As someone already mentioned, you would have to account for all the interactions with light -> everywhere at once.

With a effective speed limit to space-time, you can "localize" the computation to the spaces where light has reached. And who knows, maybe light can't travel forever, it might just disappear after crossing some distance we still haven't measured (how we'd do that, who knows).

Giving yet another evidence to the "grand simulation" theory. "The universe" is just a group of simulated worlds connected by interacting photon particles (light).