The path of objects through space-time

If one neglects gravitational effects, as Einstein and Poincarè did in 1905, one has the special theory of relativity. For every event in space-time we may construct a light cone (set of all possible paths of light in space-time emitted at that event), and since the speed of light is the same at every event and in every direction, all the light cones will be identical and will all the point in the same direction. 

The theory also tells us that nothing can travel faster than light. This means that the path of any object through space and time must be represented by a line that lies within the light cone at each event on it.