The kilogram changed while you were sleeping


The original way to define the kilogram has been retired. Physics professor Pete Markowitz explains what this means and why it matters.

Here’s what you need to know.

  • Out with the old, in with the new. The way the kilogram is measured has officially changed. It is no longer based on a chunk of metal kept in a vault in Paris, France. It is defined using Physics — Planck’s constant to be exact.
  • You won’t notice a big change. It will not affect how much you pay for bread or the price of meat at the grocery store, but it is important for scientists trying to understand the scale of the universe.
  • Why the change? Using constants of nature to define the kilogram puts in place a system that is more accurate, precise and more useful.