Time



Two distinct views exist on the meaning of time. One view is that time is part of the fundamental structure of the universe, a dimension in which events occur in sequence. This is the realist view, to which Isaac Newton subscribed, in which time itself is something that can be measured. A contrasting view is that time is part of the fundamental intellectual structure (together with space and number) within which we sequence events, quantify the duration of events and the intervals between them, and compare the motions of objects. In this view, time does not refer to any kind of entity that “flows”, that objects “move through”, or that is a “container” for events. This view is in the tradition of Gottfried Leibniz and Immanuel Kant, in which time, rather than a thing to be measured, is part of the measuring system.







The Oxford English Dictionary defines time as “the indefinite continued progress of existence and events in the past, present, and future, regarded as a whole.” The American Heritage Dictionary defines time as “a nonspatial linear continuum in which events occur in an apparently irreversible succession.” Encarta, Microsoft’s Digital Multimedia Encyclopedia, gives the definition of time as “System of distinguishing events: a dimension that enables two identical events occurring at the same point in space to be distinguished, measured by the interval between the events.”







Many fields avoid the problem of defining time itself by using operational definitions that specify the units of measurement that quantify time. Regularly recurring events and objects with apparent periodic motion have long served as standards for units of time. Examples are the apparent motion of the sun across the sky, the phases of the moon, and the swing of a pendulum.







Time has historically been closely related with space, most obviously with spacetime in Einstein’s general relativity. According to the scientific theory of special relativity, the concept of time depends on the spatial context, and the human perception is only a local observed quantity which has meaning only in a relative sense ?ie. between object and observer.







Time has long been a major subject of science, philosophy and art. The measurement of time has also occupied scientists and technologists, and was a prime motivation in astronomy. Time is also a matter of significant social importance, having economic value (“time is money”) as well as personal value, due to an awareness of the limited time in each day and in our lives. This article looks at some of the main philosophical and scientific issues relating to time.







Interpretations



Many ancient philosophers wrote lengthy essays on time, believing it to be the essence around which life was based. A famous analogy was one that compares the time of life to the passing of sand through an hourglass. The sand at the top is the future, and, one tiny grain at a time, the future flows through the present into the past. The past ever expanding, the future ever decreasing, but the future grains being moulded into the past through the present. This was widely discussed in around the 3rd century.







The earliest recorded philosophy of time was expounded by Ptahhotep, who lived 2650-2600 BC said: “Do not lessen the time of following desire, for the wasting of time is an abomination to the spirit.”







In the Old Testament book Ecclesiastes, traditionally thought to have been written by King Solomon (970-928 BC), time was regarded as a medium for the passage of predestined events.







“There is an appointed time for everything. And there is a time for every event under heaven ? A time to give birth, and a time to die; A time to plant, and a time to uproot what is planted. A time to kill, and a time to heal; A time to tear down, and a time to build up. A time to weep, and a time to laugh; A time to mourn, and a time to dance. A time to throw stones, and a time to gather stones; A time to embrace, and a time to shun embracing. A time to search, and a time to give up as lost; A time to keep, and a time to throw away. A time to tear apart, and a time to sew together; A time to be silent, and a time to speak. A time to love, and a time to hate; A time for war, and a time for peace.” (Ecclesiastes 3:1?8)







Around 500 BC Heraclitus, a fatalist held that the passage of time and the future both lay beyond the possibility of human influence: “Everything flows and nothing abides; everything gives way and nothing stays fixed. You cannot step twice into the same river, for other waters and yet others, go flowing on. Time is a child, moving counters in a game; the royal power is a child’s.”







Time in philosophy



Newton believed time and space form a container for events, which is as real as the objects it contains.







“Absolute, true, and mathematical time, in and of itself and of its own nature, without reference to anything external, flows uniformly and by another name is called duration. Relative, apparent, and common time is any sensible and external measure (precise or imprecise) of duration by means of motion; such a measure ? for example, an hour, a day, a month, a year ? is commonly used instead of true time.”







In contrast to Newton’s belief in absolute space, and closely related to Kantian time, Leibniz believed that time and space are a conceptual apparatus describing the interrelations between events. The differences between Leibniz’s and Newton’s interpretations came to a head in the famous Leibniz-Clark Correspondence. Leibniz thought of time as a fundamental part of an abstract conceptual framework, together with space and number, within which we sequence events, quantify their duration, and compare the motions of objects. In this view, time does not refer to any kind of entity that “flows,” that objects “move through,” or that is a “container” for events.







Immanuel Kant, in the Critique of Pure Reason, described time as an a priori notion that allows us (together with other a priori notions such as space) to comprehend sense experience. With Kant, neither space nor time are conceived as substances, but rather both are elements of a systematic mental framework necessarily structuring the experiences of any rational agent, or observing subject. Spatial measurements are used to quantify how far apart objects are, and temporal measurements are used to quantify how far apart events occur. Similarly, Schopenhauer stated in the preface to his On the Will in Nature that “Time is the condition of the possibility of succession.”







In Existentialism, time is considered fundamental to the question of being, in particular by the philosopher Martin Heidegger.







Time as “unreal”



In 5th century BC Greece, Antiphon the Sophist, in a fragment preserved from his chief work Truth held that: “Time is not a reality (hupostasis), but a concept (noema) or a measure (metron).” Similarly, Parmenides believed that time, motion, and change were illusions, leading to Zeno’s paradoxes (Zeno was a follower of Parmenides).







Emerson considers time as presentness, where past and future are but our present projections (of our memory, hope, etc.). For Emerson, time needs a qualitative measurement rather than a quantitative one.







Julian Barbour believes time to be an illusion which we interpret through what he calls “time capsules,” which are “any fixed pattern that creates or encodes the appearance of motion, change or history.” One example of this is the arrow of time.







Linear time versus circular time



In general, the Judaeo-Christian concept, based on the Bible, is that time is linear, with a beginning, the act of creation by God. The Christian view assumes also an end, the eschaton, expected to happen when Christ returns to earth in the Second Coming to judge the living and the dead. This will be the consummation of the world and time. St Augustine’s City of God was the first developed application of this concept to world history. The Christian view is that God and the supernatural world are outside time and exist in eternity. This view relies on interpretation however, for some Jewish and Christian sects believe time may in fact be cyclical. On the other hand, the dharmic religions such as Buddhism and Hinduism, have a concept of a wheel of time, that regards time as cyclical and quantic consisting of repeating ages that happen to every being of the Universe between birth and extinction. In recent years this cyclical vision of time has been embraced by theorists of quantic space-time and systems theory.