  Current quantum orthodoxy claims that the statistical collapse of the
wave-function arises from the interaction of the measuring instrument with its
environment through the phenomenon known as environment induced decoherence.
Here it is shown that there exists a measurement scheme that is exactly
decohering without the aid of an environment. The scheme relies on the
assumption that the meter is decomposable into probe and pointer, with the
probe taken to be inaccessible for observation. Under the assumption that the
probe and the pointer initial states are momentum limited, it is shown that
coherences die out within a finite interval of time and the pointer states are
exactly orthogonal. These lead to the fundamental realization that dispersion
of correlation does not require an external infinite number of degrees of
freedom. An internal one degree of freedom is already sufficient to delocalize
the correlations and leave its subparts in a classical mixed state, so that
decoherence may occur even for isolated measuring instruments.
