Breathless press reports notwithstanding, string theory is very far from being dead. If you’re interested in what it is and what’s going on within the field, I can recommend a new website called Why String Theory? (And of course, accompanying twitter feed @WhyStringTheory.) It was set up by Oxford undergraduates Charlotte Mason and Edward Hughes, working under Joseph Conlon. It’s a very engaging and professional-looking site, featuring a great deal of explanatory material.
Developing pedagogical sites like this is a great project for undergrads; the only looming issue is keeping the site going once the students move on to bigger and better things. Hopefully this one is kept up — I think an initial surge of interest has already been taxing the poor web server.
#50 The equivalence principle holds in 11 dimensions, and if the shape and size of the extra dimensions is stable, then it will also hold (to great precision) in 4 dimensions, but if the extra dimensions are changing, then you will get EP violations in 4 dimensions. The dilaton is the radius of the 11th dimension, so it is one of the “moduli” that parametrize the extra dimensions. But phenomenologists normally assume that the moduli are stable (because changing moduli could e.g. make the fine structure constant vary), which is why this scenario is in the theoretical core but not in the phenomenological core – it is dynamically possible but normally you wouldn’t think that it was happening in the real world.
I have not seen Gates vs Greene, but apparently Gates was talking about non-critical string theory, like Nanopoulos. String theory normally starts in 10 dimensions (the “critical dimension”) in order to avoid a quantum inconsistency (the “conformal anomaly”), and then 6 of the dimensions are assumed to be small. Non-critical string theory can start in any number of dimensions, and deals with the anomaly by adding an extra “Liouville” field along the string to compensate. It’s not a subject I know about and I don’t understand what its foundations are supposed to be. There are a few notable string theorists who take an interest in it, but most stick to the normal theory. Extra time dimensions are a similar story, it’s a minority interest and I can’t make any sense of it as physics. I can assure you that most string models only assume one dimension of time. 🙂
@Mitchell Porter you seem to forget what nice phenomenology Cumrun Vafa gets from F-theory … 😉
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