IT WAS Isaac Newton who finally showed why the heavenly bodies move in predictable ways. He proved that the planets move in response to the sun's gravitational pull, endlessly repeating their orbits like celestial clockwork. If you know the position and velocity of a planet today, you can work out its motion far into the future.
Or so we thought until recently. "Our research shows that for tens of millions of years, the planets orbit the sun with the regularity of clockwork," says geophysicist Michael Ghil. "Then, quite unexpectedly, everything goes crazy." According to Ghil, who works at the École Normale Supérieure in Paris and the University of California at Los Angeles, this planetary madness is all down to chaos. In chaotic systems, tiny changes in conditions can lead to huge differences in outcome. Though you can predict what the changes will do in theory, the system is so sensitive ...
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