Heidelberg 2007 – scientific programme

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AKPhil: Arbeitskreis Philosophie der Physik

AKPhil 2: Cosmology 2

AKPhil 2.1: Talk

Tuesday, March 6, 2007, 15:15–15:45, KIP SR 3.401

What is a gravitational field? — •Dennis Lehmkuhl — Faculty of Philosophy, Oxford University

It is often claimed that the theory of General Relativity (GR) shows that what we perceive as gravity is ``in fact'' just a consequence of the geometry of spacetime. Others claim that the very core of GR is that it actually gives an account of the gravitational field, an account which unifies the latter with the inertial field (sometimes also called the guidance field) such that the theory postulates the existence of a single gravito-inertial field. I will briefly review these apparently contradicting interpretations of GR, and discuss whether they do indeed exclude one another. This will lead me on to ask: ``What is a gravitational field in GR?''; or more precisely: ``What is the mathematical representative of the gravitational field in GR?'' Some have argued that the curvature tensor should be seen as representing the gravitational field (most prominently Synge), others claim that the connection is the gravitational field's mathematical representative (e.g. Ehlers and Giulini). Both possibilities have in common that they presuppose the standard formulation of GR; nevertheless, there are striking conceptual differences between the proposals. After reviewing these differences, I will discuss a number of topics which could throw some new light on the issue; most importantly the similarity/dissimilarity between gravitational waves and electromagnetic waves, and the role GR plays as compared to non-metric gravitational theories on the one hand, and bimetric theories on the other hand.