One of the most important lessons offered by astronomy, astrophysics, and cosmology is that the physical laws that govern life on Earth are the same everywhere in the universe. Knowing this helps us better understand how our universe works.

Isaac Newton showed the laws of gravity apply not only to objects in everyday life—apples falling from trees, for example—but also to the heavenly bodies beyond the sky, like the Sun, Moon, and planets: “This universality of physical laws drives scientific discovery like nothing else” (35). In the 20th century, scientists realized the Milky Way, the long streak of stars across the night sky, is part of a galaxy of stars that we live in and that there are billions of such galaxies in an expanding universe. Studies of these distant objects show they obey the same laws of gravity, motion, and energy as the apples in an orchard here on Earth.

Newton’s realization changed humanity’s attitudes about their place in the cosmos: “Again and again across the centuries, cosmic discoveries have demoted our self-image” (204). No longer was Earth the special center of everything; instead, it’s one of many planets orbiting a star that, in turn, is one of many stars.