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The light clock is an interesting example that is used to demonstrate how relative motion affects time and space. The construction of the light clock consists of two mirrors facing each other with a given space in between. A photon, which is generated within the system associated with the light clock, is considered to be traveling back and forth between the mirrors. Two such clocks are generally shown, with a stationary one representing how the clock is viewed within the moving system and a moving one representing how the same clock is viewed by an observer outside the system. This is shown in the following animated illustration:
Illustration 1
The usual analysis of the light clock is based on the assumption that the speed of light is always the same, in which case both time and space dilation are supposedly demonstrated by the analysis. This analysis is readily available in many books and on the web and will not be repeated here.
Another way to view the illustration is to consider that there is a light clock in each of two different systems that have some relative velocity to each other. The views of the clocks are then those of an observer in the system containing the stationary clock in the illustration. The two systems in that case would have the same clock rate under the existing conditions. Relative velocity between two systems does not necessarily imply that the system clock rates are different.
The analysis of the horizontal light clock is somewhat similar to that of the vertical one, at least when using the theoretical concepts discussed in this site.
It will be left as an exercise for the viewer to analyze the light clock using the theoretical considerations presented in this site. Eventually an analysis will be placed on this site that can be reached by clicking here when it is activated.
