Experiment Finds That Gravity Still Works Down To 50 Micrometers

An anonymous reader shares an excerpt from a report via Ars Technica: To make small-scale gravity measurements, researchers rely on conceptually simple experiments: measure the changes in rotational speed of an oscillating disc that is subject to a periodically changing gravitational force. The periodic force is supplied by a spinning disc. Both discs have wedges cut out so that the force due to gravity varies as the gaps spin past each other. The two discs are arranged right on top of each other. One is attached to a thin cable and is set in motion by twisting the cable, while the other rotates at a constant rotational speed. As the oscillating disc changes its direction of rotation, it is still subject to a periodic torque from the rotating disc. These torque changes are highly periodic and can be measured very accurately. The wedged disc design gives a set of three rotational frequencies, so the instrumentation errors can be filtered out by examining changes that are common to all three frequencies. The researchers have gone through several iterations to slowly improve their sensitivity over the last decade. Their experiment eliminates -- so far as possible -- all forces due to electrical and magnetic fields. The researchers have a set of three test masses that sit on top of the experiment to allow them to calibrate their analysis against a larger signal.

The major improvement, however, was in the analysis. To extract the force due to gravity, careful modeling is required. The researchers changed the design of the pattern cut out of the test mass so that analytical solutions to the model were obtainable for the torques involved. This eliminated many of the uncertainties due to computer modeling. This and many other experimental refinements have allowed them to measure gravitational attraction down to a distance of just 52 micrometers. Once they add additional stabilization against vibration, they will be able to measure at even smaller separations. In the meantime, they have verified that the inverse-square law holds for distances shorter than 50m, and therefore we have no New Physics. The findings have been published in the journal Physical Review Letters.

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