Cosmic Microwave Background
Relic blackbody radiation from the epoch when photons decoupled from matter.
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Cosmic Microwave Background
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Origin
The early universe was hot and ionized, so photons scattered frequently from free electrons. When the universe cooled enough for neutral atoms to form, photons decoupled and began to travel freely.
Temperature Scaling
Radiation temperature scales as
The observed microwave background is the redshifted remnant of this early hot radiation field.
Why It Matters
The CMB is evidence for a hot early universe. Its anisotropies encode the initial conditions for structure formation.
Complete Cosmology
A standard introductory path through expansion, Friedmann dynamics, distance scales, and the thermal history of the universe.
Friedmann Equations
The equations governing the expansion of a homogeneous and isotropic universe.
Scale Factor and Redshift
Cosmological redshift is the stretching of photon wavelengths by the expansion of space.