File:Causality and Superluminal information flow1.svg

English: Extra elements were added to file:Causality and Superluminal information flow.svg. It is convenient if the train is one light-year long. A time traveller who "dropped" into an empty seat on the diagonal train might witness that this is the day when the majic telephone sent the instantaneous message from the front to the back of the train. A time traveller who "dropped" onto the read digital clock line would be at the center of the train where a one-year clock was marking the time between when two pulses of light were emitted at the center of the train. The endpoints of this digital clock line mark when the pulses were emitted and when they return. Since the train is one light-year long in the reference frame of Alice and Bob, the digital time clock must mark more than one year because the "proper" length of the train is longer than one light-year. See also File:Minkowski diagram p-template.svg for an even more detailed diagram.