Everybody should read this all important text (with excellent clarifications by R. Geroch) about one of the most devastating scientific discoveries, together with quantum physics and Darwinism, ever made by a human mind. It reveals that time and space are not absolute (Kant would say `a priori'), but relative. Einstein's insights shattered existing philosophical, theological, ideological and scientific dogmas.
A basic knowledge of mathematics is necessary for the understanding of the whole text. However, the main reasoning can be followed without the math.
Special and general relativity
The special theory is based on the principle of relativity between uniformly moving co-ordinate systems devoid of rotation, and the constant speed of light (in vacuo) for all observers.
The general theory incorporates gravity. Space-time is curved through attraction by the gravitational force. The shortest distance between two points in the universe is not a straight line, but a curve.
Cosmological constant
As R. Penrose notes in his excellent introduction, Einstein's `greatest mistake', the cosmological constant, has been re-introduced in modern cosmology. It implicates that the remote future of the universe will be an exponential expansion.
Personal comment (promises shattered)
In his equally excellent afterword, D. Cassidy shows that Einstein's bright vision of science `ennobling man's life, lifting it from the sphere of mere physical existence and leading the individual toward freedom' turned rather into `moral decay'.
As B. Russell said, `science is ethically neutral. It confers power, but for evil as much as for good.' Not every scientist is a Faraday. Science produced the atom bomb and politicians used it.
Today there is a new backlash against reason (science) for apparently religious and ideological reasons. But those are merely a veil for vested `sinister' (B.R.) interests.
This book is a must read for all those who want to understand the universe we live in.