Time passes faster in the mountains than it does by the sea. The difference is small but it can be measured with precision timepieces. In specialized laboratories, this slowing down of time can be detected between levels just a few centimeters apart: a clock on the floor runs a little bit more slowly than one on the table. Einstein understood this almost a century before we had clocks precise enough to measure these discrepancies. This equation describes the slowing down of time closer to the Earth.

Revisiting Newton’s laws of gravitation, Einstein asked himself how the Earth and the Sun can attract each other without touching? He looked at what lies between—space and time. He imagined that the Sun and the Earth must modify space and time the way a body immersed in water displaces the liquid around it. This modification of the structure of time influences the movement of bodies, causing them to “fall” towards each other. If things fall, it is due to this slowing down of time. Where time passes uniformly, there is no falling, there is floating. Here on the surface of our planet, however, movements incline naturally toward where time passes more slowly. Things fall downward because time is slowed by the Earth.