Is the Universe between the atoms expanding at the same rate as the universe between the galaxies? and if it?

Question

isn't, then what is the difference between the two spaces?

Answer 1

Good question. Nope. Gravitationally-bound systems like the atoms in your body and the planets in the solar system don't expand. Even the 17 or so galaxies in our local group; the Milky Way, Andromeda, and Magellanic clouds stay together; gravity holds them. But the Virgo galaxy cluster, 20 million light years away, is receding from us. Where do you draw the dividing line? Well, for every megaparsec distance, a galaxy recedes from us at 70 km/sec. So a galaxy 10 megaparsecs away is receding at 700 km/sec. This is called the Hubble constant. If you know how far away a galaxy is from our Milky Way and you know the mass of both galaxies, you can use Newton's universal gravitation law to work out their escape velocities from each other. GMm/r^2 and all that. If the escape velocity is greater than the Hubble speed, they'll stay bound together.

Answer 2

No, the nuclear forces that hold atoms together keep it from expanding at all, unless that expansion is adding electrons to the outer shell of the atom.