We know that order in time between two events with causal relation is invariant under relativistic transformation. Now if order in time between two events is invariant under every relativistic transformation, must there be causal relation between the two events?
updat given any two event $p$, and $q$, $ds^2=(x_p-x_q)^2+(y_p-y_q)^2+(z_p-z_q)^2+(ict)^2\leq 0$ and it is invariant that $p$, is before $q$ or simultaneous with $q$ under relativistic transformation. must there be causal relation between $p$ and $q$ the two events??
