Learning is Architecture: From Backpropagation's Structural Flaw to Nested Co-Adaptation Across Timescales

We argue that backpropagation's dependence on externally supplied targets is not a technical limitation but a structural flaw revealing a fundamental misconception about learning. We develop a physical theory of learning defined as the adaptation of physical architecture to the informational structure of the environment, identify four nested layers of adaptation (evolution, development, plasticity, dynamics), and present MNIST experiments validating the theory. We extend the framework to memory, disease, trauma, pain, and consciousness.