摘要
相对论存在一些概念上的误区，因此产生了不少似是而非的佯谬，争论了一个多世纪。本文通过实例严格分析了相对论中坐标系和同时性等基本概念，揭示了现实时空只存在一个整体同时超曲面，现实世界的演化具有同步性，同时性具有客观性和唯一性。整体同时超曲面定义了客观的宇宙时间以及与这个宇宙时间垂直的客观空间，进而建立了一个普遍有效的自然坐标系ds2 = gttdt2−gkldxkdxl。自然坐标系具有特殊的物理意义，其空间坐标相对于宇宙微波背景是静止的，gtt描述了引力场，不能并入时间坐标。通常的观点把时间坐标的等时性等同于世界演化的同步性，混淆了客观的现实时空和人为设定的坐标系，因此产生了逻辑混乱。只要澄清了这些概念，相对论就会变得很好理解，所有疑难问题都能迎刃而解。
关键词： 同时性；时间膨胀；洛伦兹变换；宇宙微波背景；自然坐标系
Abstract
There are some conceptual misunderstandings in relativity, generating a lot of specious paradoxes, and leading to arguments for more than a century. In this paper, we strictly analyze the true meanings of coordinate system and simultaneity in relativity, reveal that there is only one global simultaneous hypersurface in the realistic space-time, the evolution of the world has synchronization, and the simultaneity is of objectivity and uniqueness. The global simultaneous hypersurface defines the objective cosmic time and the perpendicular cosmic space, thus establishing a generally effective Gu’s natural coordinate system ds2 = gttdt2−gkldxkdxl. The natural coordinate system has special physical significances, its spatial coordinates are static with respect to the cosmic microwave background, and gtt describes the gravity which cannot be incorporated into the temporal coordinates. The usual point of view equated the isochronism of the time coordinates with the simultaneity of the world evolution, confused the objective space-time and the artificial coordinate system, thus led to logic confusions. Once these concepts are clarified, relativity becomes well understood and all puzzling problems can be easily solved.
Key words： Simultaneity; Time dilation; Lorentz transformation; Cosmic microwave background; Natural coordinate system
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