The Picard ManeuverThe speed of light
teftThe speed of light is a tautology. We define it via how many meters light travels in a second. And we define the meter by the same measure. It’s just the distance light travels in 1⁄299792458
wolframhydroxidec is a measurable constant, not come unit that is arbitrarily defined. Like Boltzmann’s Constant, or the ground state hyperfine transition frequency of the Cesium-133 atom… it just… Is.
Therefore, it is a useful tool to define units. You claim it is a tautology because we write it in units of meters per second, while the meter is defined based on c. This is easily disproven, as you can represent the speed of light in any unit of velocity. It is a fundamental constant, derivable through experiment without any unit a priori.
It’s not about the units i used. It’s about using something to define itself. The same problem happens when you use c to define empty space since empty space can define c.
Once you decide which units are used in maxwells equations then the electromagnetic permeabikity and permissivity pops out as a proportions of c.
Read more Feynman if you don’t believe me.
That may be, and I’ve been meaning to dig into my copy of the Lectures, but that’s moving the goalposts. You said that it was a tautology because it was defined by the meter, and the meter was defined on it. That statement is demonstrably false.
I used the meter because that’s generally what is used for measurement in scientific endeavors. There was no goal post moving if the statement applies for all SI measurements.
Literally the entire point of the comment that you’re responding to is that it isn’t true for the metre, and it isn’t true for any SI units.
Your entire claim of tautology rests on the assertion that the speed of light is defined by something external to light itself. That’s false. It remains false irrespective of which SI measurements you swap in.
Just because the speed of light can be expressed in terms of SI units, doesn’t mean its definition depends on them. Which is the point that wolframhydroxide was making.
This directly disproves your original assertion of tautology.
Every metric of speed of light is necessarily relative to other things. Even if you define as 1, now you must be able to know what one unit of time is relative to one unit of distance, and if you do not know that then you do not know that your speed of 1 means.
All fundamental units are defined relative to each other in physics, and all other units are defined relative to the fundamental units.