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The speed of light need not be constant

Asher Peres
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Abstract

Recent observations of the fine structure of spectral lines in the early universe have been interpreted as a variation of the fine structure constant. From the assumed validity of Maxwell equations in general relativity and well known experimental facts, it is proved that $e$ and $\hbar$ are absolute constants. On the other hand, the speed of light need not be constant.

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Asher Peres. 2002-10-19. The speed of light need not be constant. https://arxiv.org/abs/gr-qc/0210066

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