Unless the pursuit of dreadfulness results in a tie, each year will possess its own worst book. But identifying the winner in this dubious competition poses difficulties. Surely even a well-read literary editor of The New Republic must wonder whether among all those inevitably unturned pages lurks something even more atrocious than his favorite candidate. How then could Leon Wieseltier select THE ATHEIST’S GUIDE TO REALITY: Enjoying Life Without Illusions (Norton, $25.95), by Alex Rosenberg, as the “worst book” of 2011?

Although the award is almost certainly misplaced, what inspired it is readily understood. The book expands the campaign of militant modern atheism, the offensive launched against religion by Richard Dawkins and Christopher Hitchens. Rosenberg’s broadsides attack a wider horizon. Since atheism is thought to be territory already secured, the targets now in view are the Big Questions, questions about morality, purpose and consciousness that puzzle softheaded people who muddle over them. Science brings good news. The answers are now all in. This conviction that science can resolve all questions is known as “scientism” — a label typically used pejoratively (as by Wieseltier), but one Rosenberg seizes as a badge of honor.

The evangelical scientism of “The Atheist’s Guide” rests on three principal ideas. The facts of microphysics determine everything under the sun (beyond it, too); Darwinian natural selection explains human behavior; and brilliant work in the still-young brain sciences shows us as we really are. Physics, in other words, is “the whole truth about reality”; we should achieve “a thoroughly Darwinian understanding of humans”; and neuroscience makes the abandonment of illusions “inescapable.” Morality, purpose and the quaint conceit of an enduring self all have to go.

The conclusions are premature. Although microphysics can help illuminate the chemical bond and the periodic table, very little physics and chemistry can actually be done with its fundamental concepts and methods, and using it to explain life, human behavior or human society is a greater challenge still. Many informed scholars doubt the possibility, even in principle, of understanding, say, economic transactions as complex interactions of subatomic particles. Rosenberg’s cheerful Darwinizing is no more convincing than his imperialist physics, and his tales about the evolutionary origins of everything from our penchant for narratives to our supposed dispositions to be nice to one another are throwbacks to the sociobiology of an earlier era, unfettered by methodological cautions that students of human evolution have learned: much of Rosenberg’s book is evolutionary psychology on stilts. Similarly, the neuroscientific discussions serenely extrapolate from what has been carefully demonstrated for the sea slug to conclusions about Homo sapiens.