Gravitational crumbs

Tobias Westphal et al. measure the direct gravitational coupling between two gold spheres of 1 mm radius with a torsional pendulum, providing the first ever test of gravitational coupling from source masses below 100 mg. Although no anomalous behaviour is found, this type of experiment represents an important step towards reaching mass ranges that ought to give us access to experimental tests of the interplay between quantum physics and gravity.