[scott_s]

That's not the question. Macroscopic behavior as described by Schrodinger's equation has never been observed. Because of having no observations, we assume it does not exist.

The linked paper is arguing, "Because solving Schrodinger's equation is non-polynomial, and such solutions are infeasible when N is large, then they can't exist." The linked paper is stating that the phenomenon has not been observed, assuming it does not exist, and then trying to explain why.

tomp's point is that we observe systems in our Universe that we can't model efficiently all the time. Hence, the line of argument in the paper doesn't hold up.