[n3k5]

> If there is no difference between reality and a simulation

That's the crux, I guess. There's this ‘Matrix’ idea that the universe might be a simulation, but here we have a much weaker, more plausible property; I would describe it as: could real-world processes be simulated exactly? That's what I meant by ‘can be run on a Turing machine’: is the organism equivalent to a simulated version.

Two quick addenda:

(i) This doesn't require the hypothetical Turing machine to exist; as you said, it's an abstract idea. In the strict sense, where it can have potentially unlimited memory, a Turing machine can't exist in the real world. Even so, we can ask whether an entity that has wants/needs/desires can exist in a Turing machine in theory. If yes, it's easier to show that it can exist in practice, in reality.

(ii) Maybe physics is non-deterministic and the equivalent mathematical model requires a non-deterministic Turing machine or something else still. But whatever physics does can be done by a physical computer; I believe there's nothing a natural person can think that can't in principle also be thought by an artificial machine.

There has got to be a difference between the pain a real ER patient feels and the simulation a training dummy for medical students is running. It's just so hard to come up with a clear definition of that difference. Let's try something simpler.

“When squeezed, Elmo shakes, vibrates, and recites his trademark giggle, "Uh-ha-ha-ha-hee-hee!".” — https://en.wikipedia.org/wiki/Tickle_Me_Elmo

Elmo isn't really giggling. But I think it's possible for a digital circuit to ‘get’ a joke. Or, indeed, to be ticklish.

As shkkmo mentioned, one could just postulate the existence of a ‘soul’ and be done with it. I'd prefer something more rigorous; something falsifiable.