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The strength of gravity has been measured to new precision

Pinpointing Big G could help refine mass measurements for Earth and other celestial objects

HOMING IN Gravity (illustrated here bending spacetime) has been notoriously hard to measure. Now two new lab experiments estimate the strength of gravity, or Big G, with record precision.

We now have the most precise estimates for the strength of gravity yet. Two experiments measuring the tiny gravitational attraction between objects in a lab have measured Newton's gravitational constant, or Big G, with an uncertainty of only about 0.00116 percent. Until now, the smallest margin of uncertainty for any G measurement has been 0.00137 percent.

The new set of G values, reported in the Aug. 30 Nature, is not the final word on G. The two values disagree slightly, and they don't explain why previous G-measuring experiments have produced such a wide spread of estimates (SN Online: 4/30/15). Still, researchers may be able to use the new values, along with other estimates of G, to discover why measurements for this key fundamental constant are so finicky - and perhaps pin down the strength of gravity once and for all.

The exact value of G, which relates mass and distance to the force of gravity in Newton's law of universal gravitation, has eluded scientists for centuries. That's because the gravitational attraction between a pair of objects in a lab experiment is extremely small and susceptible to the gravitational influence of other nearby objects, often leaving researchers with high uncertainty about their measurements.