I would say you have to start by defining "real". Surely a simulation is real in the sense that it takes up physical resources, has to be internally consistent and other such criteria. Importantly, abstractions within it can have experiences that are just as meaningful as those outside.
Maybe it's about being a "top-level" universe, which is self-defining and without physical constraints? It seems ours is unlikely that if inflation theory pans out, instead being just a self-contained world in the multiverse, not so different than any other simulation.
Personally, but without much evidence, I suspect there are no top-level universes; perhaps they do cycle around though, so very large scales eventually become the very small.
We store reduced-precision, reduced-accuracy copies of the mass data wherever we keep the logs for our measurement devices. We can't get at the "real" numbers, anyway, so we just go by what our instruments say.
We can, however, "write" to the real data store for mass--by doing things like picking up rocks and throwing them. If we are living in a simulation, and it is imperfect, we could potentially exploit an imperfection by manipulating the simulation in just the right way.
Maybe it's about being a "top-level" universe, which is self-defining and without physical constraints? It seems ours is unlikely that if inflation theory pans out, instead being just a self-contained world in the multiverse, not so different than any other simulation.
Personally, but without much evidence, I suspect there are no top-level universes; perhaps they do cycle around though, so very large scales eventually become the very small.