Reality Is Not What It Seems: The Journey to Quantum Gravity

by Carlo Rovelli

Between the past and the future of an event (for example, between the past and the future for you, where you are, and in the precise moment in which you are reading), there exists an “intermediate zone,” an “extended present”; a zone that is neither past nor future. This is the discovery made with special relativity. The duration of this “intermediate zone,”* which is neither in your past nor in your future, is very small and depends on where an event takes place relative to you, as illustrated in figure 3.2: the greater the distance of the event from you, the longer the duration of the extended present. At a distance of a few meters from your nose, the duration of what for you is the “intermediate zone,” neither past nor future, is no more than a few nanoseconds: next to nothing (the number of nanoseconds in a second is the same as the number of seconds in thirty years). This is much less than we could possibly notice. On the other side of the ocean, the duration of this “intermediate zone” is a thousandth of a second, still well below the threshold of our perception of time, the minimum amount of time we perceive with our senses, which is somewhere on the order of a tenth of a second. But on the moon, the duration of the “extended present” is a few seconds, and on Mars it is a quarter of an hour. This means we can say that on Mars there are events that in this precise moment have already happened, events that are yet to happen, but also a quarter-of-an-hour of events dur...

Special relativity