The cosmic far-infrared background is half of everything galaxies ever emitted: the nearly isotropic glow of dust-reprocessed starlight integrated over cosmic time carries roughly as much energy as all the optical and ultraviolet light that escaped unabsorbed (Hauser and Dwek 2001; Dole et al. 2006). Whatever made the stars made this glow, so its intensity, spectrum, and clustering are a closed account of cosmic star formation that no galaxy-formation model can evade.
The account does not quite balance. ΛCDM-based models of galaxy formation and dust emission match the broad CFIRB spectrum and source counts, but persistent hints of excess far-infrared intensity and excess clustering on particular angular scales resist the standard bookkeeping, suggesting either dusty source populations earlier than standard assembly provides or revisions to how and when galaxies made their dust (Lagache et al. 2005; Bethermin et al. 2017). The strain compounds the resolved-source problem: dust requires metals, metals require prior stellar generations, and a far-infrared excess at high redshift demands chemical maturity on timescales hierarchical growth cannot meet, the background-light version of the oxygen-rich z above 14 galaxies JWST keeps confirming.
The standing is a closing budget: as ALMA and JWST resolve more of the glow into sources, the room for hiding the excess in modeling freedom shrinks, and the question of when the universe made its dust becomes an observation rather than a prescription.