Proper time is a simple classical observable, but its correlations are less well understood. We define correlation functions of proper time for massive worldlines coupled to quantum field theory and quantum gravity, and we show how to compute perturbative corrections using Feynman diagrams.
When the worldline endpoints are held fixed, proper time correlators are derivatives of the on-shell action with respect to mass, or more generally, derivatives of the logarithm of local correlators. This clarifies how CFT correlators encode AdS worldline data. When the worldline endpoints are dynamical and determined relationally in a gravitational system, the proper time delay operator is a smeared graviton operator to leading order. The proper time two-point function computes the leading-order signature of quantum gravity in a toy model of a LIGO-type interferometer. This prediction agrees qualitatively with the experimental observable computed in a more realistic model.