  This note has no new results and is therefore not intended to be submitted to
a "research" journal in the foreseeable future, but to be available to the
numerous individuals who are interested in this issue. Several of those have
approached the author for his opinion, which is summarized here in a hopefully
pedagogical manner, for convenience. It is demonstrated, using essentially only
energy conservation and elementary quantum mechanics, that true decoherence by
a normal environment approaching the zero-temperature limit is impossible for a
test particle which can not give or lose energy. Prime examples are: Bragg
scattering, the M\"ossbauer effect and related phenomena at zero temperature,
as well as quantum corrections for the transport of conduction electrons in
solids. The last example is valid within the scattering formulation for the
transport. Similar statements apply also to interference properties in
equilibrium.
