Don't stop the quest to measure Big G

摘要

Plans are well under way to redefine the International System of Units (SI) by basing it on seven physical constants - the kilogram, for instance, is to be linked to the numerical value of Planck's constant, rather than the current definition of the mass of a platinum-iridium cylinder. The seven constants help to explain and predict the motion and actions of the Universe. But one that is not included is what we in the business call Big G: the coupling constant in Newton's law of gravity. There is a problem with Big G (so called to distinguish it from little g, the acceleration due to gravity at Earth's surface). Current measurements of it are, frankly, all over the place. Seven separate experiments in the past decade or so have given results that have a spread of about 0.05%. For a fundamental constant of physics, that is extraordinarily imprecise.