The idea is simple. Let's say we arrange similar bodies (call them planets, ions, anything) in an infinite crystal structure, but the only possible interactions are gravitational interactions.
A sensible guess is, the system will be unstable, it won't change unless it's perturbed, and if it is, it would not go back to the previous state after the perturbation.
Now, that was an obvious thing to guess. My question is, what else would change? What properties would disappear? Can we recover some of them?
Could we have, for example, lattice vibrations, and so on?