Each of the following eight reported experiments tests exactly one of the equivalence…
PHYSICS · Multi-part · Fermi University Physics · Relativity & Gravitation · The equivalence principle and gravity as geometry · The equivalence principle and gravity as geometry
The Geometry of Gravity, Ch The equivalence principle under test
Problem
Each of the following eight reported experiments tests exactly one of the equivalence principle's pillars. Label each with one of: UFF (universality of free fall), LLI (local Lorentz invariance), LPI (local position invariance), or SEP (the strong equivalence principle, the Nordtvedt effect). State for each whether it tests the Einstein form or the strong form.
((a)) The Eot-Wash torsion balance (2008): compares the free fall of beryllium and titanium test masses of a few grams.
((b)) The Pound-Rebka experiment (1960): compares the frequency of a gamma ray emitted at the bottom of a tower with its frequency measured at the top.
((c)) A rotating optical-resonator repeat of the Michelson-Morley experiment: compares the resonance frequencies of two perpendicular cavities as the apparatus is rotated.
((d)) The Roll-Krotkov-Dicke torsion balance (1964): compares the accelerations of aluminium and gold test masses towards the Sun.
((e)) A torsion balance suspends a small sample of terrestrial basalt against a small sample of a synthetic lunar-regolith simulant, each of mass a few hundred grams, and looks for a differential torque as the Earth rotates.
((f)) A 2021 result combines a lunar laser ranging measurement with a laboratory composition-dependence result to quote a single bound on ηN.
((g)) An atomic-clock comparison flies a clock at high altitude and compares its accumulated time against an identical ground clock, testing the predicted gravitational time dilation.
((h)) A Hughes-Drever-type test monitors a spinning-nucleus resonance frequency as the laboratory is reoriented, looking for a dependence on direction in space.