3-D Einstein theory chronology continuity continuum theory cosmic constant cubic dimensional duration duree flat four-dimensional geometry four-dimensional space fourth dimension fourth-dimensional lastingness other continuums period principle of equivalence principle of relativity proportional psychological time relativity space space-time continuum spatial spatiotemporal spherical stereoscopic superficial surface tense term the future the past the present theory of relativity three-dimensional tide time time-space timebinding two-dimensional volumetric while