Physics describes the universe through fundamental forces and interactions. Biology describes systems through sensing, signalling, regulation, and adaptation. These two descriptions coexist without being unified at the level of mechanism. There is no widely accepted account of how interaction becomes sensing, how sensing becomes capability, and how capability scales into consciousness and biological evolution. This paper provides that account. The framework proceeds from two prior foundations. The Big Flare-Up Theory (BFUT, Layer 1) established that the physical substrate of spacetime is the Spaticle field, from which the four fundamental interaction channels emerge sequentially, each requiring a different level of structural complexity. Vijay's Law (Layer 2) established that all systems in the universe exhibit a non-zero degree of consciousness, that consciousness is a fundamental property of all matter expressed differently at different scales, and that what physics describes as forces and interactions are the elementary expressions of consciousness at the atomic and subatomic scale. The present paper, BFUT Paper 20, provides the formal physical mechanism connecting these two claims. The central result is the Hierarchical Channel Accessibility (HCA) framework, comprising four interlocking components. First, a formal three-condition definition of sensing that distinguishes sensing from mere interaction through structural coupling, information-specific state change, and state persistence. Second, the HCA Law: a system can exhibit a capability only if it possesses the structural configuration required to couple to the interaction channels that implement that capability, with access to higher-order channels implying all lower-order structural prerequisites. Third, the Structural Inclusion Principle: the presence of a higher-order sensing capability implies the structural presence of all lower-order channel prerequisites. Fourth, the distinction between controlled and forced signal emission as the physically grounded separator between systems that merely interact and systems that actively sense. The paper introduces the Consciousness Index (CI), a physically grounded scalar measure of the degree of consciousness derivable from the Spaticle field channel structure, addressing limitations of existing measures such as Tononi's phi by grounding the measure in a physical substrate derivation. The paper also derives the governing state-change functional dS/dt consistent with the Spaticle field Lagrangian, provides worked channel-level effective representations with biological examples, demonstrates the Structural Inclusion Principle across five sensing modalities with suppression tests, states five falsifiable predictions, connects the framework to Layer 2 (consciousness as fundamental), Layer 3 (evolution as channel expansion under conscious drive), and Layer 5 (the cellular civilisation and governance model). Consciousness is defined as the integrated multi-channel state of a system with feedback and memory, graded continuously from the gravitational coupling of a single atom to the full multi-channel integration of a mammalian nervous system. This paper is the final paper in the BFUT programme and closes the arc from the physical substrate of spacetime to the emergence of life, consciousness, and evolution within a single unified derivation. Part of the Big Flare-Up Theory (BFUT) research programme.
V. K. Sharma (Wed,) studied this question.