>>14298517For starters, some cellular automata are Turing-complete, so you could have structures on a 2D grid playing out processes isomorphic to a simulation of a 3D universe. Maybe the people inside it would perceive it as a 3D universe, but someone watching from outside would see that it's 2D. In fact, it's conceivable for an intelligent being to perceive the "true" structure of such a universe even from inside it, if it had sufficient intelligence to interpret such an input. On a less theoretical level, I've seen modernized takes on Conway's Game of Life, with self-replicating creatures made of 2D particles, that seek out "nutrients" or merge with other creatures, in an emergent beavior that arises from a set of very simple rules. Unfortunately, I don't remember what it was called. As for intelligence, you could have something like a slime mold; for all logical intents and purposes, that thing exists on a plane, anyway.