Rotation, the Equivalence Principle, and the Gravity Probe B Experiment

The ultraprecise Gravity Probe B experiment measured the frame-dragging effect and geodetic precession on four quartz gyros. We use this result to test WEP II (weak equivalence principle II) which includes rotation in the universal free-fall motion. The free-fall Eotvos parameter eta for a rotating body is <= 10(-11) with a four-order improvement over previous results. The anomalous torque per unit angular momentum parameter lambda is constrained to d (-0.05 +/- 3.67) x 10(-15) s(-1), (0.24 +/- 0.98) x 10(-15) s(-1), and (0 +/- 3.6) x 10(-13) s(-1), respectively, in the directions of geodetic effect, frame-dragging effect, and angular momentum axis; the dimensionless frequency-dependence parameter kappa is constrained to (1.75 +/- 4.96) x 10(-17), (1.80 +/- 1.34) x 10(-17), and (0 +/- 3) x 10(-14), respectively.