Eötvös experiment

[1] A much more accurate experiment using a torsion balance was carried out by Loránd Eötvös starting around 1885, with further improvements in a lengthy run between 1906 and 1909.

In turn, these experiments led to the modern understanding of the equivalence principle encoded in general relativity, which states that the gravitational and inertial masses are the same.

[2] Eötvös's original experimental device consisted of two masses on opposite ends of a rod, hung from a thin fiber.

The experiment was arranged so that if the two types of masses were different, the two forces will not act in exactly the same way on the two bodies, and over time the rod will rotate.

Now generally referred to as the Eötvös balance, this device is commonly used today in prospecting by searching for local mass concentrations.

Re-examining the data in light of these concerns led to an apparent very slight effect that appeared to suggest that the equivalence principle was not exact, and changed with different types of material.

In the 1980s several new physics theories attempting to combine gravitation and quantum mechanics suggested that matter and anti-matter would be affected slightly differently by gravity.

Combined with Dicke's claims there appeared to be a possibility that such a difference could be measured, this led to a new series of Eötvös-type experiments (as well as timed falls in evacuated columns) that eventually demonstrated no such effect.