Define distance (the only true and fundamental quantity of the three - time, distance, velocity):
https://en.wikipedia.org/wiki/DistanceDistance is a numerical measurement of how far apart objects are. In physics or everyday usage, distance may refer to a physical length
Then, define "meter":
https://en.wikipedia.org/wiki/MetreThe metre is defined as the length of the path travelled by light in vacuum in 1/299 792 458 of a second.
Meaning: meter = velocity * time. But - what is velocity? Velocity = distance/time.If distance (meter) depends on a velocity and the velocity depends on distance, what can we obtain?...
Define time:
https://en.wikipedia.org/wiki/TimeTime in physics is unambiguously operationally defined as "what a clock reads".[6][15][16] See Units of Time. Time is one of the seven fundamental physical quantities in both the International System of Units and International System of Quantities. Time is used to define other quantities – such as velocity
Then, define "second":
https://en.wikipedia.org/wiki/Second"the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom" (at a temperature of 0 K
What to they use to measure the
duration for 9192631770 periods? Another clock of course. How to they know if the clock they use to measure has errors - or is it the caesium atom that is not quite precise? They can't. Time = measuring cyclic events. We cannot obtain a fixed reference like the platinum meter or kilogram.
Define speed:
https://en.wikipedia.org/wiki/SpeedThe average speed of an object in an interval of time is the distance travelled by the object divided by the duration of the interval;
The problem is - the unit of the fundamental quantity for distance (meters) - is defined in terms of the derived quantity speed - see above. And nobody sees any problem with circular references - because c is constant. How can it not be constant if we defined it to be constant?...
Same thing with the caesium atom. We defined it to be
the constant rate. It cannot vary, because that's what the definition says - and definition trumps reality, do you think anyone who wants a career in physics will start an investigation about these "holy thruths"?
This means - velocity, not distance is the fundamental unit, not quite a smart definition I say.