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1. Note that ironically, quantum mechanics was discovered via the classical limit
of a radiation law! In fact, the Rayleigh-Jeans-law contains no Planck constant , whereas
the parameters and in the 19th-century `thermodynamic' Wien law contain and
, both fundamental constants in microscopic theories
(although at that time, the deep physical meaning of and was of course not understood).
2. Nowadays, instead of one often uses
. Instead of the frequency
one often uses the angular frequency
. If is used instead of ,
the spectral energy density
is defined as
. Since
, this gives
. Therefore, be careful when comparing
different definitions and doing calculations because a wrong factor
gives a result that is wrong by nearly one order of magnitude!
3. Cosmic black body radiation is a consequence of the `Big Bang Model'. Measurements
of the cosmic background radiation corresponding to a temperature
K were
performed by R. H. Dicke and co-workers.
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Tobias Brandes
2004-02-04