BRAINCAKECosmic Microwave Background Radiation
The cosmic microwave background radiation (CMB) is electromagnetic radiation in the microwave region that reaches the Earth from all directions in space. It was discovered by accident in 1965 by Penzias and Wilson.
Its spectrum is almost exactly that of a black body at a temperature of about 2.7 K. It is also almost perfectly isotropic: its intensity is the same in every direction to about 1 part in 100 000.
Origin: about 380 000 years after the Big Bang, the universe had cooled to about 3000 K. At this temperature, electrons and nuclei could combine to form neutral atoms. Before this, photons were constantly scattered by free charged particles, so the universe was opaque. Once atoms had formed, the photons could travel freely and the universe became transparent. Those photons are the CMB.
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More in Astrophysics and Cosmology
- The Cosmological Principle
- The Doppler Effect and Red Shift
- Hubble's Law
- The Big Bang Theory
- The Age of the Universe
- Evolution of the Universe
- Dark Matter
- Dark Energy
All 24 lessons in Astrophysics and Cosmology · All OCR A-level Physics topics