It is necessary to make assumptions in order to derive models to be used for cosmological predictions and comparison with observational data .
In particular , in standard cosmology the spatial curvature is assumed to be constant and zero ( or at least very small ) .
But there is , as yet , no fully independent constraint with an appropriate accuracy that gaurentees a value for the magnitude of the effective normalized spatial curvature \Omega _ { k } of less than approximately 0.01 .
Moreover , a small non-zero measurement of \Omega _ { k } at such a level perhaps indicates that the assumptions in the standard model are not satisfied .
It has also been increasingly emphasised that spatial curvature is , in general , evolving in relativistic cosmological models .
We review the current situation , and conclude that the possibility of such a non-zero value of \Omega _ { k } should be taken seriously .