Philosophical appraisal of E. A. Milne's alternative to Einstein's STR

pp. 410-417

in: Adolf Grünbaum, Philosophical problems of space and time, Berlin, Springer, 1973

Abstract

E. A. Milne, whose two logarithmically related t and τ scales of time were mentioned in Chapter One, Section C, has attempted to erect the usual space-time structure of the STR on the basis of a light signal kinematics of particle observers purportedly dispensing with the use of rigid solids and isochronous material clocks.¹ In his Modern Cosmology and the Christian Idea of God,² Milne begins his discussion of time and space by incorrectly charging Einstein with failure to realize that the concept of a rigid body as a body whose rest length is invariant under transport contains a conventional ingredient just as much as does the concept of metrical simultaneity at a distance.³ Milne then proposes to improve upon a rigid body criterion of spatial congruence by proceeding in the manner of radar ranging and using instead the round-trip times required by light to traverse the corresponding closed paths, these times not being measured by material clocks but, in outline, as follows.⁴ Each particle is equipped with a device for ordering the genidentical events belonging to it temporally in a linear Cantorean continuum. Such a device is called a "clock," and the single observer at the particle using such a local clock is called a "particle-observer."