Against the Gravity/Inertia split? - a podcast by MCMP Team

Dennis Lehmkuhl (Wuppertal) and Oliver Pooley (Oxford) give a talk in the colloquium "On the Split Between Gravity and Inertia in Different Spacetime Theories" at the 17th UK and European Meeting on the Foundations of Physics (29-31 July, 2013) titled "Against the Gravity/Inertia split?". Abstract: To make sense of talk of a frame-dependent inertia–gravity split in General relativity, one needs to relate the theory to Newtonian gravity, and to recognise that two routes to privileged frames of reference need not yield the same sets of frames. On the first route, which paths in spacetime correspond to unaccelerated (“inertial”) motions is an absolute, coordinate-independent matter. The privileged frames are those whose standard of rest corresponds to inertial motion. On the second route, privileged frames are identified via classes of co-moving coordinate systems with respect to which dynamical equations take a simple, canonical form. In Newtonian gravity, the second route yields globally-defined frames with respect to which freely-falling bodies are (in general) accelerating. In practice, however, the theory cannot distinguish between frames that are relatively translationally accelerated. At best, therefore, an empirically undetectable proper subset of these frames encode inertial motion. The idea of a frame-dependent inertia–gravity split arises when one combines the idea that these frames encode inertia (and thus that free-fall motions involve gravitational deflection from inertial motion) with the idea that they are fundamentally physically equivalent. This combination, however, is not coherent. A preferable viewpoint reconciles an absolute notion of inertia with the physical equivalence of the frames identified via the second route by denying that they encode inertial motion. They are, instead, frames with respect to which the components of the connection take a particularly simple form, even though they do not all vanish. We will argue that Einstein’s central claims concerning the equivalence principle, and the frame-dependence of the gravitational field, are compatible with this second viewpoint.

Further episodes of MCMP – Philosophy of Physics

Further podcasts by MCMP Team

Website of MCMP Team