From the beginning of quantum mechanics, there has been the problem of interpretation, and, even today, the variety of interpretations continues to multiply . ... mathematics itself contains a very basic duality that can be associated with two meta-physical types of reality:The quantum indefiniteness is not so hard to understand, and it is implicit in the uncertainty principle. An electron is really a wave, and its position and momentum cannot be simultaneously observed. You can accept the objectivity of the electron, but the position and momentum are indefinite until observed.
1. the common-sense notion of objectively definite reality assumed in classical physics, and
2. the notion of objectively indefinite reality suggested by quantum physics.
The "problem" of interpreting quantum mechanics (QM) is essentially the problem of making sense out of the notion of objective indefiniteness. ...
There has long been the notion of subjective or epistemic indefiniteness ("cloud of ignorance") that is slowly cleared up with more discrimination and distinctions (as in the game of Twenty Questions). But the vision of reality that seems appropriate for quantum mechanics is objective or ontological indefiniteness. The notion of objective indefiniteness in QM has been most emphasized by Abner Shimony (, , ). ...
In addition to Shimony's "objective indefiniteness" (the phrase used here), other philosophers of physics have suggested related ideas such as:
Peter Mittelstaedtís "incompletely determined" quantum states with "objective indeterminateness" ,
Paul Busch and Greg Jaegerís "unsharp quantum reality" ,
Paul Feyerabendís "inherent indeÖniteness" ,
Allen Stairsí"value indeÖniteness" and "disjunctive facts" ,
E. J. Loweís "vague identity" and "indeterminacy" that is "ontic" ,
Steven French and Decio Krauseís "ontic vagueness" ,
Paul Tellerís "relational holism" , and so forth.
Indeed, the idea that a quantum state is in some sense "blurred" or "like a cloud" is now rather commonplace even in the popular literature. The problem of making sense out of quantum reality is the problem of making sense out of the notion of objective indefiniteness that "conflicts sharply with common sense."
A reader questions whether Bohr really won the Bohr-Einstein debates. F.A. Muller writes:
In his Nobel Lecture of 1969, Murray Gell-Mann notoriously declared that an entire generation of physicists was brainwashed into believing that the interpretation problems of QM were solved, by the Great Dane.Gell-Mann also called quarks a useful mathematical figment.
I guess a lot of physicists and philosophers still do not accept what Bohr had to say, but it is a historical fact that Bohr's side of the argument is what made it into the textbooks. (Gell-Mann's lecture is not on the Nobel Sweden site, so I could not confirm his statement. He got the prize for discovering quarks, but he was always afraid to say that the quarks were real, until after everyone else accepted them.)
For a more level-headed explanation of quantum mechanics, see Why Delayed Choice Experiments do NOT imply Retrocausality. Those experiments are a little puzzling, and they do demonstrate quantum indefiniteness, but they not imply retrocausality, nonlocality, or other mystical concepts.