Physicists have used the quantum nature of matter to obtain a highly precise value for the universal gravitational constant, the 'big G' that appears in Isaac Newton's law of how gravity pulls together everything, from planets to apples. Although the technique still needs refinements, physicists believe that in the future it will beat the precision of conventional methods — and hopefully solve apparent discrepancies between measurements that have long puzzled physicists.

In a study described today in Nature1, researchers measured the minuscule gravitational tug between rubidium atoms and a 516-kilogram array of tungsten cylinders. The uncertainty in the latest measurement is 150 parts per million, or 0.015% — only slightly larger than that of the conventional method of determining G, which is to quantify the mutual pull of two macroscopic masses.

The measurement is “a marvellous experimental achievement and an important contribution to the knowledge of G”, says Holger Müller, a physicist at the University of California, Berkeley, who was not involved in the study.

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