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?
There are three major sources of the 'randomness' underlying noise phenomena. These are the random outcomes of quantum 'measurement' processes, the random ensembles of statistical mechanics, and the algorithmic complexity of many dynamical processes. Here I dwell on the possible connections between the first two sources of randomness. It is often held that the empirical irreversibility of quantum measurement arises from statistical mechanics. I present somewhat speculative arguments that in fact the irreversible approach to statistical ensembles may be rooted in an irreversible quantum decoherence process.
The quantum measurement problem persists because quantum mechanics provides no physical criterion for when a measurement occurs or why outcome selection is irreversible. We propose a resolution based on a single principle: a measurement occurs precisely when entropy irreversibly flows from a quantum system into its environment, producing distinguishable environmental states and eliminating interference. Within this framework, wavefunction “collapse” is not an additional axiom but a physical consequence of thermodynamic irreversibility.