Time, Emergence of

“Time is inseparably connected with history. Everything that exists in time has its history. Time and history are almost synonymous: History is measured by time, and time flows together with historical processes.” These are commonsense views, and there certainly is a grain of truth in them, but they also need to be revised in the light of contemporary physics. This entry reviews the findings of recent physical theory and research, discusses linear and cyclic models of time, and [Page 1261]links the temporality of the world to change and the creative process.

History is doubtlessly rooted in the physical world, and the laws of physics that shape the physical world provide constraints for possible histories. The laws of classical physics seem to corroborate the aforementioned commonsense view regarding the connection between time and history. However, classical physics is valid only as a limiting case of some more fundamental theories, and the real roots of time and history should be looked for in these more fundamental strata of the world's structure.

In the theory of relativity, of which classical mechanics is a limiting case, it is not space and time taken separately that form a stage for physical processes, but their combination into a single geometric entity, called spacetime. Any particular decomposition of spacetime into space and time depends on the choice of a local reference frame; that is, on the state of motion of the observer connected with this reference frame. Only spacetime itself, and not space and time taken separately, has the invariant meaning—in other words, the meaning independent of the choice of a reference frame. Consequently, if history is measured by time, history is also dependent on the state of motion of a given observer. A typical example is provided by the process of a gravitational collapse. If it is viewed by an observer collapsing together with a dying massive star, its history will end up cata-strophically in a finite time, but when it is viewed by an observer regarding the process “from outside,” that is, from a safe distance, the history of the collapsing observer will last forever only asymptotically approaching the “nonreturn” surface. Human history is notoriously accused of lacking objectivity: No two accounts of the same event coincide. But the present case is much more dramatic: Physically, the history of a process is not constituted by this process alone, but rather by a relationship between this process and a particular reference frame.

As for cosmic history, the history of the universe, local time (time within a cosmologically small neighborhood of a given observer) is usually identified with the first coordinate of a local coordinate system. But, in general, there is no unique coordinate system that would cover all of space-time, nor is there any guarantee that if we cover spacetime by many coordinate systems, all local times determined by them could be smoothly joined together to form a single cosmic time. This could be done only if certain conditions were satisfied. And what is extremely interesting—these conditions seem to be very exceptional in the collection of all possible universes.

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