We explore the space of scalar-tensor theories containing two non-conformal metrics , and find a discontinuity pointing to a “ critical ” cosmological solution . Due to the different maximal speeds of propagation for matter and gravity , the cosmological fluctuations start off inside the horizon even without inflation , and will more naturally have a thermal origin ( since there is never vacuum domination ) . The critical model makes an unambiguous , non-tuned prediction for the spectral index of the scalar fluctuations : n _ { S } = 0.96478 ( 64 ) . Considering also that no gravitational waves are produced , we have unveiled the most predictive model on offer . The model has a simple geometrical interpretation as a probe 3-brane embedded in an EAdS _ { 2 } \times E _ { 3 } geometry .