徐一鸿：物理学的十大基石理念 | 新书推荐|宇宙|徐一鸿|数学|爱因斯坦|物理学家

Top Ten Ideas of Physics: Foundations for Understanding the Universe

徐一鸿著

普林斯顿大学出版社

读者福利

想获得该书的读者可以在后台留言，写下与本书试读内容有关的体会，留言点赞数排名前2位的读者，将各获得限量且旗舰店独售的作者签印版书一本。截止时间是12月8日早8点，10点会公布2位获奖者名单。期待您的参与！

。聚合

Editor's Note

在追逐“最热最新”科研热点的时代，著名物理学家徐一鸿（Anthony Zee）选择回到起点，书写一部聚焦于学科基础思想的作品。

在新作

Top Ten Ideas of Physics: Foundations for Understanding the Universe

中，徐教授以严谨的科学思维、小说式的叙事节奏和独特的幽默感，描绘了支撑理论物理大厦的十大最重要的支柱理念，和其背后上下求索的学者群像。

徐教授自叙，他在近三、四十年来反复思索这份“Top10理念清单”，尽管排序有变，其中的核心内容却历经时间考验，始终稳固。这些思想不仅关乎物理学本身，对不同背景的读者同样具有启发价值。正如作者所言：这本书适合所有真正意义上的“智识读者”——无论年长年少，只要你渴望一睹宇宙真理的本质与真容。

作者简介

徐一鸿

Anthony Zee

徐一鸿教授是著名美籍华裔物理学家、作家，籍贯上海，出生于昆明，后移民到巴西。在普林斯顿大学取得学士学位，在哈佛大学取得博士学位。现任美国加州大学圣塔芭芭拉分校物理系教授。

恒久而冷清

我在此务请读者首先阅读这篇序言，以了解本书的宗旨。若读者是来寻找物理学“最热最新”的课题，还请上网搜索爆款热帖，本书恐怕会令你失望。

我构思这本书已至少三十年，也许有四十年了，早在我写下第一本学术专著《自然力的统一》（译者注：原著为 Unity of Forces in the Universe，无中译本，为行文通畅，特添加译名）以及第一本通俗科普《可畏的对称》（Fearful Symmetry）之后不久。1（译者注：如无特别说明，本文所有注释均为作者自注）在写作这些书时，我会思索“统一”（unity）和“对称”（symmetry）如何成为了理论物理学的两大基石理念。此后多年间，我陆续写下了自己心目中“理论物理十大理念”的清单。这本书的部分灵感可说源于上世纪八十年代美国深夜电视节目中主持人宣布“十大榜单”的传统，尽管那些榜单常常荒诞不经（译者注：例如“最不受猫欢迎的十大猫粮口味”、“十大迹象表明你可能就是班里最傻的学生”）。于是我自己也会戏谑性地列出榜单，比如“凝聚态物理中最难看的十大术语”，挂在办公室门口以娱乐同事。

直到近年，当我向普林斯顿大学出版社提交本书计划，并着手动笔时，我翻出多年来零星记录下的五六份理论物理的“十大理念”清单。颇为有趣也令我欣喜的是，纵然细节略有变动，排序有所调整，但核心内容几乎一致。这让我深感安慰：经历了理论物理研究的潮流变迁，这些念兹在兹的思想到底是有恒久价值，经得起岁月淘洗。

简而言之，这本书聚焦于理论物理的智识根基，而非学界风潮。即便是学识渊博、对物理颇有研究兴趣的读者，也常被一类“哇哦”、耸人听闻的新发现所吸引——可这些发现对物理学家而言，有的不过乏味，有的则所幸能很快被遗忘。显然，这背后不乏流行媒体的推波助澜——炒作那些只有极少数物理学家相信或关心的狂想更有经济效益，翻翻目录读者应能发现，本书不谈“最热最新”，只论“恒久而冷清”。

物理学的基石性理念

本书每一章会探讨一个基本思想，简要阐述其精义，下面我将用一两句话分别对书中十章进行小结：

1. 世界是可以被理解的。

人类所怀的最不可思议的信念，正是宇宙是可以被理解的。而大自然也一次又一次对理论物理学家投以她的仁慈。

2. 物理定律无所不在、恒古不变。

若物理的存在并非普遍而永恒，我们就无法理解宇宙，亦无法追溯其“婴儿时期”。

3. 世界的本质是量子的。

我们所处日常世界之下，竟潜藏着一个神秘的量子世界——在这里，常识和传统意义上的“现实”分崩离析——堪称是人类最震撼的发现。

4. 量子场，恒久不息——爱因斯坦的至爱。

宇宙是一场量子场的交织之舞。这些永恒之场激发孕育出我们熟知的粒子：有些稍纵即逝，有些看似不朽——但也许并非如此。

5. 可畏的对称：宇宙处处是对称。

为何越深入本质，物理越对称、越简洁、越“优雅”？这是个真正深奥的谜题。

6. 爱因斯坦：用相对论终结的“相对性”，编排时空之舞。

物理定律不应物理学家的视角而变——真理并不“相对”，这与某些哲学家向你宣扬的恰恰相反。

7. 自然力的统一。

物理曾由繁杂定律构成，而20世纪几乎不可思议的成就，是将其简化为四种基本相互作用，其中三种已统一为“大一统理论”，惟独引力仍拒绝入列共舞。

8. 造物主说的是数学的语言。

维格纳（Wigner）曾质疑数学之于物理的高效是否过于“不合理”。我和多数（但非全部）理论物理学家都对此深感困惑。

9. 熵与热涨落：一切关乎“分享”。

从两个粒子的交互中无从知晓亿万粒子的集体行动——熵与时间之箭由此而生。这正是“多者异也“的体现——整体多于部分之和。

10. 物理关乎“作用量”。

从费马（Fermat）的“最短时间原理”开始，我们离开了牛顿的方程体系，转而以“作用量”构建自然的演化。这是物理最深层的语言。

以上就是十章的内容，每章探讨一个重大理念。我曾想半开玩笑地加上与破产相关的第十一章，题为：《物理危机：道德破产的警世故事》2，但最终还是删去了——不过，谁知道呢，也许将来它又会在另一本新书中冒出来。

“十大”中“十”这个数字，当然只是我们这个地球上进化的巧合。未来也许会增减。

不只是代入计算，也不是细枝末梢

物理不只是“代入公式，算出结果”。然而，中学乃至大学、研究生阶段的“题海战术”，让学生难免得出这种印象。追求“结果”确是部分物理学家的动力，但绝非全部。迪克·费曼（译者注：即著名物理学家理查德·费曼的昵称，原文为 Dick Feynman）或许以其独特的文采说得最为精辟：“物理就像性爱：当然，它可能会产生某些实在的结果，但这可不是我们做它的原因。”追逐结果或可赢得名声与财富，但许多人，包括我自己，更多的是被理解宇宙运作之奥秘的渴望所驱使。我和一些朋友沉醉于理念之间的逻辑关联，惊叹于这些理念竟让我们人类如此渺小的存在，得以理解从微观到宏观、几乎匪夷所思的复杂宇宙！“匪夷所思！”这句话似乎就是为物理学量身定制的。

爱因斯坦说：“我想知道上帝如何创造这个世界。我不关心这个或那个现象。我想知道的是祂的思想，其余皆为细枝末梢。”说得多好！但恐怕只有他这种地位，才敢一口否定物理学中的大部分知识为细枝末节。我当年在《可畏的对称》（Fearful Symmetry）中引用这句话，颇为惊艳，却也收到些“决斗状”般的邮件。有人一辈子钻研“这个”，因此愤怒非常；也有人是“那个”方面的全球权威，却从未听说“这个”。爱因斯坦已故多年，无从为这份“狂妄”买单。若他尚在，或许会调皮地建议我让“这个博士”与“那个教授”直接联系。

放轻松。其实所有物理学家都在研究“这个或那个现象”，包括爱因斯坦自己。除了探讨时空与量子，他还研究过湿沙的粘滞性3以及冰箱的热力学原理——读来妙趣横生。事实上，几乎所有物理学家4一生研究的都不过是爱因斯坦眼中的“这个或那个”。

而确然，几乎所有重大突破也都源于对“这个或那个”的研究。比如，年轻的马克思·普朗克（Max Planck）开创量子革命，并非因为哲思宇宙，而是缘于钻研加热腔体中的电磁波；又如，暗能量的发现，建立于对超新星爆炸机制的深入理解。我常说，物理有如大马戏团，万象并存：驯兽师、空中飞人到杂技小丑5，皆有其位。物理学的前沿在诸多领域推进，因此关于空间和时间本质的根本性洞见也必然——与许多物理学爱好者的想象大相径庭——千载难逢。是的，我理解“多者异也”的概念，程度或许比你认为的还要深。

尽管如此，你手中的这本书所谈的正是物理学的基础理念，不特别关注爱因斯坦口中的“这个或那个”，除非作为说明需要。所以，在读者想向我发送愤怒邮件前，请先记住这一点。固然我知道“细节决定成败”（devil is in the weeds），学会钻研细节很重要，但本书宗旨是提供全面概览。

免责声明

首先说明几点：这既不是一般的通俗读物，也不是教材。哪怕只讲其中一个思想，展开来也够写一本书。比如第四章所讲的量子场论，我就写过一本科普书、一本专业教材和一本半科普半专业读物。我常需在简洁与“不让读者完全懵圈”之间寻找平衡。因此许多必要主题被省略或一笔带过6。可想而知有些学界的同行会因此不满，但我会鼓足勇气直面他们的顾虑和怒火。

我的目标是传达这些思想的意义，并略述其来龙去脉。有时我会集中讲某一专题。例如，要讲量子物理，面面俱到绝无可能，于是我选了贝尔不等式（Bell’s inequality）来切入，也因为写书时恰逢三位验证该理论的实验物理学家获得诺贝尔奖。而为解释贝尔不等式，我必须介绍电子自旋——这或许是最诡异的物理概念之一，但我们当今的科技社会正高度依赖它。

再如，熵与信息两个概念在大众认知中常被误解，我便几近教科书式地详加阐释。

我提过自己出版了多本物理科普读物和教科书，因此本书内难免会重复旧作。为什么要重复？费曼早年自问此事时给出了我十分认同的回答：“因为人类的每天里都有新的一代诞生。因为人类的历史上总有伟大理念诞生，而这些理念若不刻意、清晰地传给新的一代，就无法长存。” 7

无疑，不少专家会对书中的泛泛论述颇有微词。但若我列举所有保留条件和详细说明，要写的恐怕就不是一本书，而是一整座图书馆了。普通读者肯定会不堪重负。

我同样确定，若请别的物理学家列出物理学“十大理念”，他们的清单必然和我的不同。对此，我只能说：这份清单源于我个人在理论物理上的探索旅程；而这种书必然、且最好是：理直气壮地带有鲜明的个人观点。若你极力反对，我诚挚地邀请你写一本自己的书。

本书并非线性叙述，章节安排基于我自己的逻辑。就像前文所说，这些理念的排序亦经调整。若读者看完某章节未尽理解，请不妨继续读下去。因为你并不需要这章的前置知识才能理解后一章。然而，各章的基础理念不可避免地交织在一起。例如，“规律越深入越显对称”（第五章）与“看似不同力的最终统一”（第七章）必然相关。熟悉我其他作品的读者知道，我偏爱大量使用尾注——有些或可发人深思，有些或只为引人发噱。首次阅读时也不妨忽略尾注，稍后再回看。这纯属个人喜好问题。

最后声明，我并非历史学家，书中叙事当然不保证历史严谨性。

此书为谁而作

我在自己的数本通俗科普书的前言中都包含了这一节：“本书为谁而写？”毫无疑问，如果有中学生、大学生因本书而立志投身物理，我将无比欣慰。而在受众的另一端，我知道还有许多在职或退休的职场人士，热衷阅读通俗物理书。此书也献给他们，致敬他们追求宇宙真理的勇气与热情。

当然，读者若能略知爱因斯坦的时空观及量子物理的基础，那自是更佳；毕竟这些革命性的思想已有百年历史，本书只能粗略点到。

总之，这本书献给所有真正意义上的“智识读者”：无论年长年少，只要你渴望一识物理的本质与真容。

*强烈建议读者，特别是年轻人，细读部分尾注，那里可能有更多数学讨论，以及一些职业建议——如果你决定进入物理学领域的话。例见第三章中海森堡（Heisenberg）评论克罗宁（Kronig）的尾注。

注释：

1. 该书最初由麦克米伦出版，后由普林斯顿大学出版社在Princeton Science Library系列中重新出版。我自豪地说，它已被翻译成德语、日语、韩语、法语、西班牙语、土耳其语和中文（包括繁体和简体）。多年来，尤其是在旅行讲学途中，我非常高兴能巧遇许多在其早期物理学生涯中读过此书的物理学家们。

2. 供非美国地区读者一哂，在美国，“破产法第十一章”含义通常等同于破产。

3. 很久以前，一家石油勘探公司甚至支付酬劳让我阅读爱因斯坦这项鲜为人知的贡献。多谢了，乔！

4. 那些不这么做的，至少在我看来，应归为数学家或哲学家。

5. 可悲的是，在我们当下的堕落时代，小丑似乎常常主宰了舞台。

6. 这部分内容是为了预防亚马逊网站上那些常把教科书和科普书混为一谈的读者。

7. R. P. 费曼（R. P. Feynman）著，《这个不科学的年代》(The Meaning of It All ），1963年出版。

章节试读

Chapter 1

THE PHYSICAL WORLD IS COMPREHENSIBLE

The most incomprehensible thing about the world is that it is comprehensible.¹

Why is the world comprehensible?

Of Einstein’s many insightful sayings, this is my favorite. Indeed, this apparent miracle, that the world is comprehensible, is what motivates physicists. In a lawless universe behaving with neither rhyme nor reason, physics would be impossible.

I should hasten to say what hardly needs to be said, but with silly nit-pickers lurking about I have to say it. What Einstein meant by the world is the physical world, the world studied by physicists. Plenty of questions are beyond the comprehension and grasp of physics, of course. What is the meaning of life? Why are we here at all? Why does the universe exist? Is there another level of existence we know nothing about? You could make up your own list.

We have made stupendous progress since our days in the caves when nearly everything was incomprehensible. But even within almost living memory, the progress has been so vast that it almost beggars imagination. Two hundred years ago, physicists did not know what light was. One hundred and fifty years ago, physicists had no inkling that space-time was curved. One hundred years ago, physicists struggled to grasp the laws governing the realm of the quantum underlying our world. It is true that progress in theoretical physics has slowed nowadays. Nevertheless, progress is being made.

Why should Nature be comprehensible by the mind of these creatures that evolved recently on a dust mite of a planet orbiting an insignificant star drifting in a far-from-prestigious neighborhood of a mediocre average-looking galaxy? Why should the laws of physics be simple and beautiful? We could have found ourselves living in an intrinsically ugly universe, a chaotic world in no way graspable through thinking, as Einstein, he again, put it.

A smashingly revolutionary idea

Some readers might be surprised by my choice of the idea that tops my list of top ideas. The world is comprehensible! We tend to take for granted that physics is possible, that the physical world is comprehensible. But as far as I know, no ancient civilization, East or West, harbored the idea that the world was comprehensible, except, arguably, for a handful of Greeks. Even in the West, this enormous and profound idea surfaced only in the last four or five centuries, and the first inkling that the world could be understood without invoking the divine was met with ferocious resistance. It was a slow, gradual awakening threatened with excommunication, torture, and death.

The sun god pulling his chariot daily across the sky from east to west, and then somehow teleporting himself and his entire conveyance back to the east at night—this was our “understanding” not all that long ago. Yet now, for the first time in human history, a reasonably advanced student of physics could open a book on astrophysics and learn how to calculate the temperature and pressure inside a star, a particularly simple homework exercise for a garden-variety star like the sun, neither a red giant nor a white dwarf, without too many peculiar features.

Why versus how

I cannot tell you why the world is comprehensible. It is important to understand that physics does not answer the why questions. Physicists strive to steadily turn the whys into hows. We cannot tell you why the apple falls, but we can tell you how it falls, and reduce a variety of phenomena into an ever smaller set of underlying phenomena. Along the way, many whys were replaced by fewer whys, and whys by hows. Indeed, a crucial step in making physics possible is to separate the how questions from the why questions.

We can tell you why the sky is blue. It has to do with how light scatters off the air molecules, and after a heroic struggle we have reduced that to how two quantum particles, the photon and the electron, interact with each other. We can tell you that every massive object in the universe attracts every other massive object. We can tell you a lot about this force called gravity, and how it is equivalent to curved spacetime. But we cannot tell you why our universe contains such a force. Of course, were this force absent, then our universe would look quite different from the one we know.

The preceding sentence gives a capsule summary of the anthropic principle. It has been abused to answer every why question with the existence of humans. You know the jingle; various physical constants must have the value they have, since otherwise humans would not exist. A fascinating subject perhaps, but I will stay away from it in this book. Only the tried and true foundational ideas, as I said.

We do not know why there are four fundamental interactions in the universe, instead of two or six, but physics can tell us how three of these four interactions could be unified into a grand unified theory, as we will see in chapter 7.

That the physical world is comprehensible is miraculous

Physics as a subject wouldn’t exist were the world not comprehensible.

Yet, if you think about it, the very comprehensibility of the world is miraculous. Sad that we have grown blasé in this enlightened age and take so much for granted. But flash yourself back a few millennia when no one even presumed to imagine the possibility of comprehending the world, let alone to attempt the task of actually comprehending the world.

You need only look at ancient cultures around the world. In school, we learned about the realm of rationality that is ancient Greece. Even in Greek myths, we could discern the urge to understand. But the notion that we could comprehend the physical world was far from universal. For example, the philosophers of ancient China envisaged man in harmony with Nature and emphasized understanding human behavior rather than the physical world. The West emphasized the control of Nature. Perhaps controlling is but one small step from understanding. To some extent, the entire Greco-Roman Judeo-Christian conception of Nature to be conquered and ravaged was missing in ancient China.²

Noticing regularity alone is not enough. Certainly, Asians recorded regularity with as much diligence as the Greeks. But the notion that there might be laws governing these regularities was mostly absent. That the world was comprehensible was far from obvious to every thinker in every civilization.

Nor should we assume that the development of physics as it happened on our planet is typical. For example, a civilization could develop in a binary star system, on one of the nineteen planets orbiting the two stars, which in turn waltz around each other in a highly eccentric ellipse. The regularity of the heavens, as well as the usual law of gravitation, might remain hidden from this particular civilization for a long time, perhaps longer than the natural lifetime of the civilization.

Or imagine us in a civilization on a planet much like Terra, except that it is completely covered by a single deep ocean. Electricity might be known as an epiphenomenon associated with some peculiar fish regarded as far inferior to Pisces sapiens, which is what we call ourselves scientifically. Magnetism is however totally unknown and light is merely an exotic phenomenon near the edge of the habitable world. Physicists would have developed an extensive understanding of water waves.³ Some of our dead sink to a nether region where none of us are able to roam due to the crushing pressure. Others among our dead would float upward, and from observing these lightweight dead, politicians, celebrities, and such, some bright youngster eventually proposed the existence of a force named buoyancy. Later, a fishy Einstein would have the brilliant insight that buoyancy is due to a more fundamental force called gravity pulling the water around these lightweight objects down.⁴

We alone could understand the universe?

I do not doubt for a second what my computer science friends tell me, that with massive data analysis, artificial intelligence would in the foreseeable future allow us to communicate with animals. At that point, perhaps we could ask them what they understand of the physical world. Yet I also have no doubt that no other lifeforms on earth can understand nonabelian gauge theories (which we will encounter in chapter 7), let alone invent them. But then why is the physical world comprehensible to humans (at least thus far)?

Einstein was absolutely right that it is a profound mystery. It could well be that this particular primate species, after eons of evolution, is no more capable of fully understanding the physical world than one of the gophers in my backyard. (The emphasis is on “fully”!) It is certainly possible, of course, that we will eventually hit a brick wall. The pessimists in the physics community would say that we have already hit that proverbial wall.

I want to be optimistic because I need that optimism to buoy me professionally. Einstein expressed his profound wonderment more than a hundred years ago. He and his contemporaries could also feel, when confronted with the mysteries of the quantum world, that the striking progress in understanding of the physical world gained in the 19th century may come to a grinding halt. But they didn’t, and pressed on. And progress has been made for a century and more. Of course, in deciphering the quantum world, that generation of physicists was pushed along by an almost excessive wealth of experiments, which are now sorely lacking, no matter what the cheerleading boosters try to convince us otherwise. Needless to say, I am talking about landmark experiments that reveal some deep truths, not routine experiments measuring the decay rate of an absurdly named particle or the conductivity, super or not, of some newly minted alloy.

I am among those who believe that the universe, with its zillions of galaxies each with zillions of stars, is teeming with intelligent life. I have even thought seriously about communicating with extraterrestrial intelligence.⁵ When we finally come into contact with extraterrestrial intelligent beings, what can we talk about? Not terrestrial biology, which may or may not be similar to their biology⁶. And definitely not Tang dynasty poetry, nor Shakespearean plays, which so many scholars spent, are spending, and will spend entire lifetimes on. But surely, if the extraterrestrials have mastered enough technology to communicate with us, they could discuss the classification of Lie algebras and gauge theories with us, perhaps teaching us a thing or two. Whatever, but I could hardly doubt that they have also come to realize that the universe is comprehensible.

Notes

1 Albert Einstein “Physics and Reality,” Franklin Institute Journal (March 1936).

2 Sadly, China is coming late to this highly useful idea, and now a common attitude goes “You ravaged the world, now it is our turn, so don’t act holier than thou and preach to us.”

3 But not the surface water waves we commonly observe and teach to some undergraduates. See FbN, chapters VIII.1 and 2, in particular page 282.

4 An early example of unification that I will talk about in chapter 7.

5 See my SETI talk and the published papers mentioned therein. https://www.youtube.com/watch?v=MHuXlJzqKqs.

6 See, for example, A. Kershenbaum, The Zoologist’s Guide to the Galaxy: What Animals on

Earth Reveal about Aliens–and Ourselves, and A. Weir, Project Hail Mary.

PUP 内容速递

本书章节目录

Prologue

The physical world is comprehensible
The laws of physics are the same here, there, and everywhere, the same yesterday, today, and tomorrow
The world is quantum
Quantum fields forever: Einstein’s total love
Fearful symmetry: a universe full of symmetries
Einstein, the exterminator of relativity and the choreographer of spacetime
Unity of forces in the universe
The Creator speaks the language of mathematics
Entropy and thermal agitation: all about sharing
Physics is where the action is