Riverhead
Review by Walter Cummins
Before I attempt to say something about a book that theorizes life’s emergence from the perspective of the science of physics, I should admit that my familiarity with physics is quite limited. As a college freshman, I did pass a watered-down version of the subject for non-majors. That was back when the drawing of an atom was a simple three-part structure of nucleus, proton, and electrons, years before discoveries of quarks and bosons and all of those other mysterious miniscule bits.
I’ve always thought of physics as the branch of science that deals with physical matter—phenomena such as the elliptical rotation of planets, e=mc2, gravity, entropy, the conundrum of Heisenberg’s uncertainly principle. But life? I’d never considered that physics might answer why some matter is alive and some not. Or discover the tipping point between living and non-living matter.
Sara Imari Walker had a dissertation advisor who talked her into confronting questions such as these. Her subsequent career as a physicist became consumed with exploring these unknowns, this book one report of what she has achieved so far. Her goal is to create a branch of physics that defines what life is and explains where life came from.
Walker does not restrict herself to a quest about life on earth but expands her subject to the billions of bodies in the cosmos. We associate the presence of water on a planet or satellite a sign of life’s possibility. But what if life forms based on criteria totally unlike our assumptions for earth exist somewhere out there in the vastness of light years? There may be many ways for what we call life to be created and to exist in places that lack the components that make Earth’s version of life possible.
Walker’s new branch of physics, going beyond the limitations of this planet, seeks principles that can explain the possibilities of life forms throughout the universe: “Assembly theory makes a strong claim: all things life can build are historically contingent. Indeed, we think this contingency also becomes a way to predict novelty because it allows predicting what new forms you might expect to appear based on recombining features of the past.”
For Walker’s theory, what will exist is dependent on what already exists, an evolutionary process in which at some point the information contained in what is not yet alive develops sufficiently to become a life form. Life forms are distinctive because they possess the ability to replicate and change: “…. a unifying conceptual paradigm: if selection among the space of what is possible happens before life, the constraints on the space of possibilities can drive the emergence of what we observe in life as evolution.”
Assembly theory aims to unify physics, chemistry, and biology as an approach to understanding complexity in nature. Life emerges when objects reach a certain level of complexity, an accumulation of information and memory over time. An assembly index quantifies the complexity of an object based on the number of steps required to assemble it. High assembly indices correlate with complex, life-derived molecules, suggesting that life’s emergence is tied to the history of molecular assembly. This theory differs from Darwinian evolution, which attributes biological complexity to selection and adaptation rather than growing intricacy of information and memory.
The theory offers an explanation of the circumstances that make life possible, but as yet doesn’t explain exactly when life emerges or what it means to possess life. Is there a moment when the assembly index reaches a point that, in effect, turns on a switch that transitions from non-life to life? And what reverses the process? We know dying is complex for humans, perhaps a matter of stages, the way it is with headless chickens. What happens to all the advanced complexity and assembled information? Would the loss of life need a disassembly theory for an explanation? That’s my question, not Walker’s.
Walker predicts the possibility of new technologies that will provide a much more detailed and deeper understanding of the nature of life, continuing inventive processes of recent centuries that are accelerating today. For example, with microscopes and telescopes humans now have access to details about the physical world—the micro and the macro—that humans of the past hadn’t even imagined, just as the atom in my freshman year physics course knew nothing of quarks and bosons before the existence of particle accelerators.
Rather than fearing artificial intelligence like certain scientists, Walker welcomes its arrival and even suggests a blurring of the seeming boundary between technology and life. She claims, “the emergence of artificial intelligences and planetary-scale data and computation can be seen as an evolutionary progression—a biosphere becoming a technosphere. The question now is at what point does a biosphere emerge sufficient technology to solve its own origins, and how does this transition the future evolution, when planetary intelligence is achieved?”
Could it be that the life we seek to define is a moving target, evolving into a new reality? Will assembly theory provide an avenue to finally grasp what life is all about? My freshman physics course, which I squeaked by, left me in the dark ages when coping with Walker’s theories and projections.
