The earliest and most widely accepted school of interpretation of quantum mechanics is known as the Copenhagen interpretation, which focuses on the role of the observer or on the act of measurement.
Much to the dismay of many physicists, the Copenhagen interpretation has led to a certain degree of theological speculation about God as the conscious observer that ultimately is collapsing the wave function.
This is answered according to the Copenhagen interpretation by saying that the wavefunction collapses into one particular direction, but without explaining why one direction is chosen and not another.
The Copenhagen interpretation tries to get around real problems such as which slit the electron goes through in a double slit experiment by saying that the question is meaningless.
Here is the importance of the observerin traditional quantum mechanics under the Copenhagen Interpretation.
Weizsacker and Gornitz want to bringthe observer into the Copenhagen Interpretation, and for that purpose they have worked out an abstract quantum mechanics divorced from ordinary space and time and particles.
The Copenhagen interpretation
of Quantum Mechanics proposed a process of collapse which is responsible for the reduction of the superposition into a single state.
In the meantime, the "standard" Copenhagen interpretation emphasizes the role of observer where the "decoherence viewpoint" may not.
The electromagnetic origin of quantization and the ensuing changes of Copenhagen interpretation.
If the Copenhagen interpretation
was and is, as Herbert calls it, "establishment physics," it was that in the sense that people threw occasional grains of incense on its altar and then backed away.
During the 40 years (1922-1962) he presided over the University Institute for Theoretical Physics in Copenhagen, he and a revolving company of mostly young physicists -- over the years more than 600 from almost 40 countries -- worked out much of the quantum theory as physics and also a philosophical and epistemological atitude that became known as the Copenhagen Interpretation.
This is more or less the second tenet of the Copenhagen Interpretation.