The cosmic microwave background (CMB) is the oldest light in the universe, a relic radiation that reveals the early universe’s conditions and evolution.
Gravitational lensing of the cosmic microwave background (CMB) is the bending of CMB photons by massive structures along their path, distorting the temperature and polarization patterns we observe. This subtle effect provides a powerful probe of dark matter distribution, cosmic structure growth, and fundamental cosmology.
The COBE mission measured the cosmic microwave background with unprecedented precision, confirming its blackbody spectrum and detecting tiny temperature fluctuations that seeded galaxy formation. These results solidified the Big Bang model and earned the 2006 Nobel Prize in Physics.
The Sachs–Wolfe effect explains how gravitational potential wells and hills imprint large-scale temperature fluctuations on the cosmic microwave background. It connects the first fraction of a second after the Big Bang to the dark-energy-dominated present, offering a key test of inflation and the standard cosmological model.
The sound horizon is the maximum distance a sound wave could have traveled through the hot plasma of the early universe from the Big Bang until recombination. This fixed scale leaves a distinct imprint on the cosmic microwave background and the large-scale structure of the universe, making it a crucial ruler for measuring cosmic expansion and the geometry of space.
Primordial gravitational waves are ripples in spacetime generated during cosmic inflation. They leave a unique imprint called B-modes in the polarization of the cosmic microwave background, offering a direct window into the universe’s first fraction of a second and the physics at energies far beyond particle accelerators.
CMB lensing is the subtle gravitational deflection of cosmic microwave background photons by dark matter and large-scale structure. It turns the oldest light into a backlight that maps the invisible dark matter distribution. Measurements from Planck and future experiments use this effect to constrain dark matter, neutrino masses, and the growth of cosmic structure.
Learn how cosmic microwave background maps are made—from raw time-ordered data to full-sky images—and explore the cosmic epochs they reveal, from the Planck epoch to structure formation.
CMB foregrounds are astrophysical emissions from our galaxy and extragalactic sources that contaminate cosmic microwave background observations. They are especially problematic for polarization measurements, where synchrotron and thermal dust radiation can be polarized at 10–40%, overwhelming the faint primordial B-mode signal that would confirm cosmic inflation.
The cosmic microwave background (CMB) power spectrum is a cornerstone of modern cosmology. It maps the tiny temperature fluctuations in the universe’s oldest light, revealing the composition, geometry, and evolution of the cosmos from the Planck epoch to the present day.
The cosmic microwave background (CMB) power spectrum is a detailed map of temperature fluctuations in the oldest light of the universe, revealing the seeds of all cosmic structure. This guide explains how it is measured, what it tells us about the universe’s origin and evolution, and the key cosmic epochs it illuminates.
