The Function of the Second Postulate in Special Relativity

Alon Drory

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arXiv · 1408.3142

The Function of the Second Postulate in Special Relativity

Alon Drory

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Abstract

Many authors noted that the principle of relativity, together with space-time symmetries, suffices to derive Lorentz-like coordinate transformations between inertial frames. These contain a free parameter, $k$, (equal to $c^{-2}$ in special relativity) which is usually claimed to be empirically determinable, so that special relativity does not need the postulate of constancy of the speed of light. I analyze this claim and find that all methods destined to measure $k$ fail without further assumptions, similar to the second postulate. Specifically, measuring $k$ requires a signal that travels identically in opposite directions (this is unrelated to the conventionality of synchronization, as the one-postulate program implicitly selects the standard synchronization convention). Positing such a property about light is logically weaker than Einstein's second postulate but suffices to recover special relativity in full.

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Alon Drory. 2014-07-21. The Function of the Second Postulate in Special Relativity. https://arxiv.org/abs/1408.3142

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