The arrow of time, or time's arrow, is a concept developed in 1927 by the British astronomer Arthur Eddington involving the "one-way direction" or "asymmetry" of time. This direction, which can be determined, according to Eddington, by studying the organization of atoms, molecules and bodies, might be drawn upon a four-dimensional relativistic map of the world ("a solid block of paper").
Physical processes at the microscopic level are believed to be either entirely or mostly time-symmetric: if the direction of time were to reverse, the theoretical statements that describe them would remain true. Yet at the macroscopic level it often appears that this is not the case: there is an obvious direction (or flow) of time.
Famous quotes containing the words arrow and/or time:
“... and the next summer she died in childbirth.
That’s all. Of course, there may be some sort of sequel but it is not known to me. In such cases instead of getting bogged down in guesswork, I repeat the words of the merry king in my favorite fairy tale: Which arrow flies for ever? The arrow that has hit its mark.”
—Vladimir Nabokov (1899–1977)
“When we choose to be parents, we accept another human being as part of ourselves, and a large part of our emotional selves will stay with that person as long as we live. From that time on, there will be another person on this earth whose orbit around us will affect us as surely as the moon affects the tides, and affect us in some ways more deeply than anyone else can. Our children are extensions of ourselves in ways our parents are not, nor our brothers and sisters, nor our spouses.”
—Fred Rogers (20th century)