I hope this isn't a common question, and that I'm not breaking any rules of posting - please let me know if I am, as I'm new here. So, to describe what I'm trying to ask: Picture a very long rod, say, one light-year long. Imagine it's in space, and is free of gravitational interactions (and all other ideal requirements are met). If I were to push one end of this rod away from me, would it take one year for the information regarding the push to reach the other end of the rod? Or would that end move instantaneously? I think that should be a simple enough description to convey what I'm trying to ask - thanks to anyone that has any input on this!