The phrase "exist side-by-side" can be replaced with a multitude of synonyms to convey the same meaning. These synonyms can include "coexist," "occupy the same space," "live alongside," "exist in harmony," "share a space," "reside together," "cohabit," and "exist in parallel." Each of these synonyms highlights the idea of two or more entities existing together in the same space, sharing resources, and potentially cooperating or interacting with each other. Using these synonyms can add variety and depth to writing while still clearly conveying the intended meaning of coexistence.