Sunday, December 6, 2009


Their origin is one of the deepest questions in modern physics

Sundials and water clocks are as old as civilization. Mechanical clocks—and, with them, the word “clock”—go back to 13th-century Europe. But these contraptions do nothing that nature did not already do. The spinning Earth is a clock. A dividing cell is a clock. Radioactive isotopes are clocks. So the origin of clocks is a question not for history but for physics, and there the trouble begins. You might innocently think of clocks as things that tell time, but according to both of the pillars of modern physics, time is not something you can measure. Quantum theory describes how the world changes in time. We observe those changes and infer the passage of time, but time itself is intangible. Einstein’s theory of general relativity goes further and says that time has no objective meaning. The world does not, in fact, change in time; it is a gigantic stopped clock. This freaky revelation is known as the problem of frozen time or simply the problem of time. If clocks do not tell time, then what do they tell? A leading idea is that the universe’s components—the fact, for example, that if Earth is at a certain position in its orbit, the other planets are at specific positions in theirs. Physicist Julian Barbour developed this relational view of time in the winning entry for the Foundational Questions Institute essay contest last year. He argued that because of the cosmic patterns, each piece of the universe is a microcosm of the whole. We can use Earth’s orbit as a reference for reconstructing the positions of the other planets. In other words, Earth’s orbit serves as a clock. It does not tell time but rather the positions of the other planets.

By Barbour’s reasoning, all clocks are approximate; no single piece of a system can fully capture the whole. Any clock eventually skips a beat, runs backward or seizes up. The only true clock is the universe itself. In a sense, then, clocks have no origin. They have been here all along. They are what make the concept of “origin” possible to begin with.

Source of Information : Scientific American September 2009

No comments: