Characterizing intrinsic Lorentzian length spaces via $\tau$-midpoints

Abstract

In metric geometry, the question of whether a distance metric is given by the length of curves can be decided via the existence of midpoints with respect to the metric $d$. We adapt a similar characterization to the setting of Lorentzian pre-length spaces. In particular, we show that a given space is strictly intrinsic provided it has $\tau$-midpoints and merely intrinsic provided it has approximate $\tau$-midpoints. Our approach is based on the null distance of C. Sormani and C. Vega.