This implies that it makes no sense to say of an event on Mars that it is taking place ‘just now’, because ‘just now’ does not exist (figure 3.3).fn11 In technical terms, we say that Einstein has understood that ‘absolute simultaneity’ does not exist: there is no collection of events in the universe which exist ‘now’. The collection of all the events in the universe cannot be described as a succession of ‘now’s, of presents, one following the other; it has a more complex structure, illustrated in figure 3.2. The figure describes that which in physics is called spacetime: the set of all past
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