关于超光速运动和狭义相对论--对最近一些实验的讨论和因果粒子的解
About Superluminal motions and Special Relativity: A Discussion of some recent Experiments, and the solution of the Causal Paradoxes
摘要：
在伯克利、科隆、佛罗伦萨、维也纳、奥赛、雷恩等地进行的一些实验，导致了这样一种说法，即某些东西似乎以大于真空中光速c的群速度传播。其他各种实验结果似乎都指向同一个方向：例如，理论和实验上都发现了麦克斯韦方程组的局域小波型解，它们以超光速传播。[Evenμ子中微子和电子中微子[有人提出]可能是“快子”，因为它们的平方质量似乎是负的]。关于第一个提到的实验，最近Guenter Nimtz声称，那些与倏逝波（或隧道光子）有关的结果意味着超光速信号和脉冲传输，因此违反了爱因斯坦因果关系。在本文中，我们要强调的是，恰恰相反，所有这些结果都没有危及相对论因果关系，即使它们涉及实际的超光速运动：事实上，狭义相对论甚至可以处理超光速物体和波。例如，也有可能（至少在微观物理学中）解决已知的因果悖论，这些悖论是为比光速更快的运动而设计的，尽管这还没有得到广泛的认可。在这里，我们详细而严格地展示了如何解决最古老的因果悖论，最初由托尔曼提出，这是许多其他快子悖论（如J.Bell，F.A.E.Pirani，J.D.Edmonds和其他人）的核心。解决的关键是仔细应用快子力学，因为它明确地遵循狭义相对论。最后，在两个附录中的一个附录中，我们提出了在倏逝波情况下如何计算群速度。[PACS编号：03.30.+ p; 03.50.De; 41.20.Jb; 73.40.Gk; 84.40.Az; 42.82.Et ]
英文摘要：
Some experiments, performed at Berkeley, Cologne, Florence, Vienna, Orsay, Rennes, etc., led to the claim that something seems to travel with a group velocity larger than the speed c of light in vacuum. Various other experimental results seem to point in the same direction: For instance, localized wavelet- type solutions to Maxwell equations have been found, both theoretically and experimentally, that travel with superluminal speed. [Even muonic and electronic neutrinos [it has been proposed] might be "tachyons", since their square mass appears to be negative]. With regard to the first-mentioned experiments, it was recently claimed by Guenter Nimtz that those results with evanescent waves (or tunneling photons) imply superluminal signal and impulse transmission, and therefore violate Einstein causality. In this note we want to stress that, on the contrary, all such results do not place relativistic causality in jeopardy, even if they referred to actual tachyonic motions: In fact, Special Relativity can cope even with superluminal objects and waves. For instance, it is possible (at least in microphysics) to solve also the known causal paradoxes, devised for faster than light motion, although this is not widely recognized yet. Here we show, in detail and rigorously, how to solve the oldest causal paradox, originally proposed by Tolman, which is the kernel of many further tachyon paradoxes (like J.Bell's, F.A.E.Pirani's, J.D.Edmonds' and others'). The key to the solution is a careful application of tachyon mechanics, as it unambiguously follows from special relativity. At Last, in one of the two Appendices, we propose how to evaluate the group-velocity in the case of evanescent waves. [PACS nos.: 03.30.+p; 03.50.De; 41.20.Jb; 73.40.Gk; 84.40.Az; 42.82.Et ]
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