time

The nature of time has been one of the major problems of philosophy since antiquity. Is time well thought of as flowing? If so, does it flow from future to past with us stuck like boats in the middle of the river, or does it flow from past to future, bearing us with it? And might it flow faster or slower? These questions seem hard (or absurd) enough to encourage us to reject the metaphor of time's flow. But if we do not think of time as flowing, how do we conceive of its passage? What distinguishes the present from the past and future, or is there no objective distinction (see a-series )? What gives time its direction—what accounts for the asymmetry between past and future? Can we make sense of timeless existence, or can we only make sense of existence in time? Is time infinitely divisible, or might it have a granular structure, with there being a smallest quantum or chunk of time? Many of these problems are first posed in Aristotle's Physics, in the form of paradoxes or problems about the very existence of time. One problem is that time cannot exist, for none of its parts exist (the present instant, having no duration, cannot count as a part of time). Again, if we ask when the present instant ceases to exist, every answer involves a contradiction: not at the present, for while it exists it exists; not at the next moment, for in the continuum there is no next moment (any more than there is such a thing as the next fraction to any given fraction); not at any subsequent moment, for then it is already gone. But we cannot think of the present instant as continuously existing, for then things that happened ten thousand years ago would be simultaneous with things that have happened today. Aristotle's puzzles, and Zeno's paradoxes of time and space, encouraged atomistic solutions, in which the structure of time is made granular. Partisans of atomism included Diodorus Cronus (fl. c. 300 BC) and Epicurus, but they were opposed by the Stoics ; the countervailing arguments on each side were marshalled by Sextus Empiricus as grist to the sceptical mill. A fundamentally idealist solution, allowing different times to exist in the sense of being simultaneous objects of contemplation, is propounded by Augustine, in the Confessions, Bk. 11, and is visible in Leibniz, Berkeley, Kant, and Bergson . Other perplexing problems include the question of whether time may have a beginning, and whether there can be eventless time. See also space-time, relativity theory.