Definition

1. Noun:
   • The cooled remnant of the hot big bang: The cosmic microwave background (CMB) is the afterglow radiation from the early universe, a nearly uniform sea of microwaves that permeates all of space.
   • A key piece of evidence for the Big Bang theory: It is the oldest light in the universe, providing a snapshot of the cosmos when it was about 380,000 years old.

Usage

• The term is used primarily in the fields of cosmology and astrophysics to describe the faint microwave radiation that is a fundamental prediction and confirmation of the Big Bang model.
• It is often discussed in the context of its discovery, its temperature, and the tiny fluctuations within it that seeded the formation of galaxies.

Examples

• Noun:
  • The discovery of the cosmic microwave background in 1965 was a major triumph for the Big Bang theory.
  • Scientists study the minute anisotropies in the cosmic microwave background to understand the universe's infancy.
  • The temperature of the cosmic microwave background is remarkably uniform, at approximately 2.725 Kelvin.

Advanced Usage

• "CMB anisotropies": Refers to the tiny temperature variations (on the order of one part in 100,000) in the CMB map. These irregularities are crucial for understanding the initial conditions of the universe.
  • The Planck satellite provided a highly detailed map of the CMB anisotropies.
• "CMB polarization": Refers to a specific pattern imprinted on the CMB radiation, which carries information about the universe's first moments and the nature of gravitational waves from the inflationary epoch.
  • Detecting specific modes of CMB polarization is a major goal of modern cosmology.

Variants and Related Words

• CMB: A common initialism for "cosmic microwave background."
  • The CMB is a cornerstone of modern cosmology.
• Cosmic Background Radiation: A broader term that can include other wavelengths, though it is often used synonymously with the microwave background.
• Recombination Epoch: The era, about 380,000 years after the Big Bang, when the universe cooled enough for protons and electrons to form neutral hydrogen atoms, making the universe transparent and releasing the photons we now see as the CMB.

Synonyms

• Relic Radiation: Emphasizes its origin as a leftover from the early universe.
• 3K Background Radiation: A historical name referencing its approximate temperature (3 Kelvin).

Related Phrases

• "The surface of last scattering": The spherical shell from which the CMB photons were emitted at the time of recombination. Observing the CMB is like looking at this surface.
  • The cosmic microwave background originates from the surface of last scattering.

Noun

1. (cosmology) the cooled remnant of the hot big bang that fills the entire universe and can be observed today with an average temperature of about 2.725 kelvin