black-body radiation and cosmic microwave background
This is hardly a question.
http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation
Black-body radiation and cosmic microwave background (CMB) are related concepts in the field of physics and cosmology.
Black-body radiation refers to the thermal radiation emitted by an idealized object called a black body. A black body is a theoretical object that absorbs all radiation incident on it and emits radiation at all frequencies and intensities in a characteristic manner. The black-body radiation spectrum is continuous and depends only on the temperature of the object.
The cosmic microwave background radiation, on the other hand, is a faint glow of electromagnetic radiation that permeates the entire universe. It is a remnant from the early stages of the universe, specifically from a time known as the "recombination era" when the universe was about 380,000 years old. Prior to this time, the universe was filled with a hot, dense plasma that essentially prevented photons from freely propagating. However, as the universe expanded and cooled down, the plasma began to cool and atoms formed, allowing photons to travel freely. The cosmic microwave background radiation represents the last scattering of these photons from the recombination era and has been redshifted and cooled down to microwave frequencies due to the expansion of the universe.
To understand the connection between black-body radiation and cosmic microwave background, it is important to consider the characteristics of the cosmic microwave background radiation. The CMB has a thermal spectrum that closely resembles that of a black body with a temperature of about 2.7 Kelvin. This means that the radiation has a Planck spectrum that follows the black-body radiation curve at this temperature. The similarity between the CMB spectrum and black-body radiation is strong evidence for the Big Bang theory and the subsequent cooling of the universe.
In summary, black-body radiation refers to the thermal radiation emitted by an idealized object, while the cosmic microwave background radiation is the thermal radiation left over from the early stages of the universe. The CMB has a thermal spectrum similar to that of a black body, which serves as evidence for the Big Bang theory.