Eli5 – How is the kilogram defined using the second and the Plank constant?

Question

The kilogram used to be defined by a specific chunk of platinum-iridium.

But now it’s defined using the second and the Plank constant, somehow.

Assuming you already have a very accurate measurement of the second, and the Plank constant, how do you combine those two things to get the kilogram?

In: 1

Answer 1

Kilogram is such a mass, that if hit by a photon with a wave period of (0.5*Plank) seconds, it reaches a speed of 1 meter per second.

Of course, “meter” can also be defined as “distance traveled by light in (1/speed_of_light) seconds”