Would gravity or spacetime under these definitions behave differently and yield something we can observe?
Or is this fancy math modeling that looks nice on paper, but that we won't be able to test until we become a Kardashev type III civilization?
If they're powerful enough to build a universe simulation, theoretically they can blur the edges so we can't discover them. They might even be able to construct and limit the systems of maths and physics we have access to.
I suppose the simulation could be smaller than a universe simulation though - and this is actually really compelling -
It could just be you that is simulated.
Maybe your consciousness and sensory inputs are simulated. You're kept largely on rails and the rest of the world is run at lower fidelity. They know you won't go poking at particle accelerators and theory, so they can keep those pieces low effort and you just get fed narrative. The only things to simulate are those that are directly in front of you now.
Almost like a movie. Not a universe at all.
We might have that capability within 50 years. All your sensory input being simulation. And the virtual brain playing with that input or replaying recordings.
That could be totally feasible. And we might have that tech soon.
Without tests it’s just pretty math that can be coaxed into agreeing with reality but that proves nothing.
Physicists try to indirectly test all the time via cosmological observations but that is extremely hard and limited to what you can infer and how well you can eliminate other explanations or sources of error.
If it is competing against another model that does both that and offers new testable hypothesis (which experiments match), the other model is the clear winner. But lacking that, if no other model explains all existing data, is new testability really necessary when it is the only model that currently explains all existing tests?
That said, aren't most of theoretical models only contenders for such, as in they haven't been expanded to actually explain all testing results, only that, as far as they have been expanded, there are no contradictions yet? So they need physicists to expand them, but if the model is wrong, the effort might largely be wasted, and we have some models that there is disdain for not because they contradict existing experiments, but because they have eaten too many careers without showing value in return?