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Why space expansion affects matter?
Why does space expansion not expand matter?

As we know, the universe is expanding, galaxies are away from each other. But what about atoms? Do they also in expanding?

What's more, Bohr radius is $$a_0=\frac{\hbar}{m_e c \alpha}$$, if it is increasing, does it means

$m_e$ is decreasing due to the density of Higgs field is getting thinner.

or

$c$ is decreasing

or

$\hbar$ is increasing?

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marked as duplicate by Qmechanic, Jerry Schirmer, David Z Sep 16 '12 at 20:26

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Possible duplicate: physics.stackexchange.com/q/2110/2451 –  Qmechanic Sep 16 '12 at 16:16
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No, the size of the atoms isn't changing as the Universe keeps on expanding. The Bohr radius will always be the same fraction of a nanometer or the same fraction of a wavelength of some light (of a certain spectral line).

Because the Universe is expanding and the size is growing, it literally means that there's "more room" and one can squeeze an increasing number of atoms in the "same" volume, i.e. into the tetrahedron with vertices located at centers of 4 galaxies.

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