Measurement Problem in Quantum Physics

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Discussion

Ulrich Mohrhoff, presenting an 'Aurobindian' view:

"As any contemporary philosopher knows, the truth of physical reality is inextricably entangled with metaphysical presuppositions. Science operates within an interpretative framework that formulates questions and interprets answers. This framework is not testable by scientific methods. Take the general theoretical framework of contemporary physics, quantum mechanics (QM, also known as quantum physics and quantum theory). According to its “bare” formulation — the “minimal instrumentalist interpretation of quantum mechanics” (Redhead, 1987) — the mathematical framework of QM is a probability calculus. It allows us to calculate the probabilities of the possible outcomes of possible measurements on the basis of actual measurement outcomes.

Differently put, it quantifies correlations between measurement outcomes.

Why is the fundamental theoretical framework of physics concerned with measurements of physical quantities, rather than the physical quantities themselves? Why does it let us predict the probabilities of the possible outcomes of a measurement but not the actual outcome? These and related questions are collectively known as “the measurement problem.” In this regard a referee for a philosophy of science journal once wrote to me: “to solve this problem means to design an interpretation in which measurement processes are not different in principle from ordinary physical interactions.” In other words, to solve the measurement problem is to sweep it under the rug. The name of the game is to design an interpretation in which measurements do not play the crucial role that they do in all standard formulations of QM. To see the impossibility of this demand, one only has to bear in mind that QM describes “ordinary physical interactions” in terms of correlations between measurement outcomes. The referee’s demand leads to a vicious circle.

How did physics get there? Under the influence of the positivism of the late 19th and early 20th Century, measurements had come to be called “observations,” and with the discovery of the special theory of relativity in 1905, reference frames had come to be called “observers.” Thus when quantum mechanics entered the scene around 1925, there was a ready answer to the question of why measurements play this crucial role in all standard formulations of QM. Measurements owe their exalted status to the consciousness of an observer (London and Bauer, 1983; von Neumann, 1955; Wigner, 1961)! The desire to rid measurements of their special status is thus in large part an overreaction to this red herring, for which the new-age community, unfortunately, appears to have fallen hook, line, and sinker.

There is another reason. In the previous lecture I mentioned that, for psychological rather than physical reasons, physicists tend to divide their field into kinematics, which is concerned with the description or state of a physical system at any one time, and dynamics, which is concerned with the state’s evolution in time. This gives them the impression that they know both the furniture of the universe and the laws it obeys. In other words, it makes them believe that they are, at least in principle, omniscient. It is also why they persist in straitjacketing contemporary physics into this conceptual scheme, and why, as a result, QM “makes absolutely no sense” (Penrose, 1986). If, on the other hand, one relinquishes this scientific hubris and simply looks at the manner in which QM assigns probabilities, several important ontological conclusions can be drawn, and to me, for one, they seem to make perfect sense.

As we saw last time, in the quantum world everything is possible, in the sense that every conceivable measurement outcome has a probability greater than zero unless it violates a conservation law. Physics never explains how something is possible, let alone “how nature does it.” It only explains — via its conservation laws — why certain things won’t happen. As I said last time, this is exactly what one would expect if the force at work in the world were an omnipotent force operating under self-imposed constraints. If so, what needs to be explained is not “how nature does it” but the reason why this force works under self-imposed constraints, and why under this particular set of constraints.

We also saw that this particular set of constraints — comprising all well-tested physical theories — is a consequence of the existence of (sufficiently) stable objects that (i) “occupy” space and (ii) are “made of” (finite numbers of) objects that do not “occupy” space. Since it is hard to imagine a world without objects that are stable and “occupy” space, the pivotal issue is this: why are objects that “occupy” space “made of” (finite numbers of) objects that don’t?


To be able to answer this question, I will list some further conclusions at which we arrived last time:

• Ultimately there is only one “thing,” and this is or constitutes everything. • Reality is “built from the top down,” by a self-differentiation of this one “thing.” • This self-differentiation does not go “all the way down” but instead results in a multitude of fuzzy spatial relations. • Matter is the corresponding multitude of relata — an “apparent” multitude because the relations are self-relations. • Ultimately there is only one place, and this is everywhere. • To this, these self-relations owe their spatial character. • The shapes of things are particular sets of spatial relations.


If the shapes of things are sets of relations, the ultimate relata must be formless, and a formless object cannot “occupy” space. What has spatial extent is the relations between formless objects. And since these relations are self-relations, those formless objects are numerically identical: they are that one “thing” which is or constitutes everything.


So, you see, we can start with QM and arrive at a spiritual conception of reality without ever mentioning the word “consciousness.”

(https://antimatters2.files.wordpress.com/2018/04/3-1-an_aurobindonian_discourse.pdf)