Fully characterized dynamic measurements of gravitation in the laboratory have to date been restricted to frequencies in the mHz regime, due to difficulties in assessing non-gravitational crosstalk and the intrinsically weak nature of gravitational forces. Here we introduce two new, fully characterized experiments at three orders of magnitude higher frequencies where a time-harmonic gravitational force field excites the high Q bending resonance of a free-hanging titanium beam at ca. 42 Hz.
Two different excitation systems, a parallel bending beam and two rotating beams, produce gravitationally induced motion with velocity amplitudes up to 90 nm/s. The reliable measurement with sub-pm displacement resolution is made possible by a set-up which combines acoustical, mechanical and electrical isolation, a temperature-stable environment, heterodyne laser interferometry and lock-in detection. The interaction is quantitatively modelled based on Newton’s theory.
Our initial results agree with the theory to within about two percent. We determined the near-field gravitational energy flow to be up to 2.5E-20 Watt for the parallel beam setup and 4·E-18 Watt for the excitation with rotating beams. We expect our experiment to make significant progress in directions where current experimental evidence for dynamic gravitation is limited.
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