Why do critics push back on this project?

The main worry, voiced by Scott Aaronson, is that a framework where a simple rule "can do anything" is so accommodating it can be fitted to almost any observation after the fact — an "infinitely flexible philosophy" that is hard to falsify. Because the Principle of Computational Equivalence is an empirical conjecture rather than a theorem, and no specific rule for our universe has been pinned down, skeptics argue it currently explains the richness of nature without making sharp, testable predictions. Daniel Harlow called the claimed successes "at best, qualitative," and much of the work bypassed normal peer review.