Dover is a publishing house that produces an extraordinary number of books, and they make their money (largely) from reprinting old books now free from copyright, classics and the like. They have an intriguing array of art books and catalogues of things like American horse buggy designs, wallpapers, etc., etc.
The Unity of the Universe is a 1959 book by D W Sciama, available from Dover, and while some of its concepts are no doubt outmoded (not the least being the steady state theory of the universe, which Sciama apparently jettisoned after the writing of this book), it is an interesting summary of astrophysics and the like. But its particular theme is the interconnectedness of the universe, or space, something that still puzzles scientists. Developments in quantum physics seemed to indicate that sub-atomic particles that were suddenly separated would somehow communicate instantly to each other across the vastness of space. Einstein derided this as “spooky action at a distance”, but it is now a curious but proven fact of the strange properties of the quantum world. It is also merely one aspect of the puzzle of the configuration of the universe. This issue illuminates a bigger question: exactly what is space? This was a question that Einstein of course reconfigured with his work on general relativity, and that the theorist Ernst Mach (above, and an influence on Einstein’s work) pondered when (famously) he thought about inertia, and that can be summarised in the question, when an object is spinning in space, what is it spinning in relation to? For Mach, a body’s motion is only relative to other bodies, which indicates a kind of unity in all the matter in the universe. This is one of those head-spinning (no pun intended) issues in physics. Sciama, a key contributor to modern cosmology and teacher of Stephen Hawking, Martin Rees and John Barrow (amongst others), seeks to, by an entertaining and circuitous route, fathom why the universe shows this “unity”.