We propose a minimalist hypothesis in which the only fundamental entity is a real scalar field defined on four-dimensional Euclidean space (E4). An observer is modeled as a stable "cognitive tube"—a locally causal region of field projections onto a family of three-dimensional slices Sigma^3(l). From non-dynamical conditions of embodiment, local causality, stability, and unitarity, we derive:1.Emergent spacetime with a pseudo-Riemannian metric and Lorentz transformations as the only compatible symmetry group; 2.The Einstein field equations as a variational extremum of the cognitive action; 3.Quantum field theory and the Born rule as necessary conditions for cognitive reproducibility; 4.The minimal symmetry group U(1) x SU(2) x SU(3) and a cognitive Higgs mechanism. The model predicts the absence of a graviton and prohibits coherent superpositions of distinct spacetime metrics, providing clear falsifiability criteria: detection of a graviton or interference between distinct gravitational configurations would refute the hypothesis. The unified emergence of special relativity, general relativity, and Standard Model symmetries highlights the explanatory power of the approach and opens a path to experimental tests of the cognitive nature of physical laws.