Mach’s critique of Newton’s absolute space exposes the conflict between (1) the view that space-time is non-dynamical and (2) space-time realism. Meanwhile, since general relativity the predominant view of spacetime has been that it is a dynamical Riemannian manifold, and therefore Mach’s criticism does not apply. However according to Poincare’s conventionalism: (empirically speaking) there is no one true geometry of spacetime, all geometries are permissible provided the appropriate changes are made to the dynamics of the physical content contained, (i.e. only “(G) + (P)” is subject to experiment). From this standpoint we may revise Newton’s notion of ‘absolute space’ by conceding non-realism but affirming that it is non-dynamical. Absolute space becomes a principle that: ‘All that is dynamical belongs to physics, that which measures physics remains unaffected.’ I look at how this convention compares to Reichenbach’s stipulation that ‘universal forces should vanish,’ and how an analogous convention is advanced by various alternative relativistic theories of gravity (bimetric theories, particle physics accounts, Logunov’s ‘RTG’, a scalar VSL model of gravity).
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Philosophy of Physics Graduate Lunch Seminar Convenor: Caspar Jacobs