In July 2010, the editorial department of Scientific American—where at the time I was on staff—received a review copy of a book was slated to come out in September. It was a slim, drab-looking, paperback-bound volume, still without a cover design or page numbers. On the cover it carried two names, that of a respected science writer, Leonard Mlodinow—and Stephen Hawking's. Would we like to review it in our magazine?

I dropped everything I was doing that day and I proceeded to devour the book. I had never particularly been a fan of Hawking’s celebrated bestseller, A Brief History of Time, which is said to have sold 10 million copies. But I found this new tome, The Grand Design, to be a page turner.

The central thesis of the book came to me as a bit of a shock. (And no, by that I do not mean Hawking's statement that created a minor media storm: physics does not require the existence of god, which coming from him did not surprise me in the least.)

Throughout much of his career, Hawking expressed the belief that humanity was on the verge of a transformative step. He thought we were soon going to discover the ultimate set of laws that govern the universe. Along the way, physicists would reconcile various theories that seemed apt at describing some class of phenomena but not others—for example, gravitation for the formation of galaxies and quantum mechanics for the structure of atoms—and reveal a single consistent rulebook which would explain everything.

Hawking himself had given physicists some clues toward a grand unification by combining ideas from Einstein’s general theory of relativity, quantum physics and thermodynamics to understand black holes. In what is still seen as one of his most profound insights—perhaps one of the most profound of all of 20th century physics—he had calculated that black holes are not really black, but that they slowly radiate energy, losing mass in the process. That slow leak became known as Hawking radiation. Physicists still hope to observe it experimentally by producing microscopic, fleeting black holes in high-energy experiments such as the Large Hadron Collider.

With characteristic brashness Hawking, in his 1980 inaugural lecture as Cambridge University’s Lucasian Professor—the chair that had once been Isaac Newton’s—said that the problem of unification was likely to be solved by the end of the century. At the time, a theory called N=8 supergravity seemed a promising approach. The title of his talk: “Is the End in Sight for Theoretical Physics?” Later, when supergravity faded out of the picture, Hawking stated a similar optimistic expectation of string theory.

What I found shocking in Hawking and Mlodinow’s new book was that Hawking now seemed to give up on the hope that there could even be such a thing as a theory of everything. A majority of theoretical physicists now thought that string theory would turn out to hold the key to unification. The trouble is, there wasn’t one string theory, but at least five different theories. Each seemed suitable to describe one particular range of phenomena, but each failed at describing others. On the surface the theories seemed incompatible, but physicists had discovered “dualities”—a sort of Rosetta stones that could translate concepts from one theory into another.

Perhaps, the two authors wrote, this is as good as it gets. Perhaps there is no overarching way of representing reality. Instead, physics must limit itself to a “model-dependent realism” that can capture one aspect of reality or another. Different models may give vastly different representation of reality, and none can claim to reveal the “thing” as it is—the noumenon, as Immanuel Kant would have called it.

This almost postmodernist twist seemed at odds with Hawking’s lifetime convictions, but it was not the first time that the physicist (who today celebrates his 70th birthday) had dramatically changed his mind during his career, as Kitty Ferguson writes in her eminently readable new biography Stephen Hawking: An Unfettered Mind. (See a brief excerpt of the book here.)

The most celebrated such reversal was probably his concession of a bet that he had made with Leonard Susskind, a physicists now at Stanford University, concerning the so-called black hole information paradox. Hawking had pointed out that if a black hole radiates energy, and eventually shrinks to nothingness, all information concerning the stuff that had fallen into the black hole will disappear from the universe. Taken to its ultimate consequences, it meant that physicists had to abandon one of their cherished principles: that reality is predictable, and that nature evolves based on well-defined rules rather than in an arbitrary fashion. It was a hard pill to swallow, but Hawking was ready to take it if that was what the equations really implied.

Years later, Hawking announced that he no longer believed that there was a paradox. He came to the conclusion that information does not disappear after all. (Physicists now regard the information paradox to be solved by the work of Juan Maldacena, a physicist now at the Institute for Advanced Study in Princeton, N.J., based on the so-called holographic universe.)

As Ferguson rightly observes, and makes it into one of two leading themes of her book, this ability to reverse one’s convictions in the face of uncomfortable evidence—first abandoning the belief in the consistency of nature, and then saying you were wrong—is far from being a weakness. Instead, it is a mark of good science.

The other leading theme in Ferguson's book, is, of course, her subject's seemingly superhuman ability to overcome his physical condition. His physics was first-rate, but it was his ability to inspire which to a large extent made him a household name around the world. Ferguson strikes what seems to me as the right balance between telling the story of Hawking the extraordinary scientist and the one of Hawking the extraordinary man.

In her work she benefited from a close collaboration with her subject, including numerous extended interviews conducted over a period of decades. (When it comes quoting others, however, Ferguson mostly seems to rely on secondary sources—such as books and newspaper clippings—rather than on direct interviews, which takes some freshness away from the narration.)

Ferguson’s book concludes with a chapter on The Grand Design, which comes across as a summa of Hawking’s intellectual legacy. The book has not been received well by critics. My colleagues and I at Scientific American however found it compelling enough that, back in July 2010, we persuaded the publisher and the authors to let us run an excerpt in the upcoming October issue, which had a special significance for us because it inaugurated a refurbished and redesigned magazine.

At the time when we got the review copy of the book, we had already begun to lay out the October issue, but we quickly made changes to accommodate the new article. Later, the excerpt, "The Elusive Theory of Everything," would be included in an anthology of the best science writing of the year. Both The Grand Design and Stephen Hawking: An Unfettered Mind belong in the library of anyone who has an interest in the uncanny ideas and the incredible story of one of the great scientists of our time.