The reign of Le Grand K has come to an end. After 130 years, this hunk of metal sitting in a Parisian vault will no longer define the kilogram. The new kilogram mass will be defined by Planck’s constant, joining three other units for redefinition by fundamental constants. But as we measure with increasing precision – from cesium atomic clocks to gravitational wave detectors able to measure spacetime distortions to 1/1000th the width of a proton – is something fundamental lost along the way? Meanwhile, the BiPiSci team accepts the banana-measurement challenge.

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