What is the Cosmic Microwave Background (CMB)?
The Cosmic Microwave Background (CMB) is the faint, uniform radiation permeating the universe, considered the oldest light detectable. It is a residual thermal radiation from the Big Bang, originating from an epoch about 380,000 years after the Big Bang when the universe cooled sufficiently for protons and electrons to form neutral atoms, making the universe transparent to light for the first time.
Key Properties and Discovery
The CMB is observed as microwave radiation because the universe's expansion has stretched the original short-wavelength light (visible/infrared) to much longer wavelengths. It has an almost perfectly uniform temperature of about 2.725 Kelvin (-455 degrees Fahrenheit) across the entire sky. It was accidentally discovered by Arno Penzias and Robert Wilson in 1964, providing strong evidence for the Big Bang theory.
Significance in Cosmology
The CMB is a crucial pillar of modern cosmology. Its nearly uniform temperature confirms the universe was initially very hot and dense, supporting the Big Bang model. Tiny temperature fluctuations within the CMB, however, are extremely significant; they represent primordial density variations that eventually evolved into the large-scale structures we see today, like galaxies and galaxy clusters.
How We Study the CMB
Scientists study the CMB using specialized telescopes and satellites, such as COBE, WMAP, and Planck, which are designed to detect microwave radiation from space. These missions map the minuscule temperature anisotropies (variations) across the sky with incredible precision, allowing cosmologists to infer fundamental properties of the universe, including its age, composition, geometry, and expansion rate.