Faster-than-light group velocities and causality violation
Faster-than-light group velocities and causality violation
复制标题
超光速群速度和违反因果关系
DOI：
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发表时间：
1970
期刊：
影响因子：
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通讯作者：
S. Lipson
中科院分区：
文献类型：
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作者：
R. Fox;C. Kuper;S. Lipson
布里渊和索末菲的经典分析表明，在某些频率范围内，群速度超过光速并不意味着违反因果关系。群速度并不总是与信号传播速度相同。我们证明了因果关系破坏的一个必要条件是相速度的无限频率极限必须超过光速。应用该定理可以得出以下结论：（a）所有洛伦兹不变的波动方程（特别是范伯格的“快子”）都是因果的;（B）Bludman-Ruderman模型的准声学分支也是因果的。
The classical analysis of Brillouin and Sommerfeld has shown that the appearance, in some frequency range, of group velocities in excess of the speed of light does not imply causality violation. The group velocity is not always identical with the velocity of signal propagation. We show that a necessary condition for causality violation is that the infinite- frequency limit of the phase velocity shall exceed the speed of light. Application of the theorem leads to the conclusions (a) that all Lorentz-invariant wave equations (and in particular the Feinberg ‘tachyon’) are causal, and (b) that the quasi-acoustic branch of the Bludman-Ruderman model is causal.