ZP OWER C ORPORATION PAGE OF 352 Z ERO P OINT E NERGY level of x 23. If the Drever technique, or something similar to it, could be applied to a sample confined between two conducting Casimir plates, and the sensitivity of the detecting apparatus could be improved by a few orders of magnitude, then it should be possible to measure the anisotropy of inertial mass caused by two conducting plates at the level predicted by the well- accepted theory of quantum electrodynamics. The experiment would thus conclusively demonstrate, one way or the other, whether anisotropic Casimir stresses between two conducting plates can produce a change in the inertial mass of a body. Hughes-Drever Anisotropic Inertial Mass Null Experiment The motivation for the Drever experiment first carried out by Hughes in 1960 at a lower sensitivity was an experimental test of Mach's principle--that the inertial mass of a body may arise from a gravitational coupling with distant matter. Since there is a concentration of matter at the center of our Galaxy, then, depending upon what physical and mathematical models one used for Mach's principle, this excess of nearby matter might result in an anisotropy of inertia along the (bi)direction to the mass excess, which could be detected experimentally as the Earth rotated the apparatus with respect to the Galactic center. According to some theories referred to by Drever (1961), this anisotropy in inertial mass should cause shifts in the energy levels of atoms and nuclei subjected to a magnetic field. Specifically, in a nucleus with spin 1=3/2, the energies of the states with magnetic quantum numbers m 312 would be increased slightly if the magnetic field were parallel to the direction of the center of the Galaxy, while the energies of the states with ml would be decreased by an equal amount. If the magnetic field were perpendicular to the direction to the center of the Galaxy, the energies would be shifted in the opposite directions. For the models of inertia being proposed at the time, the predicted ratio of the anisotropy in inertial mass for the nucleus was in the order of 10-13. Drever found it was zero to a sensitivity of x 23. The isotope used was lithium, with a nucleus of spin 1=3/2, caused by an unpaned Pg proton. The four energy levels of a nucleus of spin 312 in a magnetic field are normally equally spaced. The three resonant frequencies between the four states are the same and there is a single resonance. If the ml energy levels are shifted with respect to the ml=fli2 levels, then the single resonance is split into a triplet. The minimum splitting detectable is usually limited by inhomogeneities in the magnetic field, so a weak uniform field is desirable. The magnetic field used in the experiment was the earth's field.