Today Slashdot brings us the news that Gamma Ray Anomaly Could Test String Theory. As usual with such media claims about the testability of string theory, this is complete nonsense. The story is based on this Scientific American blog posting, which in turn is based on this paper by the MAGIC gamma ray telescope collaboration.
The claims about testing string theory aren’t in the paper, but appear to come from string theorist Dimitri Nanopoulos who claims that he predicted (or, more accurately, “suggested”) the kind of effect seen by MAGIC using string theory. As far as I can tell though, just about no string theorists except Nanopoulos and his collaborators Nick Mavromatos and John Ellis actually believe this. Mavromatos and Nanopoulos also believe that string theory is responsible for the way that our brains work, here’s the abstract of one of their papers on this:
Microtubule (MT) networks, subneural paracrystalline cytosceletal structures, seem to play a fundamental role in the neurons. We cast here the complicated MT dynamics in the form of a 1+1-dimensional non-critical string theory, thus enabling us to provide a consistent quantum treatment of MTs, including enviromental friction effects. We suggest, thus, that the MTs are the microsites, in the brain, for the emergence of stable, macroscopic quantum coherent states, identifiable with the preconscious states. Quantum space-time effects, as described by non-critical string theory, trigger then an organized collapse of the coherent states down to a specific or conscious state.
Claims have been made by many string theorists that not only does string theory not predict this kind of violation of Lorentz invariance, but exactly the opposite: string theory predicts no such violation. String theorist Jacques Distler earlier this year even went so far as to have the University of Texas issue a press release trumpeting his claims to have shown that string theory is falsifiable, using a calculation based on the assumption that string theory preserves Lorentz invariance (either his colleagues or a PRL referee wouldn’t let him make this claim in the paper the press release was based on, but that’s another story…).
Claims have been made (although there is controversy about this), that the main competing quantum gravity research program, Loop Quantum Gravity, predicts this sort of violation of Lorentz invariance, and this would be one way of distinguishing it from string theory. Lubos Motl has a new posting about the MAGIC result, mainly concerned with knocking it down since he fears that it will be used as evidence for LQG and against string theory.
It seems to me that in any case, the actual experimental evidence here is far too weak to support any claim that a violation of Lorentz invariance has been shown. Among the usual nonsense on Slashdot, there was the following sensible comment about the MAGIC result from an astrophysicist:
What they are saying is that there are still details we don’t understand about AGN [active galactic nuclei] like Markarian 501. So, while this effect could be a first sign of quantum gravity (*not* string theory in particular, as others have pointed out), it could also simply be something going on in the intrinsic spectrum of the flares themselves. I’d personally consider the second explanation more likely at this stage.
As they also point out, one approach to sort out the ambiguity would be to observe other flary AGN at different redshifts (distances). One could then, for example, see if the delay gets shorter or longer as the distance changes, as one would expect with a quantum gravity effect due to propagation to Earth.
Utterly Off-topic, But How Can I Resist Mentioning: According to this blog entry by a USC student, not only am I the “archnemesis” of string theorist blogger Clifford Johnson, but also
If string theory were a vampire, he’d be Buffy.
I’ll have to consult my friends and colleagues on the resemblance to Buffy question, personally I don’t see it.
I don’t know about vampires, but these “tests of string theory” are kind of like the living dead, staggering around trying to get their teeth into people and turn them into string theory partisans. No matter how often you blow their heads off with a shotgun, more keep coming…
Update: Lubos and I seem to be in complete agreement about this experimental result and the Nanopoulos et. al. explanation of it. This situation appears to have driven him over the edge.
Update: See Backreaction for a more detailed posting about the MAGIC result.