A 2mm large gold sphere with a weight of 90mg initially served as the gravitational mass. The torsion pendulum consists of a 4 cm long and half a millimeter thick glass rod suspended from a glass fiber with a diameter of a few thousandths of a millimeter. Gold balls of similar size are attached to the end of the staff. The gold sphere is moved back and forth, creating a gravitational field that changes over time.
As a result, the torsion pendulum then also oscillates with this specific excitation frequency. This movement, which is only a few millionths of a millimeter, can then be read out with the help of a laser and allows conclusions to be drawn about the force. The difficulty lies in keeping other influences on the movement as small as possible. The largest non-gravitational effect in our experiment before moving to the Conrad Observatory came from seismic vibrations generated by pedestrians and tram traffic around our former laboratory on Währingerstrasse. We were therefore able to take the measurement data at night and during the Christmas holidays, when there is little traffic.
Other effects such as electrostatic attraction forces could be suppressed well below the gravitational force by a conductive shield between the gold masses. This made it possible for the first time to determine the gravitational field of an object that has about the mass of a ladybug. The unique and much more constant conditions in the observatory, no man-made seismic vibrations, no magnetic interference fields from trams, elevators and the like and the very constant temperature conditions allow us to measure much more precisely than in our laboratory in Vienna.
The mass generated by the varying gravitational field is reduced here by a factor of 1000, bringing us into the range of the Planck mass and allowing us to investigate gravity on even smaller scales.
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