Existence of uniform Temple charts and applications to null distance

In this paper, we prove that Temple's cylindrical future null coordinate charts can be constructed uniformly and we estimate the gradients of their optical functions. We then apply these charts to study a spacetime (N, g) that has been converted into a definite metric space (N, d_τ), where d_τ is the null distance of Sormani and Vega defined using a locally anti-Lipschitz (in the sense of Chrusciel, Grant, and Minguzzi) generalized time function τ. In particular, in the case when τ is Lipschitz we prove that (N, d_τ) is a rectifiable metric space, where the causal structure is locally encoded by τ and d_τ. As a consequence, applying a classical theorem of Hawking and following a technique developed by Sakovich and Sormani, we can prove a Lorentzian isometry theorem, generalizing our earlier result.