Testing Newtonian gravity in the laboratory

The search for ever smaller violations of Einstein’s weak equivalence principle continues to be an important experimental goal at the close of the 20th century, with string theory providing new motivations. Currently, the most sensitive laboratory and terrestrial-scale tests are carried out with instrumentation based on the 18th century concept of the torsion pendulum, but not with 18th century technology. The torsion pendulum has experienced a renaissance since the pioneering work of Robert Dicke in the early 1960s. This presentation describes a new observable associated with large-amplitude pendulum oscillations that provides measurement of extremely small torques with significant freedom from effects that may limit the traditional, non-cryogenic applications of the torsion pendulum.