"Why do we get older? Why do our bodies wear out? Why can't we just go on and on and on, accumulating a potentially infinite number of Frequent Flier mileage points? These are the kinds of questions that philosophers have been asking ever since they realized that being a philosopher did not involve any heavy lifting. And yet the answer is really very simple: Our bodies are mechanical devices, and like all mechanical devices, they break down. Some devices, such as battery-operated toys costing $39.95, break down almost instantly upon exposure to the Earth's atmosphere. Other devices, such as stereo systems owned by your next-door neighbor's 13-year-old son who likes to listen to bands with names like "Nerve Damage" at a volume capable of disintegrating limestone, will continue to function perfectly for many years, even if you hit them with an ax. But the fundamental law of physics is that sooner or later every mechanism ceases to function for one reason or another, and it is never covered under the warranty."