Blackbody radiation
Blackbody radiation:
If a closed box made of any material is heated to a uniform temperature, the
interior will become filled with electromagnetic radiation (photons) with an
intensity and spectrum determined by the temperature alone, independent of the
composition of the box. Radiation with this intensity and spectrum is called
blackbody, or thermal radiation. The intensity and spectrum are determined by
the criterion of thermal equilibrium; i.e., only far this intensity and
spectrum will the absorption and emission of photons by the walls be in balance
for each wavelength, so the intensity for each wavelength can be independent of
time. The universe today appears to be permeated with blackbody radiation at a
temperature of 2.73°K--the cosmic background radiation-which we interpret as a
remnant afterglow of the heat of the early universe.
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