In his earlier book "The Elegant Universe" he was after the multi-dimensions of the Universe, stressing upon the unseen factors responsible for several unaccounted observations, including speed of light. A staunch approver of strings theory, he starts with the Theory of Relativity and the Quantum aspects of the observations a Physicist would do to make the educated understand the Universe.
He suggests proof for Multiverse, both Mathematically and logically. For instance using Planck's units he estimates about 10^124 Universes!!! Suggesting, therefore, that we are not alone in the Universe. By the same measurements he estimates the amount of information contained in a region of space stored in any object of any design as always less than the area of the surface that surrounds the region. An example quoted is a hard disk with about 10^70 bits equivalent to about a billion, Trillion, Trillion, Trillion, Trillion Tera bytes!
There is also a similar calculation on the number of operations a brain can (out)perform - 10^14 to 10^17 operations/second, while the fastest Super computer presently can do about 10^12 of them.
Occasional mention about Schrodinger, Bohr, Einstein and Heisenberg adds to the credibility of the book. Bohr, always over Schrodinger, would talk about wave collapse the moment you see it (making it disappear), only to be counter viewed by the famous thought experiment of Schrodinger.
Spread over 11 chapters he describes about Nine type of Universes errr...Multiverse viz:
1. Quilted Multiverse: Conditions in an infinite universe necessarily repeat across space, yielding parallel worlds.
2. Inflationary Multiverse: Eternal cosmological inflation yields an enormous network of bubble universes, of which our universe would be one.
3. Brane Multiverse: In string/M-theory's braneworld scenario, our universe exists on one 3D-brane, which floats in a higher-dimensional expanse potentially populated by other branes - other parallel universes.
4. Cyclic Multiverse: Collisions between braneworlds can manifest as big bang-like beginnings, yielding universes that are parallel in time.
5. Landscape Multiverse: By combing inflationary cosmology and string theory, the many different shapes for string theory's extra dimensions give rise to many different bubble universes.
6. Quantum Multiverse: Quantum mechanics suggests that every possibility embodied in its probability waves is realized in one of a vast ensemble of parallel universes.
7. Holographic Multiverse: The holographic principle asserts that our universe is exactly mirrored by phenomena taking place on a distant bounding surface, a physically equivalent parallel universe.
8. Simulated Multiverse: Technological leaps suggest that simulated universes may one day be possible.
9. Ultimate Multiverse: The principle of fecundity asserts that every possible universe is a real universe, thereby obviating the question of why one possibility - ours - is special. These universes instantiate all possible mathematical equations.
With lots of theoretical information from books and a few movies on science (fiction), this book would make an interesting reading with flying thoughts around the 'Multiverse'.