To me, "exists" is stronger than "predicts observation", although I can't entirely describe how, except by example.
Let's say you're in a game. You can create a physics of the game world based on how that game behaves. However, the game world doesn't exist, as such. It's the result of a pattern produced by a computer, interpreted by our minds, which fills in the blanks and makes the game world feel more real than it is.
It makes sense that an account of existence should either include the substructure (in this case, the computer) or the observer (in this case, the mind doing the filling-in), or possibly both. On the other hand, a description of the behavior of the system is much simpler.
Another example: simulation hypothesis people sometimes talk about the possibility of "breaking out" of the simulation, as if the simulation is less somehow less true than whatever is behind it.
But from a predicting-observed-phenomenon perspective, what you describe by physics exists. So the distinction between the rules of physics that apply in a certain domain because you're in a simulation, and the rules of physics that apply in another domain once you find a way to break out, is entirely artificial. That people don't see it that way seems to indicate that they mean something else by existence.
Let's say you're in a game. You can create a physics of the game world based on how that game behaves. However, the game world doesn't exist, as such. It's the result of a pattern produced by a computer, interpreted by our minds, which fills in the blanks and makes the game world feel more real than it is.
It makes sense that an account of existence should either include the substructure (in this case, the computer) or the observer (in this case, the mind doing the filling-in), or possibly both. On the other hand, a description of the behavior of the system is much simpler.
Another example: simulation hypothesis people sometimes talk about the possibility of "breaking out" of the simulation, as if the simulation is less somehow less true than whatever is behind it.
But from a predicting-observed-phenomenon perspective, what you describe by physics exists. So the distinction between the rules of physics that apply in a certain domain because you're in a simulation, and the rules of physics that apply in another domain once you find a way to break out, is entirely artificial. That people don't see it that way seems to indicate that they mean something else by existence.