( Contemporaneous ) The Principle of Time .

From the 1928 book The Nature of the Physical World, which helped to popularize the term, Eddington states:
Let us draw an arrow arbitrarily. If as we follow the arrow we find more and more of the random element in the state of the world, then the arrow is pointing towards the future; if the random element decreases the arrow points towards the past. That is the only distinction known to physics. This follows at once if our fundamental contention is admitted that the introduction of randomness is the only thing which cannot be undone. I shall use the phrase ‘time’s arrow’ to express this one-way property of time which has no analogue in space.


Eddington then gives three points to note about this arrow:

1 It is vividly recognized by consciousness.
2 It is equally insisted on by our reasoning faculty, which tells us that a reversal of the arrow would render the external world nonsensical.
3 It makes no appearance in physical science except in the study of organization of a number of individuals.






" The inexorable direction of change, linked to the asymmetry of time ( before : now : after ), was vividly described by the scientist Arthur Eddington ( 1882 - 1944 ) on as ' the arrow of time ' . Throughout the process of continuing universal degradation, the dwindling stock of 'useful' energy encounters a hierarchy of fixed physical laws conforming to mathematical formula, and it is from the interaction of these unchanging laws with the arrow of time that comes a changing world of astonishing complexity, variety and beauty. The pendulum runs down from a state of disequilibrium to one of equilibrium, and the same is true, we are told, of the universe, the ultimate 'closed system'. From a state of extreme disequilibrium it plunged via the ' Big Bang' towards its future ultimate state of utterly dark, frozen equilibrium. Between the beginning and the end there is a continual, cumulative transformation of 'useful' energy, capable of forming temporary structures and causing events, into 'useless' energy - forever lost . " ( Source )

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