Various and Sundry

A few links for your weekend reading:

  • If you just can’t get enough of the Multiverse, Inference has commentary on Max Tegmark from Daniel Kleitman and Sheldon Glashow.
  • Coverage of the important topic of blackboards is to be found here. To those ill-informed sorts who think that blackboards are the past, whiteboards or some other technology the future, I’ll point out the following. When I came to Columbia back in 1989, there was a recently installed modest-sized whiteboard in the math department common room. Everyone hated it, and after many years it was replaced by a similar-sized blackboard. Last year, in a renovation of the lounge, that blackboard was replaced by a better one, and one whole wall of the room was replaced by a floor-to-ceiling blackboard. A year or so ago, a newly renovated Theory Center was unveiled here in the Physics department: floor-to-ceiling, wall-to-wall blackboards. That’s the future, the whiteboard is the past.
  • The latest CERN Courier has a long article by Hermann Nicolai, mostly about quantum gravity. Nicolai makes the following interesting comments about supersymmetry and unification:

    To the great disappointment of many, experimental searches at the LHC so far have found no evidence for the superpartners predicted by N = 1 supersymmetry. However, there is no reason to give up on the idea of supersymmetry as such, since the refutation of low-energy supersymmetry would only mean that the most simple-minded way of implementing this idea does not work. Indeed, the initial excitement about supersymmetry in the 1970s had nothing to do with the hierarchy problem, but rather because it offered a way to circumvent the so-called Coleman–Mandula no-go theorem – a beautiful possibility that is precisely not realised by the models currently being tested at the LHC.

    In fact, the reduplication of internal quantum numbers predicted by N = 1 supersymmetry is avoided in theories with extended (N > 1) supersymmetry. Among all supersymmetric theories, maximal N = 8 supergravity stands out as the most symmetric. Its status with regard to perturbative finiteness is still unclear, although recent work has revealed amazing and unexpected cancellations. However, there is one very strange agreement between this theory and observation, first emphasised by Gell-Mann: the number of spin-1/2 fermions remaining after complete breaking of supersymmetry is 48 = 3 × 16, equal to the number of quarks and leptons (including right-handed neutrinos) in three generations (see “The many lives of supergravity”). To go beyond the partial matching of quantum numbers achieved so far will, however, require some completely new insights, especially concerning the emergence of chiral gauge interactions.

    I think this is an interesting perspective on the main problem with supersymmetry, which I’d summarize as follows. In N=1 SUSY you can get a chiral theory like the SM, but if you get the SM this way, you predict for every SM particle a new particle with the exact same charges (behavior under internal symmetry transformation), but spin differing by 1/2. This is in radical disagreement with experiment. What you’d really like is to use SUSY to say something about internal symmetry, and this is what you can do in principle with higher values of N. The problem is that you don’t really know how to get a chiral theory this way. That may be a much more fruitful problem to focus on than the supposed hierarchy problem.

  • Progress in geometric Langlands marches on, with a new paper yesterday from Aganagic, Frenkel and Okounkov on the Quantum q-Langlands Correspondence, a two-parameter generalization of geometric Langlands. Among many other things, they formulate (Conjecture 6.3) a conjecture generalizing the characterization (using BRST methods) of affine Lie algebra representations at the critical level that from the beginning of the subject described a major aspect of how geometric Langlands works locally (for details on this, see Frenkel’s book Langlands Correspndence for Loop Groups).
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59 Responses to Various and Sundry

  1. Jeff M says:

    I’m fine with using slides (LaTeX please, not PP) for conference presentations, since I assume my audience has a pretty good idea of what I’m talking about. For classes, they’re terrible. I got stuck once teaching upper level analysis from slides, and it was really really hard to keep it interesting. I felt very detached from the material, and it was impossible to improvise when I thought of something interesting not in the slides. When I’m teaching something low level, like calculus, I don’t even like to use notes since that makes it too canned.

  2. paddy says:

    Wendell Furry used “view foils” c. ’74-’75 for his EMT class. But this due to his infirmity at the time. He did wander to the blackboard though on occasion to digress. I loved his digressions.

  3. Jonny iTouch says:

    For almost 15 years, Hermann Nicolai’s (of Nicolai map fame!) has been publishing on the program of subsuming the 48 spin 1/2 fermions as unfaithful representations of K(E10) arose from M-theory at space-like singularities (see e.g.,, …, His discussion in the article seemed, to me, to be alluding to those same publications, yet comments here seem to suggest that Nicolai’s decided the M theory was just along for the ride and has some other scenario for that E10? Can someone point to some references about that, because that would surely be an interesting read?

  4. chris says:

    I love blackboards because they don’t get in the way. No thinking about capping your pens or when they will run out. with good chalk the stroke is clear and perfectly readable down to the last inch. and you can rearrange blackboards! (why this has not been impelented with whiteboards totally eludes me).

    literally, with a blackboard i can arrange my thought process in a spatial manner and concentrate on that, forgetting chalk and board, while a whiteboard (like all higher tech) is constantly competing for your attention.

    and don’t get me started on “smart boards”. oh yes they are cool – which is another way of saying they grab your attention. more than half the brain will be dedicated to the presentation medium rather than the topic.

    maybe this will change for future generations that grow up with these things. i doubt though that the naturalness with which humans can handle simple physical objects (like chalk and moving boards) will ever be reached with more sophisticated tools and their potential for distraction will always be larger.

  5. Peter Woit says:

    Jonny iTouch,
    The fact that Nicolai doesn’t mention M-theory seems like pretty good evidence that that’s not what he sees as the solution. Note that he’s explicitly talking about the implications of non-observation of superpartners at the LHC. If he wanted to argue that this is some sort of argument for M-theory, that would be an argument I’ve never heard before and I doubt he would be making it while not mentioning M-theory.

  6. Jon Orloff says:

    Couldn’t agree more about blackboards. I had to use slides once when I had an injury and couldn’t walk. I didn’t like it because I couldn’t write addenda. Whiteboards are awful – the ink stains and it smells like it isn’t good for you. Love blackboards. I’m also retired (U. Maryland) and probably considered to be a crank on the subject.

  7. Chris:
    I don’t understand it either. The Oxford blackboard is not as well known as it should be; I was very lucky to come across it online before I submitted our paper on Einstein’s cosmological model of 1931.
    The most likely explanation is that the historians who were aware of the blackboard (as a museum exhibit) didn’t realise that the writing on the board represented a model of the universe – this is the problem with historians of science who may not have a background in science

  8. Artie Prendergast-Smith says:

    I agree with Cormac O Rafferty that the article on blackboard preference was pretty weak stuff.

    Responses here have repeatedly highlighted some of the main reasons for blackboard-boosting: tactile quality, good visibility, and (crucially for mathematicians) the natural pacing induced by blackboards.

    By contrast, the reasons offered in that article — the sound discouraging interruptions, the impossibility of total erasure — read to me like fatuous just-so stories.

  9. Alejandro Rivero says:

    For reference. Gell-Mann article cited by Nicolai is scanned in Santa Fe:

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