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I always think it's weird how we say the universe is homogenous on all scales, when it plainly isn't.
On the smaller scales (that of a single galaxy or close cluster of galaxies and smaller) the universe is contracting. Think about it. Gas and dust contracts to form stars and planets that then often form clusters of stars which all ultimately revolve around the galactic disk. Eventually, the planets will be consumed by their stars which will be in turn consumed by the black hole at the centre of the Milky Way.
At scales less than a single galaxy, the universe sucks, at scales greater than that, it blows, if you take my meaning.
The only similar thing I can think of in nature is the weak magnetic force which holds atomic nuclei together, except when they are too big and heavy. Then they spontaneously decay into lighter elements which are ejected at high energies called radioactive decay. In this case too, the weak magnetic force sucks until there are too many protons and neutrons, then it 'blows'.
Perhaps if gravity had a limited range it would explain the expansion of the universe?
Markus
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