The horizon problem asks why distant regions of the universe have nearly identical temperatures despite never being in causal contact. Cosmic inflation solves it by stretching a tiny, causally connected patch to cosmic scales, explaining the uniformity of the cosmic microwave background and the origin of structure.
The Hubble constant (H₀) quantifies the expansion rate of the universe. Astronomers measure it using two independent approaches: the local distance ladder (Cepheid variables and Type Ia supernovae) and early-universe probes (cosmic microwave background and baryon acoustic oscillations). The discrepancy between these values, known as the Hubble tension, is one of the most pressing problems in modern cosmology.
The damping tail is the high-multipole region of the cosmic microwave background power spectrum where temperature fluctuations are exponentially suppressed by photon diffusion and Silk damping. It provides a precise probe of the baryon density, the epoch of recombination, and the physics of the early universe, and has been measured by COBE, WMAP, and Planck.
The cosmic microwave background (CMB) is the oldest light in the universe, a relic of the Big Bang. Its near-perfect blackbody spectrum and tiny temperature fluctuations provide powerful evidence for cosmic inflation, the theory that the universe expanded exponentially in the first fraction of a second. This article explains how CMB observations confirm inflation and traces the cosmic epochs from the Planck era to structure formation.
The cosmic web is the largest known pattern in the universe—a vast network of filaments, sheets, and voids made of dark matter, gas, and galaxies. This article traces its origin from the Big Bang through cosmic inflation, recombination, and structure formation, and explains how missions like Planck and JWST have mapped its evolution.
Baryogenesis is the hypothesized process that created the observed imbalance between matter and antimatter in the early universe. This article explains the cosmic timeline, the Sakharov conditions, and how this asymmetry led to the universe we see today.
Cosmic microwave background anisotropies are tiny temperature fluctuations in the oldest light of the universe that encode the density perturbations seeding all cosmic structure. By decoding their angular power spectrum, cosmologists have established the ΛCDM model: a flat universe composed of roughly 5% ordinary matter, 27% dark matter, and 68% dark energy.
Dark matter is the invisible substance that makes up about 27% of the universe, shaping galaxies and cosmic structure. This guide explains its discovery, its role in the universe’s evolution from the Big Bang to today, and the evidence that confirms its existence.
Cosmic voids are vast, nearly empty regions between galaxy filaments that hold clues to the universe’s structure and evolution. This guide explains how they form, their role in the cosmic web, and how they connect to the major epochs from the Big Bang to the present day.
The cosmic scale factor a(t) is a dimensionless parameter that tracks how distances in the universe grow with time. It connects redshift to expansion and underlies the standard model of cosmology, from the Planck epoch to the dark-energy era.
