Observers in Quantum Field Theory Cannot Be Fundamental Excitations

Which physical systems can play the observer role that quantum field theory presupposes in practice? We propose two simultaneous necessity conditions: a relativistic-frame condition N_SR requiring a Poincaré-equivariant worldline-and-tetrad assignment with pointwise future-timelike four-momentum spectral support, and a record-formation condition N_QM requiring a persistent macroscopic pointer subalgebra on the candidate's own algebra under natural Standard Model dynamics. Together they yield a no-go theorem for the Standard Model's fundamental one-particle excitations as observers. Massless helicity states fail N_SR because their spectral support is null. Every one-particle Wigner sector fails N_QM because its irreducible representation lacks the tensor-product substructure needed for a macroscopic pointer subalgebra. The Higgs, W, and Z also fail dynamically because their decay widths preclude pointer persistence on macroscopic timescales. We know of no other identified Standard Model class that satisfies both conditions, leaving long-lived material composites (atoms, molecules, condensed matter, and their collective phases) built from fundamental fermions as the surviving candidates, classified by whether their constituents are fermions rather than by their total exchange statistics.