Bas van Fraassen advocates a “Copenhagen variant” of the modal interpretation of quantum mechanics. However, he believes that the Copenhagen approach to measurement is not fully satisfactory, since it seems to rule out the possibility of providing a physical account of the observation process. This was also what John Wheeler had in mind when, in the mid-1950’s, he sponsored the “relative state” formulation proposed by his student Hugh Everett. Wheeler, who considered himself an orthodox Bohrian, tried to convince Bohr to accept the improvement of the Copenhagen approach represented in his eyes by Everett’s proposal. This attempt gave rise to a lively debate, which has been only recently documented, and which provides an interesting framework for the appraisal of van Fraassen’s own programme.
Bas van Fraassen advocates a “Copenhagen variant” of the modal interpretation of quantum mechanics. However, he believes that the Copenhagen approach to measurement is not fully satisfactory, since it seems to rule out the possibility of providing a physical account of the observation process. This was also what John Wheeler had in mind when, in the mid-1950’s, he sponsored the “relative state” formulation proposed by his student Hugh Everett. Wheeler, who considered himself an orthodox Bohrian, tried to convince Bohr to accept the improvement of the Copenhagen approach represented in his eyes by Everett’s proposal. This attempt gave rise to a lively debate, which has been only recently documented, and which provides an interesting framework for the appraisal of van Fraassen’s own programme.
Bas van Fraassen in [4] has recently tried to use modal logic to solve the measurement problem of quantum mechanics. His model is based on a method of expressing quantum states developed by Hugh Everett [1] called the “relative state formulation.” Unfortunately, Everett's mathematics cannot be generalized as van Fraassen requires. The difficulty itself is elementary enough. But a revision of van Fraassen's postulates (such as the one he adopted on p. 341 after he had been told of the problem) can save the mathematics only on pain of making the whole study irrelevant to the physics. I shall explain the dilemma in this note. In a later paper [5], van Fraassen avoids this dilemma by developing an abstract modal interpretation which does not rely on any expression for quantum states.
In April of 1956, Hugh Everett III’s draft doctoral thesis, tentatively titled “Wave Mechanics without Probability”, was circulated by his thesis advisor at Princeton University John Wheeler to several leading physicists in the West, including the godfather of quantum mechanics Niels Bohr. Everett aimed at resolving the measurement problem in quantum mechanics. Everett’s solution to the mystery of how, when, where and why the wave function collapses in the measurement process was straightforward: it does not. Due to the opposition of Bohr and other adherents to the Copenhagen Interpretation of quantum mechanics, an objection by Feynman and Wheeler’s growing ambivalence, Everett was required to abridge his thesis, resulting in the publication of “’Relative State’ Formulation of Quantum Mechanics” in July 1957. Everett’s machinery of interpretation, including his information and measure theoretic interpretation of the wave function, his concept of correlation within the superposition, as well as his philosophy of science which provides important context for his theory, are largely absent from the latter “Short Thesis”. Perhaps due to the unusual publication history of his works, many critics of Everett and even many of his supporters have overlooked the significance of the arguments made in the “Long Thesis”, which was published only in 1973. Everett’s fuller exposition there answers often cited criticisms such as Adrian Kent’s “Against Many Worlds Interpretations”. Other popular misconceptions about Everett, that he was driven out of academia or that his thesis was redacted due solely or primarily to the opposition from Copenhagen, do not stand up to careful scrutiny of the historical evidence.
Introduction In the July 1957 issue of the Reviews of Modern Physics: Hugh Everett iii put forward a new interpretation of quantum mechanics (Everett 1957). John Wheeler, Everett's thesis adviser, published, in the same issue, an accompanying paper supporting Everett's views (Wheeler 1957). Everett's aim was to cut through the fuzzy thinking displayed by many authors, some of them quite prominent, who in previous years had written incredibly dull papers on how they understood quantum mechanics. Everett's idea was simply to assume that quantum mechanics provides a description of reality in exactly the same sense as classical mechanics was once thought to do. This is a shocking idea, for it leads to a multiplicity of “realities.” Few physicists in 1957 were prepared to accept it. And yet it can be shown to work. It is the purpose of this article to expand on Everett's original demonstration and to reveal the courage John Wheeler displayed in betting that his student was right. Classical theory of measurement System, apparatus, coupling Our starting point is the standard theory of measurement, which we shall first examine classically. In its simplest form a measurement involves just two dynamical entities: a system and an apparatus . It is the role of the apparatus to record the value of some system observable s . For this purpose system and apparatus must be coupled together for a certain period of time, which will be taken to be finite.
Although there has been some discussion in the literature of Bas van Fraassen's modal interpretation of Quantum Mechanics, it has for the most part been concentrated on difficulties that van Fraassen's viewpoint shares with those of some other authors, including Kochen, Dieks, and Healey. van Fraassen's approach has, however, some problems of its own; in this note we want to focus on what seems to us to be one of the most serious of these. The difficulty concerns immediately repeated non-disturbing measurements of the same observable on a single system. As is well known, von Neumann's Projection Postulate guarantees that such measurements will always give the same outcome; likewise, in the approaches of the “modalists” mentioned above, such ‘consilience of repeated measurements’ is in one way or another built into the formalism. By contrast, we shall argue, van Fraassen's modal interpretation neither guarantees this result nor adequately explains why it is unnecessary to do so.
Everett and relative states In this chapter I shall discuss briefly a number of the interesting developments – interpretational, theoretical, experimental – that have taken place in the foundations of quantum theory over the last few decades, where appropriate relating them to the work of Bohr or Einstein. While the topics considered will range well beyond the specific areas studied by John Bell, I think it is fair to say that it was the interest stimulated by his ideas that led to nearly all the work described. This could not, though, apply to the very first ideas I discuss, which date from as early as 1957, when a PhD student at Princeton University, Hugh Everett, wrote a thesis titled The Theory of the Universal Wave Function [231]. A short version of this was published [232], and it was followed by a brief positive assessment [233] of Everett's ideas by John Wheeler, who had guided and encouraged him. (Sixteen years later, both of Everett's papers, and a number of related ones, were collected in a single volume [234].) I shall now sketch his ideas. Till now, we have allowed wave-functions for microscopic systems, such as atoms or electrons, to be sums of wave-functions for highly distinct states, so that the corresponding properties of the systems – position, momentum and so on – do not usually have precise values, at least not till a measurement is made.
In quantum theory, it is widely accepted that all experimental results must agree with theoretical predictions based on the Copenhagen interpretation. However the classical system in the Copenhagen interpretation has not been defined yet. On the other hand, although ongoing research of decoherence is trying to elucidate the emergence of the classical world, it cannot answer why we observe one of eigenstates in observed system. These situations show that the relation between what we observe and physical law has not been elucidated. Here I elucidate the relation by developing Everett's suggestion. Further, from this point of view, I point out that today's brain science falls into circular argument because it is trying to assign what we observe in the brain to process of the subjective perception, and I suggest the future research line in brain science.