Experimental tests of GR are consistent with it, but don't rule out plausible variations upon the standard Einstein field equations as conventionally applied.
Canonically, `classic' tests of general relativity (GR) include perihelion precession, the bending of light around stars, and gravitational redshift; `modern' tests have to do with, inter alia, relativistic time delay, equivalence principle tests, gravitational lensing, strong field gravity, and gravitational waves. The orthodoxy is that both classic and modern tests of GR afford experimental confirmation of that theory in particular. In this article, we question this orthodoxy, by showing there are classes of both relativistic theories (with spatiotemporal geometrical properties different from those of GR) and non-relativistic theories (in which the lightcones of a relativistic spacetime are `flattened') which would also pass such tests. Thus, (a) issues of underdetermination in the context of GR loom much larger than one might have thought, and (b) given this, one has to think more carefully about what exactly such tests in fact are testing.
William J. Wolf, Marco Sanchioni, James Read, "Underdetermination in Classic and Modern Tests of General Relativity" arXiv:2307.10074 (July 19, 2023).
Classical GR = Classical TEGR in all ways that we can see.
ReplyDeleteQuantum GR is not equal to Quantum TEGR in ways that can in principle be distinguished with observations.
So, once we start observing quantum gravity effects, we might find out that the true theory of gravity is a cousin of GR instead of GR itself.