Tests of the Laws of Gravity and Search for New Forces

Newton's inverse-square (1/r²) law is a cornerstone of General Relativity. However, this law has been challenged by many modern theories of gravity and particle physics.  The supergravity and unified field theories often run into a new short-range force, with an accompanying new particle, which should appear as a violation of the 1/r² law.  More recently, a possible violation of the 1/r² law in the range below 1 mm was suggested by string theories with extra dimensions. 

In order to search for these hypothetical forces, highly sensitive superconducting gravity gradiometers (SGGs) have been developed at the University of Maryland. A null test of the 1/r² law at 1 m was carried out using a three-axis SGG, yielding the best limit of 2 parts in 10⁴.  At present, a null test of the 1/r² law at 0.1 mm is under preparation with NSF and NASA support.  This experiment will employ a Newtonian null source and a single-axis SGG.  The expected resolution of the new experiment at 0.1 mm is 1 part in 10³ on ground and better than 1 part in 10⁵ in space.

Source-detector configuration for the 1-m 1/r² test

1500-kg lead pendulum