In his lecture, “Raum und Zeit” (Space and Time) delivered at the 80th Meeting of the Natural Scientists in Cologne on September 21, 1908, German mathematician Hermann Minkowski developed his notion of the fourth dimension in which the conventional understanding of the flow of time became the perception of a shadow of reality. To demonstrate his ideas, Minkowski described a space-time position using four coordinates as a Weltpunkt (worldpoint) and a change in position in any of the coordinates as a Weltlinie (world line). Minkowski opened his lecture with this exhortation:

Gentlemen! The views of space and time which I want to present to you arose from the domain of experimental physics, and therein lies their strength. Their tendency is radical. From now onwards space by itself and time by itself will recede completely to become mere shadows and only a type of union of the two will still stand independently on its own.