Warsaw Spacetime Colloquium: Samuel C. Fletcher (25 March on Zoom)

On Friday, 25 March, Samuel C. Fletcher (University of Minnesota, Twin Cities) will give a talk titled “What Gravitational Waves Really Teach Us about Energy” (abstract below).

The meeting will be online on Zoom (17:00-19:00 CET). If you have not registered yet, you can do so here.

You can address any inquiry to antonio.vassallo@pw.edu.pl.


Gravitational wave solutions to the Einstein field equation of general relativity are commonly regarded as examples proving how gravity in general relativity transmits energy from a source body to a distant body. The famous 1955 Feynman sticky bead thought experiment illustrates the reality of this phenomenon by imagining two beads generating heat in a rod on which they slide with friction, due to their changing proper distance in the presence of the waves. I argue that while this lesson is not entirely wrong, it is much too simplistic. It does not reconcile its conclusion with the fact that conservation of local energy-momentum, in the sense that appears in the field equation, prevents energy transmission across a vacuum. Thus “energy transmission” must employ a different concept of energy, raising the possibility of pluralism with regard to the energy concept. Another (compatible) possibility is that gravitational waves, rather than transmitting energy, facilitate the transformation between different types or stores of energy locally. Key to these possibilities is analysis of the Weyl tensor. Time permitting, I discuss these possibilities’ implications for a re-evaluation of the scope of Mach’s Principle, the idea that the distribution of matter determines the geometry of spacetime.