I QM: Interesting View - Get the Inside Scoop

[WernerQH]

So, the motivation for producing the information-theoretic reconstructions of QM does not bear on their validity or value one way or another.

Agreed. The quantum formalism is flawless, and it's nice that you have found a neater (more economical) presentation. But the question remains what it is that Q(F)T describes. To my mind it's absurd to talk about "quantum objects" that can exist in different states with different properties (observables) at the same time, and that these properties become "real" when "measured". At bottom, QFT describes the correlations between events, and "particle" or "field" are just names we give to special patterns of events in spacetime.

 

[WernerQH]

How our 'healthy' brains operate is directly tied to how we perceive the reality, as just about everything we perceive is constructed in the brain with variable degrees of accuracy from this alleged "substrate".

The brain is another kind of substrate, as is a book, or a computer screen. All can be built from just 92 different kinds of atom. I don't expect neurobiology or "consciousness" to have any bearing on quantum theory.

 

[EPR]

The brain is another kind of substrate, as is a book, or a computer screen. All can be built from just 92 different kinds of atom. I don't expect neurobiology or "consciousness" to have any bearing on quantum theory.

Newton's conception of the world was a terrible misunderstanding.

 

[RUTA]

Agreed. The quantum formalism is flawless, and it's nice that you have found a neater (more economical) presentation. But the question remains what it is that Q(F)T describes. To my mind it's absurd to talk about "quantum objects" that can exist in different states with different properties (observables) at the same time, and that these properties become "real" when "measured". At bottom, QFT describes the correlations between events, and "particle" or "field" are just names we give to special patterns of events in spacetime.

A principle account doesn't say anything about ontology. That's where SR is today and QM reconstructions have gotten QM to the same place. Whether or not some consensus constructive counterpart to the relativity principle applied to the invariant measurement of c and h is ever created remains to be seen. No one has much interest in doing that for SR anymore. We'll see about QM once everyone realizes it rests on the same principle as SR.

 

[artis]

To my mind it's absurd to talk about "quantum objects" that can exist in different states with different properties (observables) at the same time, and that these properties become "real" when "measured".

I don't expect neurobiology or "consciousness" to have any bearing on quantum theory.

I'm not saying I don't agree with your first assessment but truth be told since we are the only known conscious beings and we developed quantum theory , I'd say consciousness has a lot to do with everything not just QT

 

[A. Neumaier]

That's where SR is today and QM reconstructions have gotten QM to the same place.

You reconstructed only finite-dimensional QM - the subject of quantum information theory. Real particles move and are not covered by this reconstruction.

Thus QM is far from the place where SR is today.

 

[vanhees71]

Agreed. The quantum formalism is flawless, and it's nice that you have found a neater (more economical) presentation. But the question remains what it is that Q(F)T describes. To my mind it's absurd to talk about "quantum objects" that can exist in different states with different properties (observables) at the same time, and that these properties become "real" when "measured". At bottom, QFT describes the correlations between events, and "particle" or "field" are just names we give to special patterns of events in spacetime.

Q(F)T describes Nature as we objectively observe it with our senses and with all kinds of measurement equipment. Everything except the gravitational interaction is described by Q(F)T.

 

[WernerQH]

Q(F)T describes Nature as we objectively observe it with our senses and with all kinds of measurement equipment.

What does it mean to "objectively observe"? Surely you have never watched a photon move through a slit. Everything we talk about is based on inferences. The interpretation of experiments is often compelling, but there is no guarantee that it is the only or the best one. Also the mathematical apparatus is not forced on us (e.g. field operators or functional integrals), and it has a strong effect on our thinking. In my opinion we just haven't yet found the best way to talk about quantum field theory and how it relates to the real world around us.

 

[RUTA]

You reconstructed only finite-dimensional QM - the subject of quantum information theory. Real particles move and are not covered by this reconstruction.

Thus QM is far from the place where SR is today.

I'm not sure what you mean by "real particles move." If you're simply talking about the time-evolution of the state, that is covered by the reconstructions.

 

[vanhees71]

What does it mean to "objectively observe"? Surely you have never watched a photon move through a slit. Everything we talk about is based on inferences. The interpretation of experiments is often compelling, but there is no guarantee that it is the only or the best one. Also the mathematical apparatus is not forced on us (e.g. field operators or functional integrals), and it has a strong effect on our thinking. In my opinion we just haven't yet found the best way to talk about quantum field theory and how it relates to the real world around us.

We objectively observer of course never an electromagnetic field let alone a single photon but its reaction with matter (very often the detection is through the photoelectric effect), but this leaves objective data on the action of the electromagnetic field following the laws described by (Q)ED.

Math is just the language to describe our theories. As far as we know the different formulations of relativistic QFT are equivalent. At least they are equivalent within the robust calculations physicists do. Neither formulation is mathematically strictly defined beyond (resummed) perturbation theory.

The great success of relativistic QFT (aka the Standard Model and effective theories derived from it) shows that we grasp at least a great portion of its meaning in relation to the observables made, which are described by it.

 

[rogeragrimes]

Everyone should read Philip Ball's Beyond Weird. Changed the way I think about quantum mechanics the rest of my life. And some of the things he says, against the Copenhagen interpretation, just make more sense (and are very much supported by the math). What he is saying makes so, so, so much more sense than what most new people are told to think about the way QM works and the Copenhagen interpretation. After you understand what Bell is saying you see the Copenhagen interpretation is almost certainly wrong. Also, check out his articles on Quantum Darwinism.

 

[RUTA]

Everyone should read Philip Ball's Beyond Weird. Changed the way I think about quantum mechanics the rest of my life. And some of the things he says, against the Copenhagen interpretation, just make more sense (and are very much supported by the math). What he is saying makes so, so, so much more sense than what most new people are told to think about the way QM works and the Copenhagen interpretation. After you understand what Bell is saying you see the Copenhagen interpretation is almost certainly wrong. Also, check out his articles on Quantum Darwinism.

Concerning the Copenhagen interpretation see also Adam Becker’s book What is Real?

 

[WernerQH]

We objectively observe of course never an electromagnetic field let alone a single photon but its reaction with matter (very often the detection is through the photoelectric effect), but this leaves objective data on the action of the electromagnetic field following the laws described by (Q)ED.

I'm not calling into question the huge success of QED and the objective reality of the experiments. My concern is the "photon" (or electron) concept and its connotations which are misleading and mostly left implicit. Of course you know that a photon is not a little bullet that moves from A to B. Most people think that it is "something" that exists from the time of its creation to the time of its absorption. I contend that it is more useful (and closer to the actual formalism of QED) to think of a photon as nothing but a pair of emission and absorption events. Only these events are real, and whatever "connects" them in spacetime is useful fiction to capture the ubiquitous correlations between events (aka propagators).

 

[RUTA]

I'm not calling into question the huge success of QED and the objective reality of the experiments. My concern is the "photon" (or electron) concept and its connotations which are misleading and mostly left implicit. Of course you know that a photon is not a little bullet that moves from A to B. Most people think that it is "something" that exists from the time of its creation to the time of its absorption. I contend that it is more useful (and closer to the actual formalism of QED) to think of a photon as nothing but a pair of emission and absorption events. Only these events are real, and whatever "connects" them in spacetime is useful fiction to capture the ubiquitous correlations between events (aka propagators).

That’s the way we think about it in Beyond the Dynamical Universe. See also the physics part of Re-Thinking the World with Neutral Monism in Entropy.

 

[WernerQH]

That’s the way we think about it in Beyond the Dynamical Universe.

The devil is in the details. The mathematical characterization of events requires a bit more than time and location. Does your book expand on this, or is it just discussing general principles?

 

[WernerQH]

After you understand what Bell is saying you see the Copenhagen interpretation is almost certainly wrong.

I dislike the Copenhagen interpretation since the first instant that I encountered it (1973)!
But I must say that I found Ball's talk disappointing. (More disappointing than I have come to expect for talks on this topic anyway.) I also regret to have bought his book. There was nothing that I found illuminating.

 

[vanhees71]

So what's your favorite interpretation?

I think Copenhagen is just fine, if you take away the confusing philosophy by Bohr and (even worse) Heisenberg and just stick to the no-nonsense formulations by Born, Jordan, and Dirac. The only interpretation needed is that quantum states (statistical operators) describe probabilities for the outcome of measurements at a time $t>t_0$ given the preparation of the system at some time $t_0$. There's no need for collapse nor a quantum-classical cut. That's called the "minimal statistical interpretation".

 

[A. Neumaier]

stick to the no-nonsense formulations by Born, Jordan, and Dirac. [...] There's no need for collapse nor a quantum-classical cut.

Dirac explicitly requires the collapse that you dislike!

 

[vanhees71]

That's why I added the last quoted sentence.

 

[A. Neumaier]

That's why I added the last quoted sentence.

But in a generalized form the collapse is also part of quantum information theory, where it figures as a (frequent) special case of a pure quantum channel.

Thus that you don't need the collapse (because you replace it by an equivalent amount of handwaving) does not mean that it is not needed at all!

 

[vanhees71]

Characteristically nowhere in the quoted wikipedia article you find the word collapse. I think there's not more to "collapse" than the special case of state preparation by filtering. E.g., like preparing an ensemble of Ag atoms in a Stern Gerlach experiment with a determined spin-component by dumping all the partial beams not wanted. There's no engimatic "collapse" but just the absorption of particles by matter.

 

[A. Neumaier]

Characteristically nowhere in the quoted wikipedia article you find the word collapse.

This is for two reasons :

1. The first is political, since there are many like you who take offence at that dirty word.
2. The second is pragmatic, since Dirac collapse is somewhat too special for the needs of quantum information applications.

But Dirac's collapse is precisely the special case of a pure quantum channel where the transmission operator $T$ is a projector, corresponding to a von Neumann projective measure-and-prepare situation.

 

[Lord Jestocost]

I dislike the Copenhagen interpretation since the first instant that I encountered it (1973)!

As Ethan Siegel recently puts it:

"Although there are a myriad of interpretations of quantum mechanics that are equally as successful at describing reality, none have ever disagree with the original (Copenhagen) interpretation’s predictions. Preferences for one interpretation over another — which many possess, for reasons I cannot explain — amount to nothing more than ideology."

 

[A. Neumaier]

As Ethan Siegel recently puts it:

"for reasons I cannot explain —

Thus his insight into the problem is quite limited. If he understood, he would not write this.

 

[WernerQH]

So what's your favorite interpretation?

I think Copenhagen is just fine, if you take away the confusing philosophy by Bohr [...]

After the encounter with Ballentine's Rev.Mod.Phys. article I thought I had understood QM. And I'm still convinced that QM is a statistical (stochastic) theory and not deterministic. (I'm astonished that so many people take Schrödinger's equation to be the pinnacle of quantum theory -- it is just a piece of a bigger mathematical machinery that creates the illusion of determinism.)

Of course Bell's inequalities are problematic also for the statistical interpretation if you believe in particles having definite properties at all times. But you don't have to believe in "particles", which are a classical concept anyway. To me, the Aspect et al. experiments show that it is a conceptual dead end to think that "something" travels from the source to the detectors while engaging in superluminal communication. And QFT as a microscopic theory cannot be grounded on a macroscopic concept like "measurement".

 

[Lord Jestocost]

Thus his insight into the problem is quite limited. If he understood, he would not write this.

To my mind, Ethan Siegel's insight mirrors merely that what Paul K. Feyerabend has already remarked some time ago. In his philosophical paper "Problems of Microphysics (1962)" (in "Physics and Philosophy: Volume 4: Philosophical Papers"), Paul K. Feyerabend makes the problem quite clear:

"The issue concerning the foundations of the quantum theory can therefore be solved only by the construction of a new theory as well as by the demonstration that this new theory is experimentally at least as valuable as the theory that is being used at the present time; it cannot be solved by alternative interpretations of the present theory.⁴⁹"

In footnote 49 he adds:

"If I am correct in this, then all those philosophers who try to solve the quantum riddle by trying to provide an alternative interpretation of the current theory which leaves all laws of this theory unchanged are wasting their time. Those who are not satisfied with the Copenhagen point of view must realize that only a new theory will be capable of satisfying their demands." [Italics in original, LJ]

 

[A. Neumaier]

And QFT as a microscopic theory cannot be grounded on a macroscopic concept like "measurement".

Where is your proof of this? All we know about microscopic events is based on macroscopic observations.

 

[A. Neumaier]

To my mind, Ethan Siegel's insight mirrors merely that what Paul K. Feyerabend has already remarked some time ago. In his philosophical paper "Problems of Microphysics (1962)" (in "Physics and Philosophy: Volume 4: Philosophical Papers"), Paul K. Feyerabend makes the problem quite clear:

"If I am correct in this, then all those philosophers who try to solve the quantum riddle by trying to provide an alternative interpretation of the current theory which leaves all laws of this theory unchanged are wasting their time. Those who are not satisfied with the Copenhagen point of view must realize that only a new theory will be capable of satisfying their demands."

The question remains why there are so many competent quantum physicists who disagree. The most likely answer is that the assumption of the quoted paragraph are questionable. Why should he be correct in this? He is just one voice in the myriad of diverging voices. And I bet he is wrong!

 

[WernerQH]

All we know about microscopic events is based on macroscopic observations.

Of course. But how could a microscopic theory ever be found if you insist that it be rigorously derived from classical physics using logical deduction?

John Bell wrote: "And does not any analysis of measurement require concepts more fundamental than measurement? And should not the fundamental theory be about these more fundamental concepts?" (Quantum mechanics for cosmologists)

 

[gentzen]

But how could a microscopic theory ever be found if you insist that it be rigorously derived from classical physics using logical deduction?

But pointing out that our measurements are ultimately based on macroscopic observations is not the same as insisting to derive microscopic theory from classical physics.

I have the impression that you fail to distinguish between "macroscopic phenomena" and "classical physics".