ABSTRACT
A general principle of mathematical equivalence was proposed by the eighteenth-century physicist Roger Joseph Boscovich: Whether the observer is in a state of motion relative to the world, or vice versa, are equivalent propositions. Similarly, whether the observer is subject to an internal motion (of periodic type, say) or whether the world is, are also equivalent. This unexpected generalization of relativity follows from Boscovich's own example of a breathing world. He invented the principle to explain the fact that the empirical world is rigid. He was the first to discover, and explain, a nonclassical feature of the world. The potential scope of his principle remains to be determined—whether or not, for example, all quantum features can be derived from it. To facilitate the task, a new translation of Boscovich's seminal 1755 paper is given as an appendix to this chapter.
