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The sight of day and night, and the months and the revolutions of the years, have created number, and have given us a conception of time.
-Plato, Timaeus
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<aside> đź“Ś Around the Clock
Since its first formulation, human beings have used this breakthrough idea as the basis for organizing action and recording experience. Time is change. Not change, not time. Change is observable, and you can measure changes roughly against each other, perhaps, without having an idea of time: accelerating, for instance, to elude a pursuer or capture prey, or noticing that different life-forms grow at different rates.
A universal standard of measurement is, however, an idea. It arose, of course, from observation: from awareness that some changes - especially those of the relative positions of celestial bodies - are regular, cyclical and therefore predictable. The realization that they can be used as a standard against which to measure other such changes transcends observation: it was a perception of commonplace genius that occurred in all human societies so long ago that - ironically - we are not able to estimate a date for it.
It is a fair assumption that it happened in consequence of the congruities between the cycles of the heavens and other natural rhythms - especially those of our own bodies and of the ecosystems to which we belong: the passage of the Sun roughly matches intervals of sleep and wakefulness. The Moon’s coincides with the menstrual cycle. Species we eat grow or fatten according to the season. Hence the choice of timekeeping standards. Some human groups keep star-time, usually on the basis of a cycle of Venus, but all, as far as we know, use the solar day and year, and the lunar month. Some, like ours, attempt elaborate reconciliations of the cycles of those two most conspicuous heavenly bodies, while others keep both sets of calculations going in imperfect tandem. It is a safe bet that keeping time by this means is one of the oldest and longest-enduring ideas in the world.
It remained the basis of timekeeping-and therefore of the coordination of all collaborative enterprise-until our own times.
But when did it start? The earliest known artifact that looks as though it might be a calendar was made about 30,000 years ago in the Dordogne regio of France, from a flat bone inscribed with crescents and circles: the intervals look systematic and have been read as a record of phases of the Moon. Then there is a yawning gap in the evidence until the 5th millennium BC onwards, when horizon-marking megaliths appeared, erected to track the passage of the Sun through the heavens. In the interim period, many sites have yielded what look like tally sticks, or, at least, objects scored with regular incisions, but these are not securely identifiable as calendars and are as likely to be doodles or games or decorative objects or ritual aids.
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When we do nothing for a while we say that some "time" has passed. In terms of actions, doing nothing is a special type of action. If we denote it by t, then tt is an action of waiting for two times longer than with t. When we measure time, we take some repetative process, like one swing of a pendulum, for a model of other processes. We may say, for instance, that John needes 80 'pendulums' of time to smoke a cigarette. In terms of the homomorphism picture, the state when John is lighting his cigarette is w_1; the state when he extinguishes it is w_2; the language L is the pendulum, with some kind of counter of swings; the mapping M is
registration of the current value of the counter. The process M must be a real physical process, not just a mental association of some states of the counter with some states of cigaret smoking - the truth which has been dramatically demonstrated by Einstein's relativity theory.
We often say that all real processes take place in space and time. The meaning of such statements is that in addition to what really goes on, we imagine some reference actions of consecutive shifts ("in space") and waits ("in time") and esatblish relationships between these actions and actual objects and processes. Thus, in accordance with Kant's view, space and time are not observable realities, but our ways to organize experience.
Henri Bergson was first to notice and emphasize the difference between real time, in which we live and act, and the objectified time of history and physics. Imagine a pendulum which at each swing puts a mark on a moving tape. We have a historical record of "the time moving". This historic record is an object at every moment we look at it. We use it as a part of our model of reality. We shall refer to the marks on the tape as representing a model time. It is very much different from the real time.
Real time is such that two moments of it never coexist. In model time the moments coexists as different objects in some space. Thus Bergson calls model time a projection of real time on space. Bergson's real time is irrreversible. Model time, the time of Newton's mechanics, is reversable: we read historical records equally well from left to right and from right to left. The seemingly inconceivable feature of Feynman's diagrams, the movement in the direction opposite to time, is explained simply by the fact that the time of physical theories is model time, i.e. a spacial phenomenon. Real time shows up in probability theory and statistical physics. We are dealing there with real acts of choosing from a number of possibilities. Hence this time is irreversible. In mechanics, to every action there is an inverse action which brings back the original state. So, when we project time on space the projection has an additional property of reversibility. But the act of choosing has no inverse. If you drew ticket No.13, you drew it. You can return it to the pool, but the fact will still remain that it was No.13, and nothing else, that was drawn first and then returned. You can choose, but you cannot "unchoose".
The doctrine that all reality is timeless was unequivocably held by Kant,Schopenhauer,Hegel and Bradley.
Far Eastern philosophy
What does determine the order of events in time, on the supposition, which we are now discussing, that Time is only an illusory way of regarding a timeless reality ? I believe myself that there is good reason to hold that the order is de- termined by the adequacy with which the states represent the eternal reality, so that those states come next together which only vary infinitesimally in the degree of their ad- equacy, and that the whole of the time-series shows a steady process of change of adequacy— I do not say yet in which direction.
The Fantasy of Living Outside of Time