Residual Linewidths and the First Law of Coherence Thermodynamics

Spectral line broadening is a central diagnostic in atomic physics and astrophysics, yet residual linewidths remain even after accounting for conventional mechanisms such as natural, Doppler, collisional, and Stark or Zeeman effects. This study introduces the concept of coherence restructuring work as defined in the First Law of Coherence Thermodynamics, proposing that residual broadening represents the dissipative footprint of non Markovian field engagement. The approach extends thermodynamic formalism to include a memory dependent functional derived from generalized Langevin dynamics, and applies it to atomic spectra. We explain why hydrogen spectra exhibit minimal restructuring, while multi electron atoms and astrophysical systems reveal broadened lines consistent with history dependent coherence demands. Conclusions indicate that residual linewidths encode structural learning processes, reframing quantum collapse as a thermodynamic phenomenon driven by coherence restructuring rather than observer dependent measurement. This interpretation unifies atomic, stellar, and gravitational systems under a single coherence principle, offering a measurable pathway to probe non Markovian dynamics in both laboratory and astrophysical contexts.