


The Nature of GravitationMinkowski Institute's most ambitious research project2022 March 2023  An invitation to colleagues whose research interests are in the foundations and philosophy of spacetime: Minkowski Institute is inviting colleagues who are interested in joining (as affiliated members of the Institute) its most ambitious research project  to examine rigorously whether gravitational phenomena are noting more than manifestations of the nonEuclidean geometry of spacetime, which would mean that gravitation is not a physical interaction. This project follows strictly Minkowski's program of geometrizing Physics  after discovering the spacetime structure of the world (all physical objects are, in reality, a forever given web of worldlines in spacetime), Minkowski summarized this program: "The whole world presents itself as resolved into such worldlines, and I want to say in advance, that in my understanding the laws of physics can find their most complete expression as interrelations between these worldlines." In 1921 Eddington mentioned the possibility that gravitation might not be a physical interaction almost explicitly  "gravitation as a separate agency becomes unnecessary" [A. S. Eddington, The Relativity of Time, Nature 106, 802804 (17 February 1921)]. The main theme of the Third Hermann Minkowski Meeting on the Foundations of Spacetime Physics this year (https://minkowskiinstitute.com/meetings/2023/) will be the nature of gravitation  whether it is merely spacetime geometry or it is a physical interaction. This invitation is also sent to physicists (relativists)  they will take part in analyzing the mathematical structure of general relativity with the explicit intention to derive, following Minkowski's program, all predictions of general relativity by regarding gravitational phenomena as effects of the nonEuclidean geometry of spacetime, without assuming that gravitation is a physical interaction (i.e., without assuming the existence of gravitational energy and momentum). Colleagues, whose research is in the foundations and philosophy of physics, have a significant role to play  they will take part in analyzing the conceptual structure of general relativity with the explicit intention to demonstrate that all gravitational phenomena can be fully explained as manifestations of the curvature of spacetime. Here is a specific example of the power of conceptual analysis in physics: Since the discovered by Hulse and Taylor in 1974 binary pulsar system PSR 1913+16, the decrease of the orbital period of binary systems has been regarded as being caused by the loss of energy due to gravitational waves emitted by the system. This explanation manifestly fails Wheeler's "first moral principle"  "Never make a calculation until you know the answer." Indeed, no calculations are necessary to see that this explanation is incorrect  the stars of a binary system, before they collide, are geodesic worldline, which means that the stars move by inertia and no emission of gravitational waves is involved; gravitational waves are emitted when the stars collide (when the stars are regarded as extended bodies, weak gravitational waves are emitted before the collision, but they originate from strong tidal effects). If interested, contact us at mi@minkowskiinstitute.org or at vpetkov@minkowskiinstitute.org.
Vesselin Petkov

