Not Even Wrong
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Wed, 22 Nov 2017 13:03:46 GMTFeedCreatorClass 1.0 dev (specificfeeds.com)Various Physics News
http://www.math.columbia.edu/~woit/wordpress/?p=9742
<p>First, two local events, involving well-known physics bloggers:</p>
<ul>
<li>Last Thursday I had the pleasure of attending an event at NYU featuring Sabine Hossenfelder and Natalie Wolchover in conversation. You can watch this for yourself <a href="https://livestream.com/accounts/17645697/events/7933963/videos/166054401">here</a>. If you’re not following Hossenfelder on <a href="http://backreaction.blogspot.com/">her blog</a> and at <a href="https://twitter.com/skdh">Twitter</a> (and planning to read her <a href="https://www.hachettebookgroup.com/titles/sabine-hossenfelder/lost-in-math/9780465094257/">forthcoming book</a>), as well as reading Wolchover’s <a href="https://www.quantamagazine.org/authors/natalie/">reporting at Quanta magazine</a>, you should be.</li>
<li>Next week there will be an event out in Brooklyn advertised as covering the <a href="https://pioneerworks.org/programs/scientific-controversies-no-13/">Scientific Controversy over string theory</a>. The idea seems to be to address this controversy by bringing to the public two well-known and very vocal proponents of one side of it.</li>
</ul>
<p>For a Q and A with another well-known physics blogger, there’s <a href="http://physicstoday.scitation.org/do/10.1063/PT.6.4.20171116a/full/">Tommaso Dorigo at Physics Today</a>.</p>
<p>For a couple of encouraging indications that the theoretical physics community may finally be taking seriously the need to give up on failed thinking and try something new, there’s</p>
<ul>
<li>A conference next month in Italy on <a href="https://agenda.infn.it/conferenceDisplay.py?confId=14269">Weird Theoretical Ideas (Thinking outside the box)</a>.</li>
<li>An <a href="http://indico.ipmu.jp/indico/event/134/contribution/17/material/slides/0.pdf">interesting talk</a> at a recent IPMU conference by Yuji Tachikawa. I like his conclusion:<br />
<blockquote><p>Basically, all the textbooks on quantum field theories out there use an old framework that is simply too narrow, in that it assumes the existence of a Lagrangian.</p>
<p>This is a serious issue, because whey you try to come up e.g. with a theory beyond the Standard Model, people habitually start by writing a Lagrangian … but that might be putting too strong an assumption.</p>
<p>We need to do something</p></blockquote>
</li>
</ul>
<p>In General Relativity related news, there’s a new edition out of <a href="https://press.princeton.edu/titles/11169.html">Misner, Thorne and Wheeler</a>, the book from which many of us learned both geometry and GR. It comes with new prefaces from David Kaiser as well as Misner and Thorne (which an appropriate search on the Amazon preview might show you…). In other Wheeler-related news, Paul Halpern has a new book out, <a href="https://quantumlabyrinth.com/">The Quantum Labyrinth</a>, which tells the entangled stories of Feynman and Wheeler.</p>
<p>Finally, also GR related, the Perimeter Institute has announced the <a href="https://www.theglobeandmail.com/news/national/waterloo-institute-to-take-on-the-universe-with-new-cosmology-focused-research-hub/article37035967/">formation of a new cosmology-focused “Centre for the Universe”</a>, funded by an anonymous 10-year $25 million donation. It will be led by cosmologist Neil Turok, who is soon to step down as director of Perimeter. </p>
Mon, 20 Nov 2017 16:56:32 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9742Breakthrough Prize 2018
http://www.math.columbia.edu/~woit/wordpress/?p=9737
<p>The Breakthrough Prizes for 2018 will be awarded at a ceremony on December 3, I believe at the usual NASA Hangar 1 in Mountain View. The next day Stanford will host the 2018 Breakthrough Prize symposium, which one will be able to watch live from the <a href="https://www.facebook.com/BreakthroughPrize">Breakthrough Prize Facebook page</a>.</p>
<p>The symposium schedule is available <a href="http://symposium.breakthroughprize.org/schedule">here</a>, and while it does not list the Prize awardees, it does appear to list the titles of the talks. From this it looks like the math \$3 million will go to a geometer, who will talk about “Geometry at Higher Dimensions”. There may be several \$100,000 New Horizons Prizes for younger mathematicians, but at least one will be to an analytic number theorist, who will talk about “Analytic Number Theory in Everyday Life”.</p>
<p>For the \$3 million physics prize, it looks like it is going to be split five ways and go to cosmologists/astrophysicists. The talks by laureates are “The Next Decade in Cosmology”, “Gravitational Waves and Cosmology”, “Search for Extraterrestrial Intelligence”, “A New Instrument for Listening to the Universe” and “The Beginning and End of the Universe”.</p>
Thu, 16 Nov 2017 20:07:39 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9737Various Stuff
http://www.math.columbia.edu/~woit/wordpress/?p=9708
<p>A few links that may be of interest. Mathematics first:</p>
<ul>
<li>A seminar <a href="http://www.math.ens.fr/seminaire_G/">“Lectures Grothendieckiennes”</a> on the mathematical ideas of Alexander Grothendieck is taking place this year in Paris, and has just recently started up.</li>
<li>My ex-Columbia colleague Jeff Achter is one of the authors of an unusual new math paper: <a href="https://arxiv.org/abs/1710.10726">Hasse-Witt and Cartier-Manin matrices: A warning and a request</a>. The paper points out that papers of Manin at some points confused an operator and its dual, leading to potential sign errors in later papers that reference Manin’s results. I’m quite sympathetic to the problem, having at various points fallen victim to similar confusions while writing my book (I hope they have all been resolved in the final version, wouldn’t bet anything really valuable on it…).</li>
<li>Nature has an excellent <a href="https://www.nature.com/articles/d41586-017-05477-9">obituary of Vladimir Voevodsky</a>, written by Dan Grayson.</li>
</ul>
<p>On the physics side:</p>
<ul>
<li>The LHC has now ended data-taking at 13 TeV for the year (a recent summary is <a href="https://home.cern/about/updates/2017/10/lhc-reaches-2017-targets-ahead-schedule">here</a>) and will start up again next spring. The machine ended up delivering about 50 inverse fb each to CMS/ATLAS (bettering the goal of 45), of which about 45 was recorded. Results published so far typically use 36 inverse fb from previous year’s data, so next year we should start seeing results based on a total 13 TeV data set of up to 80 inverse fb.</li>
<li><a href="https://www.nature.com/news/dark-matter-hunt-fails-to-find-the-elusive-particles-1.22970">Still no WIMPs</a>. Frank Wilczek surveys searches for his favorite dark matter alternative <a href="http://frankwilczek.com/2017/axion_searches_01.pdf">here</a>.</li>
<li>At <a href="http://bigthink.com/videos/eric-weinstein-after-einstein-we-stopped-believing-in-lone-genius-is-it-time-to-believe-again">Big Think</a>, Eric Weinstein has a take on what’s gone wrong with theoretical physics over the past 40 years that I’m mostly in agreement with.</li>
</ul>
Sun, 12 Nov 2017 23:08:14 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9708Where the Money Comes From
http://www.math.columbia.edu/~woit/wordpress/?p=9718
<p>Since returning from a vacation partly spent isolated from the internet, I’ve been catching up and noticed that some of the most prominent sources of funding for math and physics research have been making the news:</p>
<ul>
<li>The <a href="https://www.nytimes.com/2017/11/07/world/offshore-tax-havens.html">New York Times</a> and other sources have extensive reports based on leaked records from an offshore law firm that specializes in helping you avoid inconvenient US tax and reporting requirements. The story starts out with the example of Jim Simons, who has become the largest non-governmental funder of math and physics research. His Simons Foundation has been doing an excellent job of providing such funding. They have about \$3 billion in assets, annual income of around \$500 million. The Times reports that Simons (with a net worth of about \$18.5 billion) has an offshore version of the Foundation, the Simons Foundation International, with assets of \$8 billion, dwarfing the onshore version.</li>
<li>The assets of these Foundations are presumably largely invested in the secretive and extremely successful Renaissance Technologies hedge fund, which also is the employer of quite a few physicists and mathematicians. I’ve asked many people over the years, but have never found anyone who knows (or will admit to knowing) what it is that RenTech does that is so successful. A peculiar aspect of the coming age of private math/physics research funding is that no one getting this funding really knows where the money comes from.
<p>In other news while I was away the CEO of RenTech, Robert Mercer, was <a href="https://www.bloomberg.com/news/articles/2017-11-07/rentech-s-jim-simons-urged-mercer-to-step-back-to-improve-morale">finally induced to leave</a>. Mercer had drawn a lot of attention recently since he in recent years has been taking the opposite tack to Simons, funding institutions devoted to promoting untruth over truth (e.g. Breitbart News), achieving fantastic success last year. He also has branched out from doing whatever secretive things RenTech does to make mountains of money using computers and data, starting up a firm called Cambridge Analytica, a firm involved in secretively using computers and data to undermine democracy in the US and elsewhere. I had been wondering for quite a while what Simons thought of Mercer’s activities. My understanding of highly-paid finance jobs was that your employer pays you a lot of money in return for having your full attention and devotion to not having negative stories about them come to public attention, so Mercer’s continued employment was surprising. It seems that Simons finally had enough, after realizing how much damage Mercer was doing to his firm, in particular by creating a situation that would discourage many people from wanting to work there (there also was a campaign underway to get institutions to divest from investments with RenTech).</li>
<li>Another high profile source of funding for math and physics, in this case for cash prizes to mathematicians and physicists, has been venture capitalist Yuri Milner, with his Breakthrough Prize organization. New prizes will be announced in three weeks at a December 3 prize ceremony (I also believe there will be an associated Breakthrough Prize symposium held at Stanford shortly thereafter). It has always been well-known that much of Milner’s wealth derived from investments in Facebook and Twitter. Less well-known and <a href="https://www.nytimes.com/2017/11/05/world/yuri-milner-facebook-twitter-russia.html">recently revealed</a> was that a major source of the funds for these investments was Russian state organizations closely tied to Vladimir Putin.</li>
<li>Turning to sources of public funding, there’s <a href="http://www.nature.com/news/physicists-shrink-plans-for-next-major-collider-1.22983">not very positive news</a> about a possible ILC collider in Japan, with reports of a cutback of the proposal from a 500 GeV to a 250 GeV machine (which would still cost about $7 billion).</li>
<li>Foreign policy magazine has <a href="http://foreignpolicy.com/2017/11/02/the-future-of-particle-physics-will-live-and-die-in-china/">an article</a> discussing the proposal for a huge new collider in China (discussed <a href="https://www.math.columbia.edu/~woit/wordpress/?p=8114">here</a>). The point of view of the article is quite critical of the idea of locating a huge new project in a country with an increasingly authoritarian regime:<br />
<blockquote><p>China’s next-generation supercollider will unlock secrets of the universe — and destroy the ideals of the scientists running it.</p></blockquote>
<p>Luckily, for another more local prominent large country with an increasingly authoritarian and xenophobic regime, the issue of a possible problem with locating an international collider project there isn’t likely to come up since its leaders have no interest in funding such projects.</li>
</ul>
Sat, 11 Nov 2017 19:26:35 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9718Quantum Theory, Groups and Representations
http://www.math.columbia.edu/~woit/wordpress/?p=9712
<p>While I was away last week on vacation, it seems that Springer has published my book on quantum mechanics and representation theory (previously discussed in <a href="http://www.math.columbia.edu/~woit/wordpress/?cat=24">various blog posts</a>). The Springer page is <a href="https://link.springer.com/book/10.1007%2F978-3-319-64612-1">here</a>, your institution may provide access to the content (and a $24.99 MyCopy softcover) at the <a href="https://link.springer.com/book/10.1007%2F978-3-319-64612-1">Springer Link page for the book</a>. I’ve retained copyright for the content of the book and a version with essentially the same content as the Springer version is available from my website <a href="http://www.math.columbia.edu/~woit/QM/qmbook.pdf">here</a>. The Springer version has their formatting, copy-editing and metadata. The Amazon webpage for the book (if you’re in the mood to write a review there, feel free) is <a href="https://www.amazon.com/gp/product/3319646109">here</a>.</p>
<p>I haven’t yet seen a physical copy of the book, don’t know how long it will take for them to start printing copies. From people at Springer I learned last year that they no longer print and store copies of such books, they’re now always printed on demand (with the quality of the printing dependent on where you order your book from, German printers are quite good I hear..).</p>
<p>Just before leaving on vacation, I gave an introductory talk on some of the themes of the book at LaGuardia Community College (slides <a href="http://www.math.columbia.edu/~woit/laguardia.pdf">here</a>). This week I’ll be giving a similar talk at a math department colloquium at Queensboro Community College this Wednesday (1 pm, Science building, S-213).</p>
Sat, 11 Nov 2017 17:07:10 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9712This Week’s Hype
http://www.math.columbia.edu/~woit/wordpress/?p=9700
<p>Yet another entry in the long line of nonsensical hype about fundamental physics driven by misleading university press releases is today’s news that <a href="https://science.slashdot.org/story/17/10/26/149201/cern-scientists-conclude-that-the-universe-should-not-exist">CERN Scientists Conclude that the Universe Should Not Exist</a>. Tracking this back through various press stories (see <a href="https://cosmosmagazine.com/physics/universe-shouldn-t-exist-cern-physicists-conclude">here</a>, <a href="http://www.ign.com/articles/2017/10/24/cern-scientists-conclude-that-the-universe-should-not-exist">here</a> and <a href="http://www.independent.co.uk/news/science/universe-exist-cern-universe-matter-bizarre-behaviour-scientists-a8015216.html">here</a>), one finds that the original source, as always, is a university press release designed to mislead journalists. In this case it’s <a href="https://www.research-in-germany.org/en/research-landscape/news/2017/10/2017-10-19-riddle-of-matter-remains-unsolved--proton-and-antiproton-share-fundamental-properties.html">Riddle of matter remains unsolved</a> from Johannes Gutenberg University Mainz, a press release designed to promote <a href="https://www.nature.com/nature/journal/v550/n7676/full/nature24048.html">this paper in Nature</a>. </p>
<p>The paper reports a nice experimental result, a measurement of the antiproton magnetic moment showing no measurable difference with the proton magnetic moment. This is a test of CPT invariance, which everyone expects to be a fundamental property of any quantum field theory. The hype in the press release confuses CPT invariance with CP invariance. We know that physics is not CP invariant, with an open problem that of whether the currently known sources of CP non-invariance are large enough to produce in cosmological models the observed excess of baryons over antibaryons. An accurate version of the press release would be: “experiment finds expected CPT invariance, says nothing about the CP problem.”</p>
<p>If this experiment had found CPT non-invariance, the implications for early universe baryon-antibaryon asymmetry would have been of minor interest compared to the revolutionary discovery that a fundamental theorem of quantum field theory was violated, shattering our understanding of fundamental physics in terms of quantum field theory.</p>
Thu, 26 Oct 2017 16:18:06 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9700Short Items
http://www.math.columbia.edu/~woit/wordpress/?p=9691
<p>A few short items:</p>
<ul>
<li>My graduate school roommate Nathan Myhrvold has a new book coming out this month, a five-volume series about the science of bread, based on several years of research into the subject at his laboratory near Seattle. Robert Crease has gone out to visit, and gives a wonderful detailed report on <a href="http://physicsworld.com/cws/article/indepth/2017/oct/05/the-physics-of-bread">The physics of bread</a> in this month’s Physics World.</li>
<li>An <a href="http://webcache.googleusercontent.com/search?q=cache:ccdQLht2PyYJ:fqxi.org/community/articles/display/223">article at FQXI on multiverse research they are funding</a> seemed to finally give me an understanding of what this is all about:<br />
<blockquote><p>These are the two conceptually hardest questions in cosmology, according to Raphael Bousso, a theoretical physicist at the University of California, Berkeley. They go to the core of what it means to exist as a human being making sense of the universe we find ourselves in. And, he adds, unfortunately, there is very little physical knowledge to go on when it comes to working out the answer.</p>
<p>Undaunted by the lack of tools to help them, theatrical physicists Eugene Lim of King’s College London, UK, and Richard Easther of the University of Auckland, New Zealand, are…</p></blockquote>
<p>This all of a sudden made things clear: what is going on is “theatrical physics”, not “theoretical physics”. Going on like this about the multiverse is performance art.</p>
<p>Unfortunately I just noticed that this page has been edited (new version <a href="http://fqxi.org/community/articles/display/223">here</a>), removing the enlightening characterization of what this is about.</li>
<li>I’m glad to see that Natalie Wolchover has just won an <a href="https://www.aip.org/news/2017/2017-aip-science-writing-award-winners-announced">AIP award for her writing about physics</a>, in particular for a piece on <a href="https://www.quantamagazine.org/what-no-new-particles-means-for-physics-20160809">how physicists are dealing with the “nightmare scenario”</a>. While she’s perhaps the best professional journalist writing about these topics, for coverage of this from a professional physicist, the best you can find is Sabine Hossenfelder’s blogging at <a href="http://backreaction.blogspot.com/">Backreaction</a>. I’m pleased to hear that the two of them will be appearing at an event here next month in NYC, talking about <a href="https://journalism.nyu.edu/about-us/event/2017-fall/making-sense-of-mind-blowing-physics/">Making Sense of Mind-Blowing Physics</a> at NYU on Nov. 16.</li>
</ul>
Tue, 24 Oct 2017 16:37:09 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9691Shut Up and Calculate!?
http://www.math.columbia.edu/~woit/wordpress/?p=9649
<p>I noticed recently that Nima Arkani-Hamed was giving a talk at Cornell, with the title <a href="http://events.cornell.edu/event/three_cheers_for_shut_up_and_calculate_in_fundamental_physics">Three Cheers For “Shut Up And Calculate!” In Fundamental Physics</a>. No idea whether or not video is now or will become available.</p>
<p>From the abstract one can more or less guess what sort of argument he likely was making, and it’s one I’m mostly in agreement with. “Shut Up and Calculate!” is pretty much my unspoken reaction to almost everything I read purporting to be about foundational issues in quantum mechanics. I have in mind in particular discussions of the measurement problem, which often consist of endless natural language text where one struggles to figure out exactly what the author is claiming. An actual calculation showing what happens in a precise mathematical model of a “measurement” would be extremely helpful and likely make much clearer exactly what the problem is (or, sometimes, whether or not there even is a problem…). Such calculations are all too few in a huge literature.</p>
<p>Over the last few years, while teaching and writing a book about the mathematics of quantum mechanics, the tedious exercise of trying to get all signs right in calculations has sometimes turned out to be quite illuminating, with tracking down a mysterious inconsistency of minus sign leading me to realize that I wasn’t thinking correctly about what I was doing. I’m all too aware that this kind of calculational effort is something I too often avoid through laziness, in favor trying to see my way through a problem in some way that avoids calculation.</p>
<p>On the other hand, I’m not quite ready to sign up for “Three Cheers”, might just stick to “Two Cheers”. For a perfect example of what’s wrong with the “Shut Up and Calculate!” philosophy, one can take a look at the forthcoming <a href="https://web.northeastern.edu/het/string_data/">Workshop on Data Science and String Theory</a> planned for Northeastern in a month or so. They have a <a href="https://web.northeastern.edu/het/string_data/about/">Goals and Vision statement</a> which tells us that they plan to:</p>
<blockquote><p>treat the landscape as what it clearly is: a big data problem. In fact, the data that arise in string theory may be some of the largest in science.</p></blockquote>
<p>About being the “largest”, I think they’re right. The traditional number of 10<sup>500</sup> string theory vacua has now been replaced by 10<sup>272,000</sup> (and I think this is per geometry. With 10<sup>755</sup> geometries the number should be 10<sup>272,755</sup>). It’s also the case that “big data” is now about the trendiest topic around, and surely there are lots of new calculational techniques available.</p>
<p>The problem with all this is pretty obvious: what if your “data set” is huge but meaningless, with nothing in it of any significance for the problem you are interested in (explaining the Standard Model)? This is not a new project, it’s an outgrowth of the String Vacuum Project, which I wrote about <a href="http://www.math.columbia.edu/~woit/wordpress/?p=467">here</a>, <a href="http://www.math.columbia.edu/~woit/wordpress/?p=664">here</a> and <a href="http://www.math.columbia.edu/~woit/wordpress/?p=2924">here</a>. This started with a <a href="http://www.physics.rutgers.edu/~mrd/SVP-v2.ps">2005 funding proposal</a>, ended up getting <a href="http://www.nsf.gov/awardsearch/showAward.do?AwardNumber=0917807">funded by the NSF</a> during 2010-2014. From the beginning there were obvious reasons this sort of calculational activity couldn’t lead to anything interesting, and as far as I can tell, nothing of any value came out of it.</p>
<p>For an opposite take to mine on all this, see the paper <a href="https://arxiv.org/abs/1601.02462">Big Numbers in String Theory</a>, by Bert Schellekens. It contains an odd June 2017 preface explaining that it was supposed to be part of special issue of <em>Advances in High Energy Physics</em> devoted to “Big Data” in particle and string phenomenology (“all the ways we use high performance computing in addressing issues in high energy physics, and (in particular) the construction of databases of string vacua”). This issue was cancelled “as requested by the Guest Editors”. I wonder what the reason for this cancellation was, in particular whether it had anything to do with part of the topic of the special issue being considered by some to be obvious nonsense.</p>
Tue, 17 Oct 2017 21:23:28 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=964950 Years of Electroweak Unification
http://www.math.columbia.edu/~woit/wordpress/?p=9657
<p>The 50th anniversary of electroweak unification is coming up in a couple days, since Weinberg’s <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.19.1264">A Model of Leptons</a> paper was submitted to PRL on October 17, 1967. For many years this was the most heavily cited HEP paper of all time, although once HEP theory entered its “All AdS/CFT, all the time” phase, at some point it was eclipsed by the 1997 Maldacena paper (as of today it’s 13118 Maldacena vs. 10875 Weinberg). Another notable fact about the 1967 paper is that it was completely ignored when published, only cited twice from 1967 to 1971.</p>
<p>The latest CERN Courier has a <a href="http://cerncourier.com/cws/article/cern/70137">detailed history of the paper</a> and how it came about. It also contains a <a href="http://cerncourier.com/cws/article/cern/70138">long interview with Weinberg</a>. It’s interesting to compare his comments about the current state of HEP with the ones from 2011 (see <a href="http://www.math.columbia.edu/~woit/wordpress/?p=9623">here</a>), where he predicted that “If all they discover is the Higgs boson and it has the properties we expect, then No, I would say that the theorists are going to be very glum.”</p>
<p>Today he puts some hope in a non-renormalizable Majorana mass term for neutrinos as evidence for new physics. As for the future:</p>
<blockquote><p>As to what is the true high-energy theory of elementary particles, Weinberg says string theory is still the best hope we have. “I am glad people are working on string theory and trying to explore it, although I notice that the smart guys such as Witten seem to have turned their attention to solid-state physics lately. Maybe that’s a sign that they are giving up, but I hope not.” </p></blockquote>
<p>On this last sentiment, I have the opposite hope. He also shares what I think is a common hope for what will save the field (a smart graduate student with a new idea): </p>
<blockquote><p>Weinberg also still holds hope that one day a paper posted in the arXiv preprint server by some previously unknown graduate student will turn the SM on its head – a 21st century model of particles “that incorporates dark matter and dark energy and has all the hallmarks of being a correct theory, using ideas no one had thought of before”.</p></blockquote>
<p>Perhaps current training of graduate students in theory should be rethought, to optimize for this.</p>
Sat, 14 Oct 2017 14:47:58 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9657Various Topics in Interpretation of Quantum Mechanics
http://www.math.columbia.edu/~woit/wordpress/?p=9621
<p>A couple of recent discussions about quantum mechanics that may be of interest:</p>
<ul>
<li>There’s a <a href="https://arxiv.org/abs/1709.05777">recent paper</a> out by Don Weingarten that looks looks like it might have a different take on the fundamental “many-worlds” problem of, as he writes:<br />
<blockquote><p>how in principle the definite positions of the macroscopic world emerge from the microscopic matter of which it is composed, which has only wave functions but not definite positions.</p></blockquote>
<p>My naive feeling about this has always been that the answer should lie in a full understanding of the initial state of the measurement apparatus (+ environment), that it is our imperfect probabilistic understanding of the initial stat that limits us to a probabilistic understanding of the final state. I found Weingarten’s investigation of this intriguing, although I’m not sure that the language of “hidden variables” is a good one here, given the use of that language in other kinds of proposals. By the way, Weingarten is an ex-lattice gauge theorist who I had the pleasure of first meeting long ago during his lattice gauge theory days. He at some point left physics to go work for a hedge fund, I believe he’s still in that business now.</p>
<p>Luckily for all of us, Jess Riedel has looked at the paper and written up some detailed <a href="http://blog.jessriedel.com/2017/10/05/comments-on-weingartens-preferred-branch/">Comments on Weingarten’s Preferred Branch</a>, which I suggest that anyone interested in this topic look at. Discussion would best be at his blog, a much better informed source than this one.</li>
<li>Gerard ‘t Hooft has a remarkable recent preprint about quantum mechanics, with the provocative title of <a href="https://arxiv.org/abs/1709.02874">Free Will in the Theory of Everything</a>. I fear that the sort of argument he’s engaging in, trying to ground physics in very human intuitions about how the world should work, is not my cup of tea at all. Instead, what has always fascinated me about quantum mechanics has always been its grounding in very deep mathematical ideas, and the surprising way in which it challenges our conventional intuitions by telling us about an unexpected new way to think about physics at a fundamental level.
<p>For more discussion of the paper, there are Facebook posts by Tim Maudlin <a href="https://www.facebook.com/tim.maudlin/posts/10155670157528398">here</a> and <a href="https://www.facebook.com/tim.maudlin/posts/10155641145263398">here</a> in which he argues with ‘t Hooft. I confess that I wasn’t so sure whether to take the time to read these, and after a short attempt gave up, unable to figure out precisely what the argument was about (and put off by Maudlin’s style of argument. Do philosophers really normally behave like that?). Links provided here in case you have more interest in this than I do, or better luck getting something out of it. </li>
</ul>
Wed, 11 Oct 2017 18:43:04 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9621The Big Bang Theory and the Death of SUSY
http://www.math.columbia.edu/~woit/wordpress/?p=9623
<p>If you’re a fan of <a href="http://www.cbs.com/shows/big_bang_theory/">The Big Bang Theory</a>, perhaps you’ve seen the latest episode, <em><a href="http://www.cbs.com/shows/big_bang_theory/video/GTCEx8Olyltbha1m901WM_fPcj_6W139/the-big-bang-theory-the-retraction-reaction/">The Retraction Reaction</a></em>. If not, you might be interested in the following transcript (taken from <a href="https://www.springfieldspringfield.co.uk/view_episode_scripts.php?tv-show=big-bang-theory&episode=s11e02">here</a>). The show has always done a good job of getting the science right, for an interview with their physics consultant David Saltzberg, see <a href="http://www.sciencemag.org/news/2014/04/whats-it-consult-big-bang-theory">here</a>.</p>
<p>The episode begins with a Science Friday interview of physicist Leonard Hofstadter by Ira Flatow:</p>
<blockquote><p>FLATOW: So, it has been five years since the discovery of the Higgs boson– what’s the next big thing gonna be? </p>
<p>LEONARD: Wow, that’s hard to say. There’s so much going on. We’ve been collecting tons of data that could revolutionize the way we understand the universe. For instance, there’s a particle called a squark, which could prove supersymmetry.</p>
<p>FLATOW: That is interesting. Have you found it?</p>
<p>LEONARD: What, the squark?</p>
<p>FLATOW: Yes.</p>
<p>LEONARD: No, no. Wouldn’t that be exciting? But we’re also looking for the selectron, the gluino and the neutralino.</p>
<p>FLATOW: Well, and have you found that? </p>
<p>LEONARD: No. Another fun sidenote– I went to high school with a girl named Theresa Gluino, but it didn’t cost $2 billion to find her. She was smoking behind the gym. (laughs) </p>
<p>FLATOW: So, what have you found? </p>
<p>LEONARD: Uh, nothing, actually. We’ve got the best equipment and the best minds all working on it. Although, some days I’m, like, ugh we’ve spent so much money. Why haven’t we found anything? What are we doing?</p></blockquote>
<p>After a segment in which neuroscientist Amy explains that she doesn’t tell physicist boyfriend Sheldon about her new lab equipment since</p>
<blockquote><p>AMY: We’ve been getting so much more funding than physics, he’s been a little sensitive.</p></blockquote>
<p>another scene features Leonard called into the office of a university administrator:</p>
<blockquote><p>LEONARD: I have to say I’m a little nervous.</p>
<p>Ms. DAVIS: You should be.</p>
<p>LEONARD: Look, I know I screwed up, but it was only one interview.<br />
How much damage could it have caused?</p>
<p>Ms. DAVIS: Would you like for me to read you the e-mails from donors asking why are they giving us money if physics is a dead end?</p>
<p>LEONARD: I didn’t say it was a dead end. I just said that I was worried it might be.</p>
<p>Ms. DAVIS: So if I just said I was worried you might not have a job next week, how would you feel? </p>
<p>LEONARD: Light-headed, and glad you asked me to sit down. Okay, just tell me what I can do.</p>
<p>Ms. DAVIS: I’m gonna need you to make a statement saying that you misspoke, and that you’re confident the physics community is close to a major breakthrough.</p>
<p>LEONARD: You want me to lie.</p>
<p>Ms. DAVIS: Look, Dr. Hofstadter, I’m counting on you. I think that you are the smartest physicist at this university.</p>
<p>LEONARD: Really? </p>
<p>Ms. DAVIS: See? Lies. They’re not that hard.</p></blockquote>
<p>Leonard then has this exchange with Penny:</p>
<blockquote><p>PENNY: Hey, come on, look, you said a few dumb things on the radio– what is the worst that could happen?</p>
<p>LEONARD: I may get fired.</p>
<p>PENNY: Okay, well, even if you did, you could find another job.</p>
<p>LEONARD: Yeah, who wouldn’t want to hire the physicist who publicly said physics is dead? Well, I wouldn’t put that under “special skills”. I can fix it, I just need to write a retraction I don’t believe in– basically sell out to keep my job.</p>
<p>PENNY: Great, I’ll leave you to it.</p></blockquote>
<p>He then goes to talk to string theorist Sheldon Cooper:</p>
<blockquote><p>LEONARD: Sheldon, it’s me.</p>
<p>SHELDON: What? </p>
<p>LEONARD: Look, I know you’re mad, but I have to write a statement that says the physics community is close to a breakthrough, and since you actually believe that, I could really use your help.</p>
<p>SHELDON: Sorry, I can’t.</p>
<p>LEONARD: Come on, don’t be like that.</p>
<p>SHELDON: What? Look. (sighs) Not all science pans out. You know, we’ve been hoping supersymmetry was true for decades, and finally, we built the Large Hadron Collider, which is supposed to prove it by finding these new particles, and it-it hasn’t. And maybe supersymmetry, our last big idea, is simply wrong.</p>
<p>LEONARD: Well, that sounds awful. Now I get why everyone hates me.</p></blockquote>
<p>Penny later comes in:</p>
<blockquote><p>PENNY: So you guys are upset because the collider thing disproved your theories?</p>
<p>LEONARD: It’s worse than that. It hasn’t found anything in years, so we don’t know if we’re right, we don’t know if we’re wrong. We don’t know where to go next…</p>
<p>PENNY: Come on. You guys are physicists. Okay? You’re always gonna be physicists. And sure, sometimes, the physics is hard, but isn’t that what makes it boring?</p></blockquote>
<p>The episode ends with a visit to the grave of Richard Feynman, and a reference to Feynman’s story about how he got himself out of a slump in his work when he was at Cornell:</p>
<blockquote><p>WOLOWITZ: He did so much. And here we are, stuck and letting him down. You know, Feynman used to say he didn’t do physics for the glory or the awards, but just for the fun of it. He was right. Physics is only dead when we stop being excited about it.</p></blockquote>
<p>All in all, a pretty accurate portrayal of the situation in high energy physics theory, with a reasonable take on what to do about it.</p>
Thu, 05 Oct 2017 21:16:10 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=96232017 Nobel Prize in Physics
http://www.math.columbia.edu/~woit/wordpress/?p=9611
<p>At this point, Kip Thorne and Rainer Weiss of LIGO have (deservedly) won just about every scientific prize out there, for the first observation of gravitational waves. I don’t know of anyone who doesn’t believe they’ll be getting the Physics Nobel tomorrow morning. With an open spot in the usual limitation to three (Ronald Drever passed away earlier this year), perhaps Barry Barish will also get the nod. Most appropriate would be to use the third slot to give an award to the entire LIGO collaboration, but it seems likely that the tradition of not honoring collaborations will continue. There will be a live webcast of the announcement at 5:45am EST available <a href="https://youtu.be/FrutdQ5YCvs">here</a>.</p>
Mon, 02 Oct 2017 17:44:34 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9611Vladimir Voevodsky 1966-2017
http://www.math.columbia.edu/~woit/wordpress/?p=9591
<p>I was very sorry to hear yesterday of the <a href="https://www.ias.edu/news/2017/vladimir-voevodsky">announcement from the IAS</a> of the untimely death of Vladimir Voevodsky, at the age of 51. Last year I had the chance to meet Voevodsky and talk with him for a while at the Heidelberg Leader’s Forum (which I wrote about <a href="https://scilogs.spektrum.de/hlf/voevodsky-proof-assistants/">here</a>). He was a gracious and modest person, and it was fascinating to learn a bit about what he was trying to do, and his earlier experiences doing mathematics that had led him down this path. There was no indication at that time that he was ill, and I don’t know what led to his death.</p>
<p>Back in 2012 I wrote a <a href="http://www.math.columbia.edu/~woit/wordpress/?p=4975">blog post about him and his work</a>, linking to various things that may be of interest if you’d like to know more about him. Among more recent sources of information, there’s a video interview <a href="https://vimeo.com/99586217">here</a>, a popular article <a href="https://www.ias.edu/ideas/2014/voevodsky-origins">here</a>, lecture slides <a href=".math.ias.edu/vladimir/files/2014_IAS.pdf">here</a>, <a href="https://www.math.ias.edu/vladimir/sites/math.ias.edu.vladimir/files/2014_08_ASC_lecture.pdf">here</a> and <a href="https://www.math.ias.edu/vladimir/sites/math.ias.edu.vladimir/files/2015_06_30_RDP.pdf">here</a>, and a <a href="http://nautil.us/issue/24/error/in-mathematics-mistakes-arent-what-they-used-to-be">piece by Siobhan Roberts</a> which covers some of the same topics that Voevodsky told me about when I met him last year.</p>
Sun, 01 Oct 2017 18:58:14 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9591Various and Sundry
http://www.math.columbia.edu/~woit/wordpress/?p=9572
<ul>
<li>I don’t know if I ever mentioned this, but quite a while ago I replaced the “latexrender” TeX plugin being used here by a mathjax one. As I find time, I’m now going back and editing old posts to get rid of latexrender tags and make the equations more mathjax friendly. As far as comments are concerned, you can add TeX content by using standard math delimiters \$, or \$\$ for displayed math. If you want to comment about US dollars, put a backslash before your dollar signs to avoid the interpretation as TeX.
<p>One reason I hadn’t advertised this much is that I know it’s hard to get TeX right the first time, so people’s comments with TeX would be likely to often not work properly. I’ve added a plugin that lets you edit your comment for 5 minutes after you write it. This should be useful for typos, as well as for fixing TeX problems (note that you need to refresh the page to get the math to display).</li>
<li>For a philosopher’s take on evaluating string theory, see this talk by James Ladyman, on <a href="https://iai.tv/video/cosmic-dreams">Cosmic Dreams</a>. Material on string theory is near the end, and just makes the obvious point that having no experimental evidence for the theory is a huge problem, no matter what efforts are made to change the usual way scientific theories are evaluated.</li>
<li>A hot topic these days in the math community is the conjecture that local Langlands can be understood as geometric Langlands for the Fargues-Fontaine curve. My attempts to learn about this so far haven’t had a lot of success, but I now have new-found hope. At Harvard there’s a seminar going on this semester on the topic, and it has <a href="http://www.math.harvard.edu/~lurie/FF.html">a website</a> which so far features explanations of some of the mathematics involved from <a href="http://www.math.harvard.edu/~lurie/ffcurve/Lecture1-Overview.pdf">Jacob Lurie</a> and <a href="http://www.math.harvard.edu/~lurie/ffcurve/Lecture2-RelCurveI.pdf">Dennis Gaitsgory</a>. In London, the London Number Theory Seminar also has a study group devoted to this topic (website <a href="http://wwwf.imperial.ac.uk/~buzzard/LNTS/lntsg.html">here</a>, although seems to have disappeared for the moment).</li>
<li><a href="https://www.lqp2.org/">LPQ2</a> (Local Quantum Physics Crossroads, v.2.0) is a website that gathers various information about relativistic quantum theory.</li>
<li>In November Perimeter will host what should be an interesting workshop on the question of how to make sense of the <a href="https://perimeterinstitute.ca/conferences/path-integral-gravity">Path Integral for Gravity</a>.</li>
<li>A <a href="https://mathematics.stanford.edu/wp-content/uploads/2017/09/102117_Mirzakhani-memorial.pdf">memorial for Maryam Mirzakhani</a> will take place at Stanford on October 21, with a live feed available <a href="https://youtu.be/IUfB2HadIBw">here</a>.</li>
<li>As always, Quanta magazine keeps publishing a wide range of very high quality articles about math and physics, covering different topics than everyone else. Most recently, on the math side, see an article by Erica Klarreich on <a href="https://www.quantamagazine.org/moonshine-link-discovered-for-pariah-symmetries-20170922/">Pariah Moonshine</a> and on the physics side, Robert Henderson on possible <a href="https://www.quantamagazine.org/how-the-hidden-higgs-could-reveal-our-universes-dark-sector-20170926/">searches for long-lived particles possibly from a “hidden sector”.</a>.</li>
</ul>
Tue, 26 Sep 2017 21:39:35 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9572Special Relativity and Classical Field Theory
http://www.math.columbia.edu/~woit/wordpress/?p=9514
<p>For quite a while Leonard Susskind has been giving some wonderful courses on physics under the name “The Theoretical Minimum”, pitched at a level in between typical popularizations and standard advanced undergraduate courses. This is a great idea, since there is not much else of this kind, while lots of people inspired by a popular book could use something more serious to start learning what is really going on. The courses are available as Youtube lectures <a href="http://theoreticalminimum.com/courses">here</a>.</p>
<p>Book versions of some of the courses have now appeared, first one (in collaboration with George Hrabovsky) about classical mechanics, then one (with Art Friedman) about quantum mechanics. I wrote a little bit about these <a href="http://www.math.columbia.edu/~woit/wordpress/?p=5487">here</a> and <a href="http://www.math.columbia.edu/~woit/wordpress/?p=6720">here</a>, thought they were very well done. When last in Paris I noticed that there’s now a French version of these two books (with a blurb from me for the quantum mechanics one).</p>
<p>The third book in the series (also with Art Friedman) is about to appear. It’s entitled <a href="https://www.amazon.com/Special-Relativity-Classical-Field-Theory/dp/0465093345">Special Relativity and Classical Field Theory</a>, and is in much the same successful style as the first two books. Robert Crease has a <a href="http://www.nature.com/nature/journal/v549/n7672/full/549331a.html">detailed and very positive review in Nature</a> which does a good job of explaining what’s in the book and which I’d mostly agree with.</p>
<p>The basic concept of the book is to cover special relativity and electromagnetism together, getting to the point of understanding the behavior of electric and magnetic fields under Lorentz transformations, and the Lorentz invariance properties of Maxwell’s equation. Along the way, there’s quite a lot of the usual sort of discussion of special relativity in terms of understanding what happens as you change reference frame, a lot of detailed working out of gymnastics with tensors, and some discussion in the Lagrangian language of the Klein-Gordon equation as a simpler case of a (classical) relativistic field theory than the Maxwell theory. Much of what is covered is clearly overkill if you just want to understand E and M, but undoubtedly is motivated by his desire to go on to general relativity in the next volume in this series.</p>
<p>At various points along the way, the book provides a much more detailed and leisurely explanation of crucial topics that a typical textbook would cover all too quickly. This should be very helpful for students (perhaps the majority?) who have trouble following what’s going on in their textbooks or course due to not enough detail or motivation. Besides non-traditional students in a course of self-study, the book may be quite useful for conventional students as a supplement to their textbook.</p>
<p>One of the most annoying things someone can do while reviewing a book is to start going on about their own different take on the material, criticizing the author for not writing a very different book. So, the rest of this posting is no longer a review of the book, it’s now about the very different topic of what I think about this material, nothing to do with Susskind’s valuable and different approach.</p>
<p>This semester I’m teaching a graduate level course on geometry, and by chance the past week have been discussing exactly some of the same material about tensor fields that Susskind covers. The perspective is quite different, starting with trying to explain a coordinate-invariant point of view on what these things are, only then getting to the formalism Susskind discusses. I can’t help thinking that, with all the effort Susskind (and pretty much every other physics textbook…) devotes to endless gymnastics with tensors in coordinates, they could instead be providing an understanding of the geometry behind this story. It’s unfortunate that many if not most of those who study this material in physics don’t ever get exposed to this point of view. Thinking in geometrical terms, the vector potential and field strength have relatively simple interpretations, and using differential forms the equations needed for the part of E and M Susskind covers are pretty much just:</p>
<p>F=dA, dF=0, and d*F=*J</p>
<p>Similarly, for the special relativity material, there’s a danger of the basic simplicity of the story getting lost in calculations of how things appear in coordinates with respect to different reference frames. What you fundamentally need is mainly that objects are described by a (conserved in the absence of forces) energy-momentum p, which satisfies p<sup>2</sup>= -m<sup>2</sup>, with Lorentz transformations taking one such p to another. The wider principle is that things are described by solutions to wave equations, with special relativity saying that the Lorentz group takes solutions to solutions.</p>
<p>I’d like to believe that such a very different course and very different book would be possible, quite possibly am very wrong (I’ve never taught special relativity to anyone). Maybe some day someone, inspired by Susskind’s project, might try to do something at a similar level, but from a more geometric point of view.</p>
Fri, 22 Sep 2017 17:29:49 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9514QCD at $\theta=\pi$
http://www.math.columbia.edu/~woit/wordpress/?p=9509
<p>Earlier this week Zohar Komargodski (who is now at the Simons Center) visited Columbia, and gave a wonderful talk on recent work he has been involved in that provides some new insight into a very old question about QCD. Simplifying the problem by ignoring fermions, QCD is a pure SU(3) Yang-Mills gauge theory, a simple to define QFT which has been highly resistant to decades of effort to better understand it. </p>
<p>One aspect of the theory is that it can be studied as a function of an angular parameter, the so-called $\theta$-angle. Most information about the theory comes from simplifying by taking $\theta=0$, which seems to be the physically relevant value, one at which the theory is time reversal invariant. There is however another value for which the theory is time reversal invariant, $\theta=\pi$, and what happens there has always been rather mysterious.</p>
<p>The new ideas about this question that Komargodski talked about are in the paper <a href="https://arxiv.org/abs/1703.00501">Theta, Time Reversal and Temperature</a> from earlier this year, joint work with Gaiotto, Kapustin and Seiberg. Much of the talk was taken up with going over the details of the toy model described in Appendix D of this paper. This is an extremely simple quantum mechanical model, that of a particle moving on a circle, where you add to the Lagrangian a term proportional to the velocity, which is where the angle $\theta$ appears. You can also think of this as a coupling to an electromagnetic field describing flux through the circle.</p>
<p>Even if you’re put off by the difficulty of questions about quantum field theories such as QCD, I strongly recommend reading their Appendix. It’s a simple and straightforward quantum mechanics story, with the new feature of a beautiful interpretation of the model in terms of a projective representation of the group O(2), or equivalently, a representation of Pin(2), a central extension of O(2). In the analogy to SU(N) Yang-Mills, it is the $\mathbf Z_N$ symmetry of the theory that gets realized projectively.</p>
<p>Komargodski himself commented at the beginning of the talk on the reasons that people are returning to look again at old, difficult problems about QCD. The new ideas he described are closely related to ones that are part of the recent hot topic of symmetry protected phases in condensed matter theory. It’s great to see that this QFT research may not just have condensed matter applications, but seems to be leading to a renewal of interest in long-standing problems about QCD itself. </p>
<p>Besides the paper mentioned above, there are now quite a few others. One notable one is very recent work of Komargodski and collaborators, <a href="https://arxiv.org/abs/1708.06806">Time-Reversal Breaking in QCD4, Walls and Dualities in 2+1 Dimensions</a>. </p>
Fri, 15 Sep 2017 21:55:53 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9509Modern Theories of Quantum Gravity
http://www.math.columbia.edu/~woit/wordpress/?p=9505
<p>Quanta magazine today has a <a href="https://www.quantamagazine.org/to-solve-the-biggest-mystery-in-physics-join-two-kinds-of-law-20170907/">column by Robbert Dijkgraaf</a> that comes with the abstract:</p>
<blockquote><p>Reductionism breaks the world into elementary building blocks. Emergence finds the simple laws that arise out of complexity. These two complementary ways of viewing the universe come together in modern theories of quantum gravity.</p></blockquote>
<p>It struck me that at this point I don’t know what a “modern theory of quantum gravity” is. Much of the article is a clear explanation of the usual story of the renormalization group and effective field theory, but towards the end, when quantum gravity comes up, I have trouble following. String theory has gone from being an exciting new idea to being part of historical tradition:</p>
<blockquote><p>
Traditional approaches to quantum gravity, such as perturbative string theory, try to find a fully consistent microscopic description of all particles and forces. Such a “final theory” necessarily includes a theory of gravitons, the elementary particles of the gravitational field. </p></blockquote>
<p>That “reductionist” tradition is opposed to a new “emergent” holographic theory, and we’re told that</p>
<blockquote><p>The present point of view thinks of space-time not as a starting point, but as an end point, as a natural structure that emerges out of the complexity of quantum information, much like the thermodynamics that rules our glass of water. Perhaps, in retrospect, it was not an accident that the two physical laws that Einstein liked best, thermodynamics and general relativity, have a common origin as emergent phenomena.</p>
<p>In some ways, this surprising marriage of emergence and reductionism allows one to enjoy the best of both worlds. For physicists, beauty is found at both ends of the spectrum.
</p></blockquote>
<p>Dijkgraaf seems to be saying that a viable emergent theory of four-dimensional quantum gravity based on the complexity of quantum information has been found, but I seem to have missed this. Can someone point me to a paper describing it?</p>
Fri, 08 Sep 2017 01:53:32 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9505Modern Geometry
http://www.math.columbia.edu/~woit/wordpress/?p=9502
<p>This semester I’m teaching the first semester of Modern Geometry, our year-long course on differential geometry aimed at our first-year Ph.D. students. A syllabus and some other information about the course is available <a href="http://www.math.columbia.edu/~woit/geometry2017/">here</a>.</p>
<p>In the spring semester Simon Brendle will be covering Riemannian geometry, so this gives me an excuse to spend a lot of time on aspects of differential geometry that don’t use a metric. In particular, I’ll cover in detail the general theory of connections and curvature, rather than starting with the Levi-Civita connection that shows up in Riemannian geometry. I’ll be starting with connections on principal bundles, only later getting to connections on vector bundles. Most books do this in the other order, although <a href="https://en.wikipedia.org/wiki/Foundations_of_Differential_Geometry">Kobayashi and Nomizu</a> does principal bundles first. In some sense a lot of what I’ll be doing is just explicating Kobayashi and Nomizu, which is a great book, but not especially user-friendly.</p>
<p>A major goal of the course is to get to the point of writing down the main geometrically-motivated equations of fundamental physics and a few of their solutions as examples. This includes the Einstein eqs. of general relativity, although I’ll mostly be leaving that topic to the second semester course.</p>
<p>Ideally I think every theoretical physicist should know enough about geometry to appreciate the geometrical basis of gauge theories and general relativity. In addition, any geometer should know about how geometry gets used in these two areas of physics. I’ve off and on thought about writing an outline of the subject aimed at these two audiences, and thought about writing something this semester. Thinking more about it though, at this point I’m pretty sick of expository writing (proofs of my QM book are supposed to arrive any moment…). In addition, I just took a look again at the 1980 review article by Eguchi, Gilkey and Hanson (see <a href="http://www.sciencedirect.com/science/article/pii/0370157380901301">here</a> or <a href="https://www.cs.indiana.edu/~hansona/papers/EguchiGilkeyHanson1980.pdf">here</a>) from which I first learned a lot of this material. It really is very good, and anything I’d write would spend a lot of time just reproducing that material.</p>
Mon, 04 Sep 2017 19:11:15 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9502This and That
http://www.math.columbia.edu/~woit/wordpress/?p=9492
<ul>
<li>The <a href="http://stacks.math.columbia.edu/">Stacks Project</a> (see an earlier post <a href="http://www.math.columbia.edu/~woit/wordpress/?p=6164">here</a>) had a very successful <a href="https://stacks.github.io/">workshop</a> in Ann Arbor earlier this month. This is a remarkable effort pioneered by Johan de Jong to produce a high quality open source reference for the field of algebraic geometry. It now is over 6000 pages, with an increasingly large number of papers citing it (according to <a href="https://stacks.github.io/slides.pdf">data from Pieter Belmans</a>, 85 citations in the arXiv so far in 2017 alone). During the workshop plans were discussed for the future of the project, with work on a new version of the project infrastructure underway (see <a href="https://stacks.github.io/framework.pdf">slides</a> and a <a href="http://pbelmans.ncag.info/blog/2017/08/27/introduction-gerby-plastex/">blog post</a> from Belmans).</li>
<li>The latest AMS Notices has a <a href="http://www.ams.org/publications/journals/notices/201708/rnoti-p892.pdf">wonderful article</a> by my Barnard/Columbia colleague Dusa McDuff about her remarkable family history and reflecting on her equally remarkable mathematical career. A <a href="http://www.math.columbia.edu/~woit/wordpress/?p=9110">post earlier this year</a> discussed a Quanta article about her recent work with Katrin Wehrheim on technical issues in the foundations of symplectic topology. Kenji Fukaya has recently written something for the Simons Center website (see <a href="http://scgp.stonybrook.edu/archives/22091">here</a>) explaining his take on this story.</li>
<li>The Stanford Encyclopedia of Philosophy has a <a href="https://seop.illc.uva.nl/entries/fine-tuning/">new entry about the fine-tuning problem</a>, by Simon Friedrich.</li>
<li>The LHC operators have run into some difficulty in recent weeks (reflected in the accumulated luminosity plots <a href="https://cms-service-lumi.web.cern.ch/cms-service-lumi/publicplots/int_lumi_per_day_cumulative_pp_2017OnlineLumi.png">here</a> and <a href="https://atlas.web.cern.ch/Atlas/GROUPS/DATAPREPARATION/PublicPlots/2017/DataSummary/figs/sumLumiByDay.png">here</a>), with problems centered around an unknown source of gas in the beam pipe at a specific location, leading to losses of the beam. Some information about this is available <a href="https://home.cern/cern-people/updates/2017/08/lhc-report-something-nothing">here</a>. The past few days they seem to be having success running the machine with around 1500 bunches, much less than the 2500 or so of earlier in the summer. The target for the year is 40 inverse fb which may still be achieved, while more optimistic numbers that looked plausible earlier now seem less likely.</li>
</ul>
Tue, 29 Aug 2017 23:38:40 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9492Road Trip
http://www.math.columbia.edu/~woit/wordpress/?p=9481
<p>Blogging will be light to non-existent for the next ten days or so, as I head out west on a road trip to see next Monday’s solar eclipse. Current plan is to fly to Denver tomorrow, pick up a vehicle, and head up to Wyoming the next day. If weather projections look good for the Wyoming/Idaho part of the track, that’s where we’ll plan to end up, likely camping out somewhere (accommodations along the track have long been booked up).</p>
<p>This will be the ninth eclipse I’ve traveled to see, and I urge anyone thinking of making a trip to the eclipse track to do so. A total solar eclipse is something quite different than a partial one, and this is a very rare opportunity to see this in the US. Besides the eclipse, a major motivation for these trips has always been that of getting to visit a more or less random place on Earth that one wouldn’t otherwise have any excuse to see. I’ve driven quickly through Idaho and Wyoming a few times over the years, look forward to spending more time in that part of the country this coming week (unless the weather there looks bad, in which case maybe we’ll end up in Oregon or Nebraska).</p>
<p>Some other random advice about eclipses:</p>
<ul>
<li>Be very careful about use of binoculars or telescopes, improper use of these at any time other than the period of totality is what can cause serious eye damage (by itself the eye is pretty good about automatically protecting itself).</li>
<li>Don’t put a lot of effort into photography during totality, since that’s likely to lead to you spending the time you should be enjoying the experience fiddling with camera equipment (and not getting a good result anyway…). A simple thing to do is to set up a camera to take video of the overall eclipse scene as it happens, turn it on at some point then ignore it.</li>
</ul>
<p>If you miss this one, next couple are far south in South America, there will be another chance in the US relatively soon, April 2024.</p>
Mon, 14 Aug 2017 14:57:13 GMThttp://www.math.columbia.edu/~woit/wordpress/?p=9481