  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 the 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
Wojciech Zurek's primordial paper that consolidated the concept of pointer
state, previously presented by Heinz Dieter Zeh. Employing a simple physical
model consisting of a pair of two-level systems -- one representing the main
system, the other the measurement apparatus -- and a thermal bath --
representing the environment -- we show how pointer states emerge, explaining
its contributions to the question of measurement in quantum mechanics, as well
as its limitations. Finally, we briefly show some of its consequences. This
paper is accessible to readers with elementary knowledge about quantum
mechanics, on the level of graduate courses.
