  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?
