This Minkowski diagram shows two light beams (in green) reaching simultaneously an observer at rest.

It also shows, in red, the worldline of a passenger on a train moving at speed v = c /4 (not realistic, but

good for display).

The coordinates of the moving observer, and , are such that .

They are given by the Lorentz transformation formulas x' = , ct' =

In practice, it is easier to work with these formulas than with Minkowski diagrams. However, diagrams

can be of some help to visualize events in space-time.

The next diagram shows two light beams (in green) reaching simultaneously an observer on the train

It also shows, in red, the worldline of this observer and the x' axis, on which event happen at t' = 0.