GRAVITY

Although by far the feeblest of the four universal forces, gravity is the only one we experience continuously. Every inquisitive person should read a book about it, preferably this one by prolific British science writer Clegg (How to Build a Time Machine: The Real Science of Time Travel, 2011, etc.).

No revisionist, the author begins with the Greeks, who got it wrong. Believing that reason trumped observation (the senses could betray you), they thought deeply about gravity and concluded that heavy objects fell because they yearned to move toward the center of the universe (i.e., the Earth). Matters changed little for 2,000 years until Copernicus shifted the Earth away from the center, Galileo discovered the first equations of motion and Newton became the world’s first scientific superstar by producing laws that described the movement of every object, from a falling rock to an orbiting planet, a dazzling accomplishment. However, for all his brilliance, Newton couldn’t explain how gravity worked. The sun seemed to influence Earth magically across empty space. This made everyone uncomfortable, Newton included. After nearly 300 years during which scientists hypothesized a space filled with odd, invisible material that allowed one body to tug on another, Einstein solved the problem, explaining that any mass warps space-time in its vicinity. Moving through warped space changes the direction of nearby bodies, giving the impression that a force is acting.

The downside (for readers) is that Einstein’s version of gravity is more complicated than Newton’s, but Clegg’s skills never flag, and his account remains lucid and free of jargon, bad jokes and math phobia.