Since in reality the values of physical fields at distant locations are not that much correlated, the covariance matrix is tapered off artificially based on the distance, which gives rise to localized EnKF algorithms. (en.wikipedia.org)
This suggestion is no more clearly confirmed than in his discussion, in Process and Reality, of what constitutes both a physical object and a»... physical field in empty space» (PR 92). (religion-online.org)
It is interesting that Whitehead associates physical fields as well as living nexus with empty space (PR 92 / 141). (religion-online.org)