Measurement of the space - time interval between two events using the retarded and advanced times of each event with respect to a time - like world - line

Several recent studies have been devoted to investigating the limitations that ordinary quantum mechanics and/or quantum gravity might impose on the measurability of space-time observables. These analyses are often confined to the simplified context of two-dimensional flat space-time and rely on a simple procedure for the measurement of space-like distances based on the exchange of light signals. We present a generalization of this measurement procedure applicable to all three types of space-time intervals between two events in space-times of any number of dimensions. We also present some preliminary observations on an alternative measurement procedure that can be applied taking into account the gravitational field of the measuring apparatus, and briefly discuss quantum limitations of measurability in this context. ar X iv :0 71 0. 56 08 v1 [ gr -q c] 3 0 O ct 2 00 7