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Gravity measured between two milligram-scale silicon wafers

Gravity measured between two milligram-scale silicon wafers

New Capabilities

A miniature torsion balance detected a 471-attonewton pull, extending direct gravity tests to lighter masses.

2 days ago: ScienceAlert reports the result

Overview

Updated 1 hour ago

The lightest objects whose mutual gravity has been directly measured now weigh 7.6 milligrams each. A team at Sun Yat-sen University in China detected the pull between two silicon wafers at separations as small as 0.654 millimeters.

At the closest separation, the force was 471 attonewtons, or about 0.000000000000000471 newtons. The result agrees with Newton's law and yields a gravitational constant with 5.3% uncertainty. It extends direct gravity tests to smaller masses, a step toward measuring gravity between quantum objects.

Why it matters

The measurement extends direct gravity tests to smaller masses and tightens constraints on forces that would deviate from Newtonian gravity.

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Key Indicators

7.6 mg
Mass of each silicon wafer
Each test mass weighed 7.6 milligrams, down from 92 milligrams in the 2021 gold-sphere experiment.
471 aN
Measured gravitational force at closest approach
At 0.654 millimeters separation, the force matched Newtonian prediction.
50 aN
Maximum force uncertainty
The two-sigma uncertainty on the measured force at the closest separation.
5.3%
Relative uncertainty on G
The derived gravitational constant agreed with the CODATA-2022 value within one sigma.
16
Wafers on the rotating wheel
Each rotation produced 16 repeating gravitational tugs every 10 minutes.

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People Involved

SY
Shan-Qing Yang
Physicist at Sun Yat-sen University
Lead researcher on the milligram-scale gravity measurement

Organizations Involved

Sun Yat-sen University
Sun Yat-sen University
Public research university
Host institution for the milligram-scale gravity experiment

Public research university in Guangzhou and host of the milligram-scale gravity experiment.
Nature Communications
Nature Communications
Peer-reviewed scientific journal
Published the peer-reviewed measurement

Peer-reviewed scientific journal that published the milligram-scale gravity measurement.

Timeline

March 2021 November 2026

3 events Latest: 2 days ago

  1. ScienceAlert reports the result

    Latest Publication

    ScienceAlert publishes a plain-language account of the measurement.

  2. Milligram-scale gravity measurement published

    Publication

    Yang team reports 471-attonewton pull between 7.6-milligram silicon wafers.

  3. Gravity measured between 92-milligram gold spheres

    Experiment

    A team set the previous record for the lightest masses with measured mutual gravity.

Scenarios

1

Next torsion balance reaches 10^-21 Nm torque

Possible Resolves by End of 2030

Discussed by: Yang and colleagues in the Nature Communications paper

The paper calculates that a quartz fiber 3 micrometers in diameter, a quality factor near 25,000 and a 30-day integration could improve torque resolution to about 10^-21 newton-meters. That would require lower thermal noise and better isolation than the current apparatus.

2

Gravity measured between 10^-12 kg masses

Unlikely Resolves by End of 2032

Discussed by: Yang et al. and experimental quantum-gravity proposals

The paper identifies 10^-14 to 10^-12 kilograms as the mass window where gravitational entanglement might be observable. Reaching it requires smaller masses and reduced disturbances.

3

Independent group replicates milligram-scale gravity

Possible Resolves by End of 2028

Discussed by: Physics groups pursuing tabletop gravity tests

The result is a first at this mass scale. A second team using a different apparatus would test whether the 471-attonewton signal is robust.

Historical Context

2 moments from history that rhyme with this story — and how they unfolded.

1797-1798

Cavendish experiment (1797-1798)

Henry Cavendish suspended a lead rod from a torsion wire and brought larger lead weights nearby. The gravitational attraction twisted the wire by a tiny amount, letting him measure the force.

Then

Cavendish estimated Earth's density and effectively weighed the planet.

Now

The torsion balance became a standard instrument for weak-force measurements.

Why this matters now

Yang's team uses the same torsion principle at milligram scale, with a rotating wheel to create a repeating signal.

2021

Millimetre-scale gravity measurement (2021)

A team measured the gravitational attraction between two gold spheres each about 92 milligrams. The experiment used a torsion balance and a modulated source mass.

Then

It set the record for the lightest masses with measured mutual gravity.

Now

It challenged others to push the measurement to smaller masses.

Why this matters now

Yang's 7.6-milligram wafers are more than ten times lighter, extending the record.

Sources

(3)
ScienceAlert Nature Communications Nature