After a career of an engineer in telecommunications (Telecom-ParisTech) mainly with Alcatel-Lucent, I decided together with some good old friends, to return to the subject we liked best when were students: Physics. When the subject came to Relativity, we were fascinated by this revolution affecting our basic concepts of time, distance, energy and mass. Einstein said: “It is difficult to resist the appeal of Relativity”, and our experience confirmed his statement.

However we were somewhat disappointed because most books which thoroughly and rigorously explain Special Relativity privilege the mathematical approach over the physical one, and lacked explainations. These books typically are at the Master level and use unnecessary complex means for Special Relativity (tensors, Lagrangians). As a result, the time devoted to explain them is to the detriment of the physical aspects which actually are more important; thus many explanations are often missing, especially on the physical and axiomatic aspects. As a matter of fact, many science students share this dissatisfaction: they zap from one text book to another one in order to find the missing explanations.

Therefore I started to search if simpler demonstrations were possible, but without compromising on the rigor nor taking artificial assumptions, but strictly keeping on the minimum set of postulates. This search was carried out with the help a group of friends, some being highly knowledgeable in Physics. In many instances, an in-depth physical and logical analysis enabled us to find demonstrations requiring less complex maths. Then, as I managed to find the complete set of demonstrations, I decided to write this book.

Thus this book is aimed at both science students and a wider public. Science students will indeed appreciate the substantial explanations and the complementary physical approach compared to their text books. The first part on the Relativity of time and distance can even by understood by people having a low mathematical level provided they are really interested.

An introduction to General Relativity is added, as the main physical principles are not complex and enable the reader to understand the reasons why light bends near great masses and why time also is affected. The recent and amazing observations of gravitational waves are also described.

The Volume 2 is aimed at science students as it includes exercises, case studies, higher level demonstrations, and presents in detail the more complex tools (Minkowski diagrams, tensors, hyperbolic trigonometry…) which are also useful for further studies.

I wish you the same pleasure in reading this book than I had in discovering Relativity.

Paul Bruma