Why do we say spacetime, as though stressing that this is some kind of unity: space together with time?
I understand a little that mathematically we have 4 variables in the same (Einstein) equation(s) (3 for space, 1 for time), but can it be put in other words?
P.S. This question was inspired buy reading quantum origin for spacetime review (idea that entanglement produces space-time) and especially the original paper but it is another story - matter sources curvature (at macro level) and matter can be in a superposition of different positions (at quantum level), allowing superpositions of different curvatures. In other words, "quantum gravity" allows superpositions of different geometries.