Record-low 471-attonewton gravitational force measured between two tiny silicon wafers

While gravity is typically observed with large bodies such as planets and stars, every object with mass will exert a gravitational pull on every other object. However, it can be challenging to measure this interaction between two small objects due to the force becoming significantly smaller.

A team of physicists led by Shan-Qing Yang from Sun Yat-sen University, China, have measured the gravitational attraction between two 7.6-milligram silicon wafers. This provides new records for measuring gravity between low-mass objects and provides an alternative method to explore quantum gravity.

This study does not confirm that gravity is a quantum force, but it shows that Newtonian gravity is consistent with measurements made between low-mass objects.

Miniature Cavendish experiment

The team used a variation of the Cavendish experiment. In this experiment, small lead weights are connected to a rod hung from a thin wire. Large lead balls are positioned close to the weights and cause the rod to twist. Scientists can measure how much the rod twists to calculate the gravitational force.

In 2021, scientists measured the gravitational attraction between two gold spheres weighing approximately 92 mg. However, Yang’s team has created a mini torsion balance by using deep silicon etching. A 7.6-mg silicon wafer was mounted to the end of a hanging rod with a counterweight. The team created a rotating disc with 16 identical silicon wafers connected around the edge. This rotated over the test mass resulting in a periodic gravitational field. The disc only rotated once every 10 minutes helping the team differentiate between the gravitational field and noise.

The setup was contained within a vacuum chamber. A thin gold coated silicon membrane was used to reduce any unwanted electrostatic effects. The torsion balance was almost held still by using electronic feedback. The force required to counteract the gravitational force was then measured.

A force with important implications

The gravitational force measured was 471 attonewtons (0.000000000000000471 newtons) at the smallest distance of 0.654mm. This equates to around 20 billion times less force than the weight of a 1-mg grain of sand in Earth’s gravity.

Measurements were made at distances between 0.654 and 1.554mm and were consistent with Newtonian expectations. This allowed the team to calculate the gravitational constant (G) as 6.67 × 10⁻¹¹ m3 kg-1 s-2 with an error of 5.3%. This is consistent with the accepted value.

This is significant as physicists do not currently have a theory to unify general relativity, which explains gravity as a curving of space-time, with quantum mechanics which explains matter and energy at very small scales. By measuring gravity between lighter objects this may help to provide insight into where new effects could be observed.

Currently, the experiment is still in the classical domain. The next challenge is to measure gravitational interactions between quantum mechanical objects without the forces of vibration, electrostatic, magnetism etc. dominating.

Multiple avenues are being explored to improve sensitivity, such as using more sensitive torsion balances and optical or magnetic trapping of small objects. If improvements are made using these methods, experiments could be performed on objects in quantum states, Yang and colleagues explain. This may help determine if gravity has quantum properties.

The research was published in Nature Communications on October 7, 2026.

Source: https://interestingengineering.com/science/scientists-detect-gravity-between-two-7-6-milligram-objects-quantum-gravity