"# What Is Life? A Journey Through Complexity and Possibility What is life? It sounds like a simple question, doesn’t it? Yet, as astrobiologist and theoretical physicist Sara Imari Walker argues in her eye-opening Long Now Talk, this seemingly straightforward inquiry unfolds into an intricate tapestry of meaning. Walker embarks on a journey that ties together organic chemistry, the whimsical universe of Lego bricks, and, yes, even the materialist philosophy championed by none other than Madonna. Walker leads a prestigious international research group dedicated to unraveling the mysteries of life and its origins, and she presents us with a captivating framework known as assembly theory. At its core, this theory asserts that life is the only architect capable of creating complex objects—objects that are rare within the boundless expanse of the universe. This revelation is profound: the plethora of potential combinations and configurations exceeds what our universe can physically accommodate. So, if the cosmos brims with endless possibilities, what shapes the reality of what we perceive as existing? Enter the "assembly index." Here, Walker provides a tool to quantify the complexity of objects in our universe. Take adenosine triphosphate (ATP), the molecular icon of cellular energy. The assembly index measures the number of steps required to build such a structure, revealing an astonishing threshold: only items rated above an assembly index of 15 seem to escape the domain of life’s inherent complexity. This compelling argument suggests that within the atomic fabric of every object lies a trove of information—an intricately woven narrative of its own construction and history. As Walker eloquently puts it, "We are our history." Life is an ongoing story of causal histories—the lineages of information that propagate through time. With assembly theory, objects take on a new persona, for they aren’t merely physical entities but rather timelines of potential formations. This transformative perspective allows us to speak a unified language regarding selection, evolution, and the exhilarating birth of novelty. Walker’s ideas ripple outward, encouraging us to reconsider our own existence. In a world weighed down by crises and uncertainty, her research ignites questions that challenge us to expand our understanding of the present moment. Who are we, if not the culmination of our pasts? What legacies do we wish to build as we venture forward into an uncertain future? This thought-provoking talk was delivered on April 1, 2025, at the Cowell Theater in San Francisco, an event made possible by The Long Now Foundation. Founded by Stewart Brand in 2003, the foundation has curated more than 400 dialogues with visionaries across cultures to encourage long-term thinking and robust conversations about our journey through history and beyond. In these transformative times, The Long Now Foundation stands as an emblem of hope, fostering a community that encompasses 12,000 individuals from 65 countries—all united by a commitment to curiosity, bold ideas, and the audacity to imagine new possibilities. Together, we can shape a future that embraces our complex, rich histories and dares to dream of what lies ahead. Will you join us on this journey of enlightenment and exploration? The possibilities await."