On the Real-Time Criterion in Physical Resource Arguments Against the Simulation Hypothesis

Abstract

Vazza (2025) derives physical resource bounds for simulations of the Universe and Earth under physics like our own. For a low-resolution Earth model, the paper estimates that one simulated second could require roughly 4.2 x 10^13 to 3.0 x 10^15 seconds of host computation, and later treats real-time or faster-than-real-time execution as a criterion of simulation "possibility." This note isolates that criterion. A lower bound on host wall-clock time is not, by itself, a lower bound on time experienced inside the simulation. If all internal physical processes advance only when the simulated state advances, an arbitrarily slow host can still instantiate the same internal chronology, provided the host can remain physically available long enough. Real-time execution therefore requires an additional premise, such as synchronization with the parent world, a host lifetime deadline, or an external operational purpose. Without such a premise, failure to achieve a 1:1 time ratio establishes a runtime or practicality constraint, not by itself physical impossibility.