It may be instructive to look into this strange geometry of space-time a little more closely. We shall restrict ourselves to two dimensions, that is to say, to one space dimension and to the time dimension. In other words, our space-time graph will refer to the measurements of observers moving along the embankment.
Suppose, then, that a number of observers, moving with various uniform speeds to the right or to the left, pass the observer on the embankment at
, at the time zero. These observers carry ordinary clocks in their hands, and these all mark zero hour as the observers pass
simultaneously. The question we wish to decide is as follows:
“Where will the point-events of the various observers be situated on the graph when their respective clocks mark one second past zero hour?”
Fig. XIX
We know that the point-event of the observer, who does not move from the point