Rohrlich Fritz
Department of Physics, Syracuse University, Syracuse, New York 13214, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2005 Nov;72(5 Pt 2):057601. doi: 10.1103/PhysRevE.72.057601. Epub 2005 Nov 23.
Time reversal invariance, T, is well known to hold in quantum electrodynamics. However, it has caused difficulties in classical electrodynamics (CED). These are shown to be conceptual misunderstandings. When corrected: (1) the classical equations of motion of a charge are T invariant despite the explicit occurrence of retarded fields in the equations of motion. (2) Advanced fields violate causality and occur neither in nature nor in the CED that describes it. (3) The nonexistence of advanced fields in nature implies an "arrow of time" for electromagnetic radiation: radiation emission is an overall dissipative phenomenon. This electromagnetic "arrow of time" does not contradict time reversal invariance.
时间反演不变性T在量子电动力学中是成立的，这是众所周知的。然而，它在经典电动力学（CED）中却引发了难题。事实证明，这些难题是概念上的误解。纠正后发现：（1）尽管运动方程中明确出现了推迟场，但电荷的经典运动方程却是T不变的。（2）超前场违反因果律，在自然界中以及描述它的经典电动力学中都不会出现。（3）自然界中不存在超前场意味着电磁辐射存在“时间箭头”：辐射发射是一种整体的耗散现象。这种电磁“时间箭头”与时间反演不变性并不矛盾。
