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:
“Anton Petrovich turned into the passage, followed the arrow to men, mankind, human beings, marched past the toilet, past the kitchen, gave a start when a cat darted under his feet, quickened his step, reached the end of the passage, pushed open a door, and a shower of sunlight splashed his face.”
—Vladimir Nabokov (1899–1977)
“The democratic youth ... lives along day by day, gratifying the desire that occurs to him, at one time drinking and listening to the flute, at another downing water and reducing, now practising gymnastic, and again idling and neglecting everything; and sometimes spending his time as though he were occupied in philosophy.”
—Plato (c. 427–347 B.C.)