Spacetime is a colloquial term for a derivative calculation or projection which only applies within the model. It has also not proven very germane as a unit, or it would be used more like a unit, rather than as description of a picture. The term seems to relate to the rendering of space in the model via geometry, where the model is based on singularities, which are the antithesis of space, and so is the model. We experience space, but we only find singularities from within a model.

That we pretend the relative speed of light is constant, and this proves black holes and big bangs, that is pseudo science taking a model beyond it's working boundaries, where it's calculation have no meaning; to wit, this is a physical analogue in optical aberration, where the rim of the lens is asymptotic refraction to the point of unreliable measurement (not a singularity, unless of course you model it as such, in the abstract).

The real question is why so much energy is used staring at model aberration. The "Uncertainty paradox" has everyone believe the model is real, and even ask the question "at what point does the model become real". The model is never real, and never becomes real, it stays a model forever. Whether the cat is dead or not is simply a measurement where, if you mistake the paradox for theory, you don't realize the probability of dead or alive given decay is nothing more than a measurement taken ex post facto, and not proof that the real world accord to the model.