The MICROSCOPE mission: first results of a space test of the Equivalence Principle

TL;DR

The MICROSCOPE mission tested the Weak Equivalence Principle in space with unprecedented precision, finding no violation within a 10^{-15} level, thus supporting Einstein's theory.

Contribution

First space-based test of the Equivalence Principle achieving a sensitivity of 10^{-15} using differential acceleration measurements.

Findings

No violation detected within measurement uncertainty

Eötvös parameter measured as [-1 ± 9 (stat) ± 9 (syst)] × 10^{-15}

Supports the validity of the Weak Equivalence Principle at high precision.

Abstract

According to the Weak Equivalence Principle, all bodies should fall at the same rate in a gravitational field. The MICROSCOPE satellite, launched in April 2016, aims to test its validity at the $10^{-15}$ precision level, by measuring the force required to maintain two test masses (of titanium and platinum alloys) exactly in the same orbit. A non-vanishing result would correspond to a violation of the Equivalence Principle, or to the discovery of a new long-range force. Analysis of the first data gives $\delta\rm{(Ti,Pt)}= [-1 \pm 9 (\mathrm{stat}) \pm 9 (\mathrm{syst})] \times 10^{-15}$ (1$\sigma$ statistical uncertainty) for the titanium-platinum E\"otv\"os parameter characterizing the relative difference in their free-fall accelerations.