The universe is known to be expanding. There is no centre of expanision, since it's space itself that is expanding, rather than galaxies speeding away from us through space. But if the expansion is uniform, wouldn't the space between molecules expand as well as the space between galaxies? If this were the case, one would think that the expansion would go unnoticed. The proportions within a picture remains the same when the picture is enlarged and in the popular balloon illustration of expansion, it's not only the distance between the marks on the surface of the balloon that increases, but the size of the marks as well.