Some reading on the universality of free fall version of the strong equivalent principle, tested in a manifestly relativistic regime: "Even Phenomenally Dense

Some reading on the universality of free fall version of the strong equivalent principle, tested in a manifestly relativistic regime: "Even Phenomenally Dense Neutron Stars Fall like a Feather -- Einstein Gets It Right Again" https://public.nrao.edu/news/neutron-stars-fall/ https://public.nrao.edu/news/neutron-stars-fall/ More detail, Archibald et al. 2018, "Testing the universality of free fall by tracking a pulsar in a stellar triple system" (Nature volume 559, pages 73--76 (2018)) preprint: <https://arxiv.org/abs/1807.02059 https://arxiv.org/abs/1807.02059>. If universality of free fall fails, so does the single metric / purely geometrical theory of General Relativity. That would be very exciting, so it has been looked for a lot. https://duckduckgo.com/?q=tests+of+universality+of+free+fall&ia=web https://duckduckgo.com/?q=tests+of+universality+of+free+fall... You can recover a bit from your statement by considering that solutions of the geodesic equations can be a bit messy in manifestly relativistic or multi-body systems, and the equations of motion of components can be even messier. Nobody would disagree with that (it's why there's e.g. the (gravitational) Self-Force methods and the like; see e.g. <https://arxiv.org/abs/1501.07322v3 https://arxiv.org/abs/1501.07322v3>, which (cf. your second sentence) is useful when a compact mass (e.g. a neutron star) is in a close orbit around a 50x+ more massive black hole, bottom right corner of <https://en.wikipedia.org/wiki/Post-Newtonian_expansion#/media/File:GR2bodyparameterspace.png https://en.wikipedia.org/wiki/Post-Newtonian_expansion#/medi...>).