A collection of the key observational evidence that supports the Big Bang model of the universe’s origin and evolution.
The Lyman-alpha forest is a series of absorption lines in quasar spectra caused by neutral hydrogen in the intergalactic medium. It serves as a powerful probe of cosmic structure, revealing the distribution of gas from the epoch of reionization to the present day, and providing a window into the evolution of the universe.
Deuterium, a heavy isotope of hydrogen, was forged in the first minutes after the Big Bang. Its measured primordial abundance matches theoretical predictions with remarkable precision, providing powerful confirmation of the hot Big Bang model and constraining the baryon density of the universe.
The integrated Sachs–Wolfe (ISW) effect is a secondary anisotropy in the cosmic microwave background caused by the time variation of gravitational potentials along the line of sight. It arises when the universe’s expansion accelerates—most notably due to dark energy—and provides a unique probe of dark energy and the growth of cosmic structure.
The first galaxies formed a few hundred million years after the Big Bang, ending the cosmic dark ages. Their observational signatures include ultraviolet continuum, Lyman-alpha emission, and nebular lines like H-alpha, which JWST is now detecting.
Cosmic variance is the inherent statistical uncertainty in cosmological observations because we can only see one universe. This article explains its origins, its impact on measurements of the cosmic microwave background, and how it shapes our understanding of the cosmos.
The cosmic microwave background’s acoustic peaks encode the geometry and matter content of the universe. By measuring their positions and heights, cosmologists can determine the total density, baryon density, and curvature with remarkable precision.
The cosmic microwave background (CMB) is the oldest light in the universe, a relic of the hot, dense state that existed just 380,000 years after the Big Bang. Its discovery and precise measurement provided decisive evidence for the Big Bang model, ruling out steady-state alternatives and opening a new era of precision cosmology.
Baryon acoustic oscillations (BAO) are subtle ripples in the distribution of matter left over from the early universe. These patterns act as a standard ruler, allowing astronomers to measure the expansion history of the cosmos and probe the nature of dark energy.
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 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.
