I heard a speech about the changing SI unit, but then it got me concerned with a bunch of questions. Basically, they switched from sticks to some "fundamental constants".
- What is $h$?
In the Metric SI unit, $h$ can be measured. However, in the new SI, it became a unit and had always be "1". But then, it seemed to me that this brought the question about the magnitude of $h$ itself. i.e. with different measurement methods, instrument, and precision, people will get a different understanding towards the magnitude.
But how could they report such difference then? Or say how could they report weather they agree with the value and precision of $h$? After all, $h$ was defined to be unite "1".
- Question about locally.
As shown, in the past, a meter was measured from a stick, quite literately. This had yet another benefits along side the intuition, that was, they tricked the locally. For example, even one assumed there's no variation in the law of physics in terms of orthodox physics or required precision, even if one assume there's no non local effect and causality disturbance, the micro gravity, gradient difference, e.t.c. could still make changes to the experiments.
By using a fixed stick, they by passed/tricked this constrain by transforming copy of sticks around the world, which regulated the global effect by the action of transforming the sticks.(i.e. the transforming of stick actually carried information of the transforming of global model) If they using the "fundamental constants", which means measurements could be carried out anywhere, the definition of fundamental units would then become local, or at least local in the sense of the measurement. There's no way for them to simply communicate or determinte the possible global effect or noise on the local definition of "fundamental units". So, eventually, are they going to start to send "sticks"(i.e. mirrors) around the world anyway?