Traditional music theory struggles to provide a framework for the complex sonic structures of 21st-century music, often overlooking the structural roles of noise, timbre, and space. This book introduces a unified analytical framework based on Complex Systems Theory and Entropy to understand musical form. The core premise is that our perception of music is not an isolated phenomenon but is rooted in our everyday experience of our surroundings, which is governed by entropic processes. The book argues that the classical idea of cadence may have evolved beyond the strict use of pitch parameters. Drawing from original empirical psychoacoustic studies, it suggests that listeners may perceive cadence in the transition from order to disorder - in movements from structured pitches to high-entropy noise or in the perception of discontinuities in spatial sound. The book applies these concepts to analyze works by Varèse, Ligeti, Saariaho, Berio, Roads, and others, offering composers and scholars a powerful, non-ethnocentric toolkit. It is essential reading for music professionals and all readers interested in cutting-edge research on the relationships between music and nature. This book provides a theoretical foundation for music created since the mid-20th century. While contemporary composition has extensively adopted noise, inharmonicity, and spatialization as primary structural materials, analytical frameworks to account for their formal function (beyond mere timbre description) have been lacking. By transplanting concepts from physics and natural science, the book offers a solid framework to discuss emerging musical and aesthetic approaches, including Acoustic Ecology and Sound Studies. By empirically investigating the notion of musical cadence in relation to these entropic processes, the book directly bridges the historical gap between pitch-centric theory and the aesthetics of sound studies, providing a powerful tool for future musicological and compositional research.