"We have at our disposal the concept of simultaneity; and we owe this concept to our ability to perceive external flows of events either together with the flow of our own duration, or separately from it, or, still better, both separately and together, at one and the same time. If we then refer to two external flows which take up the same duration as being "simultaneous," it is because they abide within the duration of yet a third, our own. But, to be useable, these simultaneities of durations must be convert-ed into simultaneities of instants; and this we do as soon as we have learned to spatialize time." -Henri Bergson