The unit of mass has been redefined to represent a fundamental constant of nature instead of the hunk of metal that was used for the past 130 years. The new definition is based on the Planck constant and went into force on May 20th, changing what the kilogram is, as well as several other related units in the metric system. The revamp throws away old standards that were based on a metal cylinder in a vault near Paris.

The Kilogram Unit Is Now Linked to the Planck Constant

The Definition of the Kilogram Was Adjusted, and the Unit of Time Is Next

Units are what allows scientists to make precise measurements of temperatures, weights, electric currents, and other quantities. Those are laid out in the International System of Units and are used around the globe. The kilogram, which is the basic unit of mass in the metric system, is now defined by the Planck constant. It has a value that is an immutable constant of nature and is the same everywhere in the universe. The change to the definition for a kilogram will not affect the normal life of people because the difference is impossible to notice without precise measurement instruments. This means that a kilogram of flour will still make the same number of cookies.

Scientists Are Looking at Optical Atomic Clocks to Redefine the Second

The Definition of the Kilogram Was Adjusted, and the Unit of Time Is Next

Other units that were redefined are the kelvin (temperature), the ampere, (electric current), and the Mole (amount of substance). Now that these changes have settled, scientists are looking to update the unit for time — the second. They will try to do that with the help of optical atomic clocks, which are more precise than the currently used cesium atomic clocks.

Cesium atoms absorb a certain frequency of light, and when its electromagnetic wave wiggles, the pendulum of the atomic clock moves, measuring the time that has passed. This sets one second at 9,192,631,770 oscillations of the light. The new optical atomic clocks will measure time differently and will be around 100 times better than cesium-based atomic clocks.