Foundations of Quantum Mechanics by Travis Norsen

Author:Travis Norsen
Language: eng
Format: epub, pdf
Publisher: Springer International Publishing, Cham

One can see here, again, how Heisenberg’s formulations invite some of the objections we have discussed previously. For example, if the change in the quantum state (induced by observation) merely represents a change in our knowledge of the system, doesn’t that imply that the observation is simply revealing a fact about the observed system which was perfectly definite (though unknown) prior to the observation, such that the (earlier) quantum mechanical description was simply incomplete?

But on the other hand, we also begin to appreciate the very different underlying philosophical perspective that immunized Bohr and Heisenberg against such objections: if, for example, reference to unknown or unobserved elements of physical reality is literally meaningless, then the clean division between the epistemic and ontological interpretations of wave function collapse dissolves and the incompleteness objection loses its force.

Heisenberg continues, addressing (what would later become) Bell’s objection that the vagueness and arbitrariness of the division of the world implied by the distinction between “observation processes” and “regular processes”:It has been said that we always start with a division of the world into an object, which we are going to study, and the rest of the world, and that this division is to some extent arbitrary. It should indeed not make any difference in the final result if we, e.g., add some part of the measuring device or the whole device to the object and apply the laws of quantum theory to this more complicated object. It can be shown that such an alteration of the theoretical treatment would not alter the predictions concerning a given experiment. This follows mathematically from the fact that the laws of quantum theory are for the phenomena in which Planck’s constant can be considered as a very small quantity, approximately identical with the classical laws. But it would be a mistake to believe that this application of the quantum theoretical laws to the measuring device could help to avoid the fundamental paradox of quantum theory.

The measuring device deserves this name only if it is in close contact with the rest of the world, if there is an interaction between the device and the observer. Therefore, the uncertainty with respect to the microscopic behavior of the world will enter into the quantum-theoretical system here just as well as in the first interpretation. If the measuring device would be isolated from the rest of the world, it would be neither a measuring device nor could it be described in the terms of classical physics at all. ....

Certainly quantum theory does not contain genuine subjective features, it does not introduce the mind of the physicist as a part of the atomic event. But it starts from the division of the world into the ‘object’ and the rest of the world, and from the fact that at least for the rest of the world we use the classical concepts in our description. This division is arbitrary and historically a direct consequence of our scientific method; the use of the classical concepts is finally a consequence of the general human way of thinking.

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