I am trying to understand what 'violation of simultaneity' really means, and whether it has any real importance (i.e. why was it introduced?). The Wikipedia note on this (Topic: Relativity of Simultaneity): "... the relativity of simultaneity is the concept that simultaneity–whether two events occur at the same time–is not absolute, but depends on the observer's reference frame. According to [SR], it is impossible to say in an absolute sense whether two distinct events occur at the same time if those events are separated in space, such as a car crash in London and another in New York ... in some reference frames the two accidents may happen at the same time, in other frames (in a different state of motion relative to the events) the crash in London may occur first, and in still other frames the New York crash may occur first. If the two events are causally connected ("event A causes event B"), then the relativity of simultaneity preserves the causal order (i.e. "event A causes event B" in all frames of reference)..." My questions are as follows: - Assuming that signals from the crash events travel at the speed of light, I can understand that different observers (at different distances and/or moving with different speeds) somewhere between New York and London may 'perceive' the events happening in different order. Is this not a matter of perception of different observers only, while in reality there is really a specific order in which the events actually happen, even if not causally connected? Why would it be impossible to say which crash actually happened earlier in an absolute sense? - Secondly, what is the importance of this concept of simultaneity violation, if any?