能量的因果性、离域性和正性
Causality, delocalization and positivity of energy
摘要：
在一系列有趣的论文G。C.海格费尔特已经证明，具有正能量的量子系统最初局限于有限区域，立即发展出无限的尾部。本文用量子和经典波包分析了Hegerfeldt定理。我们证明了Hegerfeldt的结论在经典物理中仍然有效。爱因斯坦的因果关系从来没有被违反过。只使用正频率，复波包被构造，在$t = 0$是实的和非定域的，并且，进一步，是两个非定域波包的叠加。非定域性最初由相消干涉消除。然而，这种取消在随后的任意时间变得不完全。与相对论一致，两个非定域波包以光速反向运动。
英文摘要：
In a series of interesting papers G. C. Hegerfeldt has shown that quantum systems with positive energy initially localized in a finite region, immediately develop infinite tails. In our paper Hegerfeldt's theorem is analysed using quantum and classical wave packets. We show that Hegerfeldt's conclusion remains valid in classical physics. No violation of Einstein's causality is ever involved. Using only positive frequencies, complex wave packets are constructed which at $t = 0$ are real and finitely localized and which, furthemore, are superpositions of two nonlocal wave packets. The nonlocality is initially cancelled by destructive interference. However this cancellation becomes incomplete at arbitrary times immediately afterwards. In agreement with relativity the two nonlocal wave packets move with the velocity of light, in opposite directions.
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