Test Of The Gravitational Inverse Square Law At Millimeter Range

The natural physical laws,described by general relativity and the standard model,have both passed all experimental tests successfully,but these two theories are essentially incompatible.Many physicist have worked hardly to get a framework that uifies gravity with rest of physics. The string theory is the most popular candidate theory which may succeed to do that.Motivated by string theory.many theoretical speculations are proposed and predict that the gravitaty could display new behavior in the short range.i.e., the deviation of the Newtonian inverse square law in millimeter range. Hence any experimental effords devoted to validating the expection will help us to study the fundamental nature of gravity.We used a dual-modulation torsion pendulum to test the gravitaional inverse square law at millimeter ranges.During the design of this experiment, the parameters of the I-shaped pendulum and I-shaped attracors were optimized to make the torque tested by torsion pendulum to be smaller (the non-Newtonian signal could remain in most),and we measured the non-Newtonian interaction at this sensitivity.This kind of null experimental design reduced the positional requirements of pendulum and attracors.Furthermore electrostatic and magnetic shielding layers were used to shield the electromagnetic effects between attractors and pendulum. Finally we find no deviation from the Newtonian inverse square law with 95% confidence level,and this work estabilishes the most stringent costrains on non-Newtanion interaction in range of 0.7-5.0mm,and we improve the previous best experimental bounds at interaction of approximate 3mm by up to a factor of 8. In order to check the validity of the null experiment design, the non-null experiment was performed by extending the separation between the test mass and the source mass, where the obvious net Newtonian torque allows precision measurements with the same procedure. The total experiment results show a perfect consistence with the theoretical calculations of the change of the Newtonian torque, which further enhance the null experiment's confidence.This work was supported by the National Basic Research Program of China under Grant No.2010CB832802.