Turing-completeness is a Mathematical phenomenon which doesn't have anything to do with our Universe. Whenever we talk about Turing-completeness in relation to

Turing-completeness is a Mathematical phenomenon which doesn't have anything to do with our Universe. Whenever we talk about Turing-completeness in relation to our Universe, it is always an assumption. That's why the Church-Turing thesis isn't a theorem. Hence, if it's reasonable to go from "lots of complex stuff exists" down to "simple fundamental physics exists, complex stuff is emergent" then it's not unreasonable to go down a further layer and say "computation exists, physics is emergent". It's pure reductionism; the first step takes us from a world of "complex stuff with fundamental physics which can do computation" to a world of "fundamental physics which can do computation"; the second step goes from "fundamental physics which can do computation" to "computation".