The concept of path, in a state-space, leads to consider a set of consequent and related events, one followed by another, caused by the previous one. But, this concept is the thermodynamic expression of causality. Indeed, causality is the relationship between causes and effects . In physics, causality represents the flow of events such that the causes of an event must always be in the past light cone of the event itself, and always related to some interactions of the system. In special and general relativity, the light cone is the path that a photon of light, emitted by a single source, takes through spacetime . In special and general relativity, an effect cannot occur from a cause that is not in the past light cone of that event. Moreover, a cause cannot have an effect outside its future light cone . Consequently, an event cannot produce any effect, if it is outside of the future light cone of another event .