

If you just can’t get enough of landscape discussion, there are recent blog entries on the topic by Sabine Hossenfelder and Alejandro Satz.

Update: The last-gasp hope for getting a prediction out of the landscape is that there is some useful structure in the landscape, so that it doesn’t densely cover all possible standard model parameters. Washington Taylor and Michael Douglas have been looking for such a thing amongst vacua, trying to find some correlations between properties of these vacua. For more about this, see Taylor’s web-page. Lubos has a blog posting about all this, in which Taylor explains the philosophy:

If we find 5 models with features X and Y of the standard model which all have feature Z which is not yet observed it is not very definitive. If we look in different parts of the string theory landscape and find that all 1020 models we know how to construct with features X and Y of the standard model have feature Z also it begins to carry some weight as a possible prediction.

So far, as you might expect, since there is no known reason for such correlations, they haven’t found any. Lubos reports:

Wati’s result in his particular examples was that there was virtually no information in the correlations: the difference was one bit and the distributions of different quantities were essentially independent Gaussians.

and goes on to rant:

Surely the physicists have not been working for 30 years to extract 1 bit of information – whose probability of being correct is moreover 50 percent. Even if there were any correlation, I would probably find such a correlation physically uninteresting. We know for sure that some of these correlations would agree with those observed in the real world, and some of them would not.

What will you do with this probable outcome? Will you overhype the “successful” patterns as evidence that the landscape reasoning is good, while you will be silent about the “unsuccessful” ones? I would count this activity as a part of astrology or catastrophic global warming theory, not physics. It’s frustrating to see that this is what is apparently being intended.

I wonder whether the people who were producing the very convoluted microscopic theories of the luminiferous aether in the 19th century really believed that this was the way to say anything new about physics – or whether most of them did these things just to do something and keep their jobs. Einstein took over in 1905 and showed not only that the aether was a ludicrous fantasy – but moreover, the absence of the aether is one of the basic principles that underlies his relativistic revolution in physics. Today, all of us – except for those in loop quantum gravity – know that the aether is a silliness that is not realized physically and that was never well motivated.

My feeling about the random model building and random model guessing is somewhat analogous to the random construction of the aether from gears and wheels. We’re missing something and we should not fool ourselves into thinking that we’re not.

Update: The Harvard physics department seems to be having quite a few seminars on the Landscape, and one participant reports:

A funny aspect of these discussions is that one can’t quite distinguish which of the considerations are jokes and which of them are meant seriously. At least I can’t distinguish them.

Posted in Uncategorized | 147 Comments

arXiv Weirdness

Some rather strange things are going on at the arXiv, especially in the hep-th section:

Besides the usual string theory papers, which just get more and more pointless as time goes on, some very weird things have started to appear on hep-th. Last night, there was a new paper entitled Amplitude for existence of spacetime points that makes no sense to me. It’s by Monica Dance, who seems to have no academic affiliation, but does have a Hotmail account. Not clear why the hep-th moderator allows this kind of thing. One explanation would be that earlier this year she put Symmetry limitations on quantum mechanical observers, and conjectured link with string theory on hep-th, an equally nonsensical document which presumably was all right because it had “string theory” in the title. Maybe once you get one paper about “string theory” on hep-th, you become an “active researcher” and can put whatever you want there.

Actually, to get to be an “active researcher” according to the arXiv, as long as you’re studying string theory, you don’t need to even ever have written a paper at all. Recall that arXiv trackbacks to this blog have been banned on the grounds that I’m not an “active researcher” (for more about this, go here). But this hep-th paper has a trackback to this blog entry by Nicola Ambrosetti. Ambrosetti’s blog contains some fine entries and having trackbacks to it makes good sense, but he appears to be a student at Neuchatel who has never written a paper, so I would have guessed that according to arXiv standards he wasn’t yet an “active researcher”. Maybe standards are different when your blog entries have titles like Barton Zwiebach Rules!.

Over the last few months I’ve written quite a few blog postings that discuss arXiv papers. In many cases I happen to think that either the posting or the discussion in the comment section is something that someone interested in the paper might find worthwhile. In the case of postings about string theory papers (here and here), non-string theory papers, and non-string theory papers claiming to be string theory papers, no trackbacks to my blog were allowed. This is what I expected, but for some mysterious reason, a trackback to this blog entry about a paper critical of string theory was allowed. So, it seems that the arXiv is allowing trackbacks to my blog entries only when they are about papers criticizing string theory.

None of this makes any sense to me, so I tried politely writing to the arXiv person at Cornell that my logs showed had examined my blog entry just before their trackback system generated a trackback to it, asking about what was going on. No response to that inquiry, as to all my other inquiries about arXiv trackback policy. To find out what their policy now is, I guess I’ll just have to wait for the relevant authorities to get around to posting a blog entry or writing a comment at some blog somewhere, since that seems to be their preferred manner of dealing with this issue.

Update: I did get an e-mail response from someone at Cornell about my enquiry about trackbacks. It didn’t address the question of how hep-th trackbacks are now being moderated, but did point out that the trackback system is still in an experimental state, that they have recently had significant personnel changes, and that sorting out the trackback system hasn’t been one of their highest priorities.

Update: Lubos is even more out there than usual with his comments on this. It seems that my objections to the Dance paper are an example of sexism.

Posted in Uncategorized | 57 Comments

More Links

If you just can’t get enough of pictures of mathematicians, head over to the Oberwolfach Photo Collection. This is a huge collection, which I recently ran across when trying to locate something by Graeme Segal. It also includes a photo of a frequent contributor here.

The AMS has put quite a few whole books on-line. Recently they added the three-volume set A Century of Mathematics in America here, here, and here. Another interesting volume is Mathematics into the Twenty-First Century, which includes some wonderful survey articles, including a very long series on Lie theory by Roger Howe, and one on Geometry and Quantum Field Theory by Witten.

Terrance Tao has a sort of research blog.

In the category of interesting-looking work that I haven’t yet had time to read carefully and think about, here are two papers on an approach to studying pure Yang-Mills theory, by Freidel and Freidel and collaborators.

Update: A correspondent suggests I mention another famous mathematician whose photo is on the Oberwolfach site.

Posted in Uncategorized | 39 Comments

Discovering the Quantum Universe

HEPAP today released a new publication designed to convey to the general public excitement about prospects for particle physics in the coming years. It’s entitled Discovering the Quantum Universe, and it has a companion web-site. Both the web-site and the document itself are beautiful and impressive productions. The web-site also contains the earlier 2004 HEPAP report Quantum Universe, which was mentioned in one of the earliest posts of this blog. The newer document is based on an earlier version from last summer, and one of its main goals is to make the case for a linear collider. In some sense this is promotional material for the conclusions recently reached by the EPP2010 panel. Also part of the promotional activity today is a briefing for members of Congress that will include a talk by my colleague Brian Greene.

While I hope that this all has the intended effect of getting the public, the Congress and the Administration excited about particle physics and willing to support it at the level necessary to fund a new generation of machines and experiments, as you might guess I have my doubts about the wisdom of some of the material included in this report. Unlike the EPP2010 report, which oversold string theory a bit, this report oversells it a lot, with language like:

… preliminary studies have looked at the ability of linear collider experiments to detect the telltale harmonies of strings. Here linear collider precision is essential, since the string effects appear as small differences in the extrapolated values of the superpartner parameters. A combined analysis of simulated LHC and ILC data shows it may be possible to match the fundamental parameters of the underlying string vibrations.

The inclusion of this kind of language seems to me to be misleading and irresponsible. Ten years from now when we have real LHC data, know that the ILC can’t tell us anything about string theory, and are asking the US government to put up large sums to finish the ILC, we’ll have to hope that the relevant decision makers didn’t get convinced by this report that the ILC is a machine designed to get information about string theory.

Update: More about this at Cocktail Party Physics.

Posted in Uncategorized | 42 Comments

Dibner Institute Closes

The Dibner Institute and Burndy Library at MIT will soon be closing, with the Burndy collection moving to the Huntington Library in California near Caltech. The Dibner Institute is devoted to research in the history of science and technology, and I mentioned it a couple years ago here. Among the interesting things the Dibner has on-line are copies of lecture notes on quantum electrodynamics from Freeman Dyson in 1951 and Fritz Rohrlich in 1953.

Posted in Uncategorized | 7 Comments

Simons Donation to Stony Brook

Stony Brook announced yesterday that Jim Simons will be making a $25 million dollar donation to the university, focused in the area of mathematics and physics. This is a great deal of money for a math or physics department, and it is the largest single cash donation ever made to any of the SUNY institutions.

Simons was responsible for building up the Stony Brook math department, which he joined as chair in 1968. About his hopes for what his donation will do, he says:

During the past thirty years mathematics and physics have grown increasingly intertwined. This is particularly true in the cases of string theory, quantum field theory and cosmology, which have all depended upon and stimulated advanced work in geometry and topology. Buttressed by its close relationship with Brookhaven National Laboratory and building on a fine faculty already in place we believe our gift can help propel Stony Brook into the very top rank in these central fields.

Posted in Uncategorized | 13 Comments

Quick Links

I’ve been much too busy the past few days, so haven’t had time to write anything new here. One thing that has been keeping me busy is going over the copy-edited version of the American edition of my book, which will be published in September by Basic Books. The British edition, published by Jonathan Cape, should be available June 1, both in Britain and Canada, and presumably one can order it from the British or Canadian versions of Amazon. The American version will have a somewhat different preface, and has been separately copy-edited, so there will be minor changes (beyond just changing British spellings back to the American ones I first wrote down…). Late last week I was sent an early copy of the British version of the book itself, and I’m very happy with how it looks.

Last week I also spent a significant amount of time at my colleague John Morgan’s 60th birthday conference, which was held here in the math department. Morgan is one of the leading figures in topology, and over the years has worked on a wide range of different kinds of mathematics, often bringing the subject together with other very different parts of mathematics. At the moment he’s involved in at least two projects, one involving Calabi-Yaus with Chuck Doran, another an ambitious attempt with Gang Tian to work out the details of Perelman’s proof of the Poincare conjecture. He’s also doing a stellar job as chair of our department.

Morgan has collaborated with and interacted significantly with Witten over the years, and Witten gave a wonderful talk at the conference on Gauge Theory and the Geometric Langlands Program. This was really just a taste aimed at mathematicians of his recent work on geometric Langlands and gauge theory. He explained some of the history of Montonen-Olive duality, some of the relevance of supersymmetry to mathematics, and then explained what an ‘t Hooft operator in gauge theory is, and that it is related to the Hecke operators studied in geometric Langlands.

Here are some quick links to interesting things I’ve run across recently:

John Baez has a new edition of his proto-blog “This Week’s Finds in Mathematical Physics”. It contains a beautiful exposition of the circle of very different sorts of mathematics that all gets related via Dynkin diagrams.

Greg Moore and his recently graduated student Dmitriy Belov had a beautiful new paper on self-dual field theory in 4l+2 dimensions.

Christianity Today has an article entitled Science in Wonderland, which mentions Susskind and string theory and notes:

This theory has not met with, shall we say, universal approbation, not least because it can’t be empirically tested. You could even say it’s not science, and some have said that, but they don’t hiss the way they do when they talk about Intelligent Design.

The AMS has a new web-site devoted to Mathematical Imagery.

In the comment section here, Bert Schroer pointed to some web-sites I wasn’t aware of that contain all sorts of links to various material related to the algebraic approach to QFT. These include the home page of Stephen Summers and the Local Quantum Physics Crossroads” hosted at Gottingen.

Update: If you want to know why the mathematics associated with Dynkin diagrams can’t be usefully explained or viscerally understood without string theory, as well as why John Baez is a proto-human, you can consult the blog of a prominent Harvard faculty member. He also notes that

Peter Woit is another proto-human who eats everyone who dares to look in between the clouds. Be afraid. Be very afraid.

and explains in great detail why

it is important not only to learn string theory well but also to emphasize that and explain why people like Peter Woit are intellectual barbarian cannibals. 😉

Posted in Uncategorized | 40 Comments

Hype from the Swampland

Over the last twenty years there has been an endless stream of hype about “tests of string theory”, pretty much all of it complete nonsense. For some examples just from the first few months of this year, see here, here, and here. Most of these examples seem to have been generated by confused PR people who misunderstood carefully worded comments by various physicists about the relation of their work to string theory. The average person just finds it hard to believe that it really could be true that there is no way to test a theory that has gotten so much attention for so long from so many prominent people.

Today there’s new nonsensical hype about testing string theory, but this time it’s due not to a clueless press relations person, but to several physicists, including the one who decides what gets into the hep-th arXiv and what doesn’t. The hype isn’t buried in the article somewhere, it’s in the title: Falsifying String Theory Through WW Scattering. In their abstract, the authors claim to derive a bound on coefficients of operators in the effective electroweak Lagrangian such that “a measured violation of the bound would falsify string theory.”

The first striking thing about this paper that purports to show that string theory is falsifiable is that there’s actually nothing about string theory in it. It’s only four pages long, and the first three pages consist of an introduction followed by some calculations in the non-linear sigma model one might want to use as an effective low-energy theory of pions. This is just a warm-up exercise for the real calculation that the authors want to make some claims about, which involves the low energy effective action for a non-linear sigma-model coupled to gauge fields. This is the model that one expects to describe the low-energy behavior of the Higgs field coupled to electroweak gauge fields, if one takes the Higgs mass to be very large.

The authors go on to just copy the terms in the relevant Lagrangian down from a 1993 paper by Appelquist and Wu, then stop and promise to actually calculate the relevant bounds in a forthcoming paper. Unless one wants to try and sit down and do oneself the calculation the authors haven’t done yet, it’s hard to know what these bounds will actually say and whether they will really be non-trivial. It’s also unclear to me exactly how all of this depends on the Higgs mass, which I guess is being assumed to very high, thus violating the known indirect experimental bounds from precision electroweak measurements (which assume the standard model). Very hard to tell about any of this, since it’s dealt with in a paragraph with no equations.

It turns out that the author’s proposal isn’t a proposal to falsify string theory at all, but a proposal to falsify the idea that physics satisfies Lorentz invariance, analyticity and unitarity at high energies. This would falsify our standard ideas about QFT, but it wouldn’t falsify current ideas about string theory. The authors don’t define what they mean by “string theory”, but presumably they mean some version of perturbative string theory. This involves a divergent series (even granting the conjecture that one can make sense of these amplitudes at more than two loops), so it’s unclear how one is going to “falsify” that. Standard ideology about non-perturbative string theory (“M-theory”) is that it will involve some new ideas about space and time, so I don’t see how one can assume that it won’t violate the analyticity and Lorentz invariance properties characteristic of QFT in flat space-time. I’m not convinced that the author’s proposal will falsify anything, but if it does, it will be QFT that is falsified, not string theory. After all, this paper is a QFT calculation (or, more accurately, a promise to do a QFT calculation), not a string theory calculation.

The authors note the problems of non-predictivity generated by the Landscape, and in the first version of the paper write:

Moreover, even if it is found to be difficult to generate the proper model from string theory, one would sooner accept the notion that it is the theorist’s imaginations which are insufficient than conclude that string theory has been falsified.

In the second version of the paper, they seem to realize that this attitude of “one” is kind of unscientific, and they change it to

Moreover, even if it is found to be difficult to generate the proper model from string theory, some would sooner accept the notion that it is the theorist’s imaginations which are insufficient than conclude that string theory has been falsified.

This new version leaves it unclear who this unscientific “some” is. In both versions they note correctly that:

This line of reasoning has resulted in sharp criticism of the theory.

This paper is motivated by the “swampland” program of trying to find effective field theories that can’t be the low energy limits of a string theory. I’ve written about the problems with this elsewhere, and blog postings by Distler have amply embodied what some of them are. In his first posting on the Swampland he gave as an example of a low energy effective theory that couldn’t come from string theory one with only one or two generations, only to be told by a commenter how to construct such things from string theory. He has a more recent blog posting called Avatars of Nonlocality? about the swampland work of Arkani-Hamed and collaborators that motivated this new paper. In a comment there, Arkani-Hamed takes him to task:

This post is a great illustration of what I dislike about blogs and more specifically trackbacks. As I explained to you when you were visiting Harvard last week, your first point about the RG running is standard effective field theory (with an abbreviated discussion in our paper because it is fairly common knowledge–read Georgi’s book). I of course don’t object to your writing a paper to clarify these points to yourself or others. But this is minor. More importantly, as I also explained to you both in email and in person, what you write about the DGP model is totally wrong…

Now, in general I don’t care about what is said on blogs, as I believe they largely fulfill the primate desire to look and see what the other monkeys are doing, and I think they are a big waste of time. But I do object to having a trackback, linked from my paper, to a post about it that claims that one of the central claims is wrong, when a 45 second computation, even done for the reader’s convenience in the paper itself, refutes the argument.

This whole subject really is a swamp, if you ask me, and has nothing at all to do with physics, including nothing to do with the supposed “falsifiability of string theory”. It will be interesting to see if a referee thinks otherwise.

Update: It has been pointed out to me that I’m being a bit unfair to the authors in characterizing the calculation in this paper as a “warm-up exercise”, since they claim that it is a correct first approximation to the actual calculation that they intend to do.

Posted in Swampland | 77 Comments