If "space" within the Universe is expanding, do all objects within it also expand?

Question

Say a person could stand outside our Universe and is able to measure the progression of its expansion. And he has a twin on the other side.

At some point in time he will take another measurement and observe that the Universe has grown larger. But will an object within the Universe - in the form of his twin - be proportionately larger along with the Universe, or will he be the same size as the person outside the Universe?

I ask this because I was wondering why it is that "space" is expanding and not the objects within it.

If you have any questions before you want to answer, please post them. I will be checking in on this question over the next few days.

Answer 1

Space will expand, the objects in it will not. The reason why is that all matter is bound together by electromagnetic forces, and these forces are relatively powerful and dependent on distance. Consider a single atom. As the space between an electron and the nucleus would get bigger, the EM forces would force it to get smaller again and nothing would change. But another atom very far away feels no force from the first atom, because everything is electrically neutral on large scales (e.g. planet Earth isn't charged). So space expands between these two and it, well, stays expanded.
On the whole, things get further apart, but those things dont get bigger.

Answer 2

Pythagorus' answer is correct as far as it goes. But even larger objects do not expand with space, because of gravitational attraction. Galaxies do not expand; in fact it is now believed that clusters of galaxies do not expand either. It apparently does not take much force to resist the expansion of space.

Answer 3

I would imagine it as stretching a rubber or plastic. Eventhough the material stretches the molecules' size don't shrink or grow.

Answer 4

I don't think it's expanding, I have a whole 'nother theory that I'm working on right now and I can't tell you because you might steal it!