Foreword: why this book on Relativity?

It is often said E = mc² is the most famous equation in physics, and also the least understood.

This book aims to provide the reader a deep understanding of Special Relativity without requiring an advanced mathematical background. The required level is below university: English A-Level Maths, or French BAC S will suffice. The sections on the relativity of time and distance require even less sophisticated mathematics.

Moreover, this book includes an introduction to General Relativity. It indeed appears that several fundamental results of General Relativity can also be demonstrated without requiring complex mathematics. Besides, the important recent discovery of gravitational waves are presented.

This mathematical concision (compared to many books on the subject) was achieved by following a more physical approach, alongside an in-depth axiomatic and semantic analysis, which will satisfy those who want to take nothing for granted. Most other books which provide rigorous demonstrations use more complex mathematical means, such as tensors and Lagrangians, but Einstein said they were “superﬂuous manifestations of erudition” for Special Relativity. (However, standard formulations of General Relativity rely on them heavily).

In this book, all results are the subject of rigorous demonstrations, starting with a minimal set of postulates. Substantial explanations and numerous schematics are provided in a manner which is as physical, clear and simple as possible; and the physical concepts used are the most up-to-date ones. Despite its substantial content, the book is concise and will satisfy those who want to go directly to the point.

This book comes with two volumes:

• Volume 1 covers all the theoretical aspects.

• Volume 2 provides case studies, exercises, complementary explanations, as well as the more advanced methods and mathematical tools widely used in relativity, in particular Minkowski diagrams and tensors. Thus some parts of Volume 2 require a higher mathematical level, but these additional mathematical notions are carefully explained for those who don’t have this higher background

This book is thus an accessible reference both for science students, whom it prepares for further studies (General Relativity), and for people in general who are interested in really understanding the conceptual revolution introduced by relativity.