Berlin 2012 – wissenschaftliches Programm

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AGPhil: Arbeitsgruppe Philosophie der Physik

AGPhil 4: Spacetime Thoeries

AGPhil 4.1: Vortrag

Mittwoch, 28. März 2012, 09:30–10:00, H 2033

The difference between matter and spacetime — •Dennis Lehmkuhl — IZWT, Universität Wuppertal, Gausstrasse 20, 42119 Wuppertal

The possession of mass is widely accepted as a necessary condition for something to be a material systems in Newtonian physics. I argue that the property "possession of mass-energy-momentum" should be seen as the natural heir of the property "possession of mass" in the context of relativistic theories. Hence, possession of mass-energy-momentum (energy for short) should be counted as a necessary condition for something to be a material systems in these theories. However, we also know that gravitational waves, waves of curvature in spacetime, can possess energy, so that the question has to be posed whether gravitational waves and thus spacetimes should be counted as material systems as well. There are many definitions of gravitational energy in general relativity, all of them involving a kind of non-locality. But more importantly, all these definitions are such that gravitational/spacetime energy can only be defined for certain kinds of spacetimes. Having argued for seeing energy as a necessary condition for somethin to be a material system, I claim that spacetimes cannot be counted as material systems in GR. The theory thus leaves us with a fundamental dichotomy between spacetime and matter. I conclude with a brief discussion of whether this dichotomy might be hoped to be overcome by modifications or extensions of GR.