As human beings, we believe we know a great deal about the world we live in, but reality is not actually what it may seem. For example, we think that the sun revolves around the Earth, and not the other way around. Out of all the mysteries surrounding the cosmos, time has probably been studied and hypothesised about more than any other. Yet the idea we have of time is all wrong.
The first aspect of time that is important to mention is that it does not always pass at the same speed, and is either slower or faster, depending on altitude. The first person to discover this was Albert Einstein, well before the invention of clocks capable of measuring such a small difference. At a high altitude, time passes more quickly than at sea level, because of the mutual attraction between the sun and earth that affects space and time. Since the earth is a relatively large mass, time slows down as we get closer to it, and speeds up as we move further away, like when we climb a mountain, for example. We cannot directly observe the effects of this phenomenon with the naked eye, but it nonetheless leads to an important question: if time changes, and two clocks were to therefore measure it differently, which of the two is “right”? Meanwhile, Rovelli says that this is a pointless question, because one measurement of time cannot be more accurate than another. Each one changes in relation to the other, and there are many more than two. Therefore, there is no single universal time.