Each of the following eight reported experiments tests one or more 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 one or more of the equivalence principle's pillars. Label each with the pillar it tests, or with every pillar it cannot separate, using: 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 (UFF, LLI, LPI), the strong form (SEP), or both.
((a)) MICROSCOPE (2022): compares the free fall of titanium and platinum test masses inside a satellite in Earth orbit.
((b)) Gravity Probe A (1976): compares a hydrogen-maser clock in a rocket at altitude with an identical maser on the ground.
((c)) A Hughes-Drever-type experiment: monitors a nuclear spin resonance frequency as the laboratory's orientation relative to a preferred direction changes over a sidereal day.
((d)) Lunar laser ranging: tracks whether the Earth and the Moon fall towards the Sun with the same acceleration, looking for a polarisation of the lunar orbit along the Earth-Sun line.
((e)) A torsion balance in a laboratory suspends a small iron-nickel sample (chosen to resemble the Earth's core in composition) against a small silicate sample (chosen to resemble the Moon's mantle), each of mass a few hundred grams, and looks for a differential torque as the Earth rotates.
((f)) A rotating cryogenic optical cavity experiment: compares the round-trip light travel time along two perpendicular directions in the cavity as it is rotated.
((g)) Two Galileo navigation satellites left by launch anomalies in eccentric orbits (2018): compare their onboard clock rates against ground clocks as the satellites' gravitational potential varies around the orbit.
((h)) A 2021 combination of a lunar ranging result with a laboratory composition-dependence result, used to quote a single bound on ηN.