有 @Phosphates 的珠玉在前,我也附骥补充两个。这两个也是因为验证爱因斯坦的理论(分别是布朗运动理论和引力波理论)获得了诺贝尔奖,但是 @Phosphates 的回答有多少个诺贝尔奖成就是因为证明爱因斯坦的理论而获得的?却没有将它们明确指出来。
1926年诺贝尔奖委员会将物理学奖授予Jean Baptiste Perrin,授奖原因为"for his work on the discontinuous structure of matter, and especially for his discovery of sedimentation equilibrium."[1] Perrin因为发现物质的不连续性而被授予诺贝尔物理学奖。颁奖词则说的更加明白,就是“The object of the researches of Professor Jean Perrin which have gained for him the Nobel Prize in Physics for 1926 was to put a definite end to the long struggle regarding the real existence of molecules.” 说白了,就是因为Perrin通过实验证实了分子的存在性 。现在我们都把分子的存在当做理所当然的,特别是随着电子显微镜的发明,科学家们可以直接看到分子,甚至可以直接操纵分子。这里所说的分子是广义的分子,包括原子、分子等微观粒子。但是直到二十世纪初,科学界对于分子的真实性是有着很多质疑的,其中最著名的质疑者当属马赫。尽管麦克斯韦,玻尔兹曼和吉布斯已经在分子存在的假设下建立起了经典统计力学,而且取得了不菲的成就,但是如果没法证实分子的存在性,那么他们的工作都成了空中楼阁。玻尔兹曼就是因为不堪忍受别人对他工作的质疑最后于1906年自杀身亡。而Perrin则通过一系列的实验,最终给出了分子存在的确凿证据,由此获得了诺贝尔物理学奖。那么这个跟爱因斯坦有什么关系呢?
在玻尔兹曼自杀的前一年,也就是1905年,爱因斯坦发表了五篇划时代的论文。1905年是爱因斯坦的奇迹年,这一年他提出了狭义相对论并由此给电动力学奠定了一个坚实的理论基础,提出了光量子假说并由此解释了光电效应,写出了世界上最著名的方程(很多人误以为这就是相对论的全部内容),估计了阿伏伽德罗常数和分子半径,但是这里面我最喜欢的,恐怕也是最为人忽视的,就是他关于布朗运动的工作[2]。该理论将悬浮在水中的花粉颗粒的无规则随机游走解释为花粉颗粒受到水分子的随机撞击,并且给出花粉颗粒分布函数应该满足的方程为
爱因斯坦还根据流体力学的定律确定了扩散系数 与系统的可观测量例如花粉颗粒半径,流体黏性系数,温度和阿伏伽德罗常数 之间的关系。这个方程显然是早就被傅里叶透彻研究过的扩散方程,通过求解这个方程,爱因斯坦给出了花粉颗粒随机游走的定量的结果,例如花粉颗粒在 时刻偏移初始点的平均距离为
这个量正比于 ,说明时间越久,粒子偏移原始位置的距离越远;正比于 ,说明温度越高,粒子扩散越快;反比于 ,说明单位量水里面水分子数越小(对应了单个水分子质量越大),花粉颗粒扩散越剧烈。这些结果都定量而且直观。爱因斯坦在论文中建议可以通过实验来检验这些结果是否符合他的预测。如果实验结果跟理论计算的结果一致,那么我们就可以在没有办法直接观测到分子的前提下,给出分子存在的一个直接证据。Perrin做了相关的实验,并且确认了爱因斯坦结果的正确性。关于这项工作,诺贝尔奖的颁奖词是这样写的[3]:
Microscopic particles in a liquid are never at rest. They are in perpetual movement, even under conditions of perfect external equilibrium, constant temperature, etc. The only irrefutable explanation for this phenomenon ascribes the movements of the particles to shocks produced on them by the molecules of the liquid themselves. A mathematical theory of this phenomenon has been given by Einstein. The first experimental proof of this theory was given by a German physicist, Seddig. After him, the problem was taken up by two scientists simultaneously. One of them was Perrin; the other Svedberg. I have to speak of Perrin only. His measurements on the Brownian movement showed that Einstein’s theory was in perfect agreement with reality. Through these measurements a new determination of Avogadro’s number was obtained.
由于Perrin的这个工作,再结合他其他的工作,1926年,Perrin被单独授予诺贝尔物理学奖。但是爱因斯坦没有因此再被授予一次诺贝尔奖。其实我觉得爱因斯坦可以和Perrin分享这一年的诺贝尔物理学奖。
根据诺贝尔奖的官方网站[4],The Nobel Prize in Physics 1993 was awarded jointly to Russell A. Hulse and Joseph H. Taylor Jr. "for the discovery of a new type of pulsar, a discovery that has opened up new possibilities for the study of gravitation."
这一年Hulse和Taylor因为发现了新型脉冲星而获奖。颁奖词则将他们的成果做了详细的描述。部分颁奖词如下[5]:
…
According to Albert Einstein’s general theory of relativity, gravity is caused by changes in the geometry of space and time: space-time curves near masses. Einstein presented his theory in 1915 and became a world celebrity when in 1919 the English astrophysicist Arthur Eddington announced that one of the predictions of the theory, the deflection of starlight passing near the surface of the sun – “the light is drawn towards the sun” – had been verified during solar eclipse expeditions. This deflection of light. together with a small general-relativity contribution to the perihelion motion of ercury (a slow rotation of Mercury’s elliptical orbit round the sun), was for several decades the only, partly rather uncertain, support for Einstein’s theory.
For a long time the theory of relativity was considered aesthetically very beautiful and satisfying, probably correct, but of little practical significance to physics except in applications in cosmology, the study of the origin, development and structure of the universe.
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Hulse’s and Taylor’s discovery in 1974 of the first binary pulsar, called PSR 1913 + 16 (PSR stands for pulsar, and 1913 + 16 specifies the pulsar’s position in the sky) thus brought about a revolution in the field.
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A very important observation was made when the system had been followed for some years. This followed theoretical predictions made shortly after the original discovery of the pulsar. It was found that the orbit period is declining: the two astronomical bodies are rotating faster and faster about each other in an increasingly tight orbit. The change is very small. It corresponds to a reduction of the orbit period by about 75 millionths of a second per year, but, through observation over sufficient time, it is nevertheless fully measurable. This change was presumed to occur because the system is emitting energy in the form of gravitational waves in accordance with what Einstein in 1916 predicted should happen to masses moving relatively to each other. According to the latest data, the theoretically calculated value from the relativity theory agrees to within about one half of a percent with the observed value. The first report of this effect was made by Taylor and co-workers at the end of 1978, four years after the discovery of the binary pulsar was reported.
我大致翻译一下,颁奖词说Hulse和Taylor他们发现了一个双脉冲星系统,该系统有两个中子星绕着对方运动。通过长期观察,他们发现这个双星系统的环绕周期越来越短,大约是每年变短了百万分之七十五秒。尽管这个效应很微弱,但是经过长期观察,他们确实证实了这个效应。爱因斯坦在1916年预测过,如果两个星体环绕着对方运动,那么它们应该会辐射出引力波,而引力波会将系统的能量带走。因此,随着时间的推移,双星系统的总能量越来越小,因此它们之间的距离越来越短,相应的,它们的环绕周期也会越来越短。实验观测和理论计算的结果在一定误差范围内一致,因此这就成为引力波存在的一个间接证据。由此,他们获得了诺贝尔物理学奖。
引力波存在的直接证据2015年十月份已经得到,并于2017年获得了诺贝尔物理学奖[6]。当时发现引力波所用的设备LIGO就在我当时读博士所在学校附近,而且是我们物理系负责维护的[7][8]。尽管这个跟我也没啥关系,但是还是忍不住自豪一下。