This is a little jem of a book. The arguably two greatest living physicists of the 80s, Feynman and Weinberg, both Nobel Laureates, pay tribute to their master, the man who said that mathematical beauty is what physicists should look for in physical laws, the one and only, Paul Dirac. These memorial lectures are the best one could wish for, together with Abdus Salam's tribute a couple of years before. I derived pure delight in reading Feynman's lecture, which explains the existence of antiparticles predicted by Dirac in his equation of the electron. Weinberg however surprisingly outstands Feynman in giving a lecture on symmetry laws, etc. These lectures would have surely thrilled Dirac, without doubt. For all physicists who like to have those little precious books on their shelves, it's a very good and enjoyable buy.

As usual, the best physics books are short and to the point, as is this one. The two Dirac lectures may serve as a perfectly good mini physics course all by themselves. I always enjoy a Feynman lecture, and this is no exception. He cuts to the chase without sacrificing the plot. But, I must say, in this case the Wienberg lecture is the better of the two. Weinberg's style has a particular grace & beauty about it that gently exposes the aesthetic meaning of the search for a picture of nature.

Feynman yet again gives great insight into the laws of physics, this time exploring the reasons for existence of anti-particles, starting from the dirac equation etc.. Plus some really outstanding photographs, that fella Weinberg will be chuffed to have his name mentioned on the book cover!

"Directions in Physics" constist of edited transcripts of 5 lectures given by Professor Dirac when he was visiting Australia and New Zealand in 1975.

The five lectures are about:

1. The development of quantum mechanics.

2. Quantum electrodynamics.

3. Magnetic monopoles.

4. A positive energy, relativistic wave equation.

5. Cosmology and the gravitational constant.

In my opinion, Dirac is one of the greatest physicist ever. This book gives a unique insight his way of doing science, in which mathematical beauty plays an important role.

Lecture #1 is also very nice because Dirac has experienced much of the development of quantum mechanics himself, making him an authority on the area.

This is a very important book. In it Dirac reviews his modified Hamiltonian formalism, including constraints, so that systems which do not have a proper hamiltonian can be canonically quantized anyway. For Dirac sustains that one only knows how to quantize a system when it has a Hamiltonian. So, if the system doesn't have one, what is a guy to do? He teaches how to generalize the canonical formalism and construct an effective Hamiltonian which is sufficient to do the job. These ideas gave origin to a flow of papers dealing with the matter, and to several good books. Still, Dirac's original lectures are the best introduction, in my opinion. Not to be confused with the famous "Principles of Quantum Mechanics" , the great expository classic. This book I am reviewing is more of a research document.

First I've to say that I've read this book after learning GR on Ray d'Inverno and Misner-Thorne-Wheeler. This means that one shoud gain a little confidence with tensor calculus before using this text (otherwise one could not be able to appreciate the great physical insight of this book). One more time Dirac taught me how to study Physics: which are the right questions one has to look for an answer, without missing too much time on special cases of an idea that do not add anything fundamental to the latter. This is a book I'd recommend to everyone who already knows the subject or to anyone who feels he could know more about it: and all of that in less than 70 pages !!!

In only 69 pages, Dirac lucidly develops the major results of general relativity. Owing to its size, the book has no "introduction", meaning that, although background material is given, it consists only of those equations which are required in the latter portions of the text. If the reader has had no previous exposure to tensor analysis, this background material will not be sufficient.

Dirac's presentation is so organized and concise that the subject matter appears as a trivial application of tensor analysis. The reviewer was elated to understand the subject in such mathematically tenable terms. Of course, as with Dirac's other works, the theory is developed in the most efficient manner possible. It is a perfect *presentation* of the theory, but the reader does not *participate* in its motivation or development.

To those who seek a more complete (and leisurely) presentation of general relativity, Levi-Civita's Absolute Differential Calculus and Eddington's Mathematical Theory of Relativity are among the best classical texts.

This is a great little book for the well prepared reader. An introductory course (or two) would be very helpful before attempting this book. Once one has the basics, then this book will enhance one's understanding by emphasising through economy of word and subject matter what the theory is all about.

After missing the first collection of essays on this brilliant recluse published soon after his death, I picked up the present version as soon as I was able. It did not disappoint.

The book is a collection of four lectures given in the subject's honor in 1995 on the tenth anniversary of his death. The final lecture and the latter part of the third are highly mathematical and technical and clearly intended for a professional audience.

But for me, the first lecture by Abraham Pais is worth the purchase price alone. Pais was not only a contemporary physicist, but also a close friend and as close to a confidant as was possible with such a reticent man.

Through Pais' eyes, we see a mathematician turned physicist who was very different from the man to whom Dirac is most frequently compared, Albert Einstein. Einstein was a physicist first, mathematician second. Dirac was exactly the opposite. Einstein became a social and political critic, Dirac never strayed far from his study. The two were similar in that both viewed mathematical beauty as primary and both hated the modern remake of quantum mechanics (after the initial theory) for very similar reasons. This last point was interesting as Dirac was the first one to combine all his contemporaries' work on this improved quantum physics into a formal mathematical structure. His resulting equation, called naturally the Dirac equation, is classic Dirac, short and sweet. It combined Einsteinian relativity with the new quantum theory and Dirac considered the result to govern most of physics and all of chemistry. Stephen Hawking, the renowned theoretical physicist, says in his introductory memorial address to the book, "If Dirac had patented the equation ... he would have become one of the richest men in the world. Every television set or computer would have paid him royalties." For this work, Dirac shared the 1933 Nobel Prize with German physicist Erwin Schroedinger. One unexpected consequence of this work was a mathematical conclusion that defined a "negative energy" matter (aka antimatter) solution. Simply put, he had discovered a universe noone had imagined. To this day, we see the effects of this discovery from medical necessities (PET scan imaging-Positron Emission Tomography) to science fiction (Star Trek).

The quotations and anecdotes Pais chooses are well placed and often very funny. They are also supported by the images of Dirac portrayed in the sketch on the cover and in the few photographs scattered through the first two lectures. They reveal his character well. He saw mathematical and physical realities so clearly that he simply could not understand why others did not see them as well. The photo of him "listening" to future Nobel Laureate Richard Feynman in Maurice Jacob's section is one of the most amusing of the collection.

In the second lecture, Jacob shows the path of discovery and effect on latter day experimental physics of antimatter. He goes too long in spots but is generally fine.

We were ourselves participating in the inauguration of the Paul Dirac memorial in Westminster Abbey. Especially the speeches of Stephan Hawking and Abraham Pais were very touching as they did not only touch Dirac's work but also his personality and life. He was a very complex person and a great physicist. This book reflects that more than others about him.