In quantum mechanics, pointer states are eigenstates of the observable of the measurement apparatus
that represent the possible positions of the display pointer of the equipment. The origin of this
concept lies in attempts to fill the blanks in Everett’s relative-state interpretation, and to make
it a fully valid description of physical reality. To achieve this, it was necessary to consider not
only the main system interacting with the measurement apparatus (like von Neumann and Everett did)
but also the role of the environment in eliminating correlations between different possible
measurements when interacting with the measurement apparatus. The interaction of the environment
with the main system (and the measurement apparatus) is the core of the decoherence theory, which
followed Everett’s thesis. In this article, we review the measurement process according to von
Neumann, Everett’s relative state interpretation, the purpose of decoherence and some of its
follow-up until Wojcie…