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A baby sits in a highchair holding a spoon for the first time. After several awkward attempts, she puts it her mouth. She squeals in triumph.
Then, when she is no longer hungry, the experiments begin. The first time the spoon drops, it is accidental. But soon she begins a purposeful routine: let go of the spoon, watch it fall, laugh and wait until a parent retrieves it, then drop it repeatedly until the parent tires of the game.
The child has discovered gravity, a force that makes objects move without direct physical contact. How extraordinary it must seem to her.
And yet how unsurprising it is to us. "Hold this book in your hand and let go. What will happen?" asks Brian Clegg to open his new book, Gravity: How the Weakest Force in the Universe Shaped Our Lives. "It's such an obvious question that it feels embarrassing to have to ask it."
Yet asking that question should not feel awkward, he argues two paragraphs later: "Gravity is so familiar and apparently obvious that we often miss seeing just how remarkable it is." We should be as observant as that baby in the highchair, and thanks to Clegg's raising the question, we are.
The first chapter continues by transporting readers 4.5 billion years into the past where they watch the Solar System emerging from "a cloud of matter--gas and dust floating in space." It happens because of gravity. "Each of the specks of matter has a tiny influence on the others. Gradually, painfully slowly, the matter will be pulled together."
After millions of years, a central lump has formed with enough mass and heat that its nuclei (mainly hydrogen) are stripped of their electrons and pulled close enough together to ignite nuclear fusion. The Sun is born, and it sends out enough heat to warm the planets, also forming from the gravitational attraction between chunks of leftover matter from that primordial cloud.
The ancient Greeks knew none of that, but they were aware of gravity. In Chapter 2, Clegg takes us back to their pre-Newtonian understanding and then spends much of the rest of the book tracing a step-by-step progression through the familiar scientific cast of characters whose work led eventually to the modern description of gravity by Einstein's General Theory of Relativity.
Among the delights of the book is discovering that the hoary old stories of Galileo, Newton, and their contemporaries are not exactly as we learned them in science class. Clegg describes Galileo as "a slick publicist" and "a rebel more of the gut than the intellect." And he notes that despite Newton's mathematical triumph that describe gravity, his contemporaries viewed his explanation as a step backward. The natural tendency of matter to fall was replaced by an invisible force that acted over great distances.
The book is exceptionally strong in its explanation of General Relativity, avoiding most of the mathematical details but making clear the essential difference between space and spacetime and elucidating how the theory predicts the bending of light beams in gravitational fields.
The book is less clear in its discussion of the quantum nature of matter and energy and the other three fundamental forces of nature (electromagnetism and the strong and weak nuclear interactions). Still it does describe the main candidate theories that are trying, with limited success, to merge relativity and quantum mechanics into a coherent theory of the universe.
Most problematic is the author's choice to include a thirty-page penultimate chapter that spends a lot of time describing anti-gravity technology and other ideas that he himself calls pseudo-science. Some readers may find that an amusing diversion, but others will wonder why he chose to end his explorations in such dubious territory. To them, them it is a mis-step of some gravity.