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Rarely do the title and authorship of a book carry such high expectations as The Grand Design by Stephen Hawking and Leonard Mlodinow.
Hawking, a physicist who until retiring last year was the holder of Sir Isaac Newton's chair as Lucasian Professor of Mathematics at the University of Cambridge, startled the publishing world in 1988 with his mega-seller, A Brief History of Time. It tackled mind-bending concepts of general relativity and quantum mechanics in an engaging style that invited non-specialists, even nonscientists, to grapple with those ideas for themselves.
Most lost their way partway through the journey, but almost all declared themselves exhilarated and enlightened by the struggle and captivated by Hawking's style.
By 2005, developments in physics led Hawking to revise the book. He enlisted as a collaborator fellow physicist and author Leonard Mlodinow, who had also written scripts for Star Trek: The Next Generation. The result was the critically acclaimed A Briefer History of Time, which not only updated the original book but also made the subject matter much more accessible.
Both books enticed their readers with the same loose ends that drive theoretical physicists today: Quantum mechanics and general relativity, both remarkably successful in their qualitative and quantitative description of nature as well as their predictive power, do not mesh with each other at the subatomic level.
Because of that mismatch, physicists seek a Holy Grail, a so-called theory of everything that unites quantum theory and relativity. In their new book, Hawking and Mlodinow argue that such a theory, which they call The Grand Design, is now within reach.
Readers familiar with modern physics will find that claim both audacious and intriguing. They will open the book expecting a brief overview of Hawking's earlier work and then more detail about the mismatch between the two great theories. They will look for the authors to wade into the argument about the possibilities and limitations of string theory. (More about that below.) They will expect the book to point the way to a new theory unlike any previously proposed.
But by the time they reach the end of chapter 1 ("The Mystery of Being"), they will realize that The Grand Design is a very different kind of book. It is an odd hybrid that redefines science to include questions that are usually in the realm of philosophy and religion.
Traditionally, science has been considered descriptive, not explanatory. Yet Hawking and Mlodinow declare, "To understand the universe at the deepest level, we need to know not only how the universe behaves, but why. Why is there something rather than nothing? Why do we exist? Why this particular set of laws and not some others?"
The authors then spend two chapters in the realm of the philosophy of science. The first discusses the nature of physical law and the second asks, "What is Reality?" The text is clear and the reading is easy, with touches of humor for leavening. Yet for readers seeking in-depth science, the jokes fall flat and the material feels like a tepid review of what they probably already know about how physicists engage with nature.
The book is at its scientific best when explaining Richard Feynman's contributions to the understanding of quantum theory. The authors use the example of a light beam passing through two slits to produce an interference pattern--a wave property. Even when the beam is so dim that only single particles of light (photons) go through the slits at any one time, the net result is still interference. How can a particle interfere with itself?
"According to Newtonian physics...," they write, "each particle follows a single well-defined route from its source to the screen.... According to the quantum model, however, the particle is said to have no definite position during the time it is between the starting point and the endpoint." Feynman interpreted that to mean "that particles take every possible path connecting these points..., and they take them all simultaneously!... Feynman formulated a mathematical expression--the Feynman sum over histories--that reflects this idea and reproduces all the laws of quantum physics."
The book then goes on to discuss the quest for the theory of everything, including a history of string theory, an approach that replaces particles in conventional four-dimensional space-time with tiny vibrating strings in a ten-dimensional universe. String theory yields multiple interpretations of reality, which its practitioners view as approximations to a more fundamental eleven-dimensional theory called M-theory.
"No one seems to know what the 'M' stands for," the authors write, "but it may be 'master,' 'miracle,' or 'mystery.' It seems to be all three." A Feynman-like interpretation of M-theory predicts the simultaneous existence of multiple universes, each with different sets of fundamental constants and particles.
Because M-theory allows for so many possible universes--10 to the 500th power, give or take a factor of a googol (ten to the 100th)--critics dismiss it as not the theory of everything but the theory of anything. But Hawking and Mlodinow take a different view: "It could be that the physicists' traditional expectation of a single theory of nature is untenable."
In their view, a small fraction of those possible universes (but still a very large number) are suitable for the evolution of stars, planets, and life such as we experience on our particular world in our particular galaxy. In other words, according to M-theory, a universe like ours is not a miracle but inevitable.
M-theory, they conclude, is The Grand Design that scientists have been seeking. Furthermore, it provides a better answer to the key question of existence--why our universe behaves as it does--than either religion or philosophy can.
A lot of scientists, theologians, and philosophers will beg to differ.