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:
“O Russia! O my wife! Our long and narrow Road lies clear though distressed.
Our road with an old Tatar freedom’s arrow Has deeply pierced our breast.”
—Alexander Blok (1880–1921)
““I am of Ireland,
And the Holy Land of Ireland,
And time runs on,” cried she.
“Come out of charity
And dance with me in Ireland.””
—William Butler Yeats (1865–1939)