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Gravitational-constant mystery deepens with new precision measurements

30 Aug 2018, 14:51 UTC
Gravitational-constant mystery deepens with new precision measurements
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Two extremely precise measurements of the gravitational constant G have yielded significantly different values. The two experiments were done by physicists in China and the results deepen the mystery of why it has so far proven impossible to reach a consensus on the value of G, which is a fundamental physical constant.

According to Newton’s universal law of gravitation, the gravitational force (F) that attracts two objects of mass m1 and m2 separated by a distance d is given by Gm1m2/d2. The first measurement of G was made in 1798 by Henry Cavendish, who used a torsion balance designed by John Michell to measure the constant with 1% uncertainty.
A torsion balance comprises a dumbbell-shaped mass suspended from its centre by a thin wire. Two large external masses are positioned on either side of the dumbbell in such a way that their gravitational attraction can exert a torque on the dumbbell, causing it to rotate. As the wire twists, the gravitational torque is countered by torsion in the wire until the dumbbell comes to rest. By analysing this motion, G can be calculated.
Twisted results
Since then, more than 200 experiments have been done to measure G to ever higher ...

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