So basically the cylinder that science has used as THE kilogram since 1889 has been losing microscopic weight, like a few billionths of a kilogram. What scientists plan to do is instead of having a physical object set the standard for how much a kilogram weighs, they’re going to express it in terms of Planck’s Constant, a fundamental constant in quantum physics as unchanging as the speed of light in a vacuum. By dividing Planck’s Constant by the Meter and the Second (both already defined by fundamental constants), you get an insanely small weight. Multiply that by a big enough number and you get one kilogram!
So instead of measuring all weights against an object that can change, the kilogram is defined by unchanging physical constants and pure math.
One possible result of this is the development of “Earth kilograms.”
Weight is a function of gravity. If you’re on a planet that has twice Earth’s gravity, an object whose weight is equal to one Planck kilogram (PKg) will have a weight equal to two Planck kilograms on that planet. Conversely, if the planet has half Earth’s gravity, the same object will weigh 500 Planck grams.
A formula could then be developed to calculate relative weight on any given planet. This could be used in space engineering, including things like figuring out how much fuel power is needed to move a spacebound object the desired distance.
This is part of my issue with metric and how unintuitive it is. The Kilogram is not a measure of weight (just a kind of force). A kilogram is a measure of mass: resistance to acceleration doe to force. That’s all it is. If something “weighs three kilograms” the thing has three kilograms, and is probably under about 9.81 meters per second per second of acceleration, which comes out to a little under 30 Newtons, the actual metric unit of force.
Mass is such an unintuitive measure that even folks who grew up on metric get their own units wrong and equate it with force.
Sometimes, because nobody likes multiplying by 9.81 to convert, they will talk about force in “Kilogram force” which is 9.81 Newtons, and you could argue that this is what most people mean when they describe weight in kilograms, but I really doubt most folks are really cognizant of that distinction when they use it.
Also defining measurements in terms of a single object is like sticking to the gold standard and all your cash is defined by gold somewhere.
Moonlit Spires 