Author perspective · cosmology
The early-universe case for non-baryonic matter
Cosmology asks a different question from galaxy fitting: what mixture of components can reproduce the thermal history, acoustic pattern, geometry and growth of structure at the same time?
Why this matters
If dark matter were only a bookkeeping device for individual galaxies, cosmology would not necessarily demand the same component. The CMB and large-scale structure provide an independent scale on which the hypothesis must survive.
Background equations
w(a)=w₀+w_a(1−a)
The background determines how components dilute and how distances accumulate. Perturbations add the information carried by clustering and acoustic physics.
Why baryons are not interchangeable with cold dark matter
Before recombination, baryons are tightly coupled to photons and participate in acoustic oscillations. A collisionless non-baryonic component can begin building potential wells without joining that photon-baryon fluid. Replacing cold dark matter with baryons therefore changes the CMB structure and later growth instead of merely relabelling Ω.
What the percentages mean
Values such as Ω_b and Ω_cdm are posterior parameters inside a model and dataset combination. They are not four substances placed on a laboratory scale. This is why the project exposes h, physical densities ω=Ωh² and flat-universe closure on a separate calculation page.
My interpretation
I find cosmology strongest when used as a consistency test rather than a source of decorative percentages. A model should explain the CMB, BAO distances, growth and local structure with one parameter set—or reveal where new physics or systematics are required.
Future path
DESI, CMB lensing, Rubin, Euclid and Roman will tighten cross-checks between expansion and growth. The most interesting outcome may be a statistically credible inconsistency between probes that survives calibration changes.