The weight of a kilo has changed during the night; the length of one second can be the following / Boing Boing

A new definition of the kilogram has come into effect today. This is no longer the kilogram defined by The Great K, a weight under glass weighing 140 years, located in a secret location near Paris. This is now determined by Planck's constant, based on physicist Max Planck's theory that "electromagnetic energy at a given frequency can only be emitted in discrete quantities, or quanta, of which the energy is proportional to h, now called Planck's constant ". Scientists at the 26th General Conference of Weights and Measures also redefined the kelvin, amp and mole. UP next, the second! The good news is that the changes are so minimal that they will not affect most of us. From Science News:

Currently, the second is defined by atomic clocks consisting of cesium atoms. These atoms absorb a certain frequency of light. The electromagnetic wave tremor of the light works like a pendulum on a grandfather clock, keeping rhythmic time. One second corresponds to 9,192,631,770 oscillations of light.

But a new generation of atomic clocks, called optical atomic clocks, outperforms cesium clocks (SN: 11/11/17, p.8). "Their performances are far better than those that currently define the second," says physicist Andrew Ludlow of the National Institute of Standards and Technology in Boulder, Colorado. These optical atomic clocks operate at a higher frequency, their ticks are closer spaced, which makes them about 100 times more accurate than cesium clocks.

Ideally, the duration of one second should be set with the help of the most accurate timepieces available. A change could occur in the late 2020s, says Ludlow.

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