Untangling String Theory

The Times of London recently sent one of its reporters out to a pub to learn about string theory from Michael Green, with results available on-line here.  Green does a good job of trying to explain some physics over a few beers, and admits that:

I think, historically, when there has been a big change in a theory there is usually some qualitatively new phenomenon which will distinguish the theory. This has not happened for string theory, which is one of the reasons some people wonder whether it is real physics.

There’s an associated slide show that supposedly gives a step-by-step guide to string theory. It explains that there are ten extra dimensions of very small size, necessary because:

Beautiful as the idea sounds, when string theory is applied in the ordinary three spatial dimensions it doesn’t work mathematically, predicting the wrong numbers for constants such as pi and the speed of light. It also predicts that the whole Universe should disappear.

I do wonder what string theory’s prediction for the value of pi is…

According to the Times, the LHC has something to do with all of this, since:

Scientists hope that the smashing together of particles at the Large Hadron Collider may reveal hints of the strings lying within them.

Over at the Los Angeles Times, Steve Giddings somehow neglects to mention string theory while arguing that the LHC

  • “could open new frontiers in understanding space and time”
  • “might produce dark-matter particles so we can study their properties directly and thereby unveil a totally new face of the universe.”
  • “might also shed light on the more predominant ‘dark energy,’ which is causing the universe’s expansion to accelerate.”
  • “may reveal … the existence of a completely new type of dimension — what is called ‘supersymmetry'”.
  • “may find evidence for extra dimensions of a more ordinary type, like those that we see — still a major revolution.”
  • “could produce microscopic black holes.”
  • In case all of these discoveries seem a bit abstract and useless, there’s the possibility of

  • new energy sources, means of space travel or communication, or amazing things entirely unimagined.
  • Over at Uncertain Principles, some of the Giddings arguments about spin-offs leave Chad Orzel rather grumpy.

    Finally, also on the nothing-to-do-with-string-theory front, New Scientist has an article about this paper from Science, where the authors find some sort of relation I don’t understand between a representation of E8 and some phenomenon at the critical point of a quasi-one dimensional Ising ferromagnet.

    Although E8 does show up in string theory calculations, observing the symmetry in magnetic crystal experiments does not provide any evidence for string theory itself, Konik says.

    “The fact that you see this particular symmetry in this spin chain doesn’t say anything about string theory per se,” he says.

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    20 Responses to Untangling String Theory

    1. anon says:

      your link to the times article gives a 404 error page

    2. Peter Woit says:

      The London Times first link sometimes requires a reload to work properly for me, and the second link sometimes doesn’t work at all (but it’s a pop-up which can be found on the main story page, if you can get to that…)

    3. Ignatz Thugg says:

      Is it worth $15 to read the Science article?

    4. Peter Woit says:


      I very much doubt it, unless you have very specific and unusual research interests in quantum criticality and no other way of getting access to a copy of Science.

    5. Bee says:

      “We observe only three spatial dimensions in everyday life, but what if, on the subatomic scale, there are tiny, curled up, extra dimensions, deeply embedded within space, and so small that they can’t be seen? What if there were ten of them?”

      The explanation is badly formulated, but I believe “them” in the last sentence refers to “dimensions” and not “extra dimensions.” They don’t say one needs 10 extra dimensions of very small size as you write.

    6. Paul Wells says:

      If you define pi as the ratio of circumferance of a circle to its diameter and if the space is non-Euclidean I can see why this comment might make sense – especially in the context of a popular article where you might not want to go into details of space-time curvature etc.

    7. Tim vB says:

      @Paul Wells
      Sure, but that would be a phenomenon of non-euklidean geometry resp. of general relativity, this has nothing to do with string theory.
      And of course the definition of pi is and stays to be the “ratio of circumferance of a circle to its diameter in euklidean space time”, if you insist on a geometric definition (cumbersome).
      If you leave out the “in euklidean space time” you don’t get the definition of a constant.
      I think the author needed another “constant” beside the velocity of light to get the rhetorical figure “enumeration”, and pi was the first “constant” that came to mind, from the remnants of highschool.

    8. Steve myers says:

      Since it is common in checking smoothness of a fixture table by comparing circumference to diameter of several “circles” it is best to treat pi as a constant defined by something like 4 * Integral (0 to 1) of dx/(1 + x^2). I guess I never realized the power of string theory — it can change math constants. Is Euler’s number next? (Note: we also check the eccentricity of rolls of material by seeing how close the ratio approaches pi.)

    9. Will Orrick says:

      The E8 work was inpsired by A. Zamolodchikov’s results on integrable massive perturbations of conformal field theory. One of the simplest conformal field theories is the minimal model M(3,4) which corresponds to the critical point of the two-dimensional Ising model (or an equivalent one-dimensional quantum spin chain). What the authors have apparently done is to realize such a spin chain experimentally. There are two integrable perturbations of M(3,4), one of which corresponds to moving away from the critical temperature, the other of which corresponds to turning on an external magnetic field. Zamolodchikov discovered a connection of the latter to E8 which can be used, for example, to compute the mass ratios of the fundamental excitations in the massive theory. I have not yet read the Science article, so I’m not sure what aspects of this picture the experimentalists were able to measure.

    10. Anonymous says:

      “I do wonder what string theory’s prediction for the value of pi is…”

      Perhaps this might help:


    11. petergreat says:

      I think arXiv needs to add a rating system like in Youtube, so papers like this will be discouraged.

    12. Bob Levine says:

      “I think arXiv needs to add a rating system like in Youtube, so papers like this will be discouraged.”

      @petergreat: this is a terrific bit of *satire*. Look at the footnotes:

      [11]I could have checked the original references, but it was
      easier to look everything up on Wikipedia.
      [12][ And who isn’t? (with the passage in text footnoted as [12] reading, ‘Inspired by string theory[12]’…

      Reread it for what it is: a great spoof on the kind of efforts that we’re always reading about on Peter’s blog…

    13. Tim vB says:

      (The author missed the pi=3 statements from the bible.)
      It’s very telling that
      a) someone wrote this and uploaded it to the arxiv,
      b) I would add here that someone did not notice that it is a parody, but I’m not so sure: @petergreat, did you perhaps mean you wanted parodies to be discouraged?
      c) someone felt the need to point out that this is indeed a parody.

      You know, it’s really up to you if you get angry, cry, run away or laugh. I’m glad that some people out there chose to laugh.

    14. The Lone Haranguer says:

      (The author missed the pi=3 statements from the bible.)

      He was wise. See http://www.math.ubc.ca/~israel/bpi/bpi.html, On The Rabbinical Exegesis of an Enhanced Biblical Value Pi, of where the author shows that a value of 3.1415094…, accurate to 3 parts in 200,000 can be derived.

    15. Tim vB says:

      Interesting! Finally some numerology that makes sense.

      I may be a sceptic of numerology, espacially since I read the novel “Foucaults Pendulum” by Umberto Eco, but in this case I believe it.

      So let me correct my statement and say: The author should mention the Hebrew value of pi according to verse 1 Kings 7:23 of the Bible.

    16. Thomas Larsson says:

      April 1st 2009 was a Wednesday. Why did he upload already on Monday?

    17. Chris Oakley says:


      If he posted it from a computer travelling close to the speed of light, or close to a Black Hole, it may have been April 1st in his frame of reference.

      Who knows – maybe there are frames of reference (near a cosmic-scale superstring?) where it is always April Fool’s day.

    18. Thomas Larsson says:

      Chris, I think the explanation is simpler than that. IIRC, the deadline for submission to the arxiv is midnight GMT. If Scherrer made his submission between 0 and 6 am GMT on March 31, it would be received and time-stamped at Cornell on March 30, but appear in the April 1 listing in Germany.

    19. Chris W. says:

      NPR has some coverage of the research described in that Science paper.

    20. Bob Scherrer says:

      Papers need to be submitted a day early in order to appear on Apr. 1. If you look back for several years previously, you will see that several spoofs get published on the arXiv every Apr. 1. The arXiv administrators are obviously aware of this and have tolerated it thus far.

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