We are using different definitions of simple. Any equation can be written down and calculated by a Turing machine. By simple I mean computable.
If a simulation takes resources that are exponential in the number of particles then it fails that test. All the stars will die before you manage to calculate anything meaningful in your non-microscopic simulated world.
There's a line between things that take massive resources and things that take nearly-infinite resources. Let's say the line is somewhere around the 'Dyson sphere' range.
The former can be computed on hardware. The latter cannot be computed on hardware.
But this is different from if we can simulate some amount reality at all, which I think is possible, and I use that to demonstrate why I think computers can contain human like intelligence in theory. Of course you will see instructions and be unable to tell why it feels alive if you just look at op codes.
Then I do ask, without answering, how much can you omit and still get sentience. You can likely simulate bio chemistry alone and get consciousness. And you may be able to simulate even less than that. Though each reduction would make it easier for a simulated scientist to discover they are simulated.
In what kind of theory, though?
In mathematical theory you can use a googol watts. In "things you can do in this universe" theory you can't use a googol watts.
I understand the argument of taking a small accurate simulation as a basis point and extrapolating to a larger simulation. But if you're stuck with exponential complexity, then that extrapolation doesn't work. The demonstration of simulating 5 particles becomes useless. Even if you can massively simplify it, if you can't eliminate the exponential cost you're screwed.
But I'm more of a software guy, so it feels fair to ask if Turing completeness enough to simulate reality, and therefore human-like intelligence?
If so, what shortcuts can we take to avoid simulating "everything"?