The spacetime interval is a measure of the separation between two events in four-dimensional spacetime, defined by the equation $$s^2 = c^2(t_2 - t_1)^2 - (x_2 - x_1)^2 - (y_2 - y_1)^2 - (z_2 - z_1)^2$$. It combines both spatial and temporal dimensions and remains invariant for all observers, regardless of their relative motion. This invariant nature is crucial in understanding the fundamental principles of special relativity.
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