A result in math says that $S^n$ carries a Lorentzian metric iff $n$ is odd.
Using it we can observe that a 2-sphere spacetime is impsossibleimpossible, a 3-sphere spacetime is geometrically possible, but again a 4-sphere spacetime is impossible, and so on.
Are there resources in the literature that deal with geometrically impossible spacetime or offering a general result to be used and checked?