Element presents the philosophy of special relativity

This element covers the foundations of the theory in Newtonian mechanics, its emergence from 19th Century ether theory, and the various conceptual paradoxes it presents. It also explores some of its connections with Einstein's later theory of general relativity.

It illustrates concepts such as inertial frames, force-free motion, and dynamical versus geometrical understandings of physics. The discussion includes the standard hierarchy of classical spacetimes, the concept of a symmetry of a physical theory, Poincaré invariance, Einstein's 1905 derivation of the Lorentz transformations, and spacetime structure from Aristotle to Minkowski.

Additional topics include general covariance, dynamical and geometrical approaches to spacetime, the conventionality of simultaneity, Frame-dependent effects, and the twin paradox.