For classical physics, space and time provide the arena in which the phenomena of nature unfold. These phenomena do not change the space–time frame, which is inert and absolutely fixed for all time. Moreover, space and time are regarded as completely distinct and having no connection with each other. Relativity theory links space and time, and reaches its culmination in General Relativity, which connects the space–time properties with the dynamical processes occurring there.

Newtonian space–time

Physical space possesses the usual properties of continuity, homogeneity and isotropy which we attribute to the space R3 when equipped with its affine structure (parallelism, existence of straight lines) and its usual metric structure (Pythagoras' “theorem”). However, we must understand the physical significance of the mathematical concepts connected with R3. Thus, the existence of physical phenomena which can be represented by straight lines (mathematics) leads to the (experimental) notion of alignment: three points are (physically) aligned if we can find a viewing point from which they appear to coincide. From this it follows that light constitutes our standard of straightness; it is only by a further step (which may prove to be incorrect) that we can identify the trajectory of a light ray with a straight line in R3. Similarly, the mathematical concept of parallelism in R3 is directly related to the (physical) notion of rigid transport and of distance. Finally, we must recognise that the (mathematical) properties of homogeneity and isotropy of physical space only express our experience of mechanical systems: that these remain unaltered when placed in any position or place.