Correction- The IPK was actually created about 15 years prior to the original set of 40 replicas made in the late 1800's. Not only that, but a mass standard called the Kilogram of the Archives served as the previous standard going back to 1799. BTW, when creating that standard, they reproduced the 1 litre of water mass concept 'best guess' to within 25 parts per million over 200 years ago!
would make more sense to create an atom based measurement where a few million carbon atoms were counted one by one then weighed ..
Already done... It's called the atomic mass unit (AMU), where the carbon 12 atom is defined as having a mass of 12AMU exactly, and all other elements on the periodic table are rated relative to that. The mole is defined as the specific number of carbon 12 atoms that adds up to 12 grams of mass, tying everything back to the IPK. Avogadro's number (roughly 6.022*10^23), is the number of carbon 12 atoms in 12/1000 of the kg. If Avogadro's number was arbitrarily set to an exact value, that would redefine the kg- but by itself, that wouldn't make the kg more reproducible than it is now in independent labs. Even so, there are a few Avogadro based proposals for the kg, including the manufacture of silicon spheres of controlled diameter that are so round, that if magnified to the size of the Earth, they would have an altitude difference from highest to lowest point of 2.4 meters!.
If you consider that weight is based on gravitational pull, and that a Kg would "weigh" less on the moon, then its not hard to understand that when the earths mass changes, weight also changes.
True, but consider the way that a balance beam works- even if the local acceleration of gravity is different, you can still reliably compare one mass to another.
Weight is just a measurement of mass. As long as mass doesn't change then weight doesn't change. The perceived value might change as your measurement instruments are affected by different environments but weight stays the same as long as you are always comparing to the exact same object. That's the purpose of the standard. As long as you compare what you are measuring to the standard then it doesn't matter if you do it on the moon or in James' basement. The ratio of mass will be constant and that is what the indicated weight will be.
'Exact same object' IS the status quo, and that's how it's been done over 200 years... The goal is to redefine the unit of mass based on some immutable property of nature, where a practical technology could be employed to quantify it so that the standard can be reproduced in labs all over the world with ever increasing precision, independently.
Stay tuned for the next episode of The Culhanes of Cornfield County when we hear Grandpa say 'What about the effects of time dilation due to gravity?', and we'll hear Junior say 'Maybe we can compensate for variations in gravity using a laser interferometer.'
