The four known fundamental forces in nature, gravity, electromagnetic interaction, weak, and strong interactions, are currently described by general relativity and the standard model of particle physics respectively. Many physicists have been making efforts to connect gravity to the rest of physics. A number of theoretical scenarios, such as string theory, have been proposed and predict a deviation from the gravitational inverse-square law in short-range regime. The high precision experiments to test the gravitational inverse-square law would definitely help people understand the essence of gravity.
On April 1, 2016, a recent progress in this field from the Center for Gravitational Experiments in the School of Physics was published in PHYSICAL REVIEW LETTERS entitled as “New Test of the Gravitational Inverse-Square Law at the Submillimeter Range with Dual Modulation and Compensation”[Phys. Rev. Lett.116(2016)131101].
The team has been testing the gravitational inverse-square law using torsion pendulums since 2002. Because of the extremely weakness of gravitation comparing to other fundamental forces, a large amount of difficulties must be overcome. Thanks to the stable temperature, the low seismic noise, and the isolation from other human activities in the cave lab in HUST, the team has achieved several important results after solving the problems of the electrostatic disturbance, the capacitance feedback control of the torsion pendulum, the synchronous gravitation calibration, and the disturbance from the vibration.
In 2007, the team obtained the first result with the separation between masses down to 176 micrometers. The result shows that the gravitational inverse-square law holds down to a length scale of 66 micrometers, and excludes the possibility of two compact extra space dimensions with the same size at submillimeter scale as predicted by ADD theory. The result is close to the world’s best level reported about 3 months early.
In 2012, after 5 years of hard work, the team improved the previous best result at millimeter range by a factor of 8 after reducing the electromagnetic disturbance and the accurate compensation for the Newtonian torque.
In this work, they reduced the disturbance from the driving system and used a dual compensation design for the Newtonian torque. The precision of the measured torque was improved to 2E-17 Nm. The final result establishes the strongest bound on the Yukawa-type deviations from the new tonian gravity in the range of 70-300 micrometers, which is up to a factor of 2 of the previous bounds atthe length scale of 160micrometers.
The research is supported by the National Natural Science Foundation of China, the National Basic Research Program of China and the HUST.