Researchers have successfully measured the gravitational attraction between two objects weighing only 7.6 milligrams.
All objects with mass exert an attraction on one another. Yet between very small objects, this force is so weak that it becomes almost impossible to distinguish from disturbances present in a laboratory.
A team of physicists took on the challenge of measuring the gravitational attraction between small silicon plates. Each weighed 7.6 milligrams, far less than a grain of rice. The researchers placed them at distances ranging from 0.65 to 1.55 millimeters to measure their mutual attraction.
Experimental setup used to measure the gravitational attraction between two 7.6 mg silicon plates with a miniature torsion balance.
Source: An et al., Nature Communications (2026)
The instrument used is a torsion balance: part of the apparatus can pivot very slightly under the effect of the force exerted by a nearby mass. The stronger the attraction, the greater the measured rotation.
To avoid confusing gravity with vibrations or electrical effects, the team varied the position of the source masses, which exert the attraction on a test mass (see diagram above). This variation creates a repetitive signal that the instruments can detect, even when it is buried among other movements.
The measurements correspond to the values predicted by Newton’s law. They also make it possible to recover a value for the gravitational constant, which is used to calculate the attraction between two masses. The precision obtained remains lower than that of some conventional experiments, but the real achievement lies elsewhere.
Until now, directly measuring gravity between two objects this light had been particularly difficult. By reducing the masses, the researchers are approaching a region where quantum effects become significant. They will now be able to investigate whether gravity continues to follow the same rules at even smaller scales.
For now, this experiment confirms that the formula established by Newton remains compatible with this measurement, while showing that it is possible to test gravitation with objects weighing only a few milligrams.