contempt in physics

Posted by Steinn Sigurðsson on November 28, 2007
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The Angry Physicist is really irate

He read Jacques’ recent Musings on things Exceptionally Simple and was not amused.

Can I please first note that Lisi’s infamous title is a PUN!
It is a joke, folks, and it is funny.
See, E8… it is an exceptional Lie group, and it is simple… argh. Never mind.

Now I might have let this slide, but even Chad is getting perturbed by all the negative vibes, so may I please remind people of some history.

Once upon a time: there were some bold imaginative young theorists, somewhat fresh out of grad school.
There was a newish theory around, that boldly proposed to solve a major problem in classical physics, using a new, large symmetry with mysterious and undefined properties, many of which had not been well resolved. The young ‘uns decided to play around with bigger symmetries to see if they could do stuff, so they tried crazy stuff like SU(6) symmetry groups.
That was 40 years ago, and the problem was the strong interaction, and the solution was SU(3) colour symmetry, but it took some time to solve minor details, like the issue of asymptotic freedom.

Some of teh Young ‘Uns, went off on a tangent, they considered “dual” theories – these had some nice properties, but honestly, any rigorous theorist could see they were pathological.
Then some clever clog pointed out that these theories were equivalent to quantizing an elastic string, which had terrible problems if you tried to pull on the ends – the fundamental particles couldn’t propagate freely, and most sensible folks dropped this like a hot potato and went off to do sensible stuff like trying to calculate strong interactions using integers on a discrete lattice.

But some persisted, and played with this new concept: it had a nice property, it seemed to automatically include something that looked like gravity with something that looked like the strong force: there was a massless spin-2 state in the theory.
Yippee-ai-yay!

Ok, there were some problems, people realised:
the ground state was tachyonic – which people seemed to think was a possible model for the pion, for a while;
and, the symmetry groups were actually wrong to explain the actual real world, but they looked like they might be interesting in parts, if you kinda squinted at them;
and, it might have a graviton, but it came with a spin-3/2 “gravitino” (hah! what jokers) which didn’t seem to actually exist;
and, there was this “anomaly” – the model was pathological in the self-interaction with gravity, bummer;
oh, and the fermions had “ghost” states – negative probability propagating particles (where have I heard that one before);
but, despite all that, it was kinda an interesting theory.
Or so some people thought.

so… a decade, or so, passed…
graduate students came,
graduate students graduated,
ex-graduate students went to work for graphics companies and software companies
(before hedge funds this was…)

some few, extraordinarily smart, kind, hospitable, wonderful people worked very hard on this problem, because deep down inside they had the insight to realise that this really was important – they ignored the tauntsignoring of all the other physicists who wouldn’t let them join their reindeer games – and they came up with somethings clever.

See… if you just swap the bosons and the fermions, it kinda works.
In two dimensions, anyway.
Oh, wait, these other people decided to try it in 4-D and it works there too. Nifty.
Well, it doubles the number of particles, and we don’t actually see any of those, but we can just arbitarily break the symmetry and pretend they have masses so high we don’t see them, yet, and we need an extra particle or two anyway.
Super!

Oh, and this circumvents the Coleman-Mandula theorem also. Phew. That was fortunate, ’cause you know we didn’t actually think about that till afterwards. Worked out ok.

But it was still not a theory.

But… IF we change the number of space-time dimensions (and why not) then it all works.
At least in 26, er, 10 dimensions (actually 11 works well also, maybe).
We won’t worry about the extra dimensions, ’cause we can hide them, and it gets rid of the tachyons, and the anomalies. The ones we introduced at the beginning, remember. And we did some funky stuff to suppress the ghosts.

So we have a Theory, which has some extra hidden dimension, and it has all these super particles,
but it has some really, really nice mathematical properties.

It seems like Teh Theory includes gravity, which is good; and it has gauge symmetries, which are not actually the Standard Model but are plenty big enough to probably contain the Standard Model in a consistent way, we think, if we can ever actually calculate it.
We can do calculations in two dimensions, for some problems, and we think we can state plausible conjectures for some 10 or 11 dimensional problems, and it is terribly interesting.
Seriously, it is really a very interesting theory.

But, it took 5-10 years to realise it was really interesting, IF you were smart enough and you were there.
It took just over a decade for some extraordinarily smart people to show it was actually interesting, and then many hours for most of the rest of the theoretical physics community to jump on the bandwagon.

And in the 20+ years since, much has been conjectured, a few things have been proved and almost nothing actually calculated.
And it is still the best theory around.

So, lets not get too snide when someone points out that there may be something interesting possible in a mathematical structure that may eventually with some very hard work lead to something interesting and physically relevant.
He may be wrong, but so may all of you.
In fact most of us are wrong most of the time, comes with the turf.

PS: Lee is not paying me for this, in fact he hasn’t even bought me a cup of coffee for, like, years. John bought me a drink more recently (very nice Italian red, may I say), but even that wasn’t very recently at all. So there.

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Comments

  1. #1 Blake Stacey
    November 28, 2007

    And the process of finding out whether Theory X is really interesting begins with people poking it and pushing on it and hammering it really hard.

    CITOKATE: Criticism Is The Only Known Antidote To Error.

    Everybody knows the history you tell already (except, maybe, the bit about the pion). What matters now is, primarily, whether you can really embed SL(2,ℂ)×SU(3)×SU(2)×U(1) in a noncompact real form of E8, such that three copies of a particular representation appear. . . Secondarily, we should ask ourselves why people who haven’t the foggiest idea what the previous sentence means offer opinions about the problem with such heat!

    The sooner we have somebody hammer on the first question, the sooner we can tell whether Theory X (a) does what it’s claimed to do, (b) might be useful for something else, like a toy model or an effective field theory, or (c) belongs in the “lost causes” bin. After that, the sooner we ask the second question, the sooner we can improve science journalism beyond these penny-dreadful, sensationalist antics.

  2. #2 Steinn Sigurdsson
    November 28, 2007

    Absolutely.
    Although most of the people a) do not remember to carry this history in their forebrain where it can inform the perspective of the new history, and b) many of them think that if they had been there then they also would have done what Schwarz did.
    They are mostly wrong to think so.

    We don’t even need to do it nicely. Negative feedback is supposed to hurt.
    But a modicum of humility and civility doesn’t hurt, and just as the theory needs some hard pushback, so also does the ‘tude of some dudes need a pushback.

    On the other hand I actually like that the blogosphere is full of uncivil Dirty Fucking Hippies who are not afraid to say that something is Not Reality Based.
    We don’t need the faux civility of the balanced presentation either.

  3. #3 Blake Stacey
    November 28, 2007

    Dang it, that funky accented a should have been a C, or ideally a blackboard-bold C. The inability to do actual math notation at ScienceBlogs gets irritating, every now and then.

  4. #4 Blake Stacey
    November 28, 2007

    Oops, our comments crossed in the blogoniferous aether.

    On the other hand I actually like that the blogosphere is full of uncivil Dirty Fucking Hippies who are not afraid to say that something is Not Reality Based.
    We don’t need the faux civility of the balanced presentation either.

    Amen!

    I know from personal experience that Jacques Distler is willing to answer questions from total schmucks, so I suspect that he’s a good person at heart. Anybody who has invested as much in physics-blogging as he has and done it for so long would naturally be a little sharp-tongued when they see the physics blogosphere not doing its job.

  5. #5 Steinn Sigurdsson
    November 28, 2007

    Well html 2.0 works mostly in comments, but doesn’t seem to have the C-with-vertical-bar or related symbols (like the vertical-bar-R for reals)

    bummer

    I am actually listed somewhere as a “physicist who ripped Lisi in blog”, but I started pushing back because some of the critique was out of control.
    The reason I brought up string theory history is because it started off really half-assed and most people walked away from it because they were doing stuff that was not justified, or just not “how things were done” or because they introduced new problems or glossed over old problems to pursue solution to one or two other problems – I mean bringing gravity at the expense of a tachyonic ground state doesn’t really look that promising.

    And I am quite sure that exactly the people who are the most snide about Lisi would have been dismissive of strings back then, until someone else did the grunge work to show it was really actually interesting.
    Theoretical physicists are really conservative.
    A lot of the time that is good.

  6. #6 Aaron Bergman
    November 28, 2007

    “Exceptionally simple” is a (tired, obvious) pun. “Theory of everything”, on the other hand, is a joke.

  7. #7 Steinn Sigurdsson
    November 28, 2007

    not Lisi’s joke though, is it?

  8. #8 muse
    November 28, 2007

    You boys play funny games in this sleeazy world called Physics! ((Kudos to your crisp pen, Steinn. One would assume an equaly sharp mind behind it. But of course are these netherlands a world of deception and false appearences – as i have learned.))

  9. #9 Aaron Bergman
    November 28, 2007

    I meant joke in a non-complimentary way. My own little pun, so to speak.

  10. #10 Steinn Sigurdsson
    November 29, 2007

    I know
    Me too.

  11. #11 amused
    November 29, 2007

    “Can I please first note that Lisi’s infamous title is a PUN!
    It is a joke,…”

    Are you sure about that? He repeats it again in the paper (in the Summary, page 28):
    “The “E8 theory” proposed in this work is an exceptionally simple unification of the standard model and gravity.”
    I suspect he originally meant it seriously, but then decided to call it a joke after the reactions it provoked. But in any case, the physics content of the paper (or lack thereof) is more important than the title…

    If this paper had been posted on the arxiv under normal circumstances most people would have ignored it, some would take a look out of curiousity, and, who knows, a few might even have taken an interest and decided to follow it up. Just like with any of the multitude of other papers proposing new physics from some or other direction (brane worlds, string phenomenology or whatever). I think the reason for the strong reactions are that people felt obliged to pay attention to it because of the hype, and then got annoyed to find that it was so far from living up to it. It’s not even a theory yet, just a hope for a theory (and an ill-founded hope at that according to Dister and others who have looked into the details). But even without the problems, would it be a more well-motivated, compelling model for new physics than so many of the others out there? Does it provide an elegant way to get around problems that were encountered in other approaches (e.g. proton decay), or provide some new conceptual insights, or provide anything else that singles it out as specially deserving of attention? So the fields of (one generation of) the SM and gravity were fitted into E8 in a tight way — kind of interesting that that can be done, but is it cause for any excitement or expectations? Any more reason to expect that the new physics of this model (if it could be fixed) would show up at the LHC rather than one of the multitude of other models out there?

    The analogy with the early string theory situation is really streching it. The reason for the string theory hype was the enormous potential people saw in it despite its problems, whereas the reason for the current hype of Lisi’s paper is…er,…can someone remind me what it was again?

  12. #12 Steinn Sigurdsson
    November 29, 2007

    I don’t know, I am not Lisi.
    But my inference is that the title is a joke, but as with all such, there is seriousness behind the joke.

    The reaction is clearly to the hype, but the comparison with string theory is not entirely unwarranted – the potential was not seen by most of the community until 1984, and people were working on it for over a decade before then. A few started to realise there was something there in 1982/3, but before then the apparent problems looked pathological and took a lot of work to fix. And the motive, as I recall having been told, was that this was a theory which had gravity so it was worth working on fixing the tachyons and ghosts and anomalies. To the six or so people who actually worked on it.

    The hype here, is partly the modern world, partly the outsider aspect, and partly that that this put gravity into something like an old style gauge theory, which soaks up most of the extra particles that grand unification usually produces.
    And interestingly still leaves some beyond standard model physics in the residual symmetries. It has “predictions” in that it predicts no super particles, no extra dimensions and coloured scalar triplet, as well as some other junk.
    No masses or couplings yet, and possibly never will.

    Lisi may have factored E8 inappropriately, he does not have a theory, but the idea is not totally trivial. If it is wrong, it is possibly interestingly wrong.

    I don’t know. A case can be made that it was at least interesting enough that people had to pause to refute it. That is somewhat interesting.

  13. #13 fisics
    November 29, 2007

    Hi Steinn

    Thanks for the reasonable post. But I would like to say that the comparison with the early history of string theory is not very good. In physics, one can distinguish between works which are mathematically correct but may or may not be physically right(string theory) and the works which contain some problems at the mathematical stage itself (like Lisi’s work as pointed out by Distler). I think that’s why Distler, after mentioning several physical problems, concentrated on just checking the maths. Lisi’s work has problems even at that level. String theory, even in it’s early days, never had that sort of problems. One could have disagreed(and most scientists did) with tachyons,extra dimensions etc. But there were no calculational mistakes or mathematical misunderstandings (which Lisi’s work shows). The difference matters because calculational mistakes or mathematical misunderstandings can be avoided if the person is careful (which should be a prerequisite). One can’t compare Dirac delta function (which seemed like a mathematical mistake to mathematicians at that time) with the type of mistake which Lisi made(as pointed by Distler).

  14. #14 amused
    November 29, 2007

    There are many gauge groups into which the SM + gravity fields can be embedded, so that in itself is no big deal. The point seems to be that E8 admits a “tight fit” with relatively small amount of exotica/junk. But taking that as the sole motivation seems akin to numerology. (And it isn’t even a proper fit… the fix, if there is one, is unlikely to be pretty.)
    As for why people paused to refute it, I’m sure that has a lot more to do with the various comments/hypes that were made rather than the paper itself…
    As for predictions, the multitude of other models out there have theirs as well…

  15. #15 Steinn Sigurdsson
    November 29, 2007

    yeah, once you find a big enough a gauge group, there are lots, and lots, that are bigger.
    the problem then is you add too much stuff we don’t see, which must then be hidden or explained away
    if E8 is not a proper fit, and I will not adjudicate that claim, then it is not interesting in this way (E8xE8 is clearly big enough, so that is halfway there…)
    predictions are surprisingly rare, but good, and most predictions are of course wrong

  16. #16 Steinn Sigurdsson
    November 29, 2007

    Fisics: I’m sorry, but I disagree with your characterisation of early string theory.
    It turned out to be mathematically ok in the end, but if you look at the papers they are the normal, occasionally sloppy, piecewise, half-guess stuff you get in any half-baked theory.

    eg. Schwarz & Wu on ff amplitudes deduced two functions by “guesswork”, and Olive and Scherk missed a singular channel when deducing Lorentz invariance. This stuff was incrementally corrected and filled in, it didn’t spring like Athena from Scherk’s head.

    I’ll just point out two things: worldsheet supersymmetry AND 4-D supersymmetry notionally violated the Coleman-Mandula theorem, but it took a couple of years before it was raised and solved. These things were proposed as ad hoc “swap fermions and bosons”, not as ways around C-M, and it was not known at the time the symmetry was as nice as it actually is.
    Secondly consider Scherk & Schwarz ’75 GRF essay – this is really where the theory went from “nice toy model for strong interaction” to “hey, this could be a theory of everything”.
    That essay is a sketch, they didn’t know what half the field they threw in were or what they would end up corresponding to, they just stuck them in to fix things up and because it worked.

    I love me the “Superstrings vol I & II: the Early Years” ed Schwarz. 1200 pages of pure geek joy.

  17. #17 sally
    January 9, 2008

    The reason for the string theory hype was the enormous potential people saw in it despite its problems, whereas the reason for the current hype of Lisi’s paper is…er,…can someone remind me what it was again?