Cosmology@Home

Cosmology@Home was a long-running effort to fit theoretical models of the universe against the highest-precision observational data — primarily measurements of the Cosmic Microwave Background (CMB) from WMAP and later Planck, and the Hubble expansion rate from successive HST campaigns.

The computational task was Bayesian model comparison at scale. Each work unit generated a candidate cosmological model — picking values for parameters like the matter density Ω_m, dark-energy density Ω_Λ, the spectral index of primordial fluctuations n_s, the Hubble constant H₀, and a dozen others — then computed what CMB power spectrum and expansion history that model would produce. Volunteers' computers ran tens of thousands of these candidate universes, building up a statistical map of which corners of parameter space were consistent with what we actually see in the sky.

The project launched in 2007 at the University of Illinois at Urbana-Champaign Departments of Astronomy and Physics, and later moved to the Institut Lagrange de Paris and the Institut d'Astrophysique de Paris under Marius Millea. Across its lifespan it contributed to the parameter-fitting infrastructure used by the Planck collaboration and other CMB experiments.

By 2024 the project was effectively unmaintained — the server had been down for over five months with no active administrator for over a year. Cosmology@Home was officially retired in October 2024. Like SETI@home, it was a casualty of the slow collapse of academic stewardship for legacy volunteer-computing projects: the science had moved on, the original PIs had moved on, and the infrastructure quietly aged out. But for nearly two decades it gave home computers a direct role in some of cosmology's deepest measurements.