Beyond the unique evidence. A Philosophy of Extraterrestrial Life

In the 21st century, interest in astrobiology and the possibility of extraterrestrial life has grown exponentially, supported by technological advancements and the exploration of exoplanets. However, despite astronomical discoveries, the search for life beyond Earth remains an unresolved issue. This work addresses a fundamental epistemic question: can we go beyond the only evidence of life we possess, that of Earth? Our biological knowledge is based on a single example, which implies the so-called N=1 problem—the impossibility of determining whether Earth’s biosphere is representative of life on a universal scale. The first chapter explores the definition of life and the difficulties in establishing a single identification criterion. It examines the history of life on Earth, debates on its origins, and the role of the Last Universal Common Ancestor (LUCA). Additionally, it analyzes the relationship between living organisms and their environment, considering metabolism, biochemical communication, and autopoietic processes. The definition of life is thus approached from an epistemological perspective, avoiding a rigid ontological framework and accepting the possibility of contextual definitions. The second chapter delves into the concept of extraterrestrial life and the limitations of the geocentric paradigm. The epistemic problem of generalizing Earth-based life is discussed through the concept of the "shadow biosphere" and the principle of mediocrity. The role of astrochemistry, the environmental conditions that may support life, and the heterogeneity of extrasolar contexts are examined. A distinction is proposed between a geocentric paradigm of life and a heliocentric paradigm, which considers the relationship between life and the evolution of planetary systems as a whole. Additionally, the oxygen bottleneck for the development of technospheres and communicative civilizations is explored. The third chapter focuses on the astrobiological and philosophical implications of the search for intelligent life. It analyzes Fermi’s Paradox and the so-called "Great Silence," evaluating the Great Filter hypothesis and the limitations of assumptions about the longevity of technological civilizations. The Drake equation and its extensions are discussed, introducing stochastic models and Poisson processes to describe the emergence of communicative civilizations over time. In particular, an extension of homogeneous Poisson process models is proposed, considering the evolution of galactic habitability probability over cosmic time scales. Overall, this work highlights the epistemological limitations in the search for extraterrestrial life, proposing a philosophical-astrobiological approach that integrates probabilistic, biological, and cosmological considerations. It underscores the need for a more flexible paradigm regarding current definitions of life and extraterrestrial civilizations, to overcome the constraints of the N=1 problem and develop more suitable models for astrobiological investigation.