Time in Classical and Relativistic Physics

Time and simultaneity play a very different role in the theory of special relativity than in classical physics. This chapter provides a brief survey of some of the ways that the notion of time functions in classical physics, in the theory of special relativity, and in the theory of general relativity. It shows that while in many respects, the nature of time in general relativity is yet further removed from the nature of time in classical physics than it is in special relativity, there are also respects and circumstances relative to which general relativity supports temporal notions closer to those of classical physics than any that can be found in special relativity. Everything that happens, happens at some instant of time. It is helpful when thinking about the notion of simultaneity to think, not in terms of space and time, but in terms of a structure, spacetime, that unites them.