Life as no one knows it The physics of life's emergence

What is life and how does one recognize it? asks Walker, an astrobiology professor at Arizona State University, in her bold debut. Defining life is a deceptively tricky endeavor, she argues, noting that the claim popular in scientific circles that "life is a self-sustaining chemical system capable of Darwinian evolution" would mean that worker bees aren't alive because they can't reproduce. Instead of bickering over definitions, Walker argues it would be more productive to come up with a test for what constitutes life. To that end, she outlines the "assembly theory" she helped develop, which posits that measuring how many "steps" it took to construct an entity, from atoms on up, determines whether it is alive. (Things that require 15 or more steps should be considered living, according to Walker.) Walker contends that, among other applications, the theory provides a falsifiable means of determining whether an alien object is "alive," even if that alien bears little resemblance to life on Earth. Walker's philosophical perspective challenges prevailing understandings of basic scientific concepts (she contends that electrons don't have mass, charge, and spin so much as those properties "describe how electrons interact with certain measurement devices"), and the bracingly original assembly theory leads to some staggering conclusions ("Being alive is not a binary, it is a spectrum"). This has the potential to be a game changer. Agent: Max Brockman, Brockman Inc. (Aug.)

An astrobiologist takes a hard look at life. Walker, director of Arizona State's Beyond Center for Fundamental Concepts in Science, writes that until well into the 19th century, the vitalism movement "was driven by the idea that what makes matter come alive cannot be described mechanically and is therefore not material." But if life is not a property of matter, and matter is all there is, then what is life? Biologists approach the problem in terms of life on Earth, which hasn't proven to be an effective strategy and is even less helpful today with the discovery of innumerable planets and the possibility of sentient life throughout the universe. In addition to her work in the field of astrobiology, Walker is a theoretical physicist with a special interest in the possibilities of alien life, and she emphasizes that physics deals with "the heart of reality." She continues, "It's not that the idiosyncratic details of biology as it evolved on Earth don't matter. They just don't matter if you want to understand life as a universal phenomenon." Eschewing the anthropomorphic viewpoint, she and colleagues have developed "assembly theory," which proposes that things never form spontaneously, but must be constructed via selection and evolution. Life is an example of "high-dimensional combinatorial space of what is possible," she writes. The author's startling conclusion is that, while an alien life form may be detected first on a distant planet, it's more likely to turn up in a laboratory here on Earth, "but there is an even larger universe of chemical possibilities we may need to explore to find them." This is an honorable addition to a small genre that began with Noble Prize--winning physicist Erwin Schrodinger's What Is Life? in 1944. It's never easy, but diligent readers will be rewarded. Ingenious, but not for the faint of heart. Copyright (c) Kirkus Reviews, used with permission.