# Concern about Spacetime Invariance [duplicate]

$(c^2)(\Delta t^2) - l^2 = \rm invariant$ for any inertial frame.
Consider two events that occur at the same time in inertial frame $S$, and frame $S_1$ moves with translational speed $v$ relative to $S$. It seems that by the length contraction, the distance between these events should be shorter in $S_1$ because the events are moving, yet since these events do not happen simultaneously in frame $S_1$, then $(c^2)(\Delta t^2) - l^2$ for frame $S_1$ is larger than for $S$, which is a contradiction. Can someone please explain the issue in this contradiction (without using Minkowski diagrams)?