The fundamental unit of time is, of course, a day: the 24-hour period it takes the Earth to complete one rotation on its axis. As the Book of Genesis says: ‘There was evening and there was morning, one day.’ The value of this unit is nothing more than an accident of our planet’s rate of spin, set when the Earth first coalesced from a cloud of gas and dust (and slowing down minutely ever since). But it’s also a measure that is written into our biology, hard-coded in our DNA as circadian rhythms. This pattern of physiological events coordinates each of our bodies to the spin of the planet that
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