The Principles of QUANTUM MECHANICS

by Paul A.M. Dirac

Tankobon Hardcover

About the author

Paul Adrien Maurice Dirac was an English theoretical physicist who made fundamental contributions to the early development of both quantum mechanics and quantum electrodynamics. He was the Lucasian Professor of Mathematics at the University of Cambridge, a member of the Center for Theoretical Studies, University of Miami, and spent the last decade of his life at Florida State University.

Among other discoveries, he formulated the Dirac equation which describes the behaviour of fermions and predicted the existence of antimatter. Dirac shared the 1933 Nobel Prize in Physics with Erwin Schrödinger "for the discovery of new productive forms of atomic theory". He also made significant contributions to the reconciliation of general relativity with quantum mechanics.

Reviews

[David Skigin · Rating 5 out of 5]

Why bother reading such an outdated book on the subject?

Because this is a masterpiece.

I have heard a lot about Dirac’s penchant for crystalline beauty and the Dirac equation speaks for itself. But it is one thing to hear about this and another thing to see it live.

Dirac is truly the mathematical physicist - perhaps it's most accurate to call him a mathematician in physicists clothes. Why?

Because the physical intuition of Dirac is not any weaker than Feynman's, but unlike Feynman, Dirac values beauty above truth. The perfect beauty of mathematics. His taciturn nature is presented in each word of the book - careful, weighed, deliberate. Not a single unnecessary equation. Not a single paragraph with multiple lines of incomprehensible derivations which mathematicians so often hide behind when they’re scared to admit that they have no idea why this logic should hold on any deeper level. But Dirac takes his time to explain, and it is very much worth listening to.

In physics books we usually get some jumble of bullshit math with ‘intuition’ (Feynman was excused for this only because of his brilliance). In math we justify physical theories by appealing to theorems (eg the classic beginner’s intro to QM: well, recall the spectral theorem, wouldn’t it be nice if we can use it? Hm, ok, then let’s pretend all physically observable things magically fit this theorem. Surprise! Everything works. So do you understand the truth now?). This approach is incorrect because math cannot explain the universe - math cannot explain itself! However we can use very careful arguments to justify why a particular piece of math is likely to be useful. And this is what Dirac does masterfully. He doesn’t get caught in the Von Neumann-like rigor. As important as it is, understanding quantum mechanics through rings doesn’t give it much physical interpretation (in my mind). On the other hand he far surpasses Feynman, who, although a terrific explainer and wonderful alternative source for understanding the subject deeply, was never really able to build deep mathematical frameworks. Yes, the path integral is very deep, but it is ultimately purely visual, physical. Mathematically it is meaningless. Obviously Feynman didn’t care about that, but that goes to show how different the great physicists were.

Dirac straddles the balance perfectly and this is uniquely beautiful. I’ve never really liked algebra, but in his hands the subject comes alive and feels clear as water.

I’m really raving about this book because of this key quality - its unbelievable clarity. I have never read anything like it before.

This book is a perfect example of diracs mathematical style, and I really found it delightful. It’s very inspiring to see a master come to life.

It goes without saying that there are many better sources for learning the subject now. But there does not exist a Dirac today - at least not in the world of physics. Perhaps only witten comes close. So, while we can, I think we should read the works of great masters.