Relativity ρ – The Energetic Link of the Universe presents a new physical interpretation of time, gravitation, motion, matter, and the structure of the universe.Based on peer-reviewed articles, the book proposes that the passage of time is related to the universal density of potential energy, represented by ρ. From this principle, the author develops a universal gravitational variable and re-examines several central concepts of modern physics.The work questions the contraction of space, the absolute constancy of the speed of light, and conventional interpretations of dark matter and dark energy. It argues that the phenomena attributed to dark matter may instead result from ordinary, diffuse matter that remains difficult to detect, while cosmic expansion can be explained without invoking dark energy.Combining theoretical analysis, mathematical relations, and proposed experiments, this book offers an alternative approach that goes beyond Einstein’s geometry and seeks to describe relativity through observable physical processes.