"The world just redefined the kilogram
It involves complex science and beautifully simple philosophy."

"Currently, the kilogram has a very simple definition: It’s the mass
of a hunk of platinum-iridium alloy that’s been housed at the
International Bureau of Weights and Measures in Sèvres, France since 1889.
It’s called the International Prototype Kilogram..."

"One important reason for the change is that Big K is not constant.
It has lost around 50 micrograms (about the mass of an eyelash) since it was created."

"With the vote Friday, the world’s top measurement scientists chose
to affix the kilogram to the Planck constant, a fundamental concept
in quantum mechanics that can never, ever change — here on Earth
or in the deep reaches of the universe."

"The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the
fixed numerical value of the Planck constant h to be 6.626 070 15 × 10-34
when expressed in the unit J s, which is equal to kg m2 s -1 , where
the meter and the second are defined in terms of c and ∆νCs."

This is similar to the redefinition of the meter in terms of the speed of light and the second - all that that depends on is whether time differences or distances can be more precisely measured. The potential problem is that both the speed of light and Planck's constant are believed to be universal constants, but that is theoretical rather than empirical (unless anyone knows something I don't), so it's not entirely obvious to me whether this is the right move - what if these constants aren't as constant as we thought? Will this redefinition obscure such an anomaly?

@deepthoughtsaid This is similar to the redefinition of the meter in terms of the speed of light and the second - all that that depends on is whether time differences or distances can be more precisely measured. The potential problem is that both the speed of light and Planck's constant are believed to be universal constants, but that is theoretical rather than empirical (unless anyone k ...[text shortened]... f these constants aren't as constant as we thought? Will this redefinition obscure such an anomaly?

There is a hypothetical chance that these constants are not constants in extreem circumstances. However, our knowledge of these circumstances are slim to nothing. When we enter these domain, then we might have to rethink.

What may these domains be? In hyper-space? At an intermedium in time-travelling? Between parallel universes? And all the other domains the scifi writers can come up with.