Thus, causality, as seen by an observer, is related to the time generation due to irreversible interactions of real systems among them. If the events are correlated at the start, independently from their location, they maintain their correlation, while if they aren't correlated, they could be correlated only after an interaction. In particular, Equation (13) points out that, without interaction, time doesn't exist, so, it would be impossible to observe an order in the events. But, after any interaction, time occurs and the order of the events can be pointed out. Consequently, also the relations between two events can be highlighted, with particular regards to their causal relations. Moreover, in the theory of special relativity, causality is related to simultaneous observer-dependent . Consequently, following special relativity, the cause must precede its effect in accordance to all inertial observers; moreover, in general relativity, the effect must belong to the future light cone of its cause, even if the space-time is curved . These statements mean that the cause and its effect are separated by a time-like interval, and the effect belongs to the future of its cause . Here, we conjecture that time interval is originated only during the interaction between a system and an observer, so a time-like interval occurs only after this interaction. So, before this interaction, all the systems are in a 'contemporary' state.