March 21, 2016 feature

# Two defining features of quantum mechanics never appear together

(Phys.org)—Two of the most important ideas that distinguish the quantum world from the classical one are nonlocality and contextuality. Previously, physicists have theoretically shown that both of these phenomena cannot simultaneously exist in a quantum system, as they are both just different manifestations of a more fundamental concept, the assumption of realism. Now in a new paper, physicists have for the first time experimentally confirmed that these two defining features of quantum mechanics never appear together.

The physicists, Xiang Zhan, et al., have published a paper on the nonlocality-contextuality tradeoff in a recent issue of *Physical Review Letters*.

In the everyday world that we observe, an object can only be affected by nearby objects (locality), and when we make a measurement, the outcome does not depend on other independent measurements being made at the same time (noncontextuality).

In contrast, the quantum world is nonlocal, as demonstrated by quantum entanglement where two objects can influence each other even when separated by large distances. And in the quantum world, measurements are contextual, so quantum systems do not have predetermined values but instead their values depend on how measurements are made.

To show that a quantum system is nonlocal or contextual, physicists have defined inequalities that assume a system is the opposite (local or noncontextual). Then they perform experiments that attempt to violate these inequalities to show that the system is not local or noncontextual. So far, these two types of inequalities have never been tested simultaneously.

In the new study, the researchers have attempted to violate both inequalities at the same time, but have found that only one inequality can be violated at once. Their experiment uses entangled photons to generate photonic qutrit-qubit systems (a qubit is a superposition of two states, whereas a qutrit is a superposition of three states). By performing various measurements on these photons, the researchers could violate the inequalities separately, but not at the same time.

"The greatest significance of our work is that we provide experimental evidence of the assumption that quantum entanglement and contextuality are intertwined quantum resources," Peng Xue, a physicist at Southeast University in Nanjing, China, and one of the lead authors of the paper, told *Phys.org*.

As the physicists explain, the reason for the nonlocality-contextuality tradeoff arises from the fact that both properties have the same root: the assumption of realism, which is the assumption that the physical world exists independent of our observations, and that the act of observation does not change it.

Since nonlocality and contextuality can be thought of as two different manifestations of the basic assumption of realism, then one of them can be transformed into the other, but both cannot exist at the same time because they are essentially the same thing.

"We think the contextuality-nonlocality monogamy suggests the existence of a quantum resource of which entanglement is just a particular form," Xue said. "The resource required to violate the noncontextuality inequality and that required to violate the locality inequality are fungible through entanglement. That is, to violate the locality inequality costs entanglement as a resource, while to violate the noncontextuality inequality costs contextuality as a resource. In a quantum system, only one of the two inequalities can be violated because nothing is left to violate the other one."

The researchers hope that the new experiment will open the doors to further exploring the mutual resource in the future, as well as lead to potential applications.

"We plan to study contextuality as a resource for experimental quantum information processing, such as for quantum computation," Xue said.

**More information:**Xiang Zhan, et al. "Realization of the Contextuality-Nonlocality Tradeoff with a Qubit-Qutrit Photon Pair."

*Physical Review Letters*. DOI: 10.1103/PhysRevLett.116.090401

© 2016 Phys.org

**Citation**: Two defining features of quantum mechanics never appear together (2016, March 21) retrieved 15 July 2019 from https://phys.org/news/2016-03-features-quantum-mechanics.html

## User comments

HyperfuzzyHyperfuzzyshaverashaveraThe article misrepresents the idea of "non-real" quantum physics, and the extent to which it is quite common throughout the community.

Non-local quantum physics, where some kind of information about the "real" underlying quantum mechanics somehow goes around faster than light is also possible, but not as commonly supported in the community.

composefreestylexplorefreestylexploreNoumenonActually it does require mind setting up the apparatus,… as the apparatus design determines the possible observable states to begin with, and the observable values are conceptual values, which are not resolvable via decoherence (quantum interaction).

Decoherence does not solve the 'measurement problem'. 'Measurement' is necessarily mind-dependent….

Realism refers to assumptions that our conceptual descriptions implicit in apparatus design and interpretation (locality, counterfactuality, particle, wave, determinism, etc] correspond to mind-independent objective reality. This is what is refuted by experiment via hidden variables that assume these concepts.

obama_socks- freestylexplore (Otto's sockpuppet)

Da SchneibDa SchneibDa Schneibdan42dayNoumenonThe failure of Realism to hold, implies that.

That is only one such condition.

Superpositions [SP's] are not due to Heisenberg uncertainty relations [HUR]. HUR's concern conjugate variables, not SP's. The quantum wavefunction (in SP) is not a SP of values. To extract the observable values requires a quantum operator acting on the wavefunction to render eigenvalues [the statevector is scaled without changing it's direction in Hilbert Space]. The quantum operator is in effect, a representation of the experimental apparatus.

Da SchneibName others.

Incorrect. For example a particle whose polarization has been measured in X has its polarization in any other axis in superposition. Known fact of quantum mechanics. Please try to stay away from philosophy and stick to physics. Thanks.

[contd]

Da SchneibI don't even know what that means. Superposition means that one of a particle's parameters (the one that is superposed, specifically) has a probability to be two or more various values when measured. Superposition is precisely about values, period. Please try to stay away from philosophy and stick to physics. Thanks.

[contd]

Da SchneibWhich is exactly what I said and has nothing to do with your previous claims. Please try to stay away from philosophy and stick to physics. Thanks.

Noumenon1) locality, ....2) counterfactual definiteness -[ that entities have objective values independent of measurement so that statements can be made of experiments not actually performed], ....and the 3) no conspiracy condition,..... if the Bell inequalities rule out one, then they rule out "local realism".

For example, if one interpretation maintains locality, then it must reject counterfactual definiteness and with it the notion of properties existing independently of measurements. If another interpretation maintains counterfactual definiteness, then it must reject locality. In either case Bell's theorem disproves local-realism.

Da SchneibAgain, please try to stay away from philosophy and stick to physics. Thanks.

NoumenonYou described a superposition of states. That is NOT the Heisenberg uncertainty relation.

I explained Hilbert Space formulation to you before, in which statevectors [superposition of states] evolve, …..with a Fourier transform required for its conjugate space representation. That is where the HUR comes in.

I will school you in both topics simultaneously :). If you wish to be wrong and rude, I can put you on ignore, otherwise take advantage of my generosity.

Da SchneibMoving right along, the no-conspiracy condition is that there isn't a deity or supernatural being or superpowerful alien manipulating the results of our experiments. Realism is the statement that the parameters of a particle have real values even when they are unmeasured or unmeasurable, which is not at all the same thing.

Again, please try to stay away from philosophy and stick to physics. Thanks.

Da SchneibWe're not talking about the representation of a state in Hilbert space, we're talking about the actual values of real parameters. Please stop trying to bamboozle. It's embarrassing to watch. Thanks.

Da SchneibNoumenonThen why are you insulting me? That is the basic mathematical formulation of QM. Do you not know what a quantum operator is? What a wavefunction is? What an eigenstate, eigenfunction, and eigenvalues are? This is not philosophy, it is the Schrodinger equation,… "quantum theory as a eigenvalue problem" was the name of his famous paper.

---->

NoumenonA wavefunction, is NOT a wavefunction of VALUES. The measured values are the "eigenvalues" obtained from solving the Schrodinger equation for solutions that satisfy the eigenvalue problem [that scale the state-vector without changing its direction in Hilbert Space].

The normalized square of the wavefunction gives the probabilities, not the values.

The wavefunction Fourier transformed, can even be given a different representation of observable values,… another basis space,.. i.e. its conjugate.

The Hilbert Space formulation is the fundamental QM mathematical formulation !! The basis of that space is the actual values measured !!

Your rudeness and simultaneous ignorance is what is embarrassing here.

Da SchneibDa SchneibLike I said, stop the BS. You're going to get nowhere with it.

You said, This is egregious.

1. A wavefunction is the representation of the value of a parameter on a particle that is in superposition. So your statement is explicitly untrue.

2. There is no necessity to state that the wavefunction is in superposition; there is no need to represent it as a wavefunction if it is not because it has a real value.

Like I said, I don't even know what that means. It's a bunch of bamboozling BS.

jgmirl69NoumenonNO, the wavefunction is not a superposition of "values". To get the possible measurable values you must apply a quantum operator in the Schrodinger equation to find solutions that satisfy an eigenvalue problem. This gives discrete results. On actual measurement gives only one such result. The square of the wavefunction gives the probability.

None of this is philosophy,.... you insulting ding-bat,... it is the mathematical foundation of QM.

Particles? No. The 'quantum system' is represented by the wavefunction. Not the values. The values come in by solving the Schrodinger equation as a eigenvalue problem. You use a Quantum Operator,.... like the Hamiltonian (energy), or position or momentum operator,... to find the [eigen]values.

Da SchneibNoumenonYou are ignorant of the mathematical foundations of quantum mechanics and how that formulation works.

You attempted to correct me, but clearly have some issue with being corrected yourself, so you degenerate into insults.

Da SchneibIt's transparent.

Claiming that parameters on particles don't have values, whether they are in superposition or not, is nonsense. It's carefully crafted nonsense, by all appearances. You are a liar and a troll.

You can prove me wrong at any time: go answer my original point that you are confusing philosophical realism with physics realism.

Da SchneibDa SchneibWe think our geniuses what?

Err, perhaps you don't quite get what "realism" means. Noum isn't helping much. We're not talking about philosophical realism; we're talking about physics realism, and we knew that was broken when Heisenberg wrote his uncertainty relation.

As far as being able to guess at the eventual outcome, hate to tell you but the physics we're talking about here is all about quantifying superpositions in terms of probabilities, and knowing the exact probabilities isn't guessing. It's quantifying. It's as much as we can know about the eventual outcome; there simply isn't any more information available.

NoumenonThe wavefunction is not a superposition of values. In fact the wavefunction is a complex valued function.

Again, profound ignorance. The Hilbert Space formulation is the "mathematically rigorous formulation of quantum mechanics, developed by John von Neumann", and is entirely compatible with Dirac's bra-Ket notation. This is not philosophy.

I'm bamboozling you with orders if magnitude more knowledge of the subject, while you are bamboozling me with Jerry-Springer insults and lack of humility.

Da SchneibAnd that displays that you know little of quantum mechanics. Just sayin'.

You're lying again.

Ummm, that's true but it doesn't prove that it doesn't have a value, nor does it prove that the value is not a superposition of real values. Do try to keep your eye on the ball, there, sport. Functions get solved and the solutions yield values.

On Earth.

This isn't even a map/territory confusion; it's a complete lack of understanding of the fundamental entities that quantum mechanics is all about.

[contd]

Da SchneibBra-ket notation isn't the territory either, philosopher.

You're lying again.

NoumenonThey are both conditions for "local realism". Locality [local relativistic causality], and counterfactual definiteness, etc.

"1) locality, ....2) counterfactual definiteness -[ that entities have objective values independent of measurement so that statements can be made of experiments not actually performed], ....and the 3) no conspiracy condition,..... if the Bell inequalities rule out one, then they rule out "local realism"." - Noumenon

@CaptainStumpy, are you qualified in down-rating my posts above? Care to tell me what you object to?

Da SchneibSo? How does that contradict what I say?

Da Schneib3...

2...

1...

NoumenonThat's because quantum "particles" don't move in simple classical trajectories. There may be interference terms. This is why the wavefunction is a complex quantity and why the Hilbert Space formulation is a consistent mathematical description.

You are objecting to a more precise mathematical description of QM, and looking like a crank in doing so.

I see you didn't bother taking notes when you where schooled in This Thread, ...instead hide under your desk where you belong.

Da SchneibReal photons, polarized in a filter oriented with its axis pointing to X, are passed through another polarizer oriented with its axis pointing to Y. If we then add a third filter pointing to X again, then some of the photons make it through and some don't, indicating that they were repolarized in X by having their polarization measured in Y. No matter what math you use, no matter which interpretation you use, those are absolute facts, and the percentage that make it through the second X oriented filter is calculable and fixed, given the directions X and Y.

We're talking about stuff that basic, and you want to change the subject to Hilbert space or bra-ket notation. You're lying, Noum, and it's transparent.

Da SchneibAlso, polarization is a parameter, and it has two values. This is a real particle, and when it interacts with the environment, that interaction has consequences. This isn't some representation in Hilbert space, it isn't some equation in bra-ket notation, it's a real particle in the real world- but when its polarization in one axis has been measured, its polarization in other axes is uncertain, and subject to a quantum mechanical calculation to determine the probability of its polarization having one or the other value in the next axis you choose to measure.

NoumenonIf you reference "wavefunction" or "superpostion" you're de facto referencing the mathematical representation. The wavefunction hence its name, is any arbitrary complex valued mathematical function that is Fourier decomposable. To obtain the set of possible observable parameter values, requires solving the Schrodinger equation for eigenvalue solutions.

Da SchneibNoumenon- a single wavefunction can represent more than one "particle",

- not all quantum states (represented in a superpostion of states) are observable.

If bringing up the mathematics of QM obscures my post for you, that is a statement about your state of knowledge, not one of my honesty.

Noumenon"Please try to stay away from philosophy and stick to physics. Thanks. - DaSchnieb"

This COULD have been a cordial discussion, but for your behaviour.

ZenmasterDa SchneibSo? Each particle in the ensemble has its own individual wavefunction, and they add up to a composite one. This has nothing to do with the central question, which is whether philosophical and physics definitions of realism are the same.

This is duh; for a given particle, when the wavefunction collapses only one of the superposed states will be realized. And this also has nothing to do with the central question, which is whether philosophical and physics definitions of realism are the same.

You're bobbing and weaving, Noum. Why are you doing that if your point is straightforward?

Da SchneibJust admit you're wrong and that philosophical realism and physics realism have nothing to do with one another.

No, Noum, you lied and I pointed it out. Get over it, and while you're at it, stop pretending that philosophy is physics.

Da SchneibNoumenonWrong again. Its a SINGLE superposed wavefunction. The mathematical representation space in which such a wavefunction evolves is a tensor product space, which is how it is "separated".

-----------

Your childish and very defensive behaviour was also in display in http://phys.org/n...cal.html where you were rude also to DarkLordKelvin who had shown more knowledge of the subject than you also.

You said something in that thread that was very telling about your personality which sums up this exchange as well....

"But being told I'm "wrong" is pretty much not OK. - DaSchnieb"

Da SchneibAdmit you're wrong, Noum. I've proven it; now it's up to you to man up.

And stop trying to change the subject. It's transparent.

NoumenonNo, you didn't understand. Not all quantum states are observable, even in principle.

I can agree to discuss this point further once you firstly admit that....1) the bulk of my posts above were not about philosophy at all, but about the mathematics of QM, and.... 2) you admit that your objection to philosophical points made by me here is entirely made mute by my superior and deeper understanding of quantum mechanics.

Da SchneibSure, but the math was not relevant and you were obfuscating to avoid admitting you were wrong. When you admit that, then we will be in agreement.

[contd]

Da SchneibZenmasterDa SchneibDa SchneibNoumenonYou calling me a "liar" over and over exposes your mentality and lack of sophistication. You started this discussion by antagonizing as point out.

The subject of "https://en.wikipe...physics" is contributed to by very prominent physicists, and is ubiquitous in the history of quantum mechanics in interpretations of theory, as well as other branches of physics.

Math is relevant in QM, that is the point. The tables were turned on you, don't you understand that yet?

In this thread,.... you objected to me making philosophical statements,,,, AND objected to me making mathematical statements.

Da SchneibYou're a philosopher masquerading as a physicist.

You'll use anything, including math, to try and bolster your point, and you don't care whether you're wrong or right.

I care, and I find you to be a pretty small souled person.

This thread is about physics, and neither math nor philosophy will save you from everyone figuring out you don't really understand physics.

Da SchneibPhysics says that very small and very fast things are qualitatively different from ordinary consensus reality you see around you, but also that these very small and very fast things, and their odd behavior, *lead to* that reality you see.

Among those differences, the most important one is that things can have properties that are neither one thing nor another, but a mixture of both. But they can only have properties like that when you can't, or don't, look at them. The properties that are in this state are said to be "in superposition." If the time comes that you look at these properties, then they turn out to be a particular thing, and if you look at a lot of the same kinds of events, then there will turn out to be some that go this way, and some that go that way, and the percentage of each will be well-known, but how an individual one actually goes is random.

[contd]

Da SchneibWhen a particular property turns out, in an individual case, to be some particular thing, then the superposition is said to have "collapsed." And in fact it isn't even necessary that you have looked; if the thing with the property touches some other thing in any way, then this "collapse" will occur, and the property will be realized.

This is an essential difference from the way things around you behave; you are used to things having properties that remain static no matter what happens. Quantum things are essentially different from the things you deal with in your perception of reality in this manner. And the experiment that this thread is about is one that looks very carefully at this behavior of quantum things.

If you can follow the logic, even though it's different from what you're used to, you will understand this behavior much better, and this will help you understand quantum reality.

That's the skinny.

NoumenonQuantum mechanics requires an understanding of the mathematical formulation. If you don't understand it then you don't understand QM.

I referenced the mathematical structure to be more precise in discussion which QM requires, while you display a discovery-channel understanding, and yet have the nerve to say I don't understand the physics. You're a insulting and rude fraud and anyone who has seriously studied the subject can see this , but not people like CS.

Another example of your lack of understanding. Decoherence does NOT cause collapse of the wavefunction.

Mimath224My question is; when having more than one solution the Sch. equ. then adding the solutions, apparently, is also a solution and results in a 'wave packet'. Apparently it is the w.p. that leads to a representation of a physical particle and so I might understand that as being the way to a reality in terms of QM. But how far back (before these) should I be looking for the 'assumption of realism'? I am not sure I have put that correctly but any info would be appreciated. Thanks

shaverashaveraThe problem is that if quantum realism is true, then the blurring mechanism, pilot waves or whatever, must somehow work faster than light, if not instantaneous and backwards in time. If there are *real* properties to a particle, then these waves have to somehow communicate how they are being interacted with in an experiment.

On the other hand, if you accept that the wave *is* the particle, that the very nature of everything that exists is not precisely definite in all senses, then you no longer require the waves to be faster than light. The superposition itself accounts for the state between two entangled particles

antigoracleThe fact that Da Schneib does not realize that Maths cannot lie, just confirms his idiocy.

HyperfuzzyHence, moot! Look deeper. Anyway, + and - is not what I gain or lose but is something else. Never reconciled. Potential to kinetic and kinetic to potential with fundamentals, relative to whom? juz say'n

Mimath224While 'On the other hand, if you accept that the wave *is* the particle, that the very nature of everything that exists is not precisely definite in all senses, then you no longer require the waves to be faster than light....' might deny photon entanglement (instantaneous) by FTL travel?

Although I am aware of superposition implications etc how would this function as FTL travel for entangled particles? (my books don't seem to mention these alternatives) Perhaps you know of a website that would be useful to me and be less bother to posters here (Ha!). Thanks.

NoumenonHowever, when discussing implications of experimental results of QM in an effort to understand the physical world, as is the ultimate point of science, one naturally is going to offer explanatory hypothesis for that purpose.

In QM, there are many such 'interpretations of quantum mechanics', but what they all have in commen is that they abide to current experimental results.

IOW, if they do not offer new predictions over and above core QM, then they are not new theories over and above QM,…. they are stickily speaking a branch of Philosophy of Physics.

Noumenon"There is no way to remove the observer us from our perception of the world, which is created through our sensory processing and through the way we think and reason. Our perception and the observations upon which our theories are based are shaped by a kind of lens, the interpretive structure of our human brains." - Stephen Hawking

In interpretations of QM experiment, one has the choice of making use of one conjugate concept at the expense of another.

NoumenonThe application of the quantum-operator to this mathematical wavefunction, represents 'adding conceptual form' to obtain conceptual values, as explained above. The reason is is that the quantum-operator represents the experimental apparatus in essence. The experimental apparatus is macroscopic and so must accord with our 'forms of thought',…i.e. the assumptions made as conditions for macroscopic observation…..

NoumenonThe point here is that the 'underlying reality' is conceptually formless (as it exists independently of our knowledge of it). Experiment in effect projects a 'underlying something' into our a-priori conceptual framework [see Hawking's quote]…. so that… the non-intuitive nature of QM has established that ....

"The doctrine that the world is made up of objects whose existence is independent of human consciousness turns out to be in conflict with quantum mechanics and with facts established by experiment" - B. d'Espagnat

A physicist can have a Realist interpretation or a Positivist interpretation of QM. These are indeed philosophical positions,... however the former are refuted by experiment,.... once the elements of philosophical "Realism" are quantified as I enumerated above for "local realism".

shaveraAnyway: for details on the question of FTL, consider this. If there's a 'real' state, it may be that no physical process allows us to measure that 'real' state. Whatever my experiment is, it's made of other particles obeying the same quantum rules, so there may be no way to *actually* measure the 'real' state underneath. Therefore, if these pilot waves or whatever allow these 'real' states to communicate with each other FTL, they cannot communicate *useful information* faster than light, because they only talk to this "underlying" reality, and not to "our" reality. So the rules about "no information can pass faster than light" still hold more or less.

NoumenonA Realist in this sense believes that Reality is as we come to know it, independently of the way we must think and reason. In contrast, a Positivist, like Hawking, d'Espagnat, etc, and myself, believe that physics is not about ascertaining knowledge of Independent Reality, but rather of ascertaining knowledge of phenomena as experienced, with all the epistemological conditions implied by that.

This is the reason that experiment seems to create the attributes, and results change when we are looking!

Science studies phenomena. Phenomenal-reality has a necessary component that is mind-dependent due to the logical necessity of observation,.. the mind necessarily filters the underlying [though objective] reality through concepts, to produce Phenomenal-Reality.

Phenomenal-Reality = Mind (Noumenal Reality)

NoumenonBecause a Single wavefunction description represents Two [or more] entangled particles, no mater how far they are subsequently observed. The wavefunction can spread arbitrarily in the space of possibilities**.

Once a measurement takes place on one of the two entangled particles, this wavefunction 'collapses' resulting in say two distinct positions.

** For multiple particles this is NOT regular 3D space, but rather a tensor space, however, a lower limit for the velocity that this collapse can be experimentally determined and if I recall something of the order of magnitude of 100,000 times c. It makes more sense to just say it is not a physical wave.

NoumenonProtoplasmixI use a variety of lenses, both external and internal, and compare the results. How could I possibly know exactly, precisely how and what you (or anyone) see and feel? But if I can repeat your experiment and I get the same results, then there is consensus. And consensus is a thing greater than the sum of its parts. Maths and science – these are not rose colored glasses; they're perfect lenses if you know how to use them. At least that's been my experience. So what was your point, Noumenon?

cont'd >

ProtoplasmixIt wasn't too long ago people didn't know for sure if we would ever directly "see" gravitational waves. You can make a strong argument we didn't "see" them, we "heard" them. But then you'd make my point about no ill affect on our ever increasing knowledge and mastery over the environment from the manner in which we experience things. Does that make me a realist? Because I feel a whole lot more positive about experiencing things that a "positivist" says we can't, if I understand you correctly.

farstriderrThey assume realism in order to develop experiments that violate realism. You can't assume "non-realism", then develop experiments that violate realism. That's illogical.

farstriderrNoumenonMy use of Hawking's quote is not meant to refer to personal subjectivity. My above several posts were meant to explain this further….

HyperfuzzyNoumenonBut by "experiencing things", you are adding conditions for doing so, as pointed out by Hawking and my posts above.

A 'positivist' pointing this fact out, is in no way anti-science in any respect. In fact a Positivist is less likely to inject hypothetical metaphysical objects, than is a Realist. A Positivist would not expect QM to 'make intuitive sense', because he recognizes that our mind-dependent conceptual framework is in essence an artificial one.

I made the distinction between Realist and Positivist above.

A Positivist would confirm that physics is about acquiring predictive knowledge of experience (observation),.... just is not independent of it.

HyperfuzzyDa SchneibMore smoke.

[contd]

Da SchneibSo much for how much physics you understand.

Da SchneibJust sayin'.

Da SchneibQuestion on : how do you see this interacting with

a) the subject article of this thread,

b) the Transactional Interpretation's Wheeler-Feynman absorber theory,

c) the Bohm interpretation,

d) the Bell's Theorem proof that all hidden variable theories are ruled out, by the Aspect experiment, etc.?

Da SchneibDa SchneibMore smoke.

Da Schneib@farstriderr: Nice analysis! You're correct, this experiment has many similarities with the DCQE. And the added entanglement lets the experimenter choose between the standard DCQE approach, which violates contextuality, and the later derivative experiments of the DCQE that violate locality, and shows you can't violate both.

Da SchneibYou mean like "having a brain." Or "being made of matter." Because that's what Hawking means, not the smoke you were spouting. And what he said has nothing to do with the interpretations of QM.

We're discussing quantum realism, not Realism vs. Positivism. I defined quantum realism above. Maybe you forgot.

[contd]

Da SchneibAnd it's completely immaterial because we're not discussing Realism, we're discussing quantum realism, which you won't admit is not the same thing. And you still haven't admitted it.

Still immaterial. More smoke.

Da SchneibAnd how about admitting that Realism isn't the same thing as quantum realism? You as much as admitted it above, but then you fell off the wagon.

How about an explanation for the fact that you claim that interpretations of QM are philosophy of physics when they're not, or for the fact that they relate the formalisms to experimental results, neither of which is philosophy?

I also found it amusing that you downvoted my compliments to others. Now THAT is childish.

NoumenonDecoherence is not interaction? Are you sure about this?

Decoherence occurs when a QM system INTERACTS with its environment, which results in the loss of (off-diagonal) interference terms by the loss of phase coherence. Interaction.

You have already proven your character to me above, and so I have no interest in having a 'jerry-springer' quality debate with you. The posts I made today were not in response to anything you posted.

Da SchneibNoumenonAre you sure that interaction collapses the wavefunction? Are you sure that decoherence is not interaction,..... because it is caused by it.

The problem of how or even if wavefunction collapse occurs is at the heart of the presently unsolved 'measurement problem'. I offered an epistemological solution above, I don't expect you to follow. See "von Neumann's cut" from his preeminent text on QM.

In principal quantum reality operates according to the deterministic Schrodinger equation, and if that system was allowed to evolve without an observation, then that QM system would INTERACT with the environment,.... i.e. decoherence would occur AND yet there would be no collapses of the wavefunction.

farstriderrDa SchneibDa SchneibNoumenonIt confirms what I already posted. Interaction/Decoherence does not collapse the wavefunction.

Da SchneibNote that I never mentioned decoherence in what you quoted. Just sayin'.

More smoke.

NoumenonThat is what philosophy of physics IS,… interpretations [whether they have mathematical form or not] of the same experimental results. Did you read the link provided? It said this …. "Quantum mechanics is a large focus of contemporary philosophy of physics, specifically concerning the correct interpretation of quantum mechanics".

Are you then speaking philosophical above even while berating it, because you just uttered this gem…..

Da SchneibMore smoke.

NoumenonPlease try to stay away from philosophy and stick to physics. Thanks. \\sarcasm.

I see, but you said "collapse" and "interaction",.... I don't know how else to have interpreted that but as, decoherence or that interaction causes collapse of the WP.

If I read that wrong, then I apologize.

NoumenonBecause your behavior above certainly wasn't childish, right?

You 1 rated everyone of my posts in this thread, even while responding. Had you not done that I would not have down rated a single post of yours.

Da Schneib2. That's a statement of fact, not a statement of philosophy. "The map is not the territory" is about as basic a statement of fact as you can find. There's no water, or dirt, or rock, or hills, or forests, or anything else but ink and paper in a map. And there aren't any photons, or quarks, or leptons in a mathematical theory of physics. Just numbers.

You're not even all that good a philosopher.

[contd]

Da SchneibSince I never said "decoherence" you read it wrong. Now you need to address the other points, starting with forgetting that interaction causes the collapse of the wavefunction (if you buy Copenhagen-with-collapse, as the largest plurality of physicists do).

Da SchneibGet over it. Say something smart.

Oh and BTW you went around to other threads and downvoted posts there, without ever providing any argument to say there was anything wrong, to "get me." Since we're on the subject. Retaliation is stupid, too, and quite transparent-- and quite childish.

Stop trying to "win," Noum. It's pretty disgusting to watch. Just stick to the facts-- one of which is that physics is not philosophy.

Whydening GyreNo. It's the RESULT of interaction. Decoherence IS the wave "collapsing"...

Don't over think it...

BTW - WB, The DA (you crotchety ol' curmudgeon...:-))

Da SchneibMore to the point, decoherence is the loss of entanglement, caused by interaction with the environment. In other words, photon A interacts with proton B, causing photon A's polarization in some axis, call it X (and entangling it with proton B, which has also had its polarization in X measured); later, photon A interacts with electron C, causing photon A's polarization in some other axis, call it Y, which (under Heisenberg uncertainty) causes the polarization in X to decohere, by causing it to lose its entanglement with proton B. That's what decoherence is.

Mimath224@Noumenon, you need to be careful about implying what I am implying. I did post that I was not going to enter your discussion with Da Schneib on this article and that remains. But when you start talking about 'Positivism' you are really diving into heavy waters. First you need to define which branch of Logical Positivism you are coming from...they aren't all the same. If you take the 'empiricism' route then likewise you need to define your stance, 'restrictive' or 'lesser restrictive'. The latter could be such that it requires; (cont)

Mimath224However, basically most science started way back as a kind of philosophical question and just as Homo Sapiens carry the genes of their prehistoric beginnings I suppose science must do so also. But just as Homo Sapiens are different so is the evolved science and we need to be aware of that and act accordingly.

@Whydening Gyre & Da Schneib 'More to the point, decoherence is the loss of entanglement,....I thought that was in all basic texts on the subject, slit experiments, sunlight being only partially coherent (and incoherent) etc. Noumenon not understand the difference?

Da SchneibNoumenonDecoherence does not result in wavefunction collapse. Decoherence is the result of interaction with the environment.

"A dynamical collapse of the wave function would require nonlinear and non-unitary terms in the Schrödinger equation [not standard QM] Since nonlinear terms in the Schrödinger equation lead to observable deviations from conventional quantum theory, they should at present be disregarded for similar reasons as hidden variables." - Heinz-Dieter Zeh, the discoverer of decoherence. [see my post also wrt the Schrodinger equation and decoherence]

"Decoherence does not generate actual wave function collapse. It only provides an explanation for the observation of wave function collapse, as the quantum nature of the system "leaks" into the environment. [...] Specifically, decoherence does not attempt to explain the measurement problem." - [Link

NoumenonNo, its the gain of entanglement [coupling with the environment] such that there is a loss of phase coherence and thus loss of interference terms that are responsible for quantum behavior.

Da SchneibYou forgot again.

NoumenonThe Copenhagen interpretation which I accept, does not propose that wave function collapse occurs on account of quantum interaction. It is an additional layer of interpretation over and above the mathematical theory itself.

There is an incompatibility between the deterministic evolution of the Schrodinger equation and the state-reduction (WP collapse) upon observation. C.I. just states that incompatibility as a consequence of observation....

I posted my extended take about why this is so above. See also 'von Neumanns cut'.

NoumenonPerhaps, but since you said "interaction" and "collapse", I'm not sure how else I was expected to take that. In any case, quantum interaction according to the deterministic Schrodinger equation does result in wave function collapse either.

Da Schneib[contd]

Da SchneibWikipedia also says Copenhagen doesn't have decoherence: "The discontinuous 'wave function collapse' postulated in the Copenhagen interpretation to enable the theory to be related to the results of laboratory measurements now can be understood as an aspect of the normal dynamics of quantum mechanics via the decoherence process. Consequently, decoherence is an important part of the modern *alternative to the Copenhagen interpretation*, based on consistent histories." https://en.wikipe...surement (Emphasis mine.)

So if you're a strict Copenhagen advocate you shouldn't even be *talking* about decoherence. You don't need decoherence in Copenhagen; you got direct literal wavefunction collapse, but it's limited to the particle's contact with the measurement equipment.

[contd]

Da SchneibNow, I'm willing to be a little fuzzy and say that collapse and decoherence have something to do with one another; but get right down to it, I really don't think collapse is, and I don't mean this in any physics sense, I guess I'm doing a little philosophy here, realistic. By which I mean, I think it's so divorced from how things really happen that it's not a good enough description unless you just wanna calculate. As far as actual particles undergoing real wavefunction collapse, sorry, man, I don't believe in ghosts either. Decoherence makes a great deal more sense.

And wavefunction collapse and decoherence don't occur in the same interpretations. You don't need one if you have the other. See how that works?

Sorry if I was being a little imprecise so everyone else could kinda understand quantum mechanics.

Meanwhile,

[contd]

Da SchneibAnd CH and Bohm use decoherence to do substantially the same thing- to explain the apparent "wavefunction collapse" as the result of interactions with environmental particles, step by step. And we know by experiment that a single interaction, if it happens to measure a complementary property of an entangled property, decoheres the entanglement.

Now everybody's confused.

Da SchneibYou at least thought about these ones a little more, but your claims to know a lot about QM have just been exposed; you know only one interpretation and you don't appear to have properly studied any of the others. And you don't know enough about Copenhagen to know it doesn't have decoherence in it, either.

Da SchneibProtoplasmixNoumenonSince the element of the measurement-problem that explains why a particular outcome is realized as opposed to some other possibility, is NOT resolved by decoherence, it is still necessary to postulate an additional layer of interpretation,… in the case of C.I. this would be a non-objective collapse or state reduction. It is compatible retrospectively.

This is why Everett postulated many-worlds, which developed into consistent histories.

Here is the rest of the quote you posted….

"However, decoherence by itself may not give a complete solution of the measurement problem, […] To present a solution to the measurement problem in most interpretations of quantum mechanics, decoherence must be supplied with some nontrivial interpretational considerations."

NoumenonYou need to make an important distinction here. Are you speaking of an objective-collapse, as if the wavefunction is a physical thing? There ARE alternative objective-collapse theories. As pointed out above they require non-standard modification to the Schrodinger equation. In this case, decoherence (just a consequence of the standard Schrodinger equation), would be made compatible with wavefunction collapse (not a consequence of the standard Schrodinger equation).

If you are referring to standard QM theory instead, then they are not incompatible either due to the fact that decoherence leaves the important element of the measurement problem unresolved, thus still requiring the extra postulate of collapse (in the C.I. and extensions).

In C.I. it is an extra postulate just as the Born rule is.

NoumenonThe effective interface between these two is macroscopically evolved mind-dependent observation [insert Hawking quote]. Because decoherence does not explain why particular conceptual values are observed, this requires one to step outside the subject and into epistemology imo.

Some interpretations choose to step outside the subject, into metaphysics,... pilot-wave, Everett,... epistemology is at least investigable in principal.

This is what I attempted to convey above. Again it may not be right, but the essence of the C.I. was this, and not to make presumptions about reality that cannot be observed.

Ryan1981https://en.wikipe..._paradox

HyperfuzzycomposeWhydening GyreDisentangled tri-angles...

(Sung to the tune of "Decomposing Composers" by Ian Durry)

Da SchneibSo you favor non-traditional CI without objective wavefunction collapse?

[contd]

Da SchneibHmmm, actually I would argue that Everett's reasoning for developing the MWI was

acceptance of the objective truth of the universal wavefunction. Decoherence was an *outcome* of MWI, not its founding principle. I would also argue that the reasoning behind CH was the acceptance of the truth of both the universal wavefunction and Born's Rule, and that decoherence merely provided a path that allowed this synthesis. I would also argue that Bohm's interpretation gave as much impetus to decoherence as the MWI. As for TI, I would say that it's an attempt to move Bohm's interpretation into the mainstream, driven by Wheeler-Feynman absorber theory.

[contd]

Da SchneibThe approach of traditional CI to wavefunction collapse is to treat it as a real phenomenon; this has some pretty serious problems in terms of how we see real systems behave. In particular, the ability to create what appear to be objective superposed states in quantum optics experiments seems to indicate that interpretations that contain objective wavefunction collapse are at odds with experimental evidence. I will refer you to the DCQE and its derivatives, and I will also point out that Wikipedia statements in the article on decoherence mention ions in superposed states.

Non-traditional CI that treats wavefunction collapse as a mathematical procedure rather than an objective reality avoids this problem, but introduces the EPR-based contention that it must necessarily be incomplete; that is, it cannot model a free particle in open space, specifically the radioactive decay of an unstable nucleus unaffected by its surroundings.

[contd]

Da SchneibI would argue against "most." In fact, most interpretations yield decoherence rather than accepting it as a postulate. Most modern interpretations avoid the measurement problem, which is the result of wavefunction collapse, by substituting non-classical logic; it is the attempt to deal with QM using classical logic that gives rise to the need for wavefunction collapse in the first place, and most modern interpretations use quantum logic rather than classical logic.

[contd]

Da Schneib[contd]

Da SchneibTraditional CI is not an "alternative" interpretation; objective wavefunction collapse is the original interpretation.

Actually, von Neumann was the one who added objective wavefunction collapse to CI; Bohr's approach was the same as Feynman's: shut up and calculate. We don't know what happens there.

Errr, no. Decoherence isn't a consequence of the Shroedinger equation. It's a consequence of the development of the Everett and Bohm interpretations. And it's not a feature of CI; it's an add-on, bolted on in order to "look under the covers" of wavefunction collapse.

[contd]

Da SchneibNo. We're not talking about QM here, we're talking about interpretations of QM. The map is not the territory. We're also talking about how we, our classical selves, can come to an understanding of the meaning and implications of QM. But we are not talking directly about QM; that's why I chided you for bringing Hilbert spaces and bra-ket math into the conversation.

But all the interpretations that include decoherence don't have the measurement problem, and don't include objective collapse. Wavefunction collapse is just a mathematical procedure, just like the use of Hilbert spaces or matrices. It works; that doesn't mean it actually happens.

[contd]

Da SchneibI disagree, on two grounds:

1. Objective wavefunction collapse is silly; it leads to all sorts of paradoxes, that are avoided if it's viewed simply as a mathematical procedure that happens to work out correctly rather than an objectively verifiable fact.

2. The Born Rule is an essential fact of quantum interactions, and accepting it as reality requires nothing more than accepting that superposed states are real, but unmeasurable. Accepting the Born Rule as objective fact doesn't lead to paradoxes, as objective wavefunction collapse does, and furthermore we are actually able to generate these superposed states in real quantum optics experiments. That we cannot measure them directly is immaterial.

[contd]

Da SchneibNow that I agree with, but that is not all it does.

Also, decoherence just plain makes sense. It says that quantum states, i.e. entanglement, an objectively non-classical state, i.e. superposition, another objectively non-classical state, are *real*, but cannot be described or treated using classical mechanics. This is an obvious fact if you consider real quantum optics experiments.

Da SchneibDa SchneibNoumenonJohn Von Neumann, in formulating a consistent mathematical foundation for QM, followed Heisenberg in introducing the discontinuous change in the deterministic Schrodinger evolution of the WP upon a measurement,.... without attempting to explain state-reduction dynamically.

In fact, you may recall that Schrodinger was quit disappointed that the Copenhagen guys, with the Max Born rule [Btw, Grandfather of Olivia Newton John], ….rejected the notion that the wavefunction represented a physical wave. Schrodinger desired it to be Real as he wished to maintain a classical description.

The Born rule is an extra step of interpretation, just as state-reduction is,... precisely because neither is mathematically derivable via Schrodinger/Matrix Equations.

Noumenon---------------------------------------------------------

Objective collapse (dynamical collapse) theories require a modification to the Schrodinger equation. That is non-standard and was definitely not part of the traditional C.I. as C.I. did not treat the WP as a physical wave.

"A dynamical collapse of the wave function would require nonlinear and non-unitary terms in the Schrödinger equation [...] lead to observable deviations from conventional quantum theory." - Heinz-Dieter Zeh discoverer of decoherence.

From this it must mean that decoherence does not result in collapse of the wavefunction, but must result from the evolution of the Schrodinger equation itself.

NoumenonThese baseless accusations are unnecessary.

Da SchneibI never claimed that CI regarded the wavefunction as physical. I claimed it regarded the collapse of the wavefunction as physical.

Why do you keep trying to get away with this crap? Do you still have the illusion that I won't notice because you're a genius and I'm some sort of lower life form?

When will you stop insulting me subtly and pretending you didn't?

Errr, you just did it again.

Just stop. You're not going to "win." You're just making yourself look stupid.

Da SchneibThe Born Rule is, quite simply and basically, the statement that quantum phenomena are *intrinsically different* from classical phenomena in that they are not necessarily of definite value, but may be represented by probabilities that they may, when they interact, turn out to be one value or another. The motivation is Heisenberg uncertainty and superposition.

To put it another way, accepting the Born Rule as real means you accept that quanta can exist in real experiments in superposed states, and the experiments that prove it have been done. See Bell experiments, see Aspect, see DCQE, see superposed ion experiments.

Mimath224NoumenonThere is no physical wavefunction collapse if the wavefunction if not considered a physical wave. Who's logic chopping here?

I went out of my way to explain the difference between objective dynamical [i.e. physical] wavefunction collapse and the discontinuous state-reduction [mathematical, informational] implicit in the C.I. above because you had asked this….

NoumenonA "collapse of the wavefunction as physical" would require a dynamical explanation somehow. Many Q.M.I. avoid this altogether by avoiding the collapse. Decoherence does not explain why one state-reduction occurs as opposed to another of the many possibilities,... so it fails as a dynamical explanation linking the mathematical foundation [Schrodinger / Matrix Mechanics] to the experimental conceptual valued results.

NoumenonThe Schrodinger Equation was formulated as an eigenvalue problem, and so already implied quanta,... and Schrodinger did not even like the Born Rule.

More to the point, the Born Rule derives probabilities via the square of the [normalized] wavefunction (i.e. for the eigenvalue solutions). This is not easy to derive from the core mathematics of any Q.M.I.

As presented by C.I. (Max Born) it is an extra layer of interpretation. Another postulate.

NoumenonNot so much, as there always has to be an observer/apparatus who is outside the quantum system.

This was pointed out in the Schrodinger Cat paradox. See also Heisenberg / von Neumann's cut (Schnitt).

If you are interested I outline this argument in This Thread, .... search for the text 'Mathematical Foundations of Quantum Mechanics'.

HyperfuzzyDa Schneib[contd]

Da SchneibBoth these types of parameters can be represented in a single vector in Hilbert space, which makes Hilbert space a very convenient way to organize all the parameters (in practice, all of the parameters of interest) in the same mathematical entity. Changes can then be applied that modify the vector, or modify the particular chosen basis of the Hilbert space, and the new vector worked out, yielding the parameters that the particle will have after the change. If the vector is changed, then the particle has undergone an interaction; if the basis of the Hilbert space is changed, then the particle is being observed differently. This turns out to work very well with the ways that physicists generally deal with interactions, and changes to the means, position, etc. of observation.

[contd]

Da SchneibI'm not familiar with the theorem, so I'll have to look it up and figure it out. Gimme a while.

Da SchneibAs for who's logic chopping, it's Bohr. The CI basically says, wavefunctions are a mathematical tool, we don't really know what's going on there, but wavefunction collapse is real, it's the measurement.

Yes, really. Read the Wikipedia article.

[contd]

Da SchneibYes, but it appears you have a pretty odd conception of the CI; you appear to think that the wavefunction collapse is not real. There's nothing wrong with that, but it's not traditional CI and you're claiming it is. *That* is the problem.

Da SchneibNow do you see what the "measurement problem" is?

[contd]

Da SchneibIt has one: the measurement. Or, in interpretations that avoid dealing with measurement as a separate thing, the interaction. That's where decoherence comes in.

The ones that do use decoherence- that is, removal of entanglement and resolution of the superposed state to a single state.

Not for a single interaction, but it does for an ensemble of interactions; the probability predicted by the Schroedinger equation is always observed in the ensemble. And according to our best understanding of state reduction from a superposed state to a single state all we can know before the reduction is the probability.

[contd]

HyperfuzzyYou guys realize that the observer of the space you define is outside the space, thus ad nauseum, an infinite Hilbert Space. I know, you don't get it! Let it collapse, or rethink it!

Da SchneibI disagree. Measurement yields only one value, and an ensemble of measurements yields the probabilities of the wavefunction. Both are dynamical. The fact that we cannot predict, for an individual interaction, which state will result from the resolution of the superposed states is an inherent feature of QM. All we can know is the probability of the various possible outcomes.

This is why I say that the Born Rule is an essential feature of QM, and this is why QM is essentially different from classical mechanics.

Da SchneibJust sayin'.

[contd]

Da SchneibMore to the point, the Born Rule derives probabilities via the square of the [normalized] wavefunction (i.e. for the eigenvalue solutions). This is not easy to derive from the core mathematics of any Q.M.I. Err, interpretations don't have core mathematics. QM does. The interpretation relates the core mathematics of QM to the observed results in experiments.

Sure, but this postulate appears to be required. It's a feature of all interpretations; in some (CI) it's a bolt-on, in others (CH) it's a postulate of the interpretation itself.

My argument is, since it's an intrinsic feature of QM, any interpretation that bolts it on after the fact is inherently incomplete. That's why they say CH is "CI done right."

Da SchneibSchroedinger's Cat relies upon confusion of two incompatible views: the Born Rule is applied to a classical system. There is no confusion if one merely states that one can either look at the trajectory of the cat/box system in time, or look at the probabilities of the outcome without considering the state of the cat while its state is in superposition.

[contd]

Da SchneibThis is logically consistent; if at any time you open the box, the cat is either dead or alive. It is only in superposition while you cannot look at it, and this is consistent with the states of photons in superposition in a DCQE experiment. You can't measure a superposition directly; you can only measure an ensemble of superpositions to determine the probabilities of various outcomes. The probability of the cat being dead or alive is equal to the probability that the radioactive isotope has decayed or not decayed.

I gave you a 4 for that one because you asked a good question.

Mimath224Da SchneibIf we're going to talk about what reality is and does, we have to acknowledge that what we perceive as the most salient features of, call it "reality," don't appear to hold below a certain size, somewhere around the size of an atom. The salient features of things smaller than atoms appear to behave fundamentally differently from the everyday things we encounter. For example, Born's Rule; for example, Heisenberg uncertainty; for example, entanglement. These things simply are not so when we use classical mechanics, and simply are so when we use quantum mechanics.

The really mysterious part is how the classical behaviors arise from the quantum behaviors, and not only arise from them but do so inevitably, and by mathematical theorems. The epitome of this is the Fluctuation Theorem which I

TehDogI have a vision of black helicopters descending...

:)

TehDog(Ducks and runs, grabbing a roll of tin foil...)

Da SchneibDa SchneibMimath224Without going into one camp or another (opinions etc), let's say we have an unobserved state which might have some mathematical representation (say a wave function ) if we could know without disturbing (observing) the system. Now I know this is more De Broglie than QM but I'm trying an analogy here, but suppose the QM entity in question is an electron. We can theorize what a typical e- wave function might be because basically all e- in some given state appear identical. Then the environment reacts with this state, say through the moving of needle on a volt meter. What is the difference between the wf now 'collapsed' state and its continuing state (cont)

Mimath224Going down further into the QM world; during experiments gamma photons are produce which then disappear in pair production of say, e- and e+. If more than one pair production occurs then I assume that the e-'s are identical and e+'s are too. If my assumption is close to being correct then it seems to me that the gamma photon either combined with some other, perhaps unknown, entity to produce e- or that the photon was governed by some fundamental law to combine in a certain with itself to produce e-. Conclusion, for me such a law might fill my 'QM realism' gap. I do appreciate this then begs other questions like why isn't space filled with e- instead of gamma rays? does this law operate on other particles as well? Over simplistic but I hope not too nonsensical and maybe not a good question this time.

Captain Stumpymay i also suggest some links?

this one is free - http://ocw.mit.ed...echanics

this one will cost you, but it is a good book considering it may well have the information you seek, or at least will point you in the right direction

http://www.barnes...71455466

Not saying reading about QM above won't help, mind you

just saying that you may find those links helpful

Mimath224Mimath224NoumenonYou don't appear to understand the difference between a Postulate and a Dynamical explanation, the latter of which is not included in the basic equations of QM thus the measurement problem, and the discontinuity between unitary evolution of WP and discontinuous measurement result, …. the former of which does not attempt to explain the discontinuity.

NoumenonBy "real phenomenon" is properly meant Objective with a Dynamical explanation possible, as expressed in equations, in detail.

Yes, "collapse" occurs 'during the experiment', but it is not understood how. C.I. does not offer a dynamical explanation,… they put forth a POSTULATE instead.

Well it is, because C.I. does not even consider the WP as a Real entity! The problem is you don't seem to understand what a postulate is.

Da SchneibCan't do it. There's only one way to observe a quantum system: bounce other quanta off it. And once you do that you've disturbed it. This is a basic property of quantum systems.

Now, that said, there have been some recent advances in detecting the states of entangled particles without disturbing those states, but those are kind of outside the scope of this discussion, so far anyway.

Well, that depends on whether you include position in the state; if so, then they are not actually in the same state.

[contd]

Da SchneibIt's a new wavefunction, related to the old one by the interaction that caused the measurement/collapse. In other words, the wavefunction has been modified by the interaction. At least in interpretations that use decoherence.

It depends on the interaction, but mostly an e- remains an e- unless it interacts with a W or Z. And there aren't many measuring devices that use Ws or Zs.

[contd]

NoumenonYou are mixing QM probability and classical probability there, and indeed in CH there is that dualistic issue.

I'm ok with CH as well, however it inherits a similar issue as decoherence combined with collapse, as pointed out in the above quote,… about which set of consistent histories will actually occur.

NoumenonYou didn't understand my response. I am not claiming there that the observer is not a quantum system. I'm simply pointing out the obvious fact [see Schrodinger's cat] that the experimenter does not have such a QM mathematical description for himself and the apparatus,.. hence "outside the system".

Da SchneibYou need to be very careful using the word "identical" here. Position is part of the state of a particle, and no two fermions of the same kind can have the same position, due to Pauli exclusion (as you previously noted).

[contd]

NoumenonThe WF starts to evolve again from the collapsed state,…. say position [represented as a Dirac delta function]. If a subsequent experiment is conducted fast enough, the same collapsed state would be observed. The rest of the wavefunction superposition is simply gone in C.I. or exists in "many-worlds". CH does not propose that "histories" correspond to alternative realities.

Da SchneibNo, this is incorrect. A gamma photon of the correct energy simply decays into a particle pair (or quad, there is a process for a gamma of the correct energy to make three electrons and a neutrino, with appropriate charge conjugations). That *is* the interaction; it's a self-interaction, like the decay of a radionuclide. No other particle is involved. This existence of self-interactions is part of why physicists have sought better interpretations than CI, which doesn't handle these types of self-interactions reasonably.

[contd]

NoumenonWhat experiment are you referring to? I didn't know photon's disappear into production of electrons. If you're referring to QED diagrams, that refers to 'virtual photons'. Photon's have no mass so do not decay.

QED does not attempt to explain the dynamics here. For example, in an accelerator, it is enough that E = mc² to justify saying that the colliding particles no longer exist at all, and that the resulting energy of 1) the colliding particles and 2) the relativistic kinetic energy, produced the subsequent shower of particles.

Da SchneibI don't quite understand, but I just realized on re-reading that my explanation fits your statement after the "or," that is, "...the photon was governed by some fundamental law to combine in a certain with itself to produce e-..." That should be "e- and e+," but other than that, yes, that is what happens.

Because the probability that the gamma ray will decay like this is low, and only a gamma ray of exactly the right energy will do so. The answer then is, "because space is not filled with gamma rays of the exact right energy."

[contd]

Da SchneibYes. It operates on any particle that has the right energy and other parameters to decay into another particle or particles; there is always a possibility that this decay will occur for such a particle. Physicists refer to these possibilities as "decay channels."

No, you're still asking good questions. Keep 'em coming!

Da SchneibStart over. Try to do better before I get bored enough to put you on ignore.

Da SchneibYou're still doing boring philosophy and ignoring interesting quantum physics.

Sorry, gotta go, got pizza which is much more interesting than you are.

NoumenonI meant you're conflating QM probability and classical probability in your quote.

Since CH is an interpretation of the experimental results and does not make differing predictions from that of standard QM,... it is "Philosophy of Physics".

Da SchneibI'm amazed I'm talking to someone who claims to know physics who doesn't know that gamma ray photons of the appropriate energy have a decay channel to quark/antiquark and lepton/antilepton pairs, not to mention W/W+ and Z/Z pairs. This is kind of like talking to someone who claims to know relativity who's never heard of gravity.

No, I'm pointing out that quantum probability in the wavefunction must yield classical probability in the ensemble to be a correct description of QM.

Are you seriously arguing that QM doesn't yield classical physics?

Get a grip, dude.

Da SchneibDa Schneibhttps://en.wikipe...oduction

Note that "gamma decay" is the more general term, since as I said above these decay channels can produce more than pairs. Quartets can also be formed, for example two electrons and two positrons.

NoumenonYou're an idiot and not even an honest one. You stated this .....

....Photon's do NOT decay as they are massless. I lost count of how many times you stated things carelessly and outright wrongly. FineStructureConstant's post was spot on.

Show me a reference where gamma photons decay, that is not virtual photons and that is not the result of interaction with matter.

I already pointed out E=mc² above wrt particle production in colliders,.... in which it is the ENERGY that produces particles. Photon's don't decay,... ever!

NoumenonWhere in that link does it say "a gamma photon of the correct energy simply decays". This is patently false. If you think photons decay you are not physicist.

What it DOES say is what I had already confirmed myself wrt E = mc²... "the ENERGY OF a photon can be converted into an electron-positron pair" - your wiki source.

Now is this logic chopping? NO, it is a deeper understanding of physics. Photon's do not decay as they're massless.

My "crime" before your ignorant and rude response was to ask what experiment is being referred to so that I can understand what you meant to say, but instead wrongly stated.

NoumenonI feel compelled to correct this patently false comment for MinMath224 (though I suspect he understands this).

Pair-Production is not the same thing as particle-decay. Radio-active atoms ("radionuclide") do spontaneously decay with "no other particle is involved",... but photons will not**,.. they require some interaction event with an atom.

A gamma photon of itself will never produce an electron/positron pair. It requires interaction with matter (an atom), and then it is only the ENERGY of the gamma photon that produces the electron/positron pair. Please see my comment above wrt the energy producing particles in colliders.

A deeper understanding of physics is necessary to avoid getting tripped up by phrases they use.

**I already qualified about virtual particles above.

NoumenonC.I. is an interpretation of QM,.... quantum field theories such as QED are built upon the framework of QM.

.........................................

I probably won't continue with you because of your blatant rudeness and dishonesty, which is entirely unnecessary. I would not have been rude to you except on account of your behavior.