The Science of Natural Truth is a rigorous ontological and philosophical investigation into the thought of Ramalinga Swamigal (Vallalar), presenting him not merely as a saint or devotional poet, but as one of the most original metaphysical thinkers in the history of human thought.This work examines Vallalar's prose teachings and Arutperunjothi Agaval through a disciplined academic lens, revealing a coherent and comprehensive ontology of space, causality, matter, energy, and grace. Central to this study is Vallalar's assertion that space itself is eternal, non-empty, dynamically expansive and contractive, and governed by an intrinsic causal reality he names Arutperunjothi, the Boundless Grace Light. Remarkably, these insights precede and conceptually anticipate the foundations of modern cosmology, general relativity, quantum field theory, and atomic physics by several decades.In parallel, this study places Vallalar in comparative dialogue with major philosophical and spiritual traditions including the Upanishads, Samkhya, Vaisheshika, Jain, Buddhist, Neoplatonic, Daoist, Islamic, and Western metaphysical systems showing with precision where Vallalar converges with, extends beyond, or decisively surpasses them. Unlike most traditions that treat space as static, passive, or merely conceptual, Vallalar uniquely affirms space as an active ontological principle governed by a universal order of grace.