# Do atoms expand with universe? [duplicate]

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?

• CMB is not bound in any sense. CMB is a collection of free, non-interacting photons moving through the Universe. As the linear sizes in the Universe expand $k$ times, so do the wavelengths of the CBM photons, and their energy is therefore going down as $1/k$, on top of density like $1/k^3$. - It's meaningless to ask how "a rock on a parabollic orbit" scales. The only question that makes sense to be answered is the precise trajectory on which the rock moves. But the "place" of the rock isn't "static" in any sense, so it makes no sense to describe it as a static "object" that is just scaling. – Luboš Motl Mar 9 '17 at 10:37