The founders of quantum mechanics were believers in positivism, a philosophy that has since gone out of favor. Positivists believe in what is observable, and avoid giving opinions on what is not. I believe that the more the interpretations stray from positivism, the harder it is to make sense out of them. Therefore I propose what I call the positivist interpretation as the core minimalist way to understand the theory.
The positivist interpretation is instrumentalist. However the terms are confusing because a lot of physicists talk as if they are instrumentalists, but they are not positivists. For example, Max Tegmark (MIT) writes:
I advocate an extreme "shut-up-and-calculate" approach to physics, where our external physical reality is assumed to be purely mathematical.But that assumption is extremely dubious, and not substantiated by any observation. I cannot prove him wrong, but a positivist would reject it just because there is no observational support for it, and because it is not even particularly useful in modern physics. I have written a FQXi essay against it.
The original Copenhagen interpretation was positivist, but it is widely misunderstood. The Ensemble interpretation is supposed to be minimalist, but it is not truly positivist because it does not predict single experiments. Other interpretations assume all sorts of things that can never be observed.
English science writer Philip Ball writes:
Most physicists accept something like Bohr and Heisenberg’s Copenhagen interpretation. This holds that there is no essential reality beyond the quantum description, nothing more fundamental and definite than probabilities.This is close to being positivist, but a true positivist would not say that there is no essential reality. He would accept the observable realities, and dismiss talk of other realities as being meaningless until someone relates them to observables. He also would not say that probabilities are fundamental, as they are interpretational and not observable.
Here are characteristics of the positivist interpretation.
It is local. No action-at-a-distance has ever been observed, nor is it possible in a relativistic theory. Lumo gives recent explanation of why nonlocality research is pseudoscience.
It rejects hidden variables, as they are not observed and all evidence is to the contrary. Even the wave function is not real, as it is not directly observable.
Positivism also rejects Counterfactual definiteness. As A. Peres said, Unperformed Experiments Have no Results.
I am neutral on Determinism. I am convinced that no quantum probabilities are needed. If the theory does not need them, and they are not observable, then they are not part of the positivist interpretation.
I am also neutral on what I call the weak mathematical universe hypothesis. When a positivist says he is neutral, that means that he rejects it as extraneous. I have never seen anyone explicitly reject it, but I believe that it will eventually be seen to be false.
Explanations of quantum mechanics often get hung up on trying to attach some meaning to reality that is independent of what is observed. Physicists will even say that quantum mechanics proves that there is no such thing as reality. What they are really saying is that non-positivist interpretations are hard to understand. Adopt a positivist philosophy, and the problems disappear.
A good explanation of positivist quantum mechanics is this essay on Quantum Reality. The author favors a positivist variant of the Copenhagen interpretation that he calls the London (Ticker-Tape) Interpretation. He says "Bohr got it pretty much right" and positivism has the virtue of "no deeper meaning than that obtained through measurement".
Positivists are sometimes criticized for saying that there is no deeper meaning, when they cannot prove that there is no deeper meaning. But that criticism misunderstands positivism. The more correct statement is that positivists admit that there might be a deeper meaning involving determinism or probability, mathematical or physical universe, waves or particles, etc. But quantum mechanics experiments are unable to resolve these issues, so they are not worthy of scientific discussion.
Adding to the confusion, modern philosophers not only reject positivism, they also deny that Bohr was a positivist.
Yes, Bohr did get it right with his positivism, and he was considered the winner of the Bohr–Einstein debates. But as positivism has gone out of fashion, so has Bohr's view. Probably a lot of physicists and philosophers today would say they prefer Einstein's view because it is more realist. They cause a lot of confusion. It would be better if quantum mechanics were taught with the positivist interpretation.
The main virtue of the positivist interpretation is that it only requires you to believe in the core physics, and does not require you to take a position on determinism, many-worlds, consciousness, or anything like that.
Lumo writes today:
In the last 85+ years since the discovery of quantum mechanics, all people opposing quantum mechanics have lost, all of their predictions differing from the predictions of quantum mechanics have been proved wrong, and the whole philosophy of trying to find and promote "problems" with the proper Copenhagen quantum mechanics – and all these efforts are always driven by the desire to undo the quantum revolution and return physics to the age when the classical framework was dominant – has been an utter failure, an embarrassing pseudointellectual catastrophe, a huge pile of stinky junk that no sensible scientist would associate herself with.I agree with this. I believe that the richer interpretations of quantum mechanics are wrong for reasons explained in my FQXi essay. I differ from him in that I subscribe to an even more minimalist interpretation, as I say that no quantum probabilities are needed, not even for the double slit.
I am amazed that even this modest and balanced summary of the situation may be considered controversial by some physicists in 2012. I am amazed that Brian Greene may be on the evil side, too.
Niels Bohr treated the theories about many worlds as garbage bringing nothing new and correct to physics for a simple reason: they were garbage that was bringing nothing that was both new and correct.
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