Brian Greene, bestselling author of The Elegant Universe, has recently released a new book, The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos, in which he sets out the arguments for the theory that the universe we inhabit may in fact be just one of many universes.
The concept of this multitude of universes, or “multiverse”, arises in response to many puzzling topics in physics. It has been invoked to explain the apparent fine-tuning of physical constants, as an interpretation of the uncertain nature of quantum mechanics, and as the “braneworld” scenario of string theory - in which our universe is a three-dimensional membrane floating in a higher-dimensional space of alternate universes.
Greene tackles each of these in turn, starting in Chapter Two with the simplest reasoning behind the belief in parallel worlds: if the universe is infinite in extent, it is inevitable that one of the infinite number of planets out there is identical to our own, and that on it there are people exactly like ourselves undergoing an alternate version of our reality. Greene discusses the question of whether or not the physical size of our universe is infinite or finite, which is still very much an open question in modern physics.
Greene, as in his previous books, uses metaphor to make difficult concepts accessible to the general reader. Expect to have to take your time to wrap your brain around the subject matter, but what Greene won't do is blind you with technical jargon or assume specialist knowledge.
I have been a fan of Brian Greene since I read The Elegant Universe at seventeen. If I had to pinpoint a deciding factor in my decision to study theoretical physics, this book would probably be it. This was the book that got me hooked on strings, particles and the quest for a “theory of everything”. It was fantastic to read the author's recent follow-up and have those feelings of curiosity and excitement resparked.