The Principles of Quantum Mechanics (International Series of Monographs on Physics)

The first edition of this book (including bras, kets and all that) was published when the author was 28. Ponder that a bit, you hot-shots who would scrimp on the stars you give this book. I agree with an earlier reviewer that the first chapter alone justifies buying the book. I've long kept this book on my shelf to remind myself about how beautifully expository prose can be written, and how far I have to go to equal it. BTW, in my experience it's possible to learn a lot from it about QM even as a first book on the subject, if you know some linear algebra.

When Quantum Mechanics was being developed, during the 1920s, Dirac wrote some early papers on the subject. But they were messy, abounding with all sorts of complicated integrals! Reading them, it was easy to miss the forest for the trees. That made this book, when it came out in 1930, all the more powerful. As Dirac said in his introduction, he tried to keep physics to the forefront, and began with an entirely physical chapter. Later editions were a further improvement in that respect: this one is the fourth, and I like it very much. I think it's a good way to start learning the subject. For anyone who has made it through a college course on linear algebra, the first few chapters will be very easy. You'll enjoy superposing states, and calculating amplitudes and probabilities. That said, in no way is the whole book elementary! Quite the contrary. It covers all the main topics: harmonic oscillators, the hydrogen atom, perturbation theory including the anomalous Zeeman effect, scattering problems, emission and absorption of photons, relativistic quantum mechanics, and quantum electrodynamics, including creation and annihilation operators. Still, he's always reminding us of the underlying physics, and explaining, for example, that even quantum electrodynamics is not a complete description of nature, but breaks down at high enough energies. Even though this edition of the book is from the 1950s, it's aging very well.

First, a disclosure: this was my first QM text. That's right. I picked it up as a sophomore in electrical engineering. This could easily have nipped any hope for a career in research. Rather, I was immediately taken by the undeniable elegance of the exposition. (I distinctly recall my first impression of the discussion on page 9 which is exceptionally lucid on the subject of what QM does and does not tell us about quantized fields, because this is something I had already struggled with unsuccessfully.) Moreover, Dirac reduces QM to what it really is: a few remarkable postulates about how Nature is; and a whole lot of linear algebra. Dirac was arguably a mathematician first and asserted, elsewhere, that it is more important that out theories have beauty than truth in the physical world. Anyone who can at least entertain this notion may gain much from this often overlooked classic, largely free of the pedagogically distracting baggage of wavefunctions. One reviewer has noted that the notation is archaic or cumbersome; I must kindly demur.

Dirac's masterpiece surely needs no reviews, but I dare to write one for younger people. This is it! The first chapter alone would be worth of the price. Wonderful insights, not to be found anywhere else, in almost every page. Supremely elegant, yet natural and self-contained. The whole way of writing physics was transformed by this gem of a book. Learn, at Chapter V, what led Feynman to his version of Quantum Mechanics. Schwinger started here too (at fourteen!). Unparalleled.

Dirac's book on quantum mechanics is a classic in the field, but one finds that the master cannot stoop low enough for most students. A very difficult but rewarding book.