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The Slowing Down of Time

By Carlo Rovelli


The following is an extract from physicist Carlo Rovelli’s new book, The Order of Time, translated by Simon Carnell and Erica Segre. The book explores the mysteries of time and how we think about it, exploding preconceptions and prompting reflection.



Let’s begin with a simple fact: time passes faster in the mountains than it does as sea level. The difference is small, but it can be measured with precision timepieces that be bought today on the internet for a few thousand pounds. With practice, anyone can witness the slowing down of time. With the timepieces of specialized laboratories, this slowing down of time 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.


It is not just the clocks that slow down: lower down, all processes are slower. Two friends separate, with one of them living in the plains and the other going to live in the mountains. They meet up again years later: the one who has stayed down has lived less, aged less, the mechanism of his cuckoo clock oscillated fewer times. He has had less time to do things, his plants have grown less, his thoughts have had less time to unfold… Lower down, there is simply less time than at altitude.


Is this surprising? Perhaps it is. But this is how the world works. Time passes more slowly in some places, more rapidly in others.


The surprising thing, perhaps, is that someone understood this slowing down of time a century before we had clocks precise enough to measure it. His name, of course, was Albert Einstein.


The ability to understand something before it’s observed is at the heart of scientific thinking. In antiquity, Anaximander understood that the sky continues beneath our feet long before ships had circumnavigated the Earth. At the beginning of the modern era, Copernicus understood that the Earth turns long before astronauts had seen it do so from the moon. In a similar way, Einstein understood that time does not pass uniformly everywhere before  the development of clocks accurate enough to measure the different speeds at which it passes.


In the course of making such strides, we learn that the things which seemed self-evident to us were really no more than prejudices. It seemed obvious that the sky was above us and not below; otherwise, the Earth would fall down. It seemed self-evident that the Earth did not move; otherwise it would cause everything to crash. That time passed at the same speed everywhere seemed equally obvious to us. Children grow up and discover that the world is not as it seemed from within the four walls of their homes. Humankind as a whole does the same.


… Does this seem strange? It is like when, while watching the sun going down gloriously at sunset, disappearing slowly behind distant clouds, we suddenly remember that it’s not the sun that’s moving but the Earth that’s spinning, and we see with the unhinged eye of the mind our entire planet – and ourselves with it – rotating backwards, away from the sun.




The Order of Time by Carlo Rovelli, translated by Simon Carnell and Erica Segre, is published by Penguin. Find out more here.



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