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Interspecies Ecologies<br>Why the Physics Underlying Life is Fundamental and Computation is Not<br>Our ability to explain gravity fundamentally changed how we interact with our world. So too might an explanatory framework for life transform our future.<br>by Sara Imari Walker<br>Mar 31, 02025<br>💡<br>WATCH Sara Imari Walker's Long Now Talk, An Informational Theory of Life.

Life is undeniably real. It defines the very boundary of our reality because it is what we are. Yet despite this fundamental presence, the nature of life has defied precise scientific explanation. While we recognize “life” colloquially and can characterize its more familiar biological forms, we struggle with frontier questions: how does life emerge from non-life? How can we engineer new forms of life? How might we recognize artificial or alien life? What are the sources of novelty and creativity that underlie biology and technology?<br>These challenges mirror the limits of our ancestors’ understanding of gravity. They knew objects fell to Earth without understanding why. They observed just a few stars wandering across their night sky and lacked explanations for their motion relative to all the other stars, which remained fixed. It required technological advances — precise mechanical clocks that allowed Tycho Brahe to record planetary motions, Galileo Galilei’s concept of inertial mass, and Isaac Newton’s conception of universal laws — to develop our modern explanation of gravity. While we may be tempted to point to a particular generation that made the conceptual leaps necessary, this transformation took thousands of years of technological and intellectual development before eventually giving rise to theoretical physics as an explanatory framework. The development of physics was based on the premise that reality is comprehensible through abstract descriptions that unify our observations and allow us deeper explanations than our immediate sense perception might otherwise permit.<br>Our ability to explain gravity fundamentally changed how we interact with our world. With laws of gravitation, we launch satellites, visit distant worlds, and better understand our place in the cosmos. So too might an explanatory framework for life transform our future.<br>We now sit at an interesting point in history: one in which it is perhaps evident that we have sufficient technology to understand “life,” and according to some we may even have examples of artificial life and intelligence, but we have not yet landed on the conceptual framing and theoretical abstractions that will allow us to see what this means as clearly as we now see gravity. That is, we lack a formal language to talk about life.<br>Life versus Computation<br>“Life” has historically been difficult to formalize at this deep level of abstraction because of its complexity. Darwin and his contemporaries were successful in explaining some portion of life because their goal was not to inventory the full complexity of living forms, but merely to explain how it is that one form can change into another, and why this should lead to a diversity of forms, some of them more complex than others. It was not until the advent of the theory of computation roughly 75 years later that it became possible to systematically formalize some notions of complexity (although earlier individual examples of the difficulty of a computation date much earlier). Some thought then, and still think now, that such formalization might be relevant to understanding life. In the historical progression of ideas, proceeding over many many generations, the theory of computation may prove an important step, but not the final or most important one.<br>The theory of computation, and its derivative concepts of computational complexity, were not explicitly developed to solve the problem of life, nor were they even devised as a formal approach to life or to physical systems. It is important to maintain this distinction because many alive now confuse computation not only with physical reality, but also more specifically with life itself. In human histories, our best languages for describing the frontier of what we understand are often embedded in the technologies of our time; however, the truly fundamental breakthroughs are often those that allow us to see beyond the current technological horizon.<br>The challenge with “computation” begins with the vast spaces we must consider. In chemical space — defined as the space of all possible molecules — there are an estimated 1060 possible molecules composed of up to 30 atoms using only the elements carbon, oxygen, nitrogen, and sulfur. This is only a very small subset of all molecules we might imagine, and cheminformaticians who study chemical space have...