The SLAC web-site today has a feature article entitled SLAC Physicists Develop Test For String Theory*. The “*” refers to a footnote to the title saying “Under Certain Conditions”. This is about the 10500th news story making this kind of announcement that has appeared over the past twenty years (like this recent one), and the title is just as incorrect and misleading as all the others.
The story starts with
String theory solves many of the questions wracking the minds of physicists, but until recently it had one major flaw — it could not be tested. SLAC scientists have found a way to test this revolutionary theory, which posits that there are 10 or 11 dimensions in our universe.
and is about a paper by JoAnne Hewett, Ben Lillie and Thomas Rizzo entitled Black holes in many dimensions at the LHC: testing critical string theory. This paper is perfectly reasonable, discussing a proposal for getting information about the number of extra dimensions, assuming Tev-scale gravity (a huge assumption most people think unlikely) and thus production of black holes at the LHC. If the number of extra dimensions is bigger than 6, then 10d superstring theory is ruled out (one can make similar comments about 11d M-theory, whatever that is).
Like all news articles of this kind, this one is misleading in the extreme, since “SLAC Physicists Develop Test For String Theory” is likely to make the unwary think that string theory is now testable. In addition, it’s flat out wrong, since the writer made the critical decision to replace “critical string theory” by “string theory”. Granting the unlikely assumption that the LHC sees extra dimensions and measures their number. if this turns out to be more than 6 or 7, string theorists will likely just point out that it is only “critical” string theory which lives in 10 dimensions. In recent years there has been much talk about string theories outside the critical dimension. For some discussion of this, see the comment thread of a recent Cosmic Variance posting, where string theorists Eva Silverstein and Clifford Johnson maintain that they see reasons to believe in the existence of string theories in dimensions other than 10. For some flavor of the discussion, here’s what Clifford has to say:
…the “person on the street” all too often hears (or implicitly gathers from posts like this) the phrase “string theory requires D=10/11″, and it is simply not true and in some years we may well have to be spending a lot of time undoing yet another uncautious claim when/if after doing phenomenology better we find that we don’t need to start in higher D and then “compactify”. We’ll have to go around telling everyone (on the tv shows and radio shows and magazines) “oh…that thing we said about extra dimensions? We were just kidding”…. Just like we’re doing now with the whole “unique vacuum” and “theory of everything” phrases…
Clifford seems fond of the idea of sub-critical strings, perhaps even strings in four dimensions (another enthusiast of this idea is Warren Siegel), while Stanford string theorist Silverstein advocates the study of super-critical strings, exactly the ones that would get around the “test” promoted today by her colleagues at SLAC.
Update: SLAC has replaced this article on their website with a new, much more accurate version, entitled “SLAC Physicists Develop Framework-Dependant Test For Critical String Theory”. The original version got wide distribution, even appearing on Slashdot.