The tides are slowly stealing rotational energy from Earth and giving it to the Moon, lengthening our days while pushing the Moon about 3.8 centimetres farther away each year — a transaction scientists can measure with lasers left by Apollo astronauts.

Galileo had his own theory, that tides were just Earth’s oceans sloshing around like water in a moving bowl. That means the moon pulls the ocean nearest to it harder than it pulls the solid Earth underneath, dragging that water into a bulge reaching toward the moon. Two bulges, always on opposite sides of the planet, regardless of where the moon happens to be overhead. The date came, the planets lined up, ocean tides shifted by a matter of millimeters, and nothing else happened at all. The ocean and the moon settled it without him, and they’re still settling it, one high tide at a time.