  In the classical theory, an electromagnetic field obeying Maxwell's equations
cannot be absorbed quickly by matter, so that it remains a zero point field.
Splitting the total, genuine electromagnetic field into the sum of a
conventional field and a zero point field is physically meaningless until a
receiver attenuates the genuine field down to the zero point field, or studying
the amplification of the zero point field by a source.
  In classical optics all optical effects must be written using the genuine
field, so that at low light levels the nonlinear effects become linear in
relation to the conventional field. The result of the interpretation of all
observations, even at low light levels, is exactly the same in quantum
electrodynamics and in the semi- classical theory.
  The zero point field is stochastic only far from the sources and the
receivers; elsewhere, it is shaped by matter, it may be studied through fields
visible before an absorption or after an amplification.
  A classical study of the reduction of the wave packet extends the domain of
equivalence of the classical and quantum zero point field; using both
interpretations of this field makes the results more reliable, because the
traps are different.
