Relativity and Cosmology


On the Impossibility of Separating Clocks from Rulers

Authors: Armin Nikkhah Shirazi

The Lorentz Transformations imply that time and length are in some sense interconvertible, much in contrast to our ordinary intuitions. This paper attempts to present an approach which is supposed to make it intuitively evident that time and length are in fact interconvertible and, furthermore, that this approach is compatible with two well-known phenomena predicted by SR, namely time dilation and length contraction. This is accomplished by demonstrating how a clock can be used as a ruler, and vice versa, leading to the realization that length contraction and time dilation directly imply each other in the context of the motion of the same measurement device. What makes both kinds of measurements using the same device really possible in the first place is the existence of a finite upper limit on motion. Because of this limit, length measurements cannot be completed without involving the passage of time, and time measurements cannot be completed without involving finite displacement. But that means any clock or ruler really measures both time and length. Hence one constraint on what is fundamentally possible in physics is our ability to build measurement devices that can be exclusively used just as rulers or just as clocks

Comments: 9 pages, This essay was first submitted to the 2nd FQXi essay contest in early october 2009. The link can be found here:

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Submission history

[v1] 7 Oct 2011

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