Everybody has been taught at one point, "oh the universe expands, but that doesn't mean that everything is expanding uniformly, since that means we can't detect the expansion, but only that huge galaxies are moving away from each other".
But I'm rather confused. Can't the expanding universe simply be thought as a coordinate axis that expands? The definition of "1" on the coordinate axis constantly expands? After all, spacetime itself is expanding, and not only "average distance of galaxies".
So our Planck length would expand, light wavelengths expand, we expand, etc. But clearly this isn't happening. Of course, the handwavy explanation is "electromagnetism/gravity overcomes expansion at small scales", but the electromagnetic and gravity forces are defined in terms of constants relative to our "coordinate intervals", so if spacetime itself is expanding "under the feet" of gravity, shouldn't gravity not be able to do anything about it?
We would also be unable to measure the expansion of spacetime since all of our measurement benchmarks and tools are also expanding.
Clearly, this isn't happening. What is the precise reason?