Irreversibility and Measurement in Quantum Mechanics

Irreversibility is often considered to characterize measurements in quantum mechanics. Fundamental problems with this characterization are addressed. First, whether a measurement is made in quantum mechanics is an arbitrary decision on the part of the experimenter concerning how the experimental circumstances are structured. Second, how is irreversibility that occurs in making a measurement explained in terms of a neurophysiological mechanism where a macroscopic measuring instrument is not required in principle to make the measurement, as in macroscopic quantum tunneling? Third, how does irreversibility characterize a negative observation where there is no physical interaction in the measurement process?