Live blogging: Harvey

Mathematical consistency:

It’s been claimed that superstring theory provides a UV finite theory. There have been some nagging wories about defining amplitudes on higher genus Riemann surfaces, but these have been laid to rest by Witten and collaborators.

Audience: does UV finite mean that there’s no need for renormalization?

Harvey: Yes.

As in any interesting theory, the perturbation theory is not convergent, and non-perturbative effects must be included. This is difficult, but there’s no reason to think that it can’t be done.

Finally, on philosophy:

Historically, people in GR have been more keen to engage with philosophy. String theorists believe that GR is just another non-renormalizable effective field theory. So they take this attitude to LQG. It doesn’t exist, in the same way that QED doesn’t exist (not well-defined to all energy scales).

Audience: Do you think string theory is well-defined at all scales?

Harvey: Yes, the strings get fuzzier below the Planck length, but they’re still well-defined.

Some particle theorists have been hostile towards philosophy. But that doesn’t reflect on the extent to which string theory could use philosophical work!



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