From Copernicus to Einstein

This is a not so easy understandable popular scientific work about the theory of relativity. It is a little bit out of date, but it should be read for his examples. 4 dimensions "Three numbers are needed to determine a point in space. Suppose a lamp hangs in the room. How can we determine its place? We measure its distance from the floor, from the back-wall and from the side-wall; these three figures determine its position in space. ... If we want to determine not a point in space but an event, we require another figure, namely, the statement of time. Suppose we switch on the light for a second and produce a flash of light; this is an event. It is completely determined if we know the three numbers defining the position of the lamp and, in addition, the fourth number defining the time of the light flash. Insofar as there are four figures, space and time together are called a four-dimensional manifoldness. This is the whole secret." The author stresses also the importance of Riemann and the influence of Michelson on Einstein. But, as an introduction I prefer Bertrand Russell's 'ABC of Relativity'.

I was very much impressed by this little book. From it I first learned about Mach's Principle, and how it followed right from the concept that motion is relative. The analysis of Newton's pail experiment is astonishing. It is just a combination of powerful ideas, with no equations. Nowadays, when I happen to teach General Relativity, I begin with this analysis by Reichenbach, also because it is one of its conclusions that Newton's gravity theory is inconsistent with motion being relative. At least you have to accept that a moving mass attracts differently than one at rest. This is already extra-Newtonian. Reichenbach, a member of the famous Vienna Circle was a very sharp-minded fellow, and a very clear one too. This book is a must.