  A general physical model is presented for 1/f noise. The main questions
raised by this type of noise can be solved if at the origin of the phenomenon
we consider many similar like RTN two-state processes in co-operation among
them to generate a Gaussian average process with 1/f power spectrum. Even if
the originating RTN processes have the same relaxation time, their co-operation
produces in short times secondary RTN processes with a distribution of
relaxation times which generates again 1/f noise. An extension of the model to
a single two-state process viewed in "series" reveals once more the appearance
of 1/f noise. Experimental results, found in the literature, agree with this
model under various aspects.
