Six Not-So-Easy Pieces: Lectures on Symmetry, Relativity and Space-Time, Vol. 6 Book

Let me start with a one-sentence summary: this is a thoroughly enjoyable little book explaining, in a beautifully intuitive and holistic way, the main core features of Einstein's relativity, without getting bogged down into too much mathematical detail.

The target audience of this book is the interested layman with high school mathematics knowledge and a passion for physics: it falls into the particularly tricky (from a pedagogical standpoint) grey territory between popular science and real science. And Feynman manages, almost in a magical way, to strike a reasonable compromise, within so little space, between accuracy and level of detail on one side, and accessibility on the other side.

Now, I have read more comprehensive works on relativity, with much more emphasis on its mathematical foundational underpinnings; and I can tell you that, if you are looking for something significantly beyond the introductory level, you will not learn much from this book. However, having said that, I would still recommend this book even to a more intermediate level reader, as the way how Feynman manages to get to the core of things with lucid rigor, and simplicity, and how he manages to holistically connect all the different aspects of the physics he is explaining, is something magic and a great pleasure to experience.

Feynman is a wonderful teacher, who can get right to the core of topic with amazing clarity, and he has the gift to make even the potentially most complex concepts seem like the most obvious and commonsensical thing. Because of this, this book is highly recommended to whoever has a minimum knowledge of maths and wants to start looking at relativity from a more detailed perspective than what offered by many generic popular science books.

To make the book perfect, I would have loved to see at least some treatment of the mathematical underpinning of relativity, which would have probably made, in my opinion, some critical parts of the book more clear and rigorous: for example, there is no mention of the 4-dimensional Minkowski vector space, and its tensor (metric) whose expression is represented by equation 3.9 of the book, (which is presented in the book as a "given"). And I would have loved at least a brief introduction to the concept of geodesics and of the stress-energy tensor (and of tensors in general), which would have allowed at least a qualitative treatment of Einstein's Field Equations.
And, to be honest, I do not see much value in the first two chapters of the book, which are not much more than a very cursory introduction to mathematical objects that anybody should have learned in high school anyway (apart maybe from the concept of "symmetry")- maybe this space could have been used more efficiently by getting into some more detail in other areas.

But I realize that there is a very delicate balance between mathematical complexity and accessibility and clarity, so it must be said that it would be extremely difficult to improve on Feynman's pedagogical approach in his book.

In summary, this is a jewel of a little book that I thoroughly enjoyed and which deserves a full 5-star rating. Highly recommended. I loved it.