# Live Blogging: Vistarini

We get the Ricci flatness condition $R_{\mu\nu}=0$ (my latex skills are up to that!)

Tiziana offers to take some extra time for us and explain everything so we understand it properly – apparently we can skip lunch and our flights aren’t till the evening anyway! The audience laughs nervously. Nick Huggett points out that there’s no lunch to skip…

Why does string theory have to be conformally invariant? There are consistency reasons connected to the fact that the only recipe for calculating scattering amplitudes involves taking the partition function on the moduli Riemann space…

Why is this emergence? We’re discussing an inter-theoretic relation between GR and string theory. We need a Batterman/Butterfield approach to emergence. Notes that although Butterfield and Batterman agree about emergence involving limits, they disagree as to whether this happens before or after the limit and hence on whether emergence is compatible with reduction. Notes that the notion of novelty applicable here will be epistemic – we do get novel robust behaviour characterised by length scale that can’t be (explanatorily?) captured by the reducing theory.

What have we been doing here? Looks like a case of reduction and emergence but depends how we think about conformal invariance – this comes in as a kind of guiding principle – we’re not deriving GR from within string theory itself. There is a no man’s land between the theory in which we have to use the guiding principle.