I am reading some papers on the Measurement Problem.
What strikes me is how measurement is visualized. It is visualized as taking place in a laboratory. The system – an isolated state – encounters a macroscopic measuring device. In doing so the Hilbert Spaces of the two become entangled. A pointer state of the device signals the system’s state. This is the scheme set down by von Neumann in 1932 and explained and expanded upon by Schlosshauer in a review article. Another gripping article is by Geoffrey Sewell, who says, effectively, that there is no measurement problem.
But is measurement about laboratories?
In the laboratory a photodetector signals the arrival of each photon and a counter accumulates the counts. It works because the photon is absorbed, ejecting an electron. (A current of free electrons moves pointers.) The reaction
(photon + bound electron) yields (free electron)
is what marks the measurement.
But is not any green leaf a photodector? The photon gets absorbed via photosynthesis. The leaf’s vitality is a photon count accumulator. The reaction
(photon + water + carbon dioxide) yields (sugar + oxygen)
marks the ‘measurement’.
Surely every chemical reaction that goes to completion is a measurement event; the reactants disappear and the products appear. Isn’t every inelastic scattering a measurement event? In every such event the original quantum system is destroyed and something new emerges. It is just the property of any chemical reaction.
What, then, constitutes a measurement?
It seems to me that the essence of measurement is captured by any elemental process that procedes irreversibly. When that happens probabilities become converted into certainties. The very word, ‘happens’, captures the essentials of a measurement event. If something ‘happens’ then chemical processes are proceeding to completion. Reactants are producing products. In every such process there is an identity change. Out of the ingoing identities there arise new outgoing identities. In this view a measurement event is the creation of new identities from old. What is the elemental such chemical process where identities materialize? It is an inelastic collision – say, where two particles merge? Can one not assert, then, that an inelastic collision is the archetypical ‘measurement event’?
It seems to me that the Measurement Problem is really the Riddle of Materialization. Or perhaps it is best caste as, “What is the Law of Happen?” But, whatever the solution is, it must be perceivable in an elementary inelastic scattering event. Sewell says that the solution is contained within quantum theory itself. I would like to understand how.
Should the mechanics of materialization not be visible in a careful analysis of an idealized, say 1-D, inelastic scattering? I am going to try this and would appreciate any direction cogniscenti may wish to give. Perhaps all this has already been said and done. All are invited to comment.
To be discussed:
What is a ‘system’?
What is a ‘state of the system”?