“In a theory in which parameters are added to quantum mechanics to determine the results of individual measurements, without changing the statistical predictions, there must be a mechanism whereby the setting of one measuring device can influence the reading of another instrument, however remote. Moreover, the signal involved must propagate instantaneously, so that such a theory could not be Lorentz invariant. Of course, the situation is different if the quantum mechanical predictions are of limited validity. Conceivably they might apply only to experiments in which the settings of the instruments are made sufficiently in advance to allow them to reach some mutual rapport by exchange of signals with velocity less than or equal to that of light. In that connection, experiments of the type proposed by Bohm and Aharonov, in which the settings are changed during the flight of the particles, are crucial.”

— John S. Bell

On the Einstein-Podolsky-Rosen paradox (1964)

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John S. Bell 19

Northern Irish physicist 1928–1990

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“To know the quantum mechanical state of a system implies, in general, only statistical restrictions on the results of measurements. It seems interesting to ask if this statistical element be thought of as arising, as in classical statistical mechanics, because the states in question are averages over better defined states for which individually the results would be quite determined. These hypothetical 'dispersion free' states would be specified not only by the quantum mechanical state vector but also by additional 'hidden variables' - 'hidden' because if states with prescribed values of these variables could actually be prepared, quantum mechanics would be observably inadequate.”

John S. Bell (1928–1990) Northern Irish physicist

On the problem of hidden variables in quantum mechanics (1966)

“Einstein had drawn attention to nonlocality in 1935 in an effort to show that quantum mechanics must be flawed. …Einstein proposed a thought experiment—now called the EPR experiment—involving two particles that spring from a common source and fly in opposite directions.
According to the standard model of quantum mechanics, neither particle has a definite position or momentum before it is measured; but by measuring the momentum of one particle, the physicist instantaneously forces the other particle to assume a fixed position… Deriding this effect as "spooky action at a distance," Einstein argued that it violated both common sense and his own theory of special relativity, which prohibits the propagation of effects faster than the speed of light; quantum mechanics must therefore be an incomplete theory. In 1980, however, a group of French physicists carried out a version of the EPR experiment and showed that it did indeed give rise to spooky action.”

John Horgan (journalist) (1953) American science journalist

The reason that the experiment does not violate special relativity is that one cannot exploit nonlocality to transmit information.
Source: The End of Science (1996), p. 83

“Weinberg says that "we want to know what's happening out there". But this is just the standard anti-quantum zealots' misunderstanding of the essence of quantum mechanics. Quantum mechanics says that all knowable things about the physical system must be obtained through a measurement whose outcomes are predicted via the Born rule. There is nothing else happening out there, at least nothing else knowable that is happening out there! So quantum mechanics does answer the question what is happening out there and the claim that quantum mechanics is incomplete in this sense is simply a lie.”

Luboš Motl (1973) Czech physicist and translator

https://motls.blogspot.com/2018/09/a-recent-dissatisfied-weinbergs-talk-on.html
The Reference Frame http://motls.blogspot.com/

“It can be argued that in trying to see behind the formal predictions of quantum theory we are just making trouble for ourselves. Was not precisely this the lesson that had to be learned before quantum mechanics could be constructed, that it is futile to try to see behind the observed phenomena?”

John S. Bell (1928–1990) Northern Irish physicist

"Einstein-Podolsky-Rosen Experiments", included in Speakable and Unspeakable in Quantum Mechanics (1987), p. 82 https://books.google.com/books?id=FGnnHxh2YtQC&pg=PA82

“In relativity, movement is continuous, causally determinate and well defined, while in quantum mechanics it is discontinuous, not causally determinate and not well defined. Each theory is committed to its own notions of essentially static and fragmentary modes of existence (relativity to that of separate events, connectable by signals, and quantum mechanics to a well-defined quantum state). One thus sees that a new kind of theory is needed which drops these basic commitments and at most recovers some essential features of the older theories as abstract forms derived from a deeper reality in which what prevails in unbroken wholeness.”

David Bohm book Wholeness and the Implicate Order

Wholeness and the Implicate Order (1980)

“Although quantum theory involves the use of nonlocal states, such as wave packets and entangled states, there is nothing in the theory, or in the real world so far as it is accurately described by quantum theory, that corresponds to the sorts of instantaneous nonlocal influences which have often been thought to arise in the situation envisaged in the EPR paradox, or implied by the fact that quantum theory violates Bell inequalities.”

Robert Griffiths (physicist)

"Quantum Locality", Found Phys (2011) 41: 705–733

“In practice, quantum mechanics merely gives predictions with probabilities attached. This should be considered as a normal and quite acceptable feature of predictions made by science: different possible outcomes with different probabilities. In the world that is familiar to us, we always have such a situation when we make predictions. Thus the question remains: What is the reality described by quantum theories? I claim that we can attribute the fact that our predictions come with probability distributions to the fact that not all relevant data for the predictions are known to us, in particular important features of the initial state.”

Gerardus 't Hooft (1946) Dutch theoretical physicist and Nobel Prize winner

Q&A: Gerard 't Hooft on the future of quantum mechanics http://physicstoday.scitation.org/do/10.1063/PT.6.4.20170711a/full/, Physics Today, 11 July 2017

“Considering the pervasive importance of quantum mechanics in modern physics, it is odd how rarely one hears of efforts to test quantum mechanics experimentally with high precision.…The trouble is that it is very difficult to find any logically consistent generalization of quantum mechanics. One obvious target for generalization is the linearity of quantum mechanics, but if we arbitrarily add nonlinear terms to the Schrodinger equation, how do we know that the theory we obtain will have a sensible physical interpretation? At least in part, it is the dearth of generalized versions of quantum mechanics that has made it so hard to plan experimental tests of quantum mechanics.”

Steven Weinberg (1933) American theoretical physicist

"Testing Quantum Mechanics" http://www.sciencedirect.com/science/article/pii/0003491689902765, Annals of Physics (1989)

“My own conclusion is that today there is no interpretation of quantum mechanics that does not have serious flaws. This view is not universally shared. Indeed, many physicists are satisfied with their own interpretation of quantum mechanics. But different physicists are satisfied with different interpretations. In my view, we ought to take seriously the possibility of finding some more satisfactory other theory, to which quantum mechanics is only a good approximation.”

Steven Weinberg (1933) American theoretical physicist

Source: Lectures on Quantum Mechanics (2012, 2nd ed. 2015), Ch. 3: General Principles of Quantum Mechanics

“Prediction of the future is possible only in systems that have stable parameters like celestial mechanics. The only reason why prediction is so successful in celestial mechanics is that the evolution of the solar system has ground to a halt in what is essentially a dynamic equilibrium with stable parameters. Evolutionary systems, however, by their very nature have unstable parameters. They are disequilibrium systems and in such systems our power of prediction, though not zero, is very limited because of the unpredictability of the parameters themselves. If, of course, it were possible to predict the change in the parameters, then there would be other parameters which were unchanged, but the search for ultimately stable parameters in evolutionary systems is futile, for they probably do not exist… Social systems have Heisenberg principles all over the place, for we cannot predict the future without changing it.”

Kenneth E. Boulding (1910–1993) British-American economist

Source: 1980s, Evolutionary Economics, 1981, p. 44

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