Essay Abstract

Quantum theory curiously implies that preparers of states can know the complete initial specification of the state, but uninformed observers (UOs) are limited in what they can discover. UOs must currently use projective tests that typically destroy the original information. There is thus more to "it" than democratically available as "bit." Previous attempts to empower UOs include weak measurements and using repeated interactions between detector and one particle. A novel theoretical perspective and thought experiment are introduced to distinguish between supposedly equivalent mixtures of states. The original-spin hypothesis postulates that actual spin transfers from photon interactions remain based on the original expectation value, instead of the final apparent detection. The proposal itself uses mechanical spin transfer by statistical "runs" of same-type detections, as analyzed by the OSH, to expand what UOs can find out. It would not be practical, but stimulates theoretical insight. A supportive asymmetry claim about detection is currently testable.

Author Bio

I consider myself a "Renaissance man" because of the variety of my studies and work. That includes consulting at J-Lab using G4Beamline to model muon interactions, teaching at various levels, museum guide, and independently working on physical theory in spare time. My background is too complex to coherently summarize. I am lucky that Internet search for "quantum measurement paradox" usually brings up blog posts of mine in top hits. I've published some articles about the relativistic dynamics of extended bodies, a sadly neglected topic.

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Greetings. My apologies for the faint thin lines of my illustration (Figure 1.) I suspect this was due to directly pasting an AutoCAD drawing into MS Word instead of pasting a jpg file. Also the figure is rather small. Some magnification will make it readable. I appreciate your forbearance. Thanks.

This is a very interesting essay, Neil. I'll need to wake up and review your proposal more carefully before really commenting on it, but from a first reading, your thought experiment strikes me as very 'Einsteinian', reminiscent of the arguments he used to challenge Bohr's conception of quantum mechanics. I mean that as a compliment: Einstein may have been wrong, but his thinking nevertheless was often clearer than that of his opponents.

However, one thing I'm not sure I got is the asymmetry of knowledge between the 'preparer' and the 'measurer' of a quantum system. I mean, most preparation procedures are essentially measurements: you prepare a spin up electron by letting it traverse an appropriately aligned Stern-Gerlach apparatus and blocking the path of the spin-down component, i.e. effectively you measure, and just keep those systems whose measurement result produces the outcome you want to keep. After that measurement, the preparer has 'perfect knowledge' about the electron, at least in the 'up/down' basis.

Now consider the situation of a measurer, who perhaps might choose to measure in some orthogonal basis. He will obtain evenly distributed statistics, and after measurement, will have perfect knowledge about the state of each electron in that basis, but no knowledge about the prior state of the electron in the 'up/down' basis. But does this mean that he has access to 'less' information than the preparer has?

I think to a certain extent, two different things are being compared here: knowledge in the 'up/down' and in an orthogonal, say 'left/right'-basis. After preparation, the preparer has zero knowledge about the electron in the 'left/right'-basis, just as the measurer; after the measurement, his knowledge is perfect in that basis, but all knowledge about the 'up/down'-state is destroyed.

So at various points, both the preparer and the measurer possess perfect knowledge about the electron, but their knowledge is (as Bohr would say) complementary: it can't coexist. The asymmetry, it seems to me, comes about only if you describe things in one basis (that of the preparer). That, I think, would as a description be better suited to the case in which both measure in the same basis: but of course, then the measurer can obtain all the information the preparer has.

But anyway, I think your larger point still stands: there is indeed more information in the quantum state than can be extracted classically. The simplest demonstration of this is that it takes a huge (in principle, infinite) amount of information to perfectly describe the state of even a single qubit, since it is given by a point on the Bloch sphere, of which there are continuously many; yet one can always extract a maximum of one bit of information through measurement. In general, the extractable amount of information is of course given by Holevo's bound. Nevertheless, you can sometimes do neat tricks like dense coding, i.e. transferring two bits of information through the sending of a single qubit.

There's another way to see that quantum information exceeds classically available information, which is through considering the amount of information that can be communicated: if I have access to a qubit's worth of information, I couldn't share that with you, since I can't clone. The best I can do is to just measure, and share the result. In fact, this is one way to characterize the 'truly quantum' part of information: it's the part you can't share.

Anyway, I'll go and have a look at your essay again; hope you'll do well.

    Jochen, thanks. Sure, the privileged knowledge of the PO only applies to the initial preparation state. If a UO checks the particle later, that changes and the former UO becomes a PO regarding the new projected state of the particle. I am challenging the idea that UOs can't find more about the original state of mixtures (this essay) or single particles (my previous essay.) Very important: I am challenging ordinary assumptions about the consequences of general detection "as" a circular (spin-manifesting) state of polarization.

    Neil,

    Your very interesting essay deals with photon polarization. I have a question that no one ever asks: Can a single photon really be anything other than circularly polarized, with spin +/-1? In my view, all fundamental particles are rotating vector fields with quantized spin. (See my essay "Watching the Clock: Quantum Rotation and Relative Times", esp. Endnote 2.) And indeed, all atomic transitions involving photon absorption or emission transfer this amount of angular momentum. This question is important because virtually all quantum optical experiments establishing quantum entanglement involve measurements of linearly polarized single photons. If instead, a linearly polarized state must be the superposition of two circularly polarized photons, then the entire block of evidence for quantum non-locality is in question. Any thoughts on the subject?

    Alan

    Thanks, Alan, I will look at your essay. Yes, photons can be considered superpositions of R and L circular states - yet theory says we always "find" a photon as having either () or (-) spin (hbar or -hbar, sorry don't have time to hash out LaTeX here.) Yes, it makes sense for a photon from an atomic transition to be circular. Yet we can pass it through a linear filter and prove that the output (if it survives) is a superposition and not a circular state. I don't think non-locality is in question since the correlations of entanglement still can't be explained non-locally (more precisely, can't involve forbidden combinations of locality and realism.) The correlation of circular polarization is indeed not a true proof of NL, since it's a simple binary correspondence to satisfy conservation.

    However, I presented reason to believe that the concept of straightforward manifestation of spin is an over-simplification. Detection of a linear state by filtering (especially if very indirectly) does not logically require actual change of the expectation value of AM of the system. I think that change in an intervening element like a HWP is even less credible.

    The detailed argument is in the essay, yet for a start consider the asymmetry of the reverse process: would we really expect circular states detected "as linear" (say by filters or calcite analyzers) to *not* transfer their angular momentum? And if they did, then I repeat from my essay: "Yet why should linear detected "as circular" prompt change in angular momentum, yet circular detected "as linear" continue to exert the effects of circular?" If my hypothesis is correct, then a UO could indeed distinguish between a mixture of R,L versus a mixture of H, V - although it would require waiting for very rare runs of apparent R or L detections for the H, V mixture.

    Neil

    "In this author's view, being unable in principle to find out everything about the world's contents implies that "bit" (information) is derivative and subsidiary to "it" (real objects.)".

    Logically (ie in principle) we could find out everything, because what we can know (which is the equivalent of physical existence) is limited by the physical process which enables knowing. Though in practice I doubt we will ever achieve it, but that is a different point. I presume your statement is not an allusion to all the possible alternatives that might exist, but we can never know, as that involves belief, not science. However, that is not what causes 'bit' to be derivative. Information is information because it is representational of something else. It can be an it (ie real object), of itself. For example, light, vibration, noise, etc. And then one has to establish the extent to which it is valid information (more commonly known as knowledge), ie corresponds with physical existence, as invalid information is useless.

    In respect of observation, the more pertinent question is what has observation (informed or otherwise) got to do with it. Observation (measurement) is a process which involves the receipt of physical input (eg a photon based representation of what occurred) which is converted into a perception of that input. So observation, or indeed any form of sensing, has no effect whatsoever on the physical circumstance. Other than, somewhat obviously, the input ceases to exist in that physical form as a result of that interaction. But then that occurs if the light had interacted with a brick instead. The only difference being a brick does not have the capability to process the input receivable. Observation cannot affect physical circumstance because the sequence order precludes it (ie the input is received, it already existed before the subsequent processing), and that processing is not a physical process, it does not involve an alteration in physical form. Apart from the simple fact that what is received is not the existential sequence (commonly known as reality) anyway, but a physically existent representation of it. So there is no interaction in observation between the observer and reality.

    Put simply(!), whatever reality constitutes, it is physically independent of the mechanisms whereby it is detected. So why do we have a physical theory purporting to explain physical circumstance, where observation seems to be integral to existence, as opposed to just being the mechanism whereby we find out what happened?

    Paul

      Jochen

      More precisely, just what have observers got to do with it (see my post below).

      Re information, as per your last post to me, this notion of designating everything as information is pointless. Everything provides us with information. And we can only have information, because we cannot 'directly access' reality. But unless some proper differentiation is invoked then the label 'information' becomes meaningless.

      Paul

      Paul, you would need to study more quantum mechanics to see how important observation is. I can't really summarize how that works out, but my article attempts to show that we can at least find out more than standard theory posits. Note that even if you say "the reality" would be there anyway", we still need a way to find out what that is. To some extent you have been vindicated, in that "interaction-free measurements" are now appreciated and used.

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      • Post #11

      Why cannot we ' directly access' reality by oprning our eyes?

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      • Post #12

      As probably the most uninformed observer likely to read your essay could I please point out to you that a light is a light is a light. Light does not consist of invisible photons, klingons, croutons or carryons that can or cannot behave in positive or negative unpredictable ways. Man made particles have nothing to do with reality. Only unique real snowflakes occur. All fabricated particles have to be unique. Why cannot you understand that if nature only produces unique states, men could only produce unique states? There is only one of anything, once. There is no such thing as real scientific information. There is no such thing as real layman information. All information is abstract and has nothing to do with reality because only unique real events take place that cannot be deciphered by any abstract code.

        Joe

        Because the physical input you receive is light, and that is not the reality, it is a physically existent representation thereof. It was created as a result of an interaction with it, and light has features which make it good at representing. Hence the evolution of sight. If light was just random, or bizarre, then sight would not have rendered the possessor an advantage, ie he would not have seen the big monster coming and been eaten anyway!

        Precisely how good light is as an accurate and comprehensive representation of what occurred is a question concerning the physical properties of light, how it intereacts and how it conveys, and what influences it i susceptible to whilst travelling.

        Paul

        Neil

        It is not a matter of how important observation is, in order to discern what occurred, but that that process cannot affect the physical circumstance.

        Paul

        Neil

        This is difficult to follow in this format.

        Very early on there is a false statement, ie any two events with the same properties are identical. If they are two then they cannot be identical!! The properties, whatever that relates to, are the same. But I doubt very much anyway if an exact same set of circumstances could re-occur. This smacks of similarities being drawn at a level of conception that is higher than what actually exists. So as a methodology for categorisation, then ok, but not as a depiction/explanation of physical existence.

        And physical existence is not a series of events, it is a sequence of physically existent states. And within any given stateh there can be no form of change, otherwise it cannot exist. This is the only route out of the conundrum that existence involves existing but also difference. It therefore has to be a sequence of discrete states. That is why he then confuses time and timing. Time is not a succession of moments, that is the timing system. Time is the rate at which alteration occurs in realities.

        Paul

        Paul, Joe: I can't blame you for wanting to apply philosophical intuitions and deduction thereof to what you think the universe is like, but our intuitions are often wrong. Science is above all about "finding out" through often deep and difficult experiments, rather than working out what reality must be like through basic practical observations and reflection. We live in an unexpected universe. I still appreciate your interest.

          Neil

          There is nothing philosophical about what I am saying, or indeed what Joe has just said. They are generic statements, ie facts devoid of the detailed form. See the wood for the trees is the expression.

          And hasn't it ever struck you that the substantiation of some science as being counter intuitive rings an alarm bell?

          Science is not about "finding out", if the start premise is wrong, ie does not correspond with how physical existence must occur. Like for instance, asserting that the activity of observation has an affect on the physical circumstance, asserting that existence occurs relatively, asserting that there is time in a physical reality, not differentiating the existential sequence from the existential representation thereof (eg light), not understanding that physical existence can only occur in one definitive physically existent state at a time, etc, etc.

          Paul

          Joe

          Your essential point is correct. Physical existence comprises a sequence of discrete, definitive, physically existent states. We know there is existence, and that that involves difference. And the only way out of that conundrum is sequence. Of course one can invoke all sorts of beliefs, but this is supposed to be science. And we can only have knowledge of what occurred (this is another answer to your question above about opening our eyes.

          But, because we are in an existentially closed system (we only know because of a physical process), what we do know can be validated, albeit within that confine and then ultimately we can deem that knowledge to be the equivalent of the physical existence knowable to us. In simple language, we know all there is to know.

          Paul

          Neil, I just finished reading your very interesting and well thought out essay. You argue that "it from bit" is impossible because we cannot know all information about a state. Is "it from qubit" or "quit from qubit" possible?

          And light creates all real odors, sounds, tastes and tactile impressions. Who knew?