How Many Verses in a Multiverse?

Brian Greene's new book is called The Hidden Reality because, like all string theory, it can only be proven mathematically. I am awaiting its arrival today as I ordered it last week for half-price---having read and enjoyed Greene's previous exertions on the subject of string theory. Here's a snippet of a review:

Mr. Greene, though, does a valiant job of making the arcane world of what is known as string theory at least semi-intelligible. Briefly, string theory asserts that interactions between objects called "strings," occurring in multiple dimensions, cause the phenomena that we observe in our universe of three space dimensions and one time dimension. As readers of his earlier books will be aware, string theory is meat and drink to Mr. Greene. Yet his buildup to the sensational meat of this book—in which he proposes a system that uses string theory to explain and argue for multiverse theory—is cautious, perhaps in the hope of not frightening his readers with too much too soon.

Like many familiar accounts of our universe, Mr. Greene's begins with the Big Bang. Along the way he presents one of the best explanations that I have seen of the idea of inflation—a rapid early phase of expansion in the first split-second of the life of the universe, thought to explain the nature of the Big Bang itself. "Inflationary cosmology is a key chapter in our story," the author explains, "because scientists have gradually realized over the last few decades that the most convincing versions of the theory yield a vast collection of parallel universes, radically transforming the complexion of reality."

Following the edict that "in an infinite universe anything is possible," Mr. Greene introduces the idea of an infinite number of almost identical copies of our universe, infinitely far away from us, and the idea of universes that follow one another in time, like beads on a string. The "parallel worlds" of quantum physics, which are different from the many dimensions of string theory, make an appearance (along with Schrödinger's famous cat). There is also an all-too-brief discussion of the possibility that either our universe has been manufactured by beings in another universe or we are living in a computer simulation like that of the "Matrix" series of movies.

It's been noted before that science fiction "intuits" physical reality on a sometimes surprisingly consistent basis. However absurd a matrix universe might appear, there remains the intriguing possiblility that it does define our "reality" better than alternatives. Here's more of the review:

The laws of physics do, indeed, allow for the existence of different kinds of universe, and no fundamental reason has yet been discovered why the world we see around us should have been singled out by those laws.

To take a simple example, if the force of gravity were stronger than it is in our universe, but all other properties remained the same, stars would have to burn more fiercely to hold themselves up against the pull of gravity. They would use up their fuel more quickly and burn out in a few million years, not allowing time for life forms like us to evolve on planets orbiting those stars. So why should gravity, and the other properties of our universe, be "just right" for us to exist?

There are two possibilities, often expressed in terms of an analogy with a man who buys a suit that is a perfect fit. Either the suit has been specifically tailored for the client—made to measure—or he has visited a large store with an array of suits in all possible sizes, choosing the one right for him off the peg. The best interpretation of the laws of physics as we understand them is that we live in an off-the-peg universe. A vast array of universes exist in the multiverse, many (perhaps most) of them sterile, but since life forms like us can only exist in universes like ours, it is no surprise that we live in such a universe.

Sadly, the book contains many equations, which will hinder my understanding. Happily, it contains Schroedinger's cat, my favorite feline in the entire spectrum of science and science fiction.