• Physics 16, s97
Excessive-precision measurements of the Moon’s orbit present that iron and aluminum really feel and exert gravitational forces equally.
Which weighs extra: a ton of iron or a ton of aluminum? This query would possibly sound like the favored “gotcha” involving bricks and feathers, however for Vishwa Vijay Singh, a latest PhD graduate from Leibniz College Hannover, Germany, it’s greater than only a riddle. Utilizing high-precision measurements of the Earth–Moon distance, Singh and his colleagues have examined the concept that the energy of gravity felt by an object is determined by the thing’s composition in addition to its mass . Their null outcome constrains the dimensions of such an impact 100 instances extra tightly than earlier research.
Based on some fashions of gravity, an object’s inertial mass and its gravitational mass can differ (see Viewpoint: Satellite tv for pc Confirms the Precept of Falling). Sure fashions take that concept additional, subdividing the latter class and predicting that an object’s “energetic” gravitational mass (the property that generates a gravitational area) can differ from its “passive” gravitational mass (the property that determines how strongly the thing responds to gravity).
In 1987, scientists looked for such a disparity utilizing the lunar laser ranging (LLR) experiment. The Moon’s iron-rich maria and its aluminum-rich highlands are distributed asymmetrically, offsetting the Moon’s middle of mass from its geometrical middle. Fashions that subdivide gravitational mass predict that the precise offset is determined by the active-to-passive gravitational-mass ratios for iron and aluminum. A big sufficient discrepancy between these ratios needs to be detectable utilizing exact measurements of the Moon’s orbit. The 1987 examine discovered no such discrepancy. Now Singh and colleagues’ up to date investigation—which concerned extra knowledge factors and a extra refined evaluation—reproduces that outcome with better confidence. Additions to the LLR experiment by future Moon missions may tighten the constraints even additional.
Marric Stephens is a Corresponding Editor for Physics Journal based mostly in Bristol, UK.
- V. V. Singh et al., “Equivalence of energetic and passive gravitational mass examined with lunar laser ranging,” Phys. Rev. Lett. 131, 021401 (2023).