  We report on observation of the time reversal symmetry breaking in
unpolarized neutrons scattering experiment. Neutron transmittivity through the
system consisting of two magnetic mirrors placed in an external magnetic field
is measured. Time reversal symmetry holds for coplanar magnetic configuration,
meaning that transmitted intensity does not change when interchanging neutron
source and detector. Contrarily, for noncoplanar magnetic configuration the
time reversal symmetry breaks down. In this case the transmitted intensity
changes when interchanging the source and detector. The observed time reversal
symmetry breaking is the consequence of the one of the most fundamental
properties of quantum mechanics, namely the non-commutativity of spin algebra.
