# Why doesn't everything expand when the universe expands? [duplicate]

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?

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## marked as duplicate by Kyle Kanos, jinawee, John Rennie, Brandon Enright, Chris WhiteFeb 17 '14 at 17:34

This question was marked as an exact duplicate of an existing question.

Possible duplicates: physics.stackexchange.com/q/2110/2451 and links therein. – Qmechanic Feb 17 '14 at 15:14
yes, seems like exactly the same question... – BjornW Feb 17 '14 at 16:35
Why do you think that "The definition of "1" on the coordinate axis constantly expands"? Meter is defined as a distance travelled by light in certain time. The speed of light is locally independent of the global spacetime geometry, or its evolution, so meter does not change. Thus Planck length does not change either. – mpv Feb 18 '14 at 7:05