The four-dimensional fabric unifying three spatial dimensions with time into a single continuum.
special relativity: spacetime is flat (Minkowski), distances mix space and time depending on observer velocity
general relativity: mass and energy curve spacetime, and curvature dictates gravity
the metric tensor field encodes geometry at every point — see field
light cones define causal structure: nothing exceeds the speed of light
gravitational waves are ripples propagating through spacetime
expansion of spacetime drives cosmology — the universe grows, galaxies recede
at the Planck scale, spacetime may be quantized — frontier of quantum mechanics and gravity
entropy and the arrow of time emerge from the structure of spacetime — see entropy
in the tri-kernel model, spacetime curvature corresponds to the springs operator: the screened Laplacian on the cybergraph is the discrete analog of Einstein's field equations linking geometry to energy distribution