Measurement of the Casimir force during free fall

The Casimir effect is an attractive interaction between two uncharged and perfectly conducting plates held a short distance apart. Its force still has a lot of unknown aspects. Here, this force is measured in a tuning fork experiment during free fall and compared with a measurement on ground. It seems like the Casimir force is strongly suppressed during fall. This is a hint that the Casimir force does not have its origin in the Van der Waals force, which would not change in weightlessness. Further conclusions concerning gravitational acceleration and vacuum energy are raised by establishing a first approach based on the measurement results. The conclusions indicate that the vacuum energy density is coupled to gravitational acceleration. In the next step, drop tower experiments have to proof the results.