One way of designing an RPG is the notion of a physics engine. In this perspective the RPG mechanics and systems serve as a way to produce new events and determine how those events evolve, incorporating the input of the characters and players. Some designers strive to make a plausible physics engine that capture some intuition of how our world works. Others are willing or even eager to adopt the conceit of narrative physics, where the rules of storytelling and fiction in general have as much or more presence than adherence to a more concrete simulation. This ties into genre emulation and invention as goals of design.

In the study of formal language there is a tie between classes of language and physics. For example, the Church-Turing can be construed as an (unproved) proposition that the class of languages defining classical computing are precisely those which can be realized with discrete elements under the physics of our universe. By constraining phenomena or postulating components which exceed the laws of physics, new classes of languages are found. One way to turn this notion on its head is to think of these languages as expressing the relevant rules of their physics and translation bridges from one to the next. Translating between classes of language however leaves parts of these rules and interactions behind, they simple cannot be expressed in a class with different limits and capabilities.

This suggests as we look at the much less mathematical world of RPG design that we might encounter useful behavior in translating among games and physics engines. Perhaps some games translate among each other in powerful, expressive ways. Perhaps other classes of narrative physics may impose limits and capabilities which we simply cannot transfer into a different set of RPGs expressing their own set of physics. Perhaps one of the side effects of a culture of hacking RPGs is the discernment of which pieces translate into which new physics, like what must change or stay the same in an Apocalypse World hack to suit a new narrative structure and setting.