Some authors state that the last stage in this chain of measurements involves "consciousness," or the "intellectual inner life" of the observer, by virtue of the "principle of psycho-physical parallelism." Other authors introduce a wave function for the entire universe. In this book, I shall refrain from using concepts that I do not understand.

Asher Peres (1995). Quantum theory: concepts and methods. Springer. p. 26–27. ISBN 0792336321.