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Has superluminal light propagation been observed?

Yuan-Zhong Zhang

physics.gen-pharXiv:physics/0009034

Abstract

It says in the report1 by Wang et al. that a negative group velocity u=-c/310 is obtained and that a pulse advancement shift 62-ns is measured. The authors claim that the negative group velocity is associated with superluminal light propagation and that the pulse advancement is not at odds with causality or special relativity. However, it is shown here that their conclusions above are not true. Furthermore, I give some suggestion concerning a re-definition of group-velocity and a new explanation in special relativity of causality.

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