First, Whitehead lays out in The Principle of Relativity
assumptions carried over from his philosophy of nature which are
different from Einstein's and which imply a concept of simultaneity
different from Einstein's.1 «Second, Whitehead's concept of simultaneity can be found to be implicit in his discussions of his theory of spacetime, though he never draws specific attention to it or directly asserts the nature of his divergence from the Einsteinian concept.