adjective: (mathematics, physics) Of a four-vector in representing a point in spacetime, having a positive or negative four-vector norm for the metric signature (+, -, -, -) and (-, +, +, +) respectively.
adjective: (physics) (of the interval between two events in spacetime) Having overlapping light cones, so that information can pass from one to the other, and one can be envisaged as a cause of the other.
