The 1905 Papers

In the first of three seminal papers that were published in 1905, Einstein examined the phenomenon discovered by Max Planck, according to which electromagnetic energy seemed to be emitted from radiating objects in quantities that were ultimately discrete. The energy of these emitted quantities, the so-called light-quanta, was directly proportional to the frequency of the radiation. This circumstance was perplexing because classical electromagnetic theory, based on Maxwell's equations and the laws of thermodynamics, had assumed that electromagnetic energy consisted of waves propagating in a hypothetical, all-pervasive medium called the luminiferous ether, and that the waves could contain any amount of energy no matter how small. Einstein used Planck's quantum hypothesis to describe visible electromagnetic radiation, or light. According to Einstein's heuristic viewpoint, light could be imagined to consist of discrete bundles of radiation. Einstein used this interpretation to explain the photoelectric effect, by which certain metals emit electrons when illuminated by light with a given frequency. Einstein's theory, and his subsequent elaboration of it, formed the basis for much of quantum mechanics. The second of Einstein's 1905 papers proposed what is today called the special theory of relativity. At the time Einstein knew that, according to Hendrik Antoon Lorentz's theory of electrons, the mass of an electron increased as the velocity of the electron approached the velocity of light. Einstein also knew that the electron theory, based on Maxwell's equations, carried along with it the assumption of a luminiferous ether, but that attempts to detect the physical properties of the ether had not succeeded. Einstein realized that the equations describing the motion of an electron in fact could describe the nonaccelerated motion of any particle or any suitably defined rigid body. He based his new kinematics on a reinterpretation of the classical principle of relativity, that the laws of physics had to have the same form in any frame of reference. As a second fundamental hypothesis, Einstein assumed that the speed of light remained constant in all frames of reference, as required by classical Maxwellian theory. Einstein abandoned the hypothesis of the ether, for it played no role in his kinematics or in his reinterpretation of Lorentz's theory of electrons. As a consequence of his theory Einstein recovered the phenomenon of time dilatation, wherein time, analogous to length and mass, is a function of the velocity of a frame of reference. Later in 1905, Einstein elaborated how, in a certain manner of speaking, mass and energy were equivalent. Einstein was not the first to propose all the elements that went into the special theory of relativity; his contribution lies in having unified important parts of classical mechanics and Maxwellian electrodynamics. The third of Einstein's seminal papers of 1905 concerned statistical mechanics, a field of study that had been elaborated by, among others, Ludwig Boltzmann and Josiah Willard Gibbs. Unaware of Gibbs' contributions, Einstein extended Boltzmann's work and calculated the average trajectory of a microscopic particle buffeted by random collisions with molecules in a fluid or in a gas. Einstein observed that his calculations could account for brownian motion, the apparently erratic movement of pollen in fluids, which had been noted by the British botanist Robert Brown. Einstein's paper provided convincing evidence for the physical existence of atom-sized molecules, which had already received much theoretical discussion. His results were independently discovered by the Polish physicist Marian von Smoluchowski and later elaborated by the French physicist Jean Perrin.

[此贴子已经被作者于2005-4-21 7:57:10编辑过]

从纯数学上说，Einstein并没有做出多么大的突破，但他给纯数学（当然只是数学的一部分）赋予了实在的物理内容（这里的“实在”意思是每一个物理量都是由某种观测的方法定义的，不可观测的物理量是没有物理意义的），并做出了精确度更高的预测（检验预测结论的前提是相关物理概念是可观测的）。

不管人们相不相信存在“绝对时间”，如果人们始终无法观测到绝对时间，绝对时间在物理学中就是需要舍弃的；不管人们相不相信“光速绝对不变”，如果人们始终无法观测到（真空中）光速的变化，“光速绝对不变”在物理学中就是需要保留的。

经济学在这条路上还要有许多准备工作要做，最困难的在于经济学家是在同人博弈，自然科学家是在与自然博弈。做出高精确度的预测，其前提还是每个经济学概念要在可观测的意义上定义。

“不管人们相不相信存在“绝对时间”，如果人们始终无法观测到绝对时间，绝对时间在物理学中就是需要舍弃的；不管人们相不相信“光速绝对不变”，如果人们始终无法观测到（真空中）光速的变化，“光速绝对不变”在物理学中就是需要保留的。”——我怎么觉得前后两个判断是矛盾的，后面应该是如果观察不到光速的不变，那么就要舍弃吧。

根据相对论，时间和光速都是有界限的。

罗默1676年测定了光传播的有限速率。17世纪以来人们就了解了光速的有限性。

然而后来人们发现光速是绝对不变的（广义相对论提出以前），狭义相对论中，光速是绝对的、不变的；而一维时间、三维空间分别是相对的，但四维时空（作为整体）是绝对的。