This definition of Turing-completeness is useless, as nothing in the universe is infinite. Well, maybe the definition can be used for some Hilbert hotel kind-o

This definition of Turing-completeness is useless, as nothing in the universe is infinite. Well, maybe the definition can be used for some Hilbert hotel kind-of-stuff, but I would any day prefer a definition that distinguishes some software constructs as Turing-complete and others as not, where C is definitely in the "yes" camp.