(whateveryoucallit) You can call it the externalisation of inner life and time for that's how I think of it says the caretaker without apology (thinking of Immanuel Kant's description of time as the the form of the internal sense and of our internal state) because what anyone says is real in the sense that it was really said, and done, by one who is enough to authorise what s/he says and does though to repeat that is something else if repetition is mistaken for sameness and for truth. The purpose of the imaginary rock is to question the reality of things that are presented as unchanging law or theory, mechanical illusions, as well as to support the reality of what is not. The rock is thus a changing centre, not a fixed one, that can be recreated in any place at any time simply by saying so.