反常色散介质“超光速”现象研究的新进展

ON “SUPERLUMINAL” LIGHT PROPAGATION IN ANOMALOUS DISPERSION MEDIUM

文章介绍了王力军等人的光脉冲在反常色散介质中传播实验的测量结果 ,说明了实验测量的不完全性 ,因而它不可能在是否超光速的问题上给出明确的答案 .文章还介绍了近一年来相应的理论研究工作 .文章作者依据物理概念和理论研究结果论证了该实验所得的负群速度本身并不超光速 ;如果把负群速度看成是某种能量的传播 ,那么超光速出现在负群速度开始时的瞬间 ,因而它是超距作用 ,违反能量守恒或动量守恒 .因此 ,负群速度只是表观速度 ,能流的研究结果也证明了这一点 .这就是说 ,该实验并没有观察到超光速传播 .

The experimental results by Wang et al. concerning pulsed light propagation in an anomalous dispersion medium are reviewed. We argue that the incomplete measurements make the determination of the light propagation velocity impossible. The results of recent theoretical studies are also discussed. According to basic physical concepts and theoretical results we conclude that the negative group velocity itself is not superluminal. If the negative velocity were regarded as that of some energy, superluminal propagation would occur at the beginning instant of the negative group velocity propagation so that it is an action at distance which would violate causality and energy (or energy flow) conservation laws.Thus the negative group velocity is simply an apparent velocity as we shall show from the study of energy flow. This implies that no superluminal propagation was observed by Wang et al.