The Grand Design

The Grand Design, Stephen Hawking and Leonard Mlodinow, Bantam Books, New York, 2010. $28.00 (208 pp.). ISBN 978-0-553-80537-6

Philosophy is dead and unable to answer the deepest questions, such as the question of creation, but M-theory may hold the key. Such provocative statements, lightened by wonderful images from ancient Greece to the multiverse, make up The Grand Design by Stephen Hawking and Leonard Mlodinow, a handsome book about current ideas in cosmology and particle physics and about the search for a unified theory of everything.

Hawking and Mlodinow’s entertaining prose covers creation myths from different cultures and a brief history of scientific thought traced from the Greeks to Isaac Newton. Those early so-called natural philosophers allowed for exceptions to the laws of nature as a way for scientific thought to coexist with their religious beliefs. Credit goes to Pierre Simon Laplace for excluding miracles from science (as in his famous reply to Napoleon Bonaparte that God is not a necessary hypothesis) and for postulating scientific determinism: Given the state of a system, the laws of nature determine the system’s past and its future evolution.

The Grand Design reminds us of the beauty of quantum mechanics, which challenges the view held by most scientists since Laplace that the laws of nature are mathematical descriptions of an observer-independent external reality. The authors introduce readers to the quantum world of particle physics, where reality is observer dependent. They argue that their model-dependent realism resolves the tension between philosophical realism and antirealism.

Since infinities in a quantum theory of gravity are not amenable to renormalization as they are for quantum electrodynamics and quantum chromodynamics, the authors explain the need for an alternative approach to bring Einstein’s general relativity into the quantum realm. They describe the function of supersymmetry in quantizing gravity in supergravity theories and discuss the possibility of detecting the lowest-mass supersymmetric particle or the elusive dark-matter particle with CERN’s Large Hadron Collider.

Dualities between 11-dimensional supergravity and the five 10-dimensional string theories suggest a more fundamental theory. It’s called M-theory, an elegant representation of a yet-to-be specified fundamental theory of everything. And yet the authors are silent with respect to testable predictions of M-theory or any string theory. (For a discussion of some of those, see the article by Gordy Kane, PHYSICS TODAY, November 2010, page 39 .)

The book would have been more enjoyable for physicists if the basic structure of string theory and M-theory were described as in John Barrow’s New Theories of Everything (Oxford University Press, 2008) and Leonard Susskind’s The Cosmic Landscape: String Theory and the Illusion of Intelligent Design (Back Bay Books, 2006). Instead, the most appropriate audience for the book seems to be the group that was killed off on the first page—the philosophers.

Since M-theory may have 10⁵⁰⁰ possible sets of “laws of nature,” the cosmological concept of the multiverse comes in handy. The ultimate Copernican revolution, the multiverse arises naturally from inflationary cosmology, in which new universes are constantly being created and inflate into large, causally disconnected universes. Alex Vilenkin’s Many Worlds in One: The Search for Other Universes (Hill and Wang, 2007) is a good reference on the multiverse (see the review in PHYSICS TODAY, May 2007, page 66 ).

In the multiverse paradigm, our universe is nothing special. That is, except for the next ingredient that the authors throw into the grand design—humans. Instead of using God as a way to explain why the laws of nature are what they are, the authors use our presence in the universe—the anthropic principle—as the way to select our universe and its laws and so proclaim that we are “in a sense the lords of creation.”

The book’s assertion that physics has all the answers may be especially provocative in a time of growing intolerance toward science, but certainly it is not accurate. Many fundamental unknowns remain, such as the nature of dark matter, which can hopefully be answered with the traditional use of the scientific method. The success of inflationary cosmology in predicting the spectrum of fluctuations observed in the cosmic microwave background encourages the search for gravitational signatures of the inflationary phase. And the surprising energy scale of dark energy may be an accident of the grand design, but for now it should keep physicists humble and busy testing possible explanations while the philosophers grapple with theories that cannot be tested.