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Move over, Stephen Hawking. Make way for Penn State physics professor Martin Bojowald!

Bojowald's new book,

Bojowald's story begins in 2000 when he was a 27-year-old postdoctoral researcher in cosmology at Penn State. Understanding the behavior of the universe as a whole requires a solid grasp of two remarkably successful but apparently incompatible theories: general relativity and quantum mechanics.

General relativity runs counter to our intuitive distinctions between space and time and between mass and energy. It describes gravity as the result of the warping of spacetime due to the distribution of mass-energy within it.

Quantum mechanics describes the subatomic realm, again in counter-intuitive ways. Waves and particles become two faces of the same phenomenon, described mathematically as a wave function.

The two theories, as currently constituted, are incompatible in a significant way. General relativity assumes that space and time can take on any value along a continuum, while quantum mechanics gets its name because properties of mass and energy only take on discrete values--states described by a set of quantum numbers.

Unfortunately, these apparently mismatched theories must both apply in two extreme but important cosmological circumstances: the Big Bang "singularity," in which our universe of matter, energy, space, and time emerged from a timeless, infinitely dense state; and a similar singularity that exists in the heart of a black hole.

Singularity is a mathematical term for the infinity that arises in the continuous mathematics of general relativity, a point where physical interpretation breaks down. An infinite result is likewise incompatible with the discrete, finite mathematics of quantum theory.

Since all entities in the universe appear to be quantized, the resolution to this incompatibility seems to lie in finding a way to quantize general relativity. That is what Bojowald was trying to do when he ignored a piece of conventional wisdom, and, in what he describes as a fortunate accident, emerged with a mathematical description with surprising consequences.

That approach has come to be called "loop quantum cosmology." The name is a result of its connection to loop quantum gravity, a theoretical alternative to the family of approaches that are known collectively as string theory.

That's where Hawking's new book comes in. Like Hawking, Bolowold manages to describe these complicated ideas without bogging down in mathematical notation. And like Hawking, he manages to help readers over the difficult spots with entertaining and literate prose.

But unlike Hawking, he shows a way to turn the spacetime continuum into a fabric knitted together from discrete spacetime loops, making it possible to avoid the singularity. This leads to what he calls "The astonishing result: ...unflinchingly, the wave function of the universe wends its way before and behind the big bang, without even taking notice of the potential singularity."

The astonishment arises because the theory makes it possible to speak of, and even discover, some properties of a predecessor universe. It removes a philosophical sticking point that many physicists have had with existing theories. No longer do they have to say that there was no such thing as time or space before the Big Bang.

Loop quantum cosmology is also much more satisfying than Hawking's candidate for "The Grand Design," a version of string theory called M-theory, which postulates a multiplicity of universes far more numerous than the number of protons in this one. On the other hand, Bojowald's discovery, when fully developed, has the potential to be "the ultimate theory explaining not only the temporal course of the universe but also the fact that there is only a single universe."

Yet Bojowald never loses sight of the many open questions that could completely derail his work. His closing is a refreshing contrast to Hawking, who claims that M-Theory enables science to subsume philosophy and even theology by answering the ultimate question of why a universe such as ours exists.

Instead, Bojowald closes with humility about his own theory and science in general. Science's great strength is its ability to describe the practical "what" and "how" and leave the grand "why" to philosophy. "Despite the almost intoxicating progress in science," he writes, "one must always keep in mind its limitations, which become especially clear at its frontiers."

Fred Bortz is a physicist and author of the twentieth-century scientific history,