A collection of the key observational evidence that supports the Big Bang model of the universe’s origin and evolution.
Baryon acoustic oscillations (BAO) are subtle ripples in the distribution of matter across the cosmos, frozen in when the universe was only 380,000 years old. They serve as a standard ruler for measuring cosmic distances and probing the nature of dark energy.
Galaxy redshift is the foundational observation that revealed the universe is expanding. This article traces how stretched light from distant galaxies became the cornerstone of modern cosmology, from Edwin Hubble’s discovery to the detailed cosmic timeline of the Lambda-CDM model.
Before recombination, the universe was an opaque plasma of free electrons and photons. When electrons and protons combined to form neutral hydrogen, light finally decoupled, creating the cosmic microwave background. This article explains the physics behind this cosmic milestone and why no telescope can see earlier with light.
Cosmological redshift is the stretching of light to longer wavelengths as the universe expands. This phenomenon underpins our understanding of cosmic history, from the Big Bang to the formation of galaxies, and is a cornerstone of modern cosmology.
Big Bang nucleosynthesis (BBN) is the production of light elements during the first minutes of cosmic time. Its evidence comes from the remarkable agreement between predicted and observed primordial abundances, which also constrains the baryon density and supports the standard hot Big Bang model.
In the late 1990s, two independent teams used Type Ia supernovae as standard candles to trace the universe’s expansion history. Their surprising conclusion—that cosmic expansion is accelerating—revolutionized cosmology and led to the concept of dark energy, a mysterious force driving the universe apart.
Primordial helium, forged in the first minutes after the Big Bang, provides a crucial test of the hot Big Bang model. Its measured abundance matches theoretical predictions, reinforcing our understanding of the universe’s origin and evolution.
The cosmic microwave background (CMB) is the oldest light in the universe, a relic of the hot Big Bang. This article explains how astronomers measure it from Earth, what it reveals about cosmic history, and why it anchors our modern understanding of the cosmos.
The Hubble–Lemaître law describes the expansion of the universe, showing that galaxies recede at speeds proportional to their distance. It is a cornerstone of modern cosmology, linking the Big Bang to the cosmic microwave background and the large-scale structure of the cosmos.
The universe is 13.8 billion years old. This definitive guide explains how astronomers measure the age of the cosmos using the cosmic microwave background, stellar evolution, and the expansion rate, and traces the universe’s evolution from the Planck epoch to the present day.
