text: The electron accelerating back and forth sends out electromagnetic radiation, ie radio waves, that's all. Electrons actually travel relatively slowly in metals, due to frequent collisions with the metallic lattice. So there is no  fantastic disruptions to the space-time continuum. It is electric pressure that moves very quickly which allows eletrical signals to be sent so quickly. The effect is the same as turning on a tap to a long hose already full of water. Water will start coming out the other end of the hose long before the water at the tap reaches the nozzle.