爱因斯坦的狭义相对论基于光速不变假设，而无光相对论（Relativity without Light）就是试图去掉这个假设，完全利用时空的性质（如均匀性和各向同性）来说明洛仑兹变换的存在。无光相对论的历史可以追溯到相对论刚刚发表之后。1910年，俄国物理学家 Vladimir Ignatowski 最早利用时空性质来试图推导洛仑兹变换。之后，这一推导被很多物理学家不断改进。 A more detailed references in chronological order are Ignatowski (1910, 1911a, 1911b); Frank and Rothe (1911, 1912); Pars (1921); Kaluza (1924); Lalan (1937); Dixon (1940); Weinstock (1965); Mitavalsky (1966); Terletskii (1968); Berzi and Gorini (1969); Gorini and Zecca (1970); Lee and Kalatos (1975); Lvy-Leblond (1976); Srivastava (1981); Mermin (1984); Schwartz (1984, 1985); Singh (1986); Sen (1994); Field (1997); Coleman (2003); Pal (2003); Sonego and Pin (2005); Gannett (2007); Silagadze (2007); Certik (2007); Feigenbaum (2008). 但其中有一个关键问题仍未解决，就是如何确定所导出的类洛仑兹变换中的常数。如果这一常数为无穷大，则对应的变换为伽利略变换。只有这一常数为有限值，其变换才是真正的洛仑兹变换。在我的论文中，我提出了一个论证，认为时空的分立性可以决定这一常数的有限数值，从而最终将爱因斯坦的相对论表述为一个关于时空本身的无光相对论。 It is well known that c is the speed of light in vacuum, which enters into modern physics through one of its foundation stones, the special theory of relativity. Special relativity was originally based on two postulates: the principle of relativity and the constancy of the speed of light. But, as Einstein later admitted to some extent (Einstein 1935), it is an incoherent mixture (Stachel 1995); the first principle is universal in scope, while the second is only a particular property of light, which has obvious electrodynamical origins in Maxwells theory. In fact, there has been a lasting attempt that tries to drop the light postulate from special relativity, which can be traced back to Ignatowski (1910) (see also Torretti 1983; Brown 2005). It is found that, based only on homogeneity of space and time, isotropy of space and the principle of relativity, one can deduce Lorentz-like transformations with an undetermined invariant speed. Unlike special relativity that needs to assume the constancy of the speed of light, an invariant speed naturally appears in the theory, which is usually called relativity without light. This is a surprise indeed. Since the value of the invariant speed can be infinite or finite, the theory of relativity without light actually allows two possible transformations: Galilean and Lorentzian. An empirical element is still needed to determine the invariant speed and further eliminate the Galilean transformations. This raises serious doubts about the connection between the theory and special relativity. Some authors insisted that the light postulate in special relativity is still needed to derive the Lorentz transformations (Pauli 1921; Resnick 1967; Miller 1981). Others doubted that the theory is indeed relativistic in nature (Brown 2005). However, it can be argued that the empirical element may not refer to any properties of light in an essential way (see, e.g. Lvy-Leblond 1976; Mermin 1984). Thus, the existing theory of relativity without light is definitely an advance, but admittedly there is still a step away between it and the Lorentz transformations in special relativity; resorting to experience to determine its invariant speed is just a makeshift. The challenge for future work is two-fold. On the one hand, we need to further determine the invariant speed, not by experience but by some deeper postulates (e.g. postulates about space and time). If successful, this will establish a more complete theory of relativity without light, which can be taken as a further development of special relativity; On the other hand, we need to re-explain the constant c in special relativity. It should be not (only) the speed of light. What is its real meaning then? These two problems are intimately connected as a matter of fact. The purpose of this paper is to solve them. 我的论文： Relativity without light: a further suggestion 推荐阅读： Mermin, N. D. (1984). Relativity without light. Am. J. Phys. 52, 119-124. Stachel, J. (1995). History of relativity. In L. M. Brown, A. Pais, and B. Pippard, (eds.) Twentieth Century Physics, vol.1, pp. 249356. New York: American Institute of Physics. Brown, H. (2005). Physical Relativity: Spacetime structure from a dynamical perspective. Oxford: Clarendon Press.
我的专业是物理学基础，这也是我多年研究的主要兴趣。具体地说，这些研究主要集中于量子理论和相对论的逻辑基础和解释问题。本文提出了一个解释光速不变的假说，写于2004年，此处稍有改动。另附一英文论文，写于2009年，其中介绍了在物理学界被广泛讨论的无光相对论（Relativity without Light）。希望能对大家理解狭义相对论有所帮助。 在相对论框架内，尽管单向光速不可测量，但是回路光速却是一个可测量的物理量。这种测量只需一个处于固定位置的时钟，而不需要两个预先同步的异地时钟。根据相对论，回路光速具有一种与惯性系无关的不变性，并且它是物体运动速度的上限。这是相对论最不可思议、也最令人困惑的地方。那么，为什么存在一个运动速度的上限呢？这一最大运动速度（即回路光速，以下简称光速）又为何不变呢？存在更深层的原因吗？！ 相对论的创立者爱因斯坦似乎从未考察过光速为何不变的问题。在他看来，光速不变原理不仅是麦克斯韦方程的优美性的体现，同时也已经为严格的实验所证实。于是，爱因斯坦大胆地将这一原理提升为与热力学第二定律具有同等地位的基本原理或公设，并作为构建相对论的一个基石。然而，他并未进一步论证这一原理的内在合理性，而只满足于它的外部证实。一种普遍存在的观点认为，洛伦兹时空变换已经解释了光速的不变性，理由是光速不变性可以通过基于洛伦兹时空变换的速度叠加原理导出。然而，这只是一种循环论证，因为洛伦兹时空变换正是基于光速不变原理和相对性原理导出的。实际上，针对这种观点我们可以继续追问，为什么时空变换遵循洛伦兹变换呢？于是我们又不得不回到问题的起点。 人们普遍认为，相对论的第二个假设---相对性假设可能会由于量子非定域性的存在而被修正，但它的第一个假设---光速不变假设将会顽强地存活下来。存在必然具有存在的合理性。找寻到光速不变的逻辑基础无疑是对相对论的进一步深化和发展，它也是爱因斯坦未竟的科学探险。这里我们将对此进行较深入的分析。 由于速度性质本质上依赖于物体运动于其中的时空，因此可以预计，光速最大性与光速不变性可能隐含着时空结构的一种深层性质，并且是这种性质的一种最明显的外部表现，而这种性质将是相对论的更深层的物理基础。下面我们将试图发现时空的这种性质，并给出光速最大且不变的进一步原因。 我们知道，如果光是一种在媒介中传播的波，那么可以设想存在一个与媒介性质有关的最大传播速度，尽管这一传播速度与观测参照系的无关性仍很难解释。然而，光并不是一种经典波，而是一种进行量子运动的粒子（即光子）。于是，粒子的运动速度存在一个有限的最大值似乎很奇怪，同时，这一最大速度与观测参照系的无关性更加令人困惑。应当指出，人们在理解相对论时所存在的这种困惑是有道理的，原因在于，相对论只是对经验的一种直接的理论表达，它并未进一步解释这些经验存在并违反直观的深层原因。只有找到这些内在的逻辑原因，人们才能真正理解相对论，才会真正没有困惑。（待续） Why is the speed of light constant?
标签: 光速不变
