Spacetime atoms and extrinsic curvature of equi-geodesic surfaces

Abstract

A recently-introduced function $\rho$ of spacetime event $P$ expressing spacetime as made of 'spacetime atoms' of quantum origin is considered. Using its defining relation, we provide an exact expression for $\rho$ involving the van Vleck biscalar, and show it can be recast in terms of the extrinsic curvature of suitable equi-geodesic surfaces centered at $P$. Moreover, looking at the role $\rho$ plays in the statistical description of spacetime, we point out that this quantity should actually be understood as counting the quantum states of the collection of spacetime atoms rather than counting directly the spacetime atoms themselves (or the degrees of freedom associated to them), and would correspond to the ratio of the number of quantum states 'at $P$' for an assigned spacetime configuration to the number of quantum states for flat spacetime.