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Starting in 1927, those two great minds had a debate over the correctness of quantum mechanics. Einstein came up with several thought experiments to which Neils Bohr responded to. It's been suggested that Einstein may have won if he had used spooky-action-at-a-distance. So you decide. Who actually won the debate? (the internet has several articles)

PhilX

Philosophy Explorer wrote:Starting in 1927, those two great minds had a debate over the correctness of quantum mechanics. Einstein came up with several thought experiments to which Neils Bohr responded to. It's been suggested that Einstein may have won if he had used spooky-action-at-a-distance. So you decide. Who actually won the debate? (the internet has several articles)

PhilX

Spooky action at a distance is not so spooky if you consider the mechanics of motion of a rotating spiral. The spiral turns clock wise on one side and anti-clock wise on the other side, both at the same time. Thus, two opposite polarities can exist within one action. Thus, light must have some kind of a spiral action which allows two opposite polarities to exist simultaneously. Thus, quantum mechanics is a scam.

Bohr won. At the time of the debate, there was no way to confirm "spooky action at a distance." Now it is one of the most confirmed facts of science there is. However, it is poorly understood and its implications so radical that many scientists, if not most, would rather just "shut-up and calculate."

Radar wrote:At the time of the debate, there was no way to confirm "spooky action at a distance." Now it is one of the most confirmed facts of science there is. However, it is poorly understood and its implications so radical that many scientists, if not most, would rather just "shut-up and calculate."

There is still debate on this area. And the 'shut-up and calculate' is not the most popular position. The two major views with quotes from leading physicists in quantum foundations:

1. Observed violations of Bell's inequalities implies that nature is non-local.

In 1964, Bell proved that any serious version of quantum theory (regardless of whether or not it is based on microscopic realism) must violate locality. He showed that if nature is governed by the predictions of quantum theory, the "locality principle," precluding any sort of instantaneous (or superluminal) action-at-a-distance, is simply wrong, and our world is nonlocal.

What is most relevant to Bell's Theorem is that the non-locality which it makes explicit in Quantum Mechanics is a small indication of pervasive ultramicroscopic nonlocality. If this conjecture is taken seriously, then the baffling tension between Quantum nonlocality and Relativistic locality is a clue to physics in the small.

2. Observed violations of Bell's inequalities implies anti-realism (e.g. quantum measurement results do not pre-exist).

...quantum measurement results do not preexist in any logically determined way before the act of measurement.

...unperformed tests have no outcomes: it is wrong to try to account for the outcomes of all the tests you might have performed but didn’t.

Bohm2 wrote: There is still debate on this area. And the 'shut-up and calculate' is not the most popular position. The two major views with quotes from leading physicists in quantum foundations:

I disagree. Only a pathological skeptic would dispute “spooky action at a distance.” And while the religious and philosophical implications are clear, most scientists are too busy wandering through equation after equation to delve deeply into such matters, and those that do are often held in contempt.

Radar wrote:Only a pathological skeptic would dispute “spooky action at a distance.” And while the religious and philosophical implications are clear, most scientists are too busy wandering through equation after equation to delve deeply into such matters, and those that do are often held in contempt.

With respect to the "spooky action at a distance" issue, I think it depends on what one means by that term. From the polls I've looked at, most physicists do believe in some notion of non-locality but the majority do not believe in 'action at a distance' (e.g. that nature is non-local), primarily because this would be at odds with relativity. With respect to the issue of interpretation, there are a number of reasons why the "shut up and calculate" approach may not be the most productive approach to take and why interpretation is important. Some of the reasons are spelled out in these articles by physicists:

Quantum Theory: Interpretation Cannot be Avoided
http://arxiv.org/pdf/quant-ph/0408178v1.pdf

Shut up and let me think! Or why you should work on the foundations of quantum mechanics as much as you please
http://arxiv.org/pdf/1308.5619.pdf

Does Quantum Mechanics Need Interpretation?
http://arxiv.org/pdf/0902.3005v1.pdf

Interview with a Quantum Bayesian
http://arxiv.org/pdf/1207.2141v1.pdf

Why Physics Needs Quantum Foundations
http://arxiv.org/pdf/1003.5008.pdf

Bohm2 wrote: With respect to the "spooky action at a distance" issue, I think it depends on what one means by that term. From the polls I've looked at, most physicists do believe in some notion of non-locality but the majority do not believe in 'action at a distance' (e.g. that nature is non-local), primarily because this would be at odds with relativity.

That's what I call "pathological skepticism."

I'm talking about the deeper philosophical questions it raises, not the mere mechanics.

I'm more or less a Copenhagenist with just a few adjustments, so I'd say it is fairly obvious that Bohr won the debate. But I personally believe that if Einstein had lived to see the empirical proofs of Bell's Theorem, he would have graciously conceded to Bohr that he was wrong.

I think it is sad that the one part of Bohr's ideology that is so easily dismissed, even by Copenhagenists, is Bohr's Principle of Complementarity. In my opinion, the Principle of Complementarity is one of the most valuable philosophical concepts I have encountered in all of 20th century philosophy, and it came from a man who was not even a philosopher per se!

Bohr would have viewed the entire "conundrum" of spooky action at a distance (quantum entanglement) versus the limits of Special Relativity as a beautiful example of complementarity in action, citing how both the quantum scale and macroscopic scale's respective physical theories (namely, QM and Relativity) are both necessary but mutually exclusive.

The pejorative "shut up and calculate" is an unfair slap at Bohr since it misrepresents the spirit of what he meant when he said that physics is merely what we can say about the world. His point was that we CAN calculate DESPITE not having a deterministic description of reality. Anyone willing to take one step back from the issue should be able to see that this is exactly what history shows all of Science to be anyway, and a great thing too that is so! Well, it probably makes more sense if you share his appreciation for complementarity as I do.

A Poster He or I wrote:But I personally believe that if Einstein had lived to see the empirical proofs of Bell's Theorem, he would have graciously conceded to Bohr that he was wrong.

But violation of Bell's inequalities Bell's also doesn't completely support Bohr's position either. The standard interpretation of experimental violations of Bell's inequalities is that either we accept non-locality or non-realism. In fact, there are physicists who argue that Bell's theorem implies non-locality irrespective of other issues like realism/non-realism, hidden variables, etc. For example, Laudisa writes:

...the role of Bell’s theorem is not to set constraints on how ‘realist’ we are allowed to be about quantum systems but rather, much more interestingly, to characterize a structural property of any theory that aims to cover the domain of validity covered so far by quantum mechanics, namely non-locality. As a consequence, whether a theory aiming to supersede quantum theory will be ‘realist’, ‘non-realist’, ‘half-realist’ or ‘one-third realist’, this will concern the further conceptual and formal resources of that theory and not at all the Bell theorem.

Non-Local Realistic Theories and the Scope of the Bell Theorem
http://arxiv.org/ftp/arxiv/papers/0811/0811.2862.pdf

But let's assume that one prefers non-realism to non-locality, as Bohr might have preferred. Can you provide an example of a local but non-realist model that accounts for the perfect correlations seen in Bell-type experiments?

The Copenhagen position seems pretty comfortable with non-realism, I grant that. But it certainly need not insist on a local universe. I personally don't see any compelling reason to believe in a local universe. The empirical displays of Bell's Inequality make more sense in a non-local framework and, as an aside, a non-local universe is much more consistent with a holistic universe such as is implied by later developments in 20th-century mathematics (namely, complexity theory). And Bohr's Principle of Complementarity makes it easy for me to accept that Relativity Theory and QM are ultimately incommensurable while still allowing both theories to be valid.

As to what Bohr would have preferred, I'm not aware, but keep in mind that Bohr's defense against the challenge of the EPR Paradox came from the very core of what the Copenhagen position is all about: You cannot assume that measurements made in one respect are commensurable with measurements made in a different respect. If we assume a position of locality from the get-go, we commit the same error Einstein made in thinking the EPR Paradox was a valid challenge to QM. It is non-realism (implicit in the Copenhagenist's mindset) that best allows us to accept what our experiments tell us about our experience of the universe, and so feel more comfortable in accepting the validity of non-locality as a better model of that universe than a local model.

A Poster He or I wrote:But it certainly need not insist on a local universe. I personally don't see any compelling reason to believe in a local universe...It is non-realism (implicit in the Copenhagenist's mindset) that best allows us to accept what our experiments tell us about our experience of the universe, and so feel more comfortable in accepting the validity of non-locality as a better model of that universe than a local model.

But if one is willing to accept non-locality then why give up realism? Realistic models like deBroglie-Bohmian are both non-local and realistic and fully compatible with all quantum predictions. I mean, why give up both locality and realism when giving up locality alone is enough? Moreover, if one is willing to subscribe to non-realism, what is the difference between a non-local, non-realistic model versus a local, non-realistic model? As Maudlin points out:

The microscopic world, Bohr assured us, is at least unanschaulich (unvisualizable) or even non-existent. Unvisualizable we can deal with—a 10-dimensional space with compactified dimensions is, I suppose, unvisualizable but still clearly describable. Non-existent is a different matter. If the subatomic world is non-existent, then there is no ontological work to be done at all, since there is nothing to describe. Bohr sometimes sounds like this: there is a classical world, a world of laboratory equipment and middle-sized dry goods, but it is not composed of atoms or electrons or anything at all. All of the mathematical machinery that seems to be about atoms and electrons is just part of an uninterpreted apparatus designed to predict correlations among the behaviors of the classical objects. I take it that no one pretends anymore to understand this sort of gobbledegook, but a generation of physicists raised on it might well be inclined to consider a theory adequately understood if it provides a predictive apparatus for macroscopic events, and does not require that the apparatus itself be comprehensible in any way.

If one takes this attitude, then the problem I have been trying to present will seem trivial. For there is a simple algorithm for associating certain clumped up wavefunctions with experimental situations: simply pretend that the wavefunction is defined on a configuration space, and pretend that there are atoms in a configuration, and read off the pretend configuration where the wavefunction is clumped up, and associate this with the state of the laboratory equipment in the obvious way. If there are no microscopic objects from which macroscopic objects are composed, then as long as the method works, there is nothing more to say. Needless to say, no one interested in the ontology of the world (such as a many-worlds theorist) can take this sort of instrumentalist approach.

Can the world be only wavefunction? In Ch. 4 of "Many Worlds?: Everett, Quantum Theory, and Reality"


So , if non-realism, then the issue of locality vs non-locality seems kind of pointless since there doesn't appear to be any ontological issues. I mean what ontological difference would there be between the local vs non-local version of non-realism? Anyway, that's how I understood it or I'm not getting it. I think Gisin argues similarily here:

What is surprising is that so many good physicists interpret the violation of Bell’s inequality as an argument against realism. Apparently their hope is to thus save locality, though I have no idea what locality of a non-real world could mean? It might be interesting to remember that no physicist before the advent of relativity interpreted the instantaneous action at a distance of Newton’s gravity as a sign of non-realism...

Is realism compatible with true randomness?
http://arxiv.org/pdf/1012.2536v1.pdf

But if one is willing to accept non-locality then why give up realism? Realistic models like deBroglie-Bohmian are both non-local and realistic and fully compatible with all quantum predictions. I mean, why give up both locality and realism when giving up locality alone is enough?

From the Copenhagen viewpoint, you're asking the wrong question. It is not an issue of giving up realism. It is an issue of why embrace it when the applicable science (QM) doesn't support it.

Moreover, if one is willing to subscribe to non-realism, what is the difference between a non-local, non-realistic model versus a local, non-realistic model?

The difference is in the interpretation of the empirical evidence. Such evidence flies in the face of locality (namely, its concomitant limits as described by Special Relativity). Non-locality, on the other hand, is consistent with the empirical evidence, and non-realism ALLOWS us to accept it as valid hypothesis until contradicted by further scientific development. Realism, by contrast, REQUIRES us to accept it as valid hypothesis (or at least requires us to eschew any non-deterministic hypothesis and settle on a deterministic one). Philosophically, this makes realism anti-scientific by imposing an ontological/metaphysical "mandate" upon scientific interpretation. Copenhagenism is spared this burden, allowing scientific inquiry to proceed without any predisposition toward the results.

Regarding Maudlin's comentary, it is the sort of thing I've come to expect from reading non-Copenhagenists, particularly those who are realists or closet realists. The misunderstanding is exacerbated by Bohr himself, whose florid writing was often counterproductive. But the reason that Maudlin is wrong is simply that non-realism does not imply non-existence. Rather, it implies that existence (that is, any ontological underpinnings for the fruits of science) is necessarily outside the realm of scientific inquiry on science's own terms.

Personally, I'm a big fan of David Bohm. His descriptions of how a holographic universe can work are immensely clever, and to be able to fashion a formal mathematics for it consistent with QM is truly impressive. But on what basis would I call it science? Speculative hypothesis, yes. But until we have a practical methodology for testability, I'm afraid that Bohm's ideas, formalism and all, are merely science fiction.

In a nutshell: Ontology and metaphysics are for philosophy, fiction, and mysticism, not science.

Here's a QM type of question I've been thinking about for years. Let's take a hydrogen atom which we know is made up of a proton and an electron.

I've been taught that the orbit that the electron assumes is a fuzzy sort of shell around the proton, fuzzy because it spends most of its time within that shell. This means it spends some of its time elsewhere which leads to my question. Now I believe calculation shows that the electron can assume any of a number of infinite orbits about the proton. My question is whether there is a limit on how far the electron can be from the proton? I'm not aware of any limit that the electron may be from the proton. What does QM say about this?

PhilX

PhilX,

A couple of things to clarify. When a hydrogen atom's electron is not interacting with other quanta (other than its orbit about the proton) it is not behaving as a particle per se, so it does not (1) spend most of its time within that shell (called a valence); rather, it is the shell in a manner of speaking; and (2) this valence shell does not allow for "any number of infinite orbits about the proton." Rather it is a fixed (quantized) energy state.

All this changes when the hydrogen atom begins interacting with other quanta. At that point, the electron may gain energy whereby new valences can be established "further" from the proton. Each higher valence is strictly quantized (at a very specific energy state), so again there cannot be an infinite number of orbits, only specific quantized orbits, and the "shape" of the shell gets more-and-more elaborate and bizarre with each new valence.

In principle (pure mathematical abstraction) an electron could keep gaining energy and assume more and more complex valence configurations further from the nucleus. Such atoms have been artificially engineered in laboratories and I think I recall that they were instrumental for creation of the "correspondence principle" advocated by QM pioneers to try to explain the emergence of classical macroscopic reality from quantum states before more modern theories came along.

But in practice, we need to consider that whatever interaction is energizing the electron is a 2-way "handshake" which typically means that the hydrogen atom will end up chemically bonding to other atoms, stabilizing (and therefore limiting) the electron in a new relationship within other atoms' electron valences.

A Poster He or I wrote:Realism, by contrast, REQUIRES us to accept it as valid hypothesis (or at least requires us to eschew any non-deterministic hypothesis and settle on a deterministic one). Philosophically, this makes realism anti-scientific by imposing an ontological/metaphysical "mandate" upon scientific interpretation. Copenhagenism is spared this burden, allowing scientific inquiry to proceed without any predisposition toward the results.

Can you clarify what you mean by "realism"? Are you equating realism with determinism?