Cosmic microwave background

Acoustic peaks

Acoustic peaks are peaks in the cosmic microwave background power spectrum from sound waves in the early universe; they measure the universe's geometry and composition.

ACTPol

ACTPol (Atacama Cosmology Telescope Polarimeter) was a receiver on the six-meter Atacama Cosmology Telescope in Chile that measured cosmic microwave background polarization from 2013 until 2016.

Advanced ACTPol, also known as AdvACT, was the second-generation polarization receiver on the Atacama Cosmology Telescope in Chile, which replaced ACTPol and observed the cosmic microwave background from 2016 to 2022.

Axis of evil (cosmology)

The axis of evil, also called the ecliptic alignment anisotropy of the CMB, is a claimed alignment of large-scale cosmic microwave background patterns, named in 2005.

B-mode polarization

B-mode polarization is the curl-like, handed component of the cosmic microwave background's polarization, a distinctive fingerprint of primordial gravitational waves from inflation, with dust and lensing as contaminants.

BICEP / Keck Array

BICEP / Keck Array is a series of cosmic microwave background polarization experiments at the South Pole, searching for primordial gravitational waves from cosmic inflation.

Sep 29, 2026

Boltzmann solver

A Boltzmann solver is a numerical code integrating the Einstein–Boltzmann equations to compute cosmic microwave background spectra and the matter power spectrum of cosmological models.

CMB angular power spectrum

The CMB angular power spectrum measures cosmic microwave background temperature fluctuations by angular size on the sky; its acoustic peaks encode the universe's geometry and composition.

CMB circular polarization

CMB circular polarization is a hypothetical Stokes V component of the cosmic microwave background's polarization, constrained only by upper limits because it is never detected.

CMB cold spot

The CMB cold spot, or WMAP Cold Spot, is an unusually cold region in the cosmic microwave background in the constellation Eridanus, found in WMAP data.

CMB delensing

CMB delensing is the removal of gravitational-lensing distortions that intervening matter imprints on cosmic microwave background maps, mainly to reduce lensing B-modes that limit primordial gravitational-wave searches.

CMB dipole

The CMB dipole is the largest temperature anisotropy in the cosmic microwave background, about 3.36 mK, caused by the Solar System's motion at roughly 370 km/s.

CMB lensing reconstruction

CMB lensing reconstruction is the statistical estimation of the gravitational lensing potential that distorts the cosmic microwave background, using quadratic estimators of temperature and polarization correlations.

CMB polarization

CMB polarization is the linear polarization of the cosmic microwave background, first detected in 2002, whose B modes are a sought signature of primordial gravitational waves from inflation.

CMB-S4

CMB-S4 (Cosmic Microwave Background Stage 4) was a proposed next-generation experiment, planned by the Department of Energy and NSF for the South Pole and Chile, canceled in 2025.

Cosmic Background Imager

The Cosmic Background Imager (CBI) was a 13-element radio interferometer built by Caltech that operated on Chile's Chajnantor Plateau from 1999 to 2008, measuring cosmic microwave background temperature and polarization.

Cosmic birefringence

Cosmic birefringence is the rotation of light's polarization plane as it crosses the universe, sought in the cosmic microwave background as a sign of parity-violating physics.

Cosmic dipole

The cosmic dipole is a large-scale sky anisotropy seen in the cosmic microwave background and in distant quasars, whose mismatch, the cosmic dipole anomaly, exceeds 5σ.

Cosmic microwave background

The cosmic microwave background (CMB), also called relic radiation, is leftover light from the universe at 380,000 years old, detected as microwaves near 2.725 K.

Cosmic microwave background spectral distortions

Cosmic microwave background spectral distortions are departures of the CMB's spectrum from a perfect blackbody, caused by energy released after thermalization fails in the early universe.

Cosmic variance

Cosmic variance is the fundamental sampling uncertainty in cosmology that comes from observing only one Universe, limiting measurements like the cosmic microwave background power spectrum.

Cosmology Large Angular Scale Surveyor

The Cosmology Large Angular Scale Surveyor (CLASS) is an array of four microwave telescopes in Chile's Atacama Desert, led by Johns Hopkins University, that measures cosmic microwave background polarization.

DASI

DASI, the Degree Angular Scale Interferometer, was a 13-element radio interferometer at the Amundsen-Scott South Pole station that measured cosmic microwave background anisotropy and its angular power spectrum.

Discovery of cosmic microwave background radiation

The discovery of the cosmic microwave background radiation was made by Arno Penzias and Robert Wilson at Bell Labs in Holmdel, New Jersey, in 1964–65.

Doppler peak

The Doppler peak, also called the acoustic or Sakharov peak, is a prominent peak in the cosmic microwave background's power spectrum, produced by acoustic oscillations of the early photon-baryon plasma.

E-mode polarization

E-mode polarization is the curl-free (gradient-like) component of the cosmic microwave background's linear polarization, produced by Thomson scattering and first detected by DASI in 2002.

EBEX

EBEX, the E and B Experiment, was a balloon-borne polarimeter that measured cosmic microwave background polarization, flying near the South Pole for about 25 days in 2012-13.

Gravitational lensing of the cosmic microwave background

CMB weak lensing is the gravitational distortion of the cosmic microwave background by intervening matter, which traces the universe's projected mass distribution and constrains dark energy and neutrino mass.

Hemispherical power asymmetry

The hemispherical power asymmetry is a cosmic microwave background anomaly where temperature fluctuations are larger on one hemisphere, first seen in WMAP data in 2004.