Gravity

Gravity

Hold this book in your hand and let go. What will happen? It’s such an obvious question that it feels embarrassing to have to ask it. But humor me. What will happen? You don’t have to carry out the experiment to know the answer. The book will fall. Why? Just as embarrassingly obvious. Because of gravity.

This is the most directly obvious force of nature. Its influence is programmed into our expectations of the world around us. If we let go of something and it drifts upward instead of falling, it’s a double-take moment. Either we’re dealing with something special, like a helium balloon, or we’re not firmly planted on the Earth. When we drop things, they fall, simple as that. And yet, as we will discover, the story of gravity is anything but simple.

Gravity is so familiar and apparently obvious that we often miss seeing just how remarkable it is. Most rational people laugh at the idea of astrology. They may tolerate it as fun, but they accept that it is garbage. It’s bizarre, they say, that anyone should believe that our lives are influenced in any way by astronomical bodies that are millions of miles away. Yet we accept that gravity—an invisible force with no detectable mechanism for exerting an influence—can have a real effect across just such distances. After all, the only thing that keeps the Earth in orbit is the gravitational attraction between it and the Sun, 93 million miles away.

You will sometimes see this distant reach of gravity being used to try to give astrology a scientific basis. We are subject to the gravitational attraction of the planets, the argument goes, so they can have an influence on our lives. While this is strictly true, it is worth bearing in mind that the gravitational force between a human body and the distant planets is tiny. By comparison, the gravitational attraction between a baby and the midwife is greater. So if astrology really were based on this idea, we should have astrological charts including the position and mass of the midwife, and everything else that was present at the birth.

In the real world of science, gravity has a much greater effect on us than anything astrologers could even imagine. Without gravity there are just so many ways that we wouldn’t exist or be able to carry out our everyday activities. It isn’t just a convenient way of sticking to the surface of the Earth.

It is thanks to gravity that bodies like planets and stars came into existence in the first place. Just imagine you are visiting the site of the solar system before it formed, around 4.5 billion years ago. You are looking at a cloud of matter—gas and dust floating in space. There is no wind to disturb this collection of material, so it will not be blown from place to place, but there is gravity. Each of the specks of matter has a tiny influence on the others. Gradually, painfully slowly, the matter will be pulled together.

At the same time the whole thing is rotating. That’s the way it started out, and there is nothing to stop it. So as the matter bunches together, it is also whirling around, like the disk of a pizza as the dough is spun between the hands of the baker. Eventually, at the center of this whirling cloud will be a large clump of matter. As each new particle comes crashing in, it will add energy, producing heat.

From GRAVITY by Brian Clegg, copyright © 2012 by the author, and reprinted by permission of St. Martin’s Press, LLC.