Polchinski on Smolin on Polchinski on Smolin

Over at Cosmic Variance, Sean Carroll has just posted a guest essay by Joe Polchinski replying to Lee Smolin’s response to Polchinski’s review of Smolin’s book. I managed to snag the first comment spot; I predict that Peter Woit will show up within ten. With any luck, the ensuing comments will contain much good talk about physics, though the signal-to-noise ratio is a perennial problem. (Even Sean admits that he doesn’t read every comment.)

I would like to skim past several details of the physics and pull out for special consideration a passage of Polchinski’s which concerns, ironically, what happens when you think in text instead of physics:

This process of translation of an idea from words to calculation will be familiar to any theoretical physicist. It is often the hardest part of a problem, and the point where the greatest creativity enters. Many word-ideas die quickly at this point, or are transmuted or sharpened. Had you applied it to your word-ideas, you would probably have quickly recognized their falsehood. Further, over-reliance on the imprecise language of words is surely correlated with the tendency to confuse scientific arguments with sociological ones.

Polchinski is speaking about the standards one must maintain while doing science, but similar concerns apply to the process of explaining science. Of course, the latter process is one ingredient in the former, but we often think of “popularizing” (or vulgarisation if we want to be Gallic) as a distinct enterprise from communicating with fellow researchers and educating the next round of students. John Armstrong’s recent post on this topic addresses the same question from the opposite direction: according to Polchinski, going from words to equations is the hard part of getting work done, while Armstrong points out that when “vulgarizing” the science, that’s the very step we omit!

Armstrong amplified his point in the comments here at Sunclipse:

Roger Penrose noted specifically in his introduction to The Road To Reality that modern physics is no longer accessible to anyone — specialists included — except through the mathematics. We understand quantum field theory as well as we do because we understand the mathematics. To avoid the mathematics in its entirely [sic] cuts the legs out from under any popularization of physics, and risks becoming The Tao of Physics or The Dancing Wu Li Masters.

A subject like the AdS/CFT correspondence is not just mathematical, but abstrusely so: not only do the individual statements we make require sophisticated jargon, but also the reasoning which connects one statement to another is mathematical in character. It seems to me that a duality between theories is among the hardest of physical notions to translate into “layman’s terms,” because one can’t appreciate a duality using words alone.

In The Character of Physical Law, Feynman gives an example which I’d like to appropriate. I can say that when a planet travels in its orbit, a line from the planet to the Sun sweeps out equal areas in equal times. I can also say that the force pulling on the planet is always directed toward the Sun. Both of these statements require a little math — “equal areas,” “equal times” — but it’s not really math, not a kind to give the layman heebie-jeebies. Given some time for elaboration, one could translate both of these statements into “layman language.” However, one cannot explain in lay terminology why the two statements are equivalent.

If planets looping around the Sun can give us so much trouble, imagine having to explain the relation between gravity in anti-de Sitter spacetime and conformal field theory. Even if you could cook up a lay explanation of either one, you’re hamstrung when you try to connect them. And if you don’t even have an analogy for the situation — if the meta-concepts of duality, equivalence, one description “reducing to” another are completely alien to you — how can you appreciate why the physicists find the situation interesting and why they want to work in that area?

[Three paragraphs added the following day] Another complicating factor is that one cannot reason about physics by thinking about the everyday meanings of words. In their dark comedy Intellectual Impostures, Alan Sokal and Jean Bricmont mention a social-studies friend of theirs who asked them, in quite a puzzled manner, how it was that quantum mechanics could say the world was both discontinuous and interconnected? Looking at the everyday meanings of these two words, they do seem rather inconsistent; at least, though we could twist and turn using various definitions of these terms, we should forgive anyone who at first glance takes them to be contradictory.

The short answer, Sokal and Bricmont say, is that scientists working with quantum phenomena do not use these words in their everyday senses, but give them meanings which depend upon a web of ideas, mathematical equations and experiments. (My best guess is that the social-studies person had heard about “entanglement,” which led to “interconnectedness,” while also receiving some garbled notion of “quantization,” the fact that systems like atoms come in states of different energies with nothing in between allowed.) One cannot think about physics as if it were a novel whose great themes were “chaos,” “probability” and “uncertainty!”

It would be like studying music by looking only at the descriptions critics gave in reviews: “bright,” “rich,” “brooding,” “colorful,” etc.

I think we find ourselves in the unhappy situation where no matter how informed the lay audience feels they are, they can’t render a reasonable judgment.

UPDATE (24 June 2007): The video of Feynman making the point I paraphrased above is now available ontube:

8 thoughts on “Polchinski on Smolin on Polchinski on Smolin”

  1. You’re making very interesting points here, extremely relevant stuff, which confuses me even more – if you’re concerned about the signal-to-noise ratio at CV, why did you “snag the first comment spot” with a joke? Since you quite obviously *do* have meaningful comments…I suppose it is to drive traffic here?

    Not trying to start a snarkfest, I’m geniunely curious.

    I find this topic especially interesting as someone whose limitations inunderstanding physics are, specifcally, mathematical in nature. So I must rely on analogies built by those who can master the math, but then I find myself frustrated by the limitations imposed by them. Your point that the weakness is particularly troubling when it comes to drawing connections or comparisons is a very insightful one.

  2. I am getting oh so tired of mathematicians (and mathematicians pretending to be physicists) not apologising (in lieu of an excuse) for people failing to understand them.

    I’m a mathematician and I don’t understand some of these people!

    Off to communication courses with the lot of them.

  3. Tyler:
    Thanks to the magic of trackbacks, the column above is in the comments at CV. So, by a roundabout route, Blake’s serious contribution has been made.

  4. Tyler:

    The short answer is that I thought of the “joke” before I realized I could make a serious point, or rather that my serious point was sufficiently non-obvious to require some explication. Also, I personally find that quick jokes clearly labeled as such (with emoticons and the like) are less intrusive than long, crankish diatribes, which CV threads have in plenty. My guess is that a reader not deeply versed in the physics would be able to recognize a two-line joke, particularly if it has a smiley face attached, and say either “That’s funny” or “I don’t get it.” The same reader would have to work through a long rant for some considerable time before judging it, and even then they might not be able to detect the telltale signs of crackpottery.

    My personal standards of what constitute “signal” and “noise” may, of course, not be the best ones possible.

  5. I’m just glad you went back and decided to chime in. A lot of ppl read CV and never follow trackback links (such as myself, this is the first time I have ever followed such a link, and I read every physics-related discussion thread on CV).

    FWIW, this exact point you raise is why I never, ever, ever try to learn about science from science journalists or writers anymore – actual working scientists only. The writer has to use a metaphoric filter to learn the information, then another one to transmit their partial understanding. It is like compressing a high quality audio file twice at sequentially lower settings. The resulting output is not just degraded, lossy and compressed, it’s full of artifacts that distort the intended meaning.

    One layer of lossy compression is bad enough. I’d like to read the original files, but my physics player lacks the codec.

  6. I never meta meta-metaphor I didn’t like.


    While I appreciate your point, and while I really like the “codec” analogy, I think there are good popular and semi-popular science writers out there. Isaac Asimov and Carl Sagan were two; both, of course, were trained as scientists while the latter was an active, practicing researcher. Among the people still active, Larry Gonick, James Gleick and Carl Zimmer spring to mind. On the more mathy side are John Allen Paulos and Ian Stewart. (These are just people whose books I’ve found, read and liked. It’s not an exhaustive list.) Like anything else worth doing, explaining what you mean is a skill that takes effort to learn, and it’s not in exactly the same skill-set as the one taught to up-and-coming scientists. Also, the “raw communication” in journal articles, textbooks and so forth often loses important information like historical perspectives (what motivated person X to apply equation Y to experiment Z?).

    When they do their job properly, the popularizers are more like recording engineers and record producers than P2P users encoding with lossy codecs. They can arrange, edit and orchestrate the raw output of the musicians themselves. Competent popularization can serve as a complement or a warm-up for the real thing. Over-stretching the musical analogy, perhaps one could say that studio albums can be a good introduction to a band, and later the listener goes on to appreciate the raw sensations of a live concert.

    The problem of science popularization is tied up with that of science education. It’s not an easy problem, and usually, every aspect is tangled up with all the others. Of course, that also means it can be a whole lot of fun.

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