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:
“It is easy to dodge a spear in the daylight, but it is difficult to avoid an arrow in the dark.”
—Chinese proverb.
“And time brings down what is both strong and tall.
But plants new set to be eradicate,
And buds new blown, to have so short a date,
Is by his hand alone that guides nature and fate.”
—Anne Bradstreet (c. 1612–1672)