What is the mechanism behind Quantum Entanglement?

[PeroK]

You may just have to accept the fact that you will never understand what bothered Einstein, Weinberg, Mermin, Gell-Mann, Feynman, and many others about QM. You simply cannot relate, so you have nothing to contribute to such discussions. I wish I could help you!

I think we all know what bothered Einstein about QM, but in 2022 is it really relevant? Human minds are difficult to change and perhaps if you brought the great man back to life he would still insist that QM is incomplete. Personally, I think Feynman understood perfectly what QM was saying and how it changed our whole perspective on physics and its relationship to the reality of natural phenomena (if I can phrase it like that).

You could equally well find a selection of physicists who want to find a place for God in the universe and then try to exclude atheists from such a discussion. (There was something pseudo-religious, IMO, about Einstein's objection to QM. He often brought "God" into the discussion.)

The worst thing you could do is discuss this issue only with physicists who are uncomfortable with QM and inexorably reinforce your views. We see this on social media and how it fundamentaly undermines the ability to analyse any subject.

 

[gentzen]

And please carefully define what you mean by an "event".

I was using "event" to mean something like "a single run of an experiment that involves spin measurements on each of an entangled pair of particles".

I would not call that an "event", but a "single trial" (or just a "trial", or a "single run"). But that is just me, I certainly don't want to prescribe to other people how to use language and words.

The important point for me is whether the chosen words are good enough to transmit the intended message to the target audience with sufficient detail.

The particles that "appear" in a particular perturbation expansion are entirely chimerical until measured otherwise.

For me, the word "event" implies a rather good localization in space and time. So I prefer to accept that my "events" are not classical events, and can be in superposition. This implies that they are to a certain extent chimerical and rather arbirarily defined. I prefer this over having to "wait" for a measurement, because that additional time delay (and distance) would destroy the good localization of my "events".

 

[vanhees71]

You're still missing the point entirely. Let's continue with what I said about "average-only" projection because it is exactly the same point, but with just one particle. Set your particular "constructive" account aside. [Random components of some hidden, underlying vector? And you always get +/- 1 for these random components? Weird.] You can have whatever view of the unseen underlying situation you like, it's absolutely irrelevant and won't affect what I'm saying at all because all I'm referring to are mathematical and empirical facts about spin.

I have no clue what you want to say here. Can you clearly state (a) about which spin we talk, (b) in which state the spin is prepared before measurement, and (c) which measurement is made on the so prepared spin and what you mean by "average-only" projection. Before you claimed, against all emprical facts, that conservation laws were valid only on average. If philosophy starts with denying empirical facts, I cannot understand what this should help with understanding quantum theory. To the contrary, it's just nonsense. Simple logic tells you that you get anything you like from false assumptions! Now you changed words again. Now it's "average-only" projection. Please give clear mathematical definitions what is done!

Again, this is your particular personal response to the situation. There are physicists who are/were not satisfied with the formalism and experiments alone, e.g., Gell-Mann, Feynman, Mermin, Bell, Einstein, etc. People with the mindset of this latter group participate in forums like this one to share ideas on how to satisfy their need for understanding.Despite reading many posts and papers on the questions researchers in foundations are trying to answer, you still don't "get it." As I said before, I infer from this history that you are unlikely to ever get it. But, let's continue here and see if you can at least understand "average-only" projection whence "average-only" conservation, even if you don't appreciate why anyone would bother to characterize the mathematical and empirical facts this way.The details I'm leaving out are those not relevant to my point. Those included are "exact science."

If you don't give details, of course there's no chance to understand each other.

I'm just stating a fact about the classical bit to contrast its difference with the qubit, i.e., "continuity." As the reconstructions show, classical probability theory and quantum probability theory only differ in this one respect -- reversible transformations between pure states are continuous for the qubit while they are discrete for the classical bit. That's the "Continuity" part of Information Invariance & Continuity.

I don't think that this part is in any way controversial.

Keep reading, I explain what is meant by "average-only" projection using the mathematical and empirical facts later in the post.

Please give a mathematical description without too many words. We have a concise mathematical language to avoid such mutual misunderstandings. Once more, the claim the conservation laws were valid only on average is an empirically disproven claim!

Yes, here's an interesting historical account.In order to understand what is meant by "average-only" projection, you have to stick to the following facts, (which hold regardless of the underlying ontology you are imagining might be responsible for them):

1. When $\hat{b} = \hat{z}$, you always get +1.
2. When $\hat{b}$ makes an angle $\theta$ with respect to $\hat{z}$, you get +1 with a frequency of $\cos^2{\left(\frac{\theta}{2}\right)}$ and you get -1 with a frequency of $\sin^2{\left(\frac{\theta}{2}\right)}$. These average to $\cos{\theta}$. You never measure anything other than +1 or -1.
3. $\cos{\theta}$ is the projection of +1 along $\hat{b}$.

This all are empty words, as long as you don't state, what is measured and how the measured system is prepared.

 

[vanhees71]

I think we all know what bothered Einstein about QM, but in 2022 is it really relevant? Human minds are difficult to change and perhaps if you brought the great man back to life he would still insist that QM is incomplete. Personally, I think Feynman understood perfectly what QM was saying and how it changed our whole perspective on physics and its relationship to the reality of natural phenomena (if I can phrase it like that).

The difference between Einstein and @RUTA is that he made clear statements. It's clear what bothered Einstein, and it's also clear that Einstein's local hidden-variable idea, as interpreted by Bell in a scientifically clearly decidable sense, is ruled out. In this sense, indeed Einstein's quibbles are resolved.

Of course, Feynman understood perfectly well, what QM is saying, and his treatment in the introductory chapter of the Feynman Lectures vol. III (concerning the double-slit experiment with particles) is all there is to say. That's why I don't understand when Feynman says, "nobody understands quantum mechanics"

 

[PeroK]

That's why I don't understand when Feynman says, "nobody understands quantum mechanics"

It was supposed to be a joke.

 

[vanhees71]

Surely he was joking ;-)).

 

[Fra]

I am sure there are those here that has studied the historical communication far better than me so I throw this ou. I wonder if Einstein fully accepted that Bell's theorem was a correct characterization of his own ideas?

what bothered Einstein, and it's also clear that Einstein's local hidden-variable idea, as interpreted by Bell in a scientifically clearly decidable sense, is ruled out. In this sense, indeed Einstein's quibbles are resolved.

The question is (and motivated by my own critical view on Bells ansatz): did Einstein never object to the ansatz of Bells theorem?

(note that the question has nothing todo with correctness of bells theorem, it's about wether einstein agreed with the formalisation that bell did)

/Fredrik

 

[vanhees71]

How could he? Einstein died in 1955, Bell's 1st paper was written in 1964...

 

[Fra]

How could he? Einstein died in 1955, Bell's 1st paper was written in 1964...

I knew there was someone that knew better

/Fredrik

 

[RUTA]

This appears to require that average-only conservation does rule out exact conservation for each individual event. Is that your intent?

Charge and energy are conserved exactly (for each trial) in these experiments. Does that bear at all on the mystery of entanglement per the Bell states? No, so why state it when doing so leads precisely to confusing statements like this one? I think I'll stick to my presentation of the empirical and mathematical facts that define "average-only" projection and "average-only" conservation (for spin angular momentum in this case) and not introduce extraneous facts. Indeed, I'll make my Posts 113 and 129 an Insight so I can just link to that concise explanation and list of the relevant facts in the future.

 

[vanhees71]

We state it, because you claim, against empirical facts, an "average-only validity" of the conservation laws. Also angular momentum is conserved event by event and not only on average, and indeed this false claim has nothing to do with any mystery of entanglement. In fact, often an entangled state results due to conservation laws, as in the original EPR gedanken experiment (for momentum) as well as in Bohm's version (for angular momentum).

 

[PeroK]

Charge and energy are conserved exactly (for each trial) in these experiments. Does that bear at all on the mystery of entanglement per the Bell states? No, so why state it when doing so leads precisely to confusing statements like this one? I think I'll stick to my presentation of the empirical and mathematical facts that define "average-only" projection and "average-only" conservation (for spin angular momentum in this case) and not introduce extraneous facts. Indeed, I'll make my Posts 113 and 129 an Insight so I can just link to that concise explanation and list of the relevant facts in the future.

Do you have experimental evidence of conservation of angular momentum being violated in a single experiment?

 

[RUTA]

We state it, because you claim, against empirical facts, an "average-only validity" of the conservation laws. Also angular momentum is conserved event by event and not only on average, and indeed this false claim has nothing to do with any mystery of entanglement. In fact, often an entangled state results due to conservation laws, as in the original EPR gedanken experiment (for momentum) as well as in Bohm's version (for angular momentum).

You're claiming the empirical and mathematical facts listed in Post 129 are false? If so, then you are denying standard textbook QM.

Here is the outline:
1. Some people find entanglement to be mysterious, despite the fact that the formalism of QM maps beautifully to the experiments and entanglement is being used to develop new technologies.
2. Entanglement is the key difference between quantum information processing and computing and its classical counterpart.
3. Quantum information theorists have reconstructed QM as a probability theory based on information-theoretic principles. In these reconstructions, they build the entirety of finite-dimensional QM from the indivisible fundamental unit of binary quantum information, i.e., the quantum bit (qubit).
4. The qubit differs from the classical bit for classical probability theory in one respect, i.e., continuous reversibility between pure states.
5. Facts 3 and 4 are summed up by Information Invariance & Continuity.
6. Therefore, the mystery of entanglement per quantum information theory ultimately resides in Information Invariance & Continuity. However, for those who are not practicing quantum information theorists, this is not a very transparent principle, so a physical example helps.
7. The qubit can be physically instantiated in any number of ways.
8. I (and Brukner, Zeilinger, Mueller, Dakic, etc.) find spin-1/2 particles to provide a nice visual example of the qubit (see figures in Post 113).
9. In that example, Information Invariance & Continuity manifests itself as "average-only" projection of spin angular momentum per the empirical and mathematical facts listed in Post 129. If you were using photons and polarizers instead, Information Invariance & Continuity manifests itself as "average-only" transmission through the polarizer (as explained in our published papers).
10. Extrapolating "average-only" projection to the corresponding Bell state, we have "average-only" conservation of spin angular momentum between different inertial reference frames related by spatial rotations in the plane of symmetry where the reference frames are those of the corresponding set of complementary spin measurements. These facts are listed in Post 129.
11. Facts 1-10 above are empirical and mathematical facts independent of interpretation.
Conclusion: The interpretation-independent "mechanism" responsible for entanglement and its "mysterious" (non-classical) behavior can be summed up most generally per information-theoretic reconstructions of QM by Information Invariance & Continuity. This is manifested in physical instantiations of Bell state entangled qubits as "average-only" conservation (as defined) of the relevant entangled property.

Everything you continue to request has already been posted, e.g., exact mathematical statements, example of state preparation, example of corresponding measurement, etc. Sorry if you still don't understand what has been presented, I can't think of any further simplifications. If anyone else sees how to make it simpler, please let me know!

 

[RUTA]

Do you have experimental evidence of conservation of angular momentum being violated in a single experiment?

See Post 155.

 

[RUTA]

I have to sign off now and get back to writing the Insight and book on what I've been presenting here. If anyone has any suggestions for how to make this presentation easier to understand, contact me directly via a Physics Forums Conversation.

 

[PeroK]

See Post 155.

My understanding of what you say is that:

a) If you measure spin angular momentum about different axes, then the question of conservation is indeterminate - but conservation is not manifestly violated. And, indeed, the incompatibility of spin AM measurements about different axes precludes a comprehensive measurement of AM about all axes in any experiment. In that sense, three-dimensional spin AM in QM is fundamentally indeterminate. There is nothing special about Bell states in that respect.

b) You have manifestly conservation on average about all axes.

If that's correct, then saying you can't prove conservation of AM about the z-axis if you don't measure both particles about the z-axis is a hollow statement.

 

[vanhees71]

You're claiming the empirical and mathematical facts listed in Post 129 are false? If so, then you are denying standard textbook QM.

I don't know, what you want to say. So I can't say whether your claims are wrong or false. What for sure is wrong is the claim that the conservation laws wouldn't hold on an event-by-event basis.

Here is the outline:
1. Some people find entanglement to be mysterious, despite the fact that the formalism of QM maps beautifully to the experiments and entanglement is being used to develop new technologies.

This is irrelevant for physics.

2. Entanglement is the key difference between quantum information processing and computing and its classical counterpart.

Nobody denies this.

3. Quantum information theorists have reconstructed QM as a probability theory based on information-theoretic principles. In these reconstructions, they build the entirety of finite-dimensional QM from the indivisible fundamental unit of binary quantum information, i.e., the quantum bit (qubit).

This is no surprise either.

4. The qubit differs from the classical bit for classical probability theory in one respect, i.e., continuous reversibility between pure states.

Also agreed.

5. Facts 3 and 4 are summed up by Information Invariance & Continuity.

It's not clear to me, what you mean with that.

6. Therefore, the mystery of entanglement per quantum information theory ultimately resides in Information Invariance & Continuity. However, for those who are not practicing quantum information theorists, this is not a very transparent principle, so a physical example helps.
7. The qubit can be physically instantiated in any number of ways.
8. I (and Brukner, Zeilinger, Mueller, Dakic, etc.) find spin-1/2 particles to provide a nice visual example of the qubit (see figures in Post 113).

Sure.

9. In that example, Information Invariance & Continuity manifests itself as "average-only" projection of spin angular momentum per the empirical and mathematical facts listed in Post 129. If you were using photons and polarizers instead, Information Invariance & Continuity manifests itself as "average-only" transmission through the polarizer (as explained in our published papers).

Please finally define what you mean with "average-only projection" with clear mathematical statements. One cannot communicate without clear mathematical definitions.

10. Extrapolating "average-only" projection to the corresponding Bell state, we have "average-only" conservation of spin angular momentum between different inertial reference frames related by spatial rotations in the plane of symmetry where the reference frames are those of the corresponding set of complementary spin measurements. These facts are listed in Post 129.
11. Facts 1-10 above are empirical and mathematical facts independent of interpretation.
Conclusion: The interpretation-independent "mechanism" responsible for entanglement and its "mysterious" (non-classical) behavior can be summed up most generally per information-theoretic reconstructions of QM by Information Invariance & Continuity. This is manifested in physical instantiations of Bell state entangled qubits as "average-only" conservation (as defined) of the relevant entangled property.

You haven't made a clear mathematical statement. So it's impossible for me to understand the meaning for your text-only vague statements.

Everything you continue to request has already been posted, e.g., exact mathematical statements, example of state preparation, example of corresponding measurement, etc. Sorry if you still don't understand what has been presented, I can't think of any further simplifications. If anyone else sees how to make it simpler, please let me know!

You have not given a clear description of what you are talking about. This would mean:

(a) the system under consideration (one spin, many spins?)
(b) the state the system is prepared in ($\hat{\rho}=...$).
(c) which (spin?) observables are measured.
(d) what does "average-only validity of conservation laws" mean for you. In the standard meaning of this words it's clearly a wrong statement.
(e) what does "average-only projection" mean. It's not defined in the standard literature, and you haven't given a clear mahthemtal definition either.

 

[Maarten Havinga]

Averages are conserved indeed, and I understand how a measurement can appear to violate conservation laws in QM. However note that a measured state is in fact a partial state of a macroscopic measurement device entangled with one measured qubit. If the quantity in the measured qubit decreases by 1, could it be that the same quantity in the measurement device is increased by $1/n$ where n is the amount of that type of quantum information?

 

[RUTA]

My understanding of what you say is that:

a) If you measure spin angular momentum about different axes, then the question of conservation is indeterminate - but conservation is not manifestly violated. And, indeed, the incompatibility of spin AM measurements about different axes precludes a comprehensive measurement of AM about all axes in any experiment. In that sense, three-dimensional spin AM in QM is fundamentally indeterminate. There is nothing special about Bell states in that respect.

b) You have manifestly conservation on average about all axes.

If that's correct, then saying you can't prove conservation of AM about the z-axis if you don't measure both particles about the z-axis is a hollow statement.

This reminds of me of something I meant to say. The key to understanding the mystery of entanglement as presented by EPR, Bell, and Mermin (and many others of course) is the assumption of counterfactual definiteness (CD) that seems to be necessary per the rotational symmetry of the Bell states giving exact conservation of spin AM in the same reference frame (aka when making the same spin measurements in the symmetry plane). However, if you assume CD when making different spin measurements, you get the Bell inequality which is violated by QM. The violation of CD is characterized in many ways, e.g., complementarity, non-Boolean algebra, non-commutativity, superposition, qubit structure, Information Invariance & Continuity, etc. We're adding one more way to characterize it, i.e., "average-only" projection/conservation as I described. Why bother adding yet another characterization? Because it leads immediately to a direct analogy with SR where NPRF has been long accepted as resolving the mysteries of time dilation and length contraction (see any intro physics textbook, for example).

If we had exact projection and conservation between different reference frames per CD, i.e., if we did measure $\cos{\theta}$ at $\hat{b}$ for $|\psi\rangle = |z+\rangle$ and Bob did measure $\cos{\theta}$ when Alice measured +1 for the Bell triplet state in the symmetry plane, then the $\hat{z}$ frame and Alice's frame would constitute "preferred frames" where you measure h while everyone else is measuring a fraction of h (like moving through the aether and getting some fraction of c for the speed of light).

I'll add that to the Insight, thnx.

 

[vanhees71]

Please make clear statements! Please define what you mean by "average-only" conservation. In the usual meaning of this word it's contradicting all empirical evidence. So you must mean something different.

The only thing I can clearly guess is that you discuss two spins $s=1/2$ in the singlet state,
$$|S=0,M=0 \rangle=\frac{1}{\sqrt{2}} (|1/2,-1/2 \rangle-|-1/2,1/2 \rangle).$$
Angular-momentum conservation can now be discussed for the usual example of Bohm's version of EPR: The spin-singlet state is prepared by the decay of a spin-0-particle in its rest frame (and there's no merit in overcomplicating things by discussing this in another frame, where the particle moves, but if you want to, you can simply make a unitary transformation to such a frame; it won't change any conclusions of course). Then angular-momentum conservation in fact dictates the above singlet state, and this implies that the angular-momentum conservation is fulfilled event by event.

To empirically check angular-momentum distribution you must measure the spin of both particles in the same direction in each measurement, i.e., you measure first in a direction $\vec{n}_1$, and the prediction is that you get with probability 1/2 either $m_1=1/2$ and $m_2=-1/2$ or $m_1=-1/2$ and $m_2=+1/2$. The sum is always $M=1/2-1/2=0$, i.e., angular-momentum conservation for this component of the spin holds event by event. Now you repeat this for another direction $\vec{n}_2$, and again you find that the angular-momentum conservation holds event by event.

It doesn't make sense to try to confirm angular-momentum conservation by measuring the spin of particle 1 in one direction $\vec{n}_1$ and that of particle 2 in another direction $\vec{n}_2$, because then you never measure any total spin component. You cannot infer from such a measurement whether any component of the total spin is the same as before the mother particle's decay. To quote Peres: "Unperformed experiments have no results".

What's for me clear with all the confirmation of quantum theory against local HV theories is that observables only take predetermined values if the system is prepared in a corresponding state (an eigenstate of the corresponding self-adjoint operators of the measured observables). Thus of course "counteractual definiteness" is violated.

 

[jbergman]

I have to sign off now and get back to writing the Insight and book on what I've been presenting here. If anyone has any suggestions for how to make this presentation easier to understand, contact me directly via a Physics Forums Conversation.

I am sympathetic to what you are working on. It reminds me of some of the other work on unifying Probability and Quantum Probability as outlined in https://www.math.ucdavis.edu/~greg/intro-2005.pdf

One suggestion is to start with a more concise and mathematical presentation that could be more quickly digested by experts.

 

[bhobba]

RUTA is insisting that the nobody understands quantum mechanics. Esp how it relates to the 'classical' world.

I know and understand Vanhees' view. But I don't think RUTA is saying nobody understands QM, except in the sense nobody understands anything. By this, I mean every theory, every single one, is based on assumptions that are simply accepted. In that sense, ultimate knowledge is unobtainable. Besides that, science rests on doubt - always, it must be somewhere in the back of your mind - this may be wrong. RUTA is saying that he believes there is a relativity principle similar to the POR (which says the laws of physics are the same in all inertial frames or frames traveling at constant velocity relative to an inertial frame). It is a beautiful principle of maximum symmetry in inertial frames. But that does not explain why it is true. Questions like that are rampant throughout science and always will be. My favourite area of science is how to formulate theories so that the assumptions are like the POR - beautiful and intuitive. But they are assumptions whose validity depends on experiments. That is the key:


And, of course, Brian Cox is right - we all should read Feynman. Caveat - not his Lectures on Physics except as a supplement to a more usual physics text or after, without going into why.

Thanks
Bill

 

[bhobba]

Without that SOLID support to make preparation and log massive amounts of data, how would you corroborate QM in the first place?

In many ways. One way often not mentioned is showing classical mechanics is a limiting case of QM. A common way is showing Feynman's path integral approach leads to the Principle Of Least Action. But a more sophisticated way is by the use of a process called coarse graining:
https://www.sciencenews.org/blog/context/gell-mann-hartle-spin-quantum-narrative-about-reality

Thanks
Bill

 

[Fra]

In many ways. One way often not mentioned is showing classical mechanics is a limiting case of QM. A common way is showing Feynman's path integral approach leads to the Principle Of Least Action. But a more sophisticated way is by the use of a process called coarse graining:
https://www.sciencenews.org/blog/context/gell-mann-hartle-spin-quantum-narrative-about-reality

Thanks
Bill

I am aware of that, but that is missing my point. I am not actually claiming that there IS a classical reality, on the contrary there is no evidence for any sharp Heisenberg cuts anywher in nature.

But if you look at the theory, to determine with certainty distributions, and process enough data to infer hamiltonians and distributions etc, IMHO at least, presumes conceptucally a SOLID reference frame for information processing and for a solid spacetime. And as this SOLID reference only exists approximately, but in the theory we use hard constraints to be eternal and timeless. This does not match to me.

If one only cares about the practical success this may seem esotheric, but if one looks at the structure of the theory, and how it's elements presumable map to nature, then QM is an effective theory at best, which means it is a potentia fallacy take the "truncated" wisdom from the effective theory and extrapolate to hold even when searching for unification (GUT as well as gravity).

/Fredrik

 

[Fra]

classical mechanics is a limiting case of QM.

Classical mechanics is not just Newtons "theory" is also represents that there is a place where information can be encoded (with certainty) and that can be SHARED among observers. Without this - we can not construct and conduct a quantum preparation an experiment and observers can't agree with certainty on distributions.

So what you say, IMO implies that not only CM but also QM is "emergent". IF you agree on that, then we agree. But I am searching for HOW QM emerges, and how that is described.

So to restate my point: What you describe, how QM works, is successful and explains CM in large limits, seems to represent what we see in nature, BUT I think theory of QM (with set hilbert spaces and god given hamiltonians) does not seem to describe the actual inferece we do.

/Fredrik

 

[Fra]

To make the point even clearer:

I am not actually claiming that there IS a classical reality, on the contrary there is no evidence for any sharp Heisenberg cuts anywher in nature.

This is also why the kind of "observers" that is required to construct QM, also does not exists. This is the core point.

Yes, it effectively works anyway. But when analysing the logical structure of the theory from inference, this is a problem for me at least.

/Fredrik

 

[bhobba]

Classical mechanics is not just Newtons "theory" is also represents that there is a place where information can be encoded (with certainty) and that can be SHARED among observers.

May I suggest you read Landau - Mechanics? It contains nothing about - information. It is, however, Classical Mechanics (non-relatvistic) based on the Principle Of Least Action, easily derivable from Feynman's Path Integral Formulation.

As I have said, we cannot directly interact with the QM world. We know about it from its interactions with the classical world of everyday experience or increasingly from strange phenomena here in the everyday world that can only be explained by QM. Now pinning what the everyday world is, is a deep philosophical issue and, by the forum rules, not on topic here. For our purpose, a world out there that we experience is taken as a given. Since everything is quantum, how such a world is a limiting case of a theory that assumes it in the first place is a deep issue. The surprising thing is that significant progress, such as using coarse-grained histories, decoherence etc, has allowed significant progress to be made - although problems remain. If you would like more detail, may I suggest a modern interpretation like Consistent Histories that delves into such issues:

https://quantum.phys.cmu.edu/CHS/histories.html

This is not an endorsement of Consistent Histories except that it is an interesting interpretation many call - Copenhagen done right. I have laid my cards on the table regarding interpretations far too many times to repeat it here. It is a reasonable starting point to answer the questions you seem interested in.

Thanks
Bill

 

[bhobba]

This is also why the kind of "observers" that is required to construct QM, also does not exists. This is the core point.

QM can be formulated in a way that does not require observers. However, it is a good place to start viewing QM as a generalised probability theory, although, strictly speaking, even that view does not require observers. It would require a deep sojourn into the philosophy of probability, again not on topic here. If it worries you look at probability as the Kolmogorov axioms and Generalised Probability Theory as a generalisation of those axioms. Applying an axiomatic mathematical system is also a deep but philosophical issue. Like Euclidian Geometry, we simply use intuitive ideas such as a point has position and no size and a line length but no breadth. Of course, such don't exist but are useful abstractions in applications. It is similar to the inertial frames of SR.

Thanks
Bill

 

[vanhees71]

May I suggest you read Landau - Mechanics? It contains nothing about - information. It is, however, Classical Mechanics (non-relatvistic) based on the Principle Of Least Action, easily derivable from Feynman's Path Integral Formulation.

As I have said, we cannot directly interact with the QM world.

How do you come to that conclusion? To the contrary, with more and more advanced technology we are more and more able to observe the "quantum world" (as if there were any other world than the "quantum world"). To handle generic quantum system nowadays becomes more and more applied, and more and more universities of applied sciences develop curricula for the development of "quantum technology".

 

[CoolMint]

We do not have direct sensory interaction with the quantum world as for example the Planck constant is very small to make any useful difference or contribution. If the quantum world exist as such between measurements. In that sense, we are probing indirectly, as you need classical-like machinery, usually bigger than а kitchen table which is already classical.
Maybe bhobba had this in mind by 'direct' experience of the quantum world.

 

[Morbert]

Obligatory Consistent Histories take: We probe the quantum world by identifying properties which are 'ambivalent' (having both a classical and a quantum description, e.g. the collective degrees of freedom of some measurement apparatus), and using quantum theory to establish a logical relation between these ambivalent properties and the quantum properties we are interested in probing. I.e. Not so much a Heisenberg cut, but a 'Heisenberg overlap'

 

[gentzen]

Classical mechanics is not just Newtons "theory" is also represents that there is a place where information can be encoded (with certainty) and that can be SHARED among observers.

May I suggest you read Landau - Mechanics? It contains nothing about - information.

A different suggestion (SCNR): Fra, your views seem to be sufficiently evolved and detailed that it would make sense to write them down in a more coherent form than just as comments on other peoples questions and answers. Maybe as an FQXi essay, maybe as a paper of some form, maybe as a series of blog post, or... I am not suggesting that you should link your PF account to those "external activities" and give away more of your identity than you want. But I do suggest that you should do some activity in that direction. Otherwise you risk kidding yourself with respect to your views and their impact.

 

[physika]

When Alice and Bob make measurements in different reference frames, Alice(Bob) says Bob(Alice) must average his(her) data according to her(his) partition of the data in order to conserve spin angular momentum. All of this follows from the exact conservation of spin angular momentum responsible for the Bell state with its rotational symmetry to begin with. As long as Alice and Bob are making measurements in the same reference frame (same orientation relative to source) their outcomes will be exactly in accord with conservation of spin angular momentum. And, not surprisingly, that can be easily accounted for via local realism. The “weirdness” of entanglement occurs for measurements in different reference frames. That’s where the relative “average-only” conservation holds

a sort of statistical consistency?

 

[Fra]

May I suggest you read Landau - Mechanics? It contains nothing about - information. It is, however, Classical Mechanics (non-relatvistic) based on the Principle Of Least Action, easily derivable from Feynman's Path Integral Formulation.

Thanks for the suggestion, I haven't read that book, but if it's point is to start with some principle of least action, given a lagrangian or hamiltonian I can't see how that will solve any of the deeper questions?

https://quantum.phys.cmu.edu/CHS/histories.html

This is not an endorsement of Consistent Histories except that it is an interesting interpretation many call - Copenhagen done right.

I'm sure it's interesting but I am not a fan of that interpretation.

/Fredrik

 

[Fra]

QM can be formulated in a way that does not require observers.

Yes, this is what many even wants to do. Ie. solve the measurement problem by REMOVING the observer.
This is the opposite strategy of what I suggest.

I take here a more qbist stance, that the agent is CENTRAL. Doing away with this, is throwing the baby out with the bathwater.

When I wrote that the observers that are needed to construct QM "does not exist", I didn't mean that the observers are not important or a problem, just that the idealisation of the "observer" that supports the theory, also defines it. Instead of doing away with the observers, I suggest only that we realized that an observer is more than merely a spacetime frame of reference?

However, it is a good place to start viewing QM as a generalised probability theory, although, strictly speaking, even that view does not require observers.

I do view it a bit like "generalised probability" as well, but I think we see it in different ways and will most certainly not agree. The "generalised probability" is what I call "inference", and it's more than just probability one fixed states spaces so I think inference is a better name. In this generalisation the "observer" is the subsystem that detects, postprocesses and encodes the "observations". (I.e the agent).

It would require a deep sojourn into the philosophy of probability, again not on topic here

Indeed, the boots are already in the mud.

/Fredrik