# Sun Yat-sen University measures gravity between two 7.6 mg silicon wafers on a torsion balance

- Published: 2026-11-12 08:09 UTC
- Section: Science › Physics
- Tags: Cavendish torsion balance, 7.6 mg silicon wafers, Yukawa-type deviations, gravitational constant measurement, rotating mass modulation, deep silicon etching, classical and quantum gravity
- URL: https://realtech.media/news/rt-09eb9a1291a7f5a0f56b1389_sun_yat_sen/

**A miniature Cavendish torsion balance measured the force between milligram-scale masses at 0.654–1.554 mm. The result matches Newtonian gravity with a maximum uncertainty of 50 aN.**

![Sun Yat-sen University measures gravity between two 7.6 mg silicon wafers on a torsion balance](https://realtech.media/media/2026/11/b00c6704c97368a4.webp)
*ScienceAlert*

A group led by Shan-Qing Yang at Sun Yat-sen University in China measured the gravitational interaction between two silicon wafers of 7.6 mg each, according to a paper in Nature Communications. The measurements used a miniature Cavendish-type torsion balance with a rotating mass-modulation technique, at separations from 0.654 to 1.554 mm. The measured forces agree with Newtonian predictions, with a maximum uncertainty of 50 aN (2σ) [1].

The authors note that gravitational experiments have covered test masses from macroscopic objects to individual quantum systems, while the interaction between small masses remains largely unexplored. In 2021 another team measured the attraction between two gold spheres of about 92 mg each. The new work goes to smaller masses and, in the authors' words, is a step toward bridging the classical and quantum regimes of gravitation [1].

## Torsion balance with rotating masses

The balance was fabricated by deep silicon etching. A 7.6 mg silicon test mass sits at one end of a suspended rod, with a counterweight at the other. Instead of a single source mass, the team built a wheel carrying 16 identical silicon wafers around its circumference. Each wafer passes close to the test mass in turn as the wheel rotates.

The wheel makes one rotation in 10 minutes, so the gravitational pull repeats 16 times per rotation. This gives a periodic signal that can be separated from background noise.

The apparatus is enclosed in a vacuum chamber. A thin gold-coated silicon membrane between the rotating masses and the balance reduces electrostatic interference. The balance is not allowed to twist freely: an electronic feedback system holds it almost still, and the force needed to do so is measured.

## Result and constraints

At the closest separation the Newtonian force was calculated at 471 aN. The measured values agree with Newton's law over the whole range of distances studied [1].

The data also allow constraints on Yukawa-type deviations from Newtonian gravitation. From the same measurements the authors determined the gravitational constant G = 6.67(35) × 10⁻¹¹ m³ kg⁻¹ s⁻² (1σ) [1].

The measurement does not reach the quantum regime itself. The authors point to other approaches under development, including levitating small objects with light or magnetic fields, whose mass ranges increasingly overlap with torsion-balance experiments. They write that gravitational interactions between objects in quantum states may be observed in the foreseeable future.

## Sources

1. [Nature Communications](https://doi.org/10.1038/s41467-026-78187-4)
2. [ScienceAlert](https://www.sciencealert.com/scientists-measure-gravitational-pull-between-the-smallest-objects-yet-in-quest-for-quantum-gravity)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-09eb9a1291a7f5a0f56b1389_sun_yat_sen/