Introduction To Cosmology

Modern cosmology combines observations with physical laws. Important cosmological observations include: motion and distribution of galaxies; redshift of distant galaxies; cosmic microwave background radiation; large-scale distribution of matter; evidence for dark matter; evidence for accelerated cosmic expansion. Cosmologists use models to explain these observations. A successful cosmological model must agree with observations. On sufficiently large scales, the universe is approximately: **homogeneous — matter is distributed roughly uniformly when averaged over very large distances. isotropic** — the universe looks broadly similar in every direction on very large scales. These ideas form an important foundation of standard cosmological models.

There is no single defining equation for cosmology at this introductory level. A central observational relation introduced later is: **v = H₀d**