It's well known that a single particle can exist in superposition, but what about the gravity of the particle? Is the gravity also in superposition? I suppose this makes it difficult to write a wavefunction, since we can't express it in terms of a field over a single spacetime. But what if we naively just assume that gravity is never in superposition and we simply calculate the stress energy density directly from the smeared out wavefunction? What problems would that cause?