Bogus media stories about how “physicists finally find a way to test string theory” have now been with us for decades, with a large number of them documented here. Recently this phenomenon seemed to finally be dying down, with such stories the province of more obscure media outlets and the press offices of not very well-known institutions. Yesterday though saw a new example of the genre, coming to us from IAS faculty and the Fermilab/SLAC publication Symmetry, which announces that Theorists from the Institute for Advanced Study have proposed a way forward in the quest to test string theory.
The source of all this is the Arkani-Hamed/Maldacena paper Cosmological Collider Physics from earlier this year. As usual with a lot of these bogus stories about “testing string theory”, the work in question actually has nothing to do with string theory. It’s about possible ways to look for particle physics effects in subtle effects in non-Gaussianities in the CMB. This is a theoretically interesting topic, but suffers from the obvious problem that, experimentally, there are no non-Gaussianities in the CMB. The limits on non-Gaussianity from Planck and other CMB experiments are quite strong.
The connection to string theory is given in the article as:
But scientists are working out ways that experiments could at least begin to test parts of string theory. One prediction that string theory makes is the existence of particles with a unique property: a spin of greater than two.
This is of course complete nonsense, since there are plenty of known particles of spin greater than two. String theory arose as an attempt to explain some of these, but it turned out that it didn’t work, the actual explanation was QCD, a quantum field theory. The author seems to have gotten this argument from the following statement in the Arkani-Hamed/Maldacena paper:
Of course, if we were to detect the contribution of a spin 4 state in the non-gaussianity, it would be a strong indication of string theory during inflation, since we suspect that a structure like string theory follows when we have weakly interacting particles with spin s greater than 2.
Knowing that there is a spin 4 state up at the inflation or Planck scale would of course be quite interesting, but I don’t see any reason to believe that effective field theory would apply to it or that this would “of course” “be a strong indication of string theory”. This argument would actually make better sense at lower energy. I suppose you could claim that lots of work being done at the LHC is “a way forward in the quest to test string theory”, since any day it could lead to evidence for a new weakly interacting spin 4 state. That would of course be pretty silly, but less silly than this article.
Combined with the bogus “test”, the article includes a large helping of the usual promotional material, ending with a section on “The value of strings”. We’re told that
Witten and others believe that such successes in other fields indicate that string theory actually underlies all other theories at some deeper level.
“All other theories”???
Update: I should make clear that my comment about the strength of the limits on non-Gaussianities was about the quality of the experimental results, and my impression that there are not near-term prospects for doing much better. Depending on what models one is talking about, such results are often not strong constraints. A correspondent suggest this source for more information about all of this.