The single quantity “time” melts into a spiderweb of times. Times are legion: a different one for every point in space.

There are two times that change relative to each other.

We might just as well ask what is most real – the value of sterling in dollars or the value of dollars in sterling. Which tells the time? The question is meaningless. In a physics laboratory, a clock on a table and another on the ground run at different speeds. Times are legion: a different one for every point in space Things fall downwards because, down there, time is slowed by the Earth. Here on the surface of our planet, on the other hand, the movement of things inclines naturally towards where time passes more slowly, as when we run down the beach into the sea and the resistance of the water on our legs makes us fall headfirst into the waves. Where time passes uniformly, in interplanetary space, things do not fall. If things fall, it is due to this slowing down of time. This is why the friend who stays at sea level ages more slowly. It does so more in the plains and less in the mountains, because the plains are closer to it. The Earth is a large mass and slows down time in its vicinity. What does it mean, this “modification of the structure of time”? It means precisely the slowing down of time described above: a mass slows down time around itself. This modification of the structure of time influences in turn the movement of bodies, causing them to “fall” towards each other. He imagined that the sun and the Earth each modified the space and time that surrounded them, just as a body immersed in water displaces the water around it. Photograph: Roberto Serra / Iguana Press / G/Iguana Press / Getty ImagesĮinstein understood this slowing down of time a century before we had clocks precise enough to measure it. Lower down, there is simply less time than at altitude.Ĭarlo Rovelli. He has had less time to do things, his plants have grown less, his thoughts have had less time to unfold. They meet up again years later: the one who has stayed down has lived less, aged less, the mechanism of his cuckoo clock has oscillated fewer times. Two friends separate, with one of them living in the plains and the other going to live in the mountains. It is not just the clocks that slow down: lower down, all processes are slower. This slowing down can be detected between levels just a few centimetres apart: a clock placed on the floor runs a little more slowly than one on a table. The difference is small but can be measured with precision timepieces that can be bought today for a few thousand pounds. Let’s begin with a simple fact: time passes faster in the mountains than it does at sea level. The sun seems to revolve in the sky when it is really we who are spinning. The Earth appears to be flat but is in fact spherical. Reality is often very different from what it seems.

The order of time rovelli