"Both were interested in how information theory could help illuminate quantum mechanics... the information you gain when you learn something about a system is mathematically defined to be the reduction in your uncertainty about it."

No. This is a fundamental misunderstanding about the nature of information, that has utterly confused physicists for generations.

"But the instant you make that measurement, the wavefunction collapses into one possibility or another"

No. There is no physical wavefunction - it is merely a computational tool.

Quantum theory only describes the probability of detecting a particle. It does not describe actual measurements, of anything, at all. Think about it. In the famous double slit experiment, the only thing ever observed/detected are spots on a screen, or detection counts of particles. The position of the particle being detected, is NEVER actually measured. Rather, which detector (from a set of detectors) detected the particle, is first observed, then the position of that detector, not the detected particle, is measured, and then, the particle's position is INFERRED, not measured, as being the same as the detector.

Nothing else is even a possibility, since the Heisenberg uncertainty principle is equivalent to the statement that only a single bit of information is being manifested, in a quantum detection process: exactly enough information to answer one yes/no question "Was something just detected?", and nothing more.

"Making sense of this measurement problem is the 'most fundamental problem in all of quantum mechanics'..." Exactly. To make sense of it, you have to first recognize the fact, that no "measurement" is actually being performed on the detected entity - only a single-bit detection-decision (AKA wavefunction collapse) is ever being performed.

Rob McEachern

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"There is no physical wavefunction - it is merely a computational tool."

True enough to Quantum Mechanics. But take a well engineered AM/FM radio with a mechanical air gap variable capacitor on the frontend tuning the antenna gain, and move it around to different places in a room. In some placements, proximity to metalic components of building construction will act as antennae and the selectivity of the radio reception will be blocked significantly, while only a few feet away the station's signal will be unobstructed and reception will have high sensitivity. We cannot 'see' what a photon, or waveform of EMR physically 'looks' like, but its physical observation by conductive elements behaves in a manner which indicates that some variable does exist which reacts across the classical spread wavefront of a modulated transmission. While also the selectivity of bandwidth is a linear LOS.

QM gets around this fundamental conundrum imposed by the dictum of all things being (tiny) hard particle interactions, by saying 'never mind aking, photons (particles) exist everywhere all at once on the expanding surface of the spherical wavefront until its observed where we want to detect it'. And the presumption that Maxwell's Demon can be put to work as a thermodynamic operator without any raise in pay, ignores that the one bit of information about entropy that has been ignored is that any form of energy is still firstly the same sort of energy in the raw. A wave form will not go from light velocity to rest instantaneously, it will slow exponentially to a density exhibiting particulate characteristics. That DOES NOT violate entropy. Its still the same quantity of existential energy.

    You don't need to do anything fancy to lose FM reception. As a result of multipath interference, I can frequently be sitting at a traffic light in my car and be getting perfect reception, but if I creep forward just a few feet, reception will be totally lost. My HDTV's reception (via a small indoor antenna) goes from perfect to terrible, on windy days, due to the fact that the demodulator cannot track the rapid variation in multipath caused by the swaying tree branches behind my house.

    A "well engineered" FM demodulator is far from a linear LOS; a phase locked loop is used to, in effect, continuously retune a narrow bandpass filter, with a bandwidth much less than the overall signal bandwidth, to track the narrow "instantaneous bandwidth" of the FM carrier and thereby greatly reduce the effective receiver noise level - but only as long as the signal remains "above threshold".

    "which indicates that some variable does exist which reacts across the classical spread wavefront of a modulated transmission" But that variable has nothing to do with any individual photon, anymore than the properties of water waves are innate properties of water molecules.

    QM does not say that "photons (particles) exist everywhere all at once"; as Einstein et. al. suggested, only the absurd interpretations of QM say that. But such interpretations are no longer required; it has been demonstrated that classical objects, constructed to manifest only a single-bit of information, will reproduce all the seemingly weird behaviors that have so befuddled the physics world, for nearly a century.

    In that context, it is important to realize that "information" as Shannon defined it, has little to do with "entropy" or even physics in general (most unfortunate that von Neumann persuaded him to name it "entropy"); it is a purely mathematical concept concerning the ability to perfectly reconstruct a continuous function from discrete samples. It is most unfortunate that the physics world has confused the two concepts. Shannon's concept, is key to understanding the "measurement problem".

    It is easy to demonstrate that QM boils down to little more than the mathematical description of an energy detecting filterbank (a Fourier transform's power spectrum). When you send particles (quanta) with equal energy into the various channels of the detector, the ratio of total energy received in a channel, divided by the energy per quanta in the channel, enables one to infer the number of received quanta in each channel, thereby rendering the entire process as being simply equivalent to a histogram; that is the origin of the Born rule. No mysterious wavefunctions, wafting through the cosmos, are required to understand what is actually going on.

    Rob McEachern

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    As usual, Robert is true enough to QM but also to interpretations thereof.

    And yes, selectivity is in and of the FM demodulator, the transmission is a linear LOS groundwave. My '92 GE superadio 2 has a switched narrow bandpass filter, allowing tuning to high gain with an ear for distortion when a desired station gets ghosted. And I'm rather fond of small Ohio Colleges and Universities. Good Hunting, Guys.

      Off topic and beyond the scope or what is appropriate here; but specialized receivers with coupled together phase locked loops have been used to track co-channel FM signals, such that each loop only tracks one signal and then uses it to cancel the interference in the other signal, thereby effectively eliminating the interference from both signals. A lot more complex than your single narrow filter, but with much higher performance.

      Rob McEachern

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      Not so off topic, Rob, this is jrc by the way... I just had to get a new laptop that is so overloaded by the OS that I don't respond if I have to open an account (for anything).

      Really, we must rely on technical higher order effects to deduce a local realistic picture of the micro realm, so specialized receivers such as you briefly describe do provide some means to figuring out what is realistically happening. And maybe, just maybe, providing some insight towards a conjecture of what a "photon' or particle would physically 'look like'. And Classicism has dropped the ball on that pursuit as badly as has the ad hoc interpretations of QM. I am in complete agreement with you as to QM being a Math, not a physical theory, and think that has to be confronted directly in any effort to rationalize QM. The symmetry is baked into the math.

      Towards that, RF signal transmission has enough infrastructure that the spherical broadcast wavefront in contrast to the localized multipath interference of reception suggests that a multitude of linearly directional 3D waveforms are more the reality of the Quantum Jump than a single 'photon'. And that the 'Quantum' photo-electric effect is time dependent on a rapidity work function. But that would mean that each Planck Quanta would only periodically precipitate at the pinch points of a volumetric wavetrain. The statistics of QM do work effectively, and the quest (however Demonic) to discover Why it does, could include a hypothesis that the wave form of EMR interacts only marginally with the electrostatic domain range of the macro world of subluminal particulate aggregates, due to velocity dependent super low densities. And only at near particulate densities periodically, does physical interaction respond to the variables inherent to matter. This creates a realistic picture of a very crowded landscape even in the most rarified regions of intergalactic free space. But then, empiricism calculates we have a lot of uncatalogued energy to yet account for.

      Best as always. jrc

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      "No physical process can have as its sole result the erasure of information."

      I suspect that conclusion would be dependent on arbitrary constraints. Information is firstly our own invention, like mathematics it is essentially experimental. The number line of equal increments is an arbitrary constraint, in contrast to the different lengths of my fingers and the asymmetry of my two hands. Entirely experimental.

      "...information...is a purely mathematical concept concerning the ability to perfectly reconstruct a continuous function from discrete samples." - R. McEachern

      We are assigning parameters before we can say that 'one bit of information' has been detected, and the best we can do is to limit to that one bit. And if we are working on the yet to be rationalized assumption of Planck's Constant being the finite least 'bit', we might be able to perfectly reconstruct it in a continuous quadratic algorithm as the root square mean. But it is quite possible to start with Planck's Constant and treat light velocity as the root exponential mean in a continuous function of energy distribution in a spherical volume, and arrive at finite results in which the tiny value of Planck, trivializes out of computation and a true continuous function is the obtained as a physical process. So would that be an erasure of information, or is Planck's Constant an arbitrary starting point and physically only represents an averaged least observable value?

      Re "In the quantum realm, observers typically know very little about where a particle is, or how fast it is moving, or how it is spinning. They have to make a measurement to reduce that uncertainty":

      This article seems to assume that the only problem is the observer: i.e. that there are "deep limits on what observers can know" about "where a particle is". The assumption is that the particle always has a definite position, and that position outcomes are 100% determined by some law of nature.

      But quantum mechanics is about the fact that, in the microrealm, particles don't always have a definite position AND particles don't exist everywhere (i.e. all positions) all at once AND particle position outcomes are inherently unpredictable to an observer (i.e. there exists no law of nature rule that always determines outcome positions for individual particles).

      The "measurement problem ... the "most fundamental problem in all of quantum mechanics,"" is only a "problem" because, like climate change deniers, physicists refuse to face quantum reality.

      The real issue is how to INTERPRET the quantum randomness and indeterminacy of the universe, as seen from the point of view of an observer of the microrealm.

        Without any context or reference, attribute such as orientation, direction of motion, even speed of motion are not applicable. Only when' in relation to this (or that) is applied can the relation of both beable and reference/apparatus/observer give a determination that in this (or that) context beable x has attribute (state) A. Attribute not intrinsic property. It doesn't mean the unmeasured is without orientation, direction and speed of motion relative to objects in its environment but the context has not been determined by the experimenter. The 'in relation to this' is not known. Orientation of the beables may be the source of randomness. As for location at one time (not a probability distribution or over time characterization), there has to be location relative to the environment even if unknown. Detection provides the 'in relation to this' context.

        In physics, there are NO relationships between THINGS. This is an important distinction. (Law of nature) relationships only ever exist between seemingly natural categories of information like particle mass, particle relative position, "how fast it is moving" [1] and "how it is spinning" [1]. So, this purportedly existing relationship does not actually exist: "the relation of both beable and reference/apparatus/observer". Similarly, there is no such thing as "motion relative to objects" or "location relative to the environment".

        And contrary to what you say, "attribute[s] such as orientation, direction of motion, even speed of motion" are ALWAYS "applicable". These seemingly natural categories of information, and their lawful relationships to other such categories, continue to apply in the universe no matter what the "context or reference" of an observer. Maybe you are trying to say something about (what we represent as) the NUMBER values that apply to the natural categories?

        But seemingly in the quantum microrealm, natural categories (e.g. relative particle position) can sometimes have NO numbers applying to them: i.e. there is no information available to an observer, there is nothing for an observer to detect.

        1. Thermo-Demonics by M. Mitchell Waldrop, https://fqxi.org/community/articles/display/234

        Lorraine, you wrote "In physics, there are NO relationships between THINGS", perhaps that is where the problem lies.I agree that properties are considered in physics and not in general the beable thing that has those properties, or attributes. Nor is the beable environment considered. Not being thought about isn't the same as not existing. It makes sense to me that the properties or attributes, even though 'distilled' at measurement, pertain to something and are not orphan information. 'Heads up' on a table is not a coin but a state that pertains to the beable coin's orientation in relation to the beable table. The motion attributed to an object is relative to the motion of the observer and the orientation relative to the reference used to describe the orientation.

        Correction:The motion attributed to an object is relative to the motion of the observer, or apparatus or other reference object.

        If velocity of X is given as 10 m/s one should ask in what context that is true. Who says so, and what is their relation to the measured or what is the motion being considered in relation to. Am I talking about number values? -yes when the state can be described with a number, otherwise not. Saying something like- orientation is not applicable in the absence of context-means orientation can not be given/told ( if it is given/told there has been a hidden reference used in the determination).

        Correction: The motion attributed to an object is relative to the motion of the observer, or apparatus or other reference object or phenomenon.

        For example; the orientation or motion state could be given in relation to the gradient of a gravitational field or a magnetic field, rather than the object sources of those phenomena.

        Georgina,

        I would question the use of the words "property" and "properties" [1] by physicists and others like yourself. Is "property" the correct term for classifications like mass and relative position?

        Clearly mass and position, for example, have no independent existence. They are not something that is "possessed" by the universe or by objects because they only exist as relationships: they are more correctly seen as relationships. Therefore, classifications like mass and position are more correctly seen as categories (i.e. as relationships).

        1. Property: "(mass noun) A thing or things belonging to someone; possessions collectively...An attribute, quality, or characteristic of something", https://en.oxforddictionaries.com/definition/property

        Lorraine, property is probably not the best term for measurables. States of being such as atomic number and chemical structure are properties belonging wholly to the beable, But a measurable is in part due to the beable measured and also in part due to the context of measurement, the method used. The state or value formed by the relation is attributed to the beable. A coin caught and revealed palm up might be heads, then flipped onto back of opposite hand and revealed as tails, then slid carefully from hand onto table top-still tails. Once the measurement relation is applied the state or value that will be 'discovered" is already 'decided'; making The model comprising different possible out comes obsolete but there needs to be a mental switch also, to thinking about the measurement, knowing it instead. What is being considered has altered, it isn't the same thing.

        I wrote'The state or value formed by the relation is attributed to the beable.' The value or state is usually attributed to a named object. (That name, in such a circumstance, even if not acknowledged, pertains to a beable.)

        If mass is a category, then is number a property carried by a particle?

        A law of nature relationship (e.g. mass can be represented as a lawful mathematical relationship) is seemingly a natural category. These lawful categories don't necessarily have to have any numbers equated to them. A category like mass or position can seemingly just "exist" as a relationship without any numbers being applied to the categories.

        But if numbers are equated to these categories then a new world of possibilities opens up. Equating a number to a category requires (what we would represent as) the introduction of a new mathematical relationship to the universe-system. These (rational? irrational?) numbers, applied to categories like mass or position, are probably best described as properties of particles; they are the specific information carried by particles. But these numbers are contextualised by being equated to categories: i.e. the number information means nothing without the category (i.e. relationship) information.

        So, what is a number? A number is not a category, because a number can be constructed by dividing a category by itself (we would represent this as a mathematical relationship between categories), leaving a thing without a category.

          Georgina,

          I think that it is necessary to attempt to conceptualise the difference between categories and properties. But as it is not directly about my original criticism of the article, I have put it in a separate spot (see below).

          Mass is a category of measurable.I'd say number is not a property carried by a particle but a measured or calculated value and units can be attributed to a particle allowing comparison with others. If different units are used the number changes. What doesn't change when the units are changed is the amount of existence as something or somethings, un-quantified; and the where, location un-quantified, in comparison to its local environment. Many different measurements of location in comparison to other things in the environment could be made, giving many different number and units outcomes. The beable stuff of the particle is a property. So atomic number and number of electrons or number of other sub atomic constituents are properties- wholly owned by the particle.

          I said mass was a category of measurable but that is only the half of it. The numerical value (and units) obtained for mass via measurement of weight or comparison of weight is the value of the mass measurable. A relation of the measured and measuring apparatus is needed to obtain it. The value output is knowable information.

          Intrinsic mass un-quantified is a beable actuality, a property belonging solely to the object. Type and number of each type of constituent are also beable actualities.

          Measurable value information and beable actuality are distinct categories.