Abstract After the excellent agreement between the theory and experimental observations was established, many workers, partly in response to EPR, returned to consider the physical meaning of the theory. Several workers, e.g., London and Bauer, Wigner, and von Neumann, believed conscious observers played a key role. The failure to observe superposition states at the macroscopic level meant that superpositions had to be destroyed (collapse) at some level. This was called the Heisenberg or von Neumann cut and played a role in the interpretation. In more modern times David Bohm resuscitated de Broglie’s pilot wave theory and Hugh Everett proposed the “many worlds interpretation.” Other modern interpretation attempts include the theory of decoherence, promoted by Zurek, and spontaneous collapse theories. These discussions should be conducted in the framework of second quantization, the most refined form of the theory, which provides a solution to the 3N dimensional problem and insights into wave-particle duality.
Abstract After the excellent agreement between the theory and experimental observations was established, many workers, partly in response to EPR, returned to consider the physical meaning of the theory. Several workers, e.g., London and Bauer, Wigner, and von Neumann, believed conscious observers played a key role. The failure to observe superposition states at the macroscopic level meant that superpositions had to be destroyed (collapse) at some level. This was called the Heisenberg or von Neumann cut and played a role in the interpretation. In more modern times David Bohm resuscitated de Broglie’s pilot wave theory and Hugh Everett proposed the “many worlds interpretation.” Other modern interpretation attempts include the theory of decoherence, promoted by Zurek, and spontaneous collapse theories. These discussions should be conducted in the framework of second quantization, the most refined form of the theory, which provides a solution to the 3N dimensional problem and insights into wave-particle duality.
The doctoral dissertation of Hugh Everett, III-written under the direction of J. A. Wheeler-was principally motivated by the wish to obtain a reasonable basis for the quantization of general relativity (see Everett [1], pp. 454, 455, 462; Wheeler [2], p. 465). To accomplish this aim, it seemed (and still does seem) necessary to eliminate from the formulation of the quantum theory the dualism of what von Neumann ([4], p. 351) called 1 2' -the former associated with of the system from outside, the latter consisting in the evolution of an isolated quantum system; for general relativity deals essentially with the universe as a whole, there no such thing as of the universe from outside. Thus Everett proposed to state the theory in such a way that all processes, including those of observation (or measurement), are of von Neumann's second type, governed uniformly by the quantum-dynamical law, the (timedependent) Schr6dinger equation. Now, it had been emphasized by von Neumann that, in distinguishing between object system apparatus-plus-observer -and, correlatively, between process 1 2 -there considerable latitude as to where to draw the line: in the direction of including more in the object system, according to von Neumann, one can go far into the body of the acual observer, can include within 2 the neural cerebral processes of sensation, as long as one does not trespass beyond the point where a result is perceived by the observer (see [4], pp. 351-2 pp. 418-420). Indeed, it not quite clear whether von Neumann intended even the last-mentioned restriction: he may have meant to allow the inclusion of arbitrary physiological occurrences within observers in process 2, to have insisted only that at some point a line must be drawn one must say and suchand-such perceived by the observer. In any case, it already implicit in Schr6dinger's famous example ([5]) of the (possibly)
What is quantum theory? For much of the twentieth century, it was widely believed that the interpretation of quantum theory had been essentially settled by Bohr and Heisenberg in 1927. But not only were the ‘dissenters’ of 1927 – in particular de Broglie, Einstein and Schrödinger – unconvinced at the time: similar dissenting points of view are not uncommon even today. What Popper called ‘the schism in physics’ (Popper 1982) never really healed. Soon after 1927 it became standard to assert that matters of interpretation had been dealt with, but the sense of puzzlement and paradox surrounding quantum theory never disappeared. As the century wore on, many of the concerns and alternative viewpoints expressed in 1927 slowly but surely revived. In 1952, Bohm revived and extended de Broglie's theory (Bohm 1952a,b), and in 1993 the de Broglie–Bohm theory finally received textbook treatment as an alternative formulation of quantum theory (Bohm and Hiley 1993; Holland 1993). In 1957, Everett (1957) revived Schrödinger's view that the wave function, and the wave function alone, is real (albeit in a very novel sense), and the resulting ‘Everett’ or ‘many-worlds’ interpretation (DeWitt and Graham 1973) gradually won widespread support, especially among physicists interested in quantum gravity and quantum cosmology.
Bohr’s approach to the measurement process implies a shifty split between the classical and quantum descriptions of the world. The current work presents arguments purporting to show that this split has not been satisfactorily removed from subsequent interpretations of the quantum theory. However, in their attempts to do so, rather obscure notions needed to be invoked, which were anticipated, explicitly or implicitly, and carefully circumvented by Bohr. We discuss von Neumann’s description of the measurement process, the decoherence approach, the de Broglie‐Bohm interpretation, and dynamical collapse models.
The interpretation of quantum mechanics has been disputed ever since the advent of the theory in the 1920’s. Famous are the discussions over long time between Einstein and Bohr. Einstein refused to accept the so‐called Copenhagen interpretation, where the wave function collapses at a measurement and where the outcome of the measurement is essentially accidental (“God does not play dice”). Alternative interpretations have appeared, but the Copenhagen school has dominated the thoughts throughout the decades. One interesting interpretation was formulated in 1957 by Hugh Everett at Princeton, a student of John Wheeler, which abandons the wave‐function collapse. In this model the universe is governed entirely by the Schrödinger equation, which does not allow for any collapse. In Everett’s model after a measurement the wave function is separated into different branches that do not interact. This model was left unnoticed for long time until Bryce DeWitt took it up in 1970 and termed it “Many‐Worlds Interpretation”, a term that in some sense is misleading. Everett’s model is incomplete, and it was later supplemented by the theory of decoherence, which explains how the different branches decouple as a result of the interaction with the environment. This extended model has in recent years gained increased respect, and some believe that it is the only model made available so far that is fully consistent with quantum mechanics. This interpretation can also shed some light on the development of the universe and, in particular, on the so‐called Anthropic principle, which puts human beings at the center of the development.
All investigators working on the foundations of quantum mechanics agree that the theory has profoundly modified our conception of reality. But there ends the consensus. The unproblematic formalism of the theory gives rise to a number of very different interpretations, each of which has consequences on the notion of reality. This paper analyses how the Copenhagen interpretation, von Neumann's state vector collapse, Bohm and de Broglie's pilot wave and Everett's many worlds modify, each in its own way, the classical conception of reality, whose local character, in particular, requires revision.
Abstract The book starts with a description of classical mechanics then discusses the quantum phenomena that require us to give up our commonsense classical intuitions. We consider the physical and conceptual arguments that led to the standard von Neumann-Dirac formulation of quantum mechanics and how the standard theory explains quantum phenomena. This includes a discussion of how the theory’s two dynamical laws work with the standard interpretation of states to explain determinate measurement records, quantum statistics, interference effects, entanglement, decoherence, and quantum nonlocality. A careful understanding of how the standard theory works ultimately leads to the quantum measurement problem. We consider how the measurement problem threatens the logical consistency of the standard theory then turn to a discussion of the main proposals for resolving it. This includes collapse formulations of quantum mechanics like Wigner’s extension of the standard theory and the GRW approach and no-collapse formulations like pure wave mechanics, the various many-worlds theories, and Bohmian mechanics. In discussing alternative formulations of quantum mechanics we pay particular attention to the explanatory role played by each theory’s empirical ontology and associated metaphysical commitments and the conceptual trade-offs between theoretical options.