Life as No One Knows It

Starred review from June 3, 2024
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.