by Laurie M Brown (ed.), World Scientific. Hardback ISBN 9812563660, £17 ($28). Paperback ISBN 9812563806, £9 ($14).
The title pretty much sums up this interesting short book, the latest Feynman work to be published since his death in 1988. It reproduces, in modern typeset, Feynman’s PhD thesis entitled “The Principle of Least Action in Quantum Mechanics”. In it Feynman outlined his brilliant reformulation of quantum mechanics in terms of the path integrals that now bear his name, together with two supporting papers and a preface.
Historians and physicists alike will enjoy this easy-to-read little book (119 pages plus the preface). Supplementing the thesis itself, which is just 69 pages long (if only all theses said so much in so little space), are reprints of Feynman’s “Space-Time Approach to Non-Relativistic Quantum Mechanics”, which was published in Reviews of Modern Physics in 1948 and Paul Dirac’s “The Lagrangian in Quantum Mechanics”. Dirac’s paper is a little harder to find since it’s from the Physikalische Zeitschrift der Sowjetunion and dates back to 1933. These provide excellent supporting material and in many ways bracket the thesis. Dirac’s paper is not as widely read as it should be, and is of great importance as it provided much of the initial impetus for Feynman’s work, making quite explicit the role of exp(iLdt/ħ) as a transition amplitude between states separated by an infinitesimal time dt, and its connection to the classical principle of least action. Feynman’s article is certainly well known and is perhaps rather more formal than the thesis itself, and therein lies much of charm of this book.
Brown also provides a 16 page introduction that essentially walks the reader through reading the thesis, summarizing the content of each section and adding many interesting historical anecdotes and quotations.
The thesis itself is a masterpiece of clear exposition. While there is little in the thesis that is likely to surprise most physicists, it is written in Feynman’s uniquely chatty style, and reminiscent of the famous Feynman lectures. It is a delight to read and is likely to offer an insight, even to non-physicists, into both physics and the workings of Feynman’s mind. I would not hesitate to recommend the book to anyone – working physicists, historians, philosophers and even “curious fellows” who would like to “peek over the shoulder” of one of the 20th century’s great physicists at work.
