I've built a rod 186K miles long, of ultra-light, ultra-rigid material. I am on one end of the rod, and an observer is at the other end (we're both in the near vacuum of space). I want to send a signal to the observer on the other end of the rod signaling whether the Packers have won the superbowl - signal received, they won, no signal, they lost. The packers win, so I bang my end of the rod with a fast and massive hammer (moving the rod quickly) and instantaneously / simultaneously on my end, there is a great flash of light sent towards the observer. The light signal reaches the observer in about a second. What prevents the observer from seeing his / her end of the rod move in say 1/2 second? (No fair blaming compression of the rod or mass of the rod).