If I have a very long rod, why can't I jab one end and cause an instantaneous faster-than-light reaction at the other? Actually, any length rod - the same question applies.
Reply
As far as I am concerned, this is indeed what happens. The jab may not immediately appear to the full extent at the other hand (the rod can not be 100% rigid, as the inertia of the atoms leads to a delay of the response), but to
some degree (even though it may be infinitesimally small) there will be an instantaneous reaction at the other end (see also my page regarding
Retarded Forces in this respect).