By 苏剑林 | June 06, 2015
Cover of "Quantum Mechanics and Path Integrals"
Today, I received the new edition of Feynman's classic work Quantum Mechanics and Path Integrals, sent by editor Wang Chao from Higher Education Press. I'm so excited...
Quantum Mechanics and Path Integrals is a classic masterpiece by Feynman, and indeed a classic of quantum mechanics—it is currently the only book I have read that starts from path integrals and treats them as the first principle (Anthony Zee's Quantum Field Theory in a Nutshell seems to be the only one I've read that is purely based on path integrals as a method for quantum field theory, which is also very good). Other types of quantum mechanics textbooks also touch on path integrals, but without exception, they all derive the path integral from the Hamiltonian formalism. In those cases, the path integral can only be considered a corollary. However, path integrals clearly constitute one of the three formulations of quantum mechanics; they should be presentable as a fundamental principle of quantum mechanics rather than a derivation from another form. Feynman made this attempt—explaining quantum mechanics starting from path integrals—and clearly, this attempt was very successful. At least for me, the path integral is a very easy-to-understand formulation of quantum mechanics. (This might be related to my mathematical background.)
Inside pages of "Quantum Mechanics and Path Integrals"
The publication of this new edition of Quantum Mechanics and Path Integrals can be traced back to this time last year. As a Feynman fan, I have always tried my best to collect and read Feynman's books and materials, while also following the publication of his works. Feynman's Quantum Electrodynamics had already been published earlier, and I bought a copy. I had also previously purchased Landau's Mechanics and The Classical Theory of Fields, through which I connected with the Weibo account "Landau Collection" (朗道集结号). I subsequently discovered that the blogger was Wang Chao, a natural science editor at Higher Education Press. Through various coincidences, we began discussing Quantum Mechanics and Path Integrals.
According to the original schedule, Quantum Mechanics and Path Integrals was supposed to be published last September. However, plans changed; first there were delays, and later Landau's Quantum Electrodynamics was published first, so Quantum Mechanics and Path Integrals was pushed back until now. During this period, I closely followed the publication progress—from the initial re-editing to reaching the halfway point, then to re-inspection and final publication. I kept in touch with Brother Wang Chao throughout and offered some suggestions for the republication of Quantum Mechanics and Path Integrals. Fortunately, Wang Chao appreciated my thoughts, and some of my suggestions were adopted into the book, which made me feel deeply honored. Feynman is the scientist I admire most. Although I only provided a few minor suggestions for the modification of his book, it gave me the joy of "walking with Feynman."
Furthermore, Brother Wang Chao kindly gifted me this new edition of Quantum Mechanics and Path Integrals, making me the first ordinary reader to receive the new book. While I was excited, I also felt very humbled. Looking back, it seems like I was helping Wang Chao with his editing, but in fact, I gained much more from the process, including a deeper understanding of path integrals. This encouragement has had both tangible and intangible effects. Regardless, it has been a very valuable experience and a rare "Feynman journey." My thanks go to editor Wang Chao.
In future blog posts, I will try to update some content related to path integrals, including the relationship between path integrals and stochastic differential equations, among other things. Readers are also welcome to discuss and share issues related to path integrals here on the blog. Readers interested in path integrals should carefully read Feynman's Quantum Mechanics and Path Integrals. It is the best book on path integrals, period. Because path integrals were proposed by Feynman, only a scientist of his "Peter Pan" style could interpret them so beautifully. (Of course, limited by the era, Feynman's theory has been greatly developed since then, but this does not prevent us from understanding the most fundamental physical ideas from the book.)