this post was submitted on 15 Oct 2023
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Is this like when they made the kilogram some function of the speed of light instead of the weight of a metal ball in a French museum?
They linked the kilogram to the gravitational force.
It's part of an effort to clarify how we define things. We're now trying to link our recorded units to the basic forces they are related to. So now, the kilogram is defined by the gravitational force, the meter by how fast light travels, etc etc
The kilogram is defined as the mass equivalent of a photon of a specific energy via the Planck constant h thus linking the speed of light and the frequency of the hyperfine level of caesium-133. The relative uncertainty of the measured value of the gravitational constant G is 10^-5 which would lead to a definition of the kilogram that has a worse relative uncertainty than using the former definition defined via an international prototype. The Wikipedka article is more detailed than this short summary.
So yes?
TiL
I knew about redifining the kilogram as it's related to gravity beforehand
But not the next part about kg and photons and planck etc etc. I learned all that just now by reading a response to my comment
I genuinely did not know about the relationship to light until just now.
So, yes. But again, your comment alone didn't help me understand about the relationship beforehand. I wasn't sure what you meant at all, so just responded with my understanding of it
I misread that as "meat ball", and now I'm kind of disappointed that we don't use meatballs as a standard unit. "I'm 6 meatball subs and 3 balls high", "The yacht is about 18 giant party subs long", etc.
Not exactly. The kilogram was redefined in a fundamentally different way, moving from an artifact, which will change with time, to a fundamental property of nature, that as far as anyone knows, will be the same at all times. The second was already defined in such a way. Any such definition still requires some sort of measurement though to get something usable. Different ways of measuring the same type of definition can be more precise, and in this redefinition they think they've found a more precise method that works in the same fundamental manner. Both measure the oscillation rate of atoms, but the proposed element is thought to give better precision.