NEWTON'S CLOCK

Peterson (math-and-physics editor at Science News) tells how science has unlocked the secrets of celestial motion. The puzzle is as ancient as cave men peering at the night sky: how to explain the weird (sometimes seemingly backwards) movements of moons and planets? Peterson anoints two scientists as patron saints in the quest: Johannes Kepler, who established physics as the basis for astronomy and demonstrated that planets travel in elliptical, not circular, orbits; and Isaac Newton, whose three laws of movement and study of gravity established a practical understanding of planetary orbits. In fact, to Newton and his heirs, cosmic motion was as reliable as the tick-tock of a clock. But is the solar system really God's windup toy? Mathematicians and scientists like Henri PoincarÇ discarded that idea through the development of chaos theory. Chaotic systems are not, emphasizes Peterson, truly random: Inexorable physical laws still apply. But in chaotic systems, such an enormous number of factors are involved that a tiny variation can lead to enormous, unpredictable changes down the road. Observations of planetary rings, asteroid placement, and the like seem to indicate that our solar system is indeed chaotic. And while computer models project no major disruptions in the next trillion years or so, one never knows: We live, says Peterson, not in a clockwork world but in one ``constantly changing, infinitely complex.'' A very tough subject made lucid. Not for science illiterates, but astronomy and physics buffs will lap it up. (B&w illustrations—115—not seen)