Talk:Philosophical interpretation of classical physics

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Contents

[edit] Kudos for Albert Messiah

I have been mining Albert Messiah's Quantum Mechanics for citations and quotations. I am extremely impressed with the lucidity of his writing and recommend his book to others who may be interested in helping with this article.

By the way, the conceptual difficulties that lie behind the need for this article also come up very clearly in quantum entanglement discussions. The common stumbling point is our macro-world assumption of the inevitability of simple location. Twins may become identical, but tickling the one in Africa does not make the one in S. America laugh, and between diving board and pool neither one of them will fail to move in a continuous manner as a function of time. If one individual disappeared from the starting block and "materialized" at the finish line a very short time later, one would quite naturally suspect twins. (Especially if his time was d/c for the mile ;-) P0M 18:26, 1 October 2005 (UTC)

[edit] " highly refined instruments of modern physics"

Quantum mechanics was discovered by the instruments of classical physics, just a chemistry was discovered with the instruments of alchemy and the first chicken hatched from an egg laid by some other type of bird.David R. Ingham 23:39, 7 October 2005 (UTC)

[edit] "But the airplane does not have a position until we have done our measuring work, and that is simply because we define position as the result of doing that work."

That is not exactly how I define position. The 747 has the potential to have its position measured. A tree makes a sound when it falls even if no-one is there to hear it.

You may be interested in the analysis of the implicit assumptions behind such assertions presented by the physicist Hans Reichenbach in his article, "The Principle of Anomaly in Quantum Mechanics," on p. 513 of Feigl and Brodbeck's Readings in the Philosophy of Science. P0M 03:49, 13 October 2005 (UTC)

[edit] Radar example

I saw the same error made by radar engineers when I was working for Lockheed Martin:

The same error as what?

They tried to measure a highly resonant target with a short pulse radar system, to range-gate out other objects in the radar range. They couldn't understand why they didn't observe the single frequency cross section.

In this case, h bar cancels out in calculating the relation and there is no definite limit to what can be measured with continued measurement and signal processing, but the relation between a function and its Fourier transform is the same. David R. Ingham 00:13, 8 October 2005 (UTC)

We may not be talking on the same wavelength. Remember the joke about the man who dropped his Rolex overboard in the middle of the lake and quickly marked an X on the bottom of the motorboat so that he could bring divers back to that very spot. He had one idea of position, but it wasn't a very useful idea as far as telling the scuba guys where to go. To communicate the location of something in a way that is useful to the general community we not only have to have a reliable way of determining position (which the Rolex guy obviously didn't have, but he was a joke anyway), but we also have to be able to communicate the idea clearly and unambiguously to other people. Otherwise we are likely to end up having, e.g., people going to different places because one person is speaking in terms of true north and the other person is speaking in terms of magnetic north.
It is possible to state the location of a macro object with good enough precision that members of the general community can locate it. We can have many levels of precision, in practice, anything from, "It's over there, about two bow shots away," to a reading from a military satellite-based position finder, etc. But saying, "I know exactly where it is" is often really the promise of being able to perform some actions that haven't been done yet. Saying that a photon has a location depends on analogous procedures.
Anybody can affirm that the body of Jimmy Hoffa has a position, but that claim in itself may not be subject to empirical verification. In other words, that claim cannot be proven and it cannot be disproven unles we can go "there" to check it out because we have specific travel instructions of some kind. Somebody might argue that his body must be somewhere, but the meaning of "somewhere" would be very diffuse if the body had been reduced to plasma and blown out the window to range, spec by spec, all over the globe.

[edit] Quantum computer?

Our use of notebooks and (non-quantum) computers depends on the classical approximation to the operation of these devices and to the information stored in them.

This statement seems to be intended to say that quantum computers could be used to obtain reliable predictions regarding quantum phenomena that could not be obtained by our current crop of computers. If a classical computer can accurately simulate a quantum computer, and the difference between classical and quantum computers is one of speed and scale of operations that can be performed, how would moving the problem to a quantum computer give a fundamentally different kind of result? P0M 01:24, 11 October 2005 (UTC)

(See http://www.cs.caltech.edu/~westside/quantum-intro.html for a discussion of what a quantum computer actually is.) P0M 01:30, 11 October 2005 (UTC)

We need someone who knows more about quantum computing. As I understand it, there is no direct translation between quantum and classical information, just as there is no direct correspondence between classical and quantum descriptions of nature. One can translate, but not without loss of information.

All I said in the article is that I am not sure the same discussion of experiment would apply if one used a quantum data acquisition computer. That is not a proposal of an experiment, it is just that I am not sure. David R. Ingham 04:24, 11 October 2005 (UTC)

[edit] Footnotes needed for Messiah's book

I still think that it is essential to provide readers with volume number and page number whenever Messiah is claimed as the authority for some statement. P0M 01:34, 11 October 2005 (UTC)

Maybe but it is not that simple. The page numbers must not be the same in different additions and there isn't anywhere he exactly says that quantum mechanics is reality. He says more like that it is an adequate description of reality, and proceeds to explain why. I did give the section heading, "Uncertainty Relations and the Measurement Process", not only for that reference but as a place to start looking in other such books. David R. Ingham 03:51, 11 October 2005 (UTC)

Page numbers will still help. If there should happen to be one version with 594 pages in volume 1 and you were to cite page 332/594 and quote a sentence or two it would be no great problem to find the material. In the version I have, the section to which you just made mention turns out to begin on p. 139, and once I knew that I was actually looking for a section by that title it wasn't hard to find even though it is not exactly at the beginning of the book. P0M 08:02, 11 October 2005 (UTC)

[edit] Repeated call for clarification

The expression "brought to the human scale" needs an operational_definition by means of which the original imprecise and misleading formulation might be redone. As it stands it does not have any clear meaning. P0M 20:27, 8 October 2005 (UTC)

I was hoping that "Our use of notebooks and (non-quantum) computers depends on the classical approximation to the operation of these devices and to the information stored in them." would clarify it. Physics experiments usually use electronics, so the experimenter himself may not directly handle the data. However the design and use of notebooks and computers depends on the classical approximation, and they store bits and not q-bits, so the classical approximation appears to be completely unavoidable. David R. Ingham 04:05, 11 October 2005 (UTC)

Unfortunately, what I would like is a clear expression of the steps that one takes to "bring something to the human scale," and the fact that computers and notebook paper express things that are formulated "on the human scale" does not at all clarify what readers need to get clear on. At present I have no certainty, from what you have said, what this quantum-scale something is, nor have I any idea of how you would propose to take that something and convert it into something that could be written into a three-ring binder or typed into a computer. Let's take something that the average well-informed reader could do on his/her desktop and a laser pointer, a double-slit experiment, tell what the description is on the level of quantum mechanics and how that description is "brought to the human scale." P0M 08:35, 11 October 2005 (UTC)
What I think David is trying to get at is that quantum states are indeterminate in some sense. A wave-function's value is not determined until it is collapsed by assuming that X is a particle and not a wave. The fact that the scale of quanta is extremely small may obscure this, but trying to measure individual quanta (rather than ex: whole light-waves) with particle-measuring sorts of equipment (as opposed to wave-measuring sorts of equipment) just assumes that the quanta actually HAVE determinate values for position and velocity (I think those are the 2 values that people try to measure for particles anyway)...
Let me know if I got something wrong, or if my comments aren't very clear. I'm not really sure what a wave-function's value actually tells you, but I think the assumption under question is that it can be collapsed to give a particle's definite position and/or velocity somehow, and that many measuring instruments do this. How, precisely, I couldn't tell you, though. WhiteC 02:58, 12 October 2005 (UTC)
I think you are likely to be incorrect. At first I would have agreed with you but I compared what David wrote with what Messiah says: "A quantum system isolated from any external influence evolves in an exactly predictable manner." It is not the "quantum states" that are indeterminate. That's David's whole point. David says, "If photons, electrons, or other quantum-scale entities used in the measurement process are described quantum mechanically, then the measurement process results in a deterministic description, i.e., a description that contains no probability factors. However, to get the information into a notebook or a computer, it must be brought to the human scale where maintaining phase coherence is impossible." When I read this description, I think of a quantum-mechanical experimental apparatus such as a double-slit experiment. The quantum-mechanical part, the part that doesn't find an appropriate explanation under the terms of Newtonian physics, extends from the time of emission of one quantum of light, a photon, to the time that one quantum of light is detected by its physical interaction with the detection scheme. According to David, and he is certainly not alone in maintaining this proposition, the "laws" of quantum dynamics are absolutely determinate. So whatever happens between t1 and t2 is going to be the same in all cases. However, the part about "getting the information into a notebook..." elides a crucial part of what must be a clearly described operation that can be reliably repeated in any laboratory. Moreover, it makes it seem that there is information that exists in one form that presumably behaves like any information that one could discuss in information theory, and that it is nevertheless information that must be translated and falsified in some sense in order to be written down in pen and ink or typed into a computer. If that is really what David means, then we have one kind of problem. If that is not what he means, then we have another kind of problem. I don't want to create a third kind of problem by guessing about what he may intend to convey.P0M 03:55, 12 October 2005 (UTC)

The discussion of the measurement/observation issue is very clearly discussed in The Elegant Universe by Brian Greene, p. 208ff. Particularly interesting is his statement on page 212: "Even though decoherence suppresses quantum interference and thereby coaxes weird quantum probabilites to be like their familiar classical counterparts, each of the potential outcomes embodied in a wavefunction still vies for realization. And so we are still left wondering how one outcome 'wins' and where the many other possibilities 'go' when that [measurement/observation] actually happens." To put that in terms of the double-slit experiment, there are only probabilities to be inferred from the psi function of the coherent radiation, but the photon doesn't manifest itself 10% in one place and 30% in another. It manifests at only one place. There is no hidden information that tells us why it has "chosen" to show up at one place or another in this run of the experiment. We, however, are left unsatisfied by this result since every analogous event in our macro environment has an explanation. If we shoot a gun at a target we expect to be able to account for any deviation of the bullet from an "ideal" path. For instance, we might find that a powerful magnetic field deflected the steel bullet. P0M 23:04, 12 October 2005 (UTC)

Another very clear discussion is given by Einstein. See the "The Fundaments of Theoretical Physics", included in Reading in the Philosophy of Science (Edited by Herbert Feigl and May Brodbeck), p. 259f. P0M 03:28, 13 October 2005 (UTC)

Yet another useful analysis is given by Hans Reichenback, "Principle of Anomaly in Quantum Mechanics," ibid, p. 515.

[edit] Dynamics versus kinematics.

No, I don't think [1] helps at all. It is not a matter of experiment. The point is that classical physics not only does not provide a framework for expressing interaction. The very description of nature itself leads to contradictory or at least ridiculously unphysical predictions without even including any forces or other interactions.

Is "It is not a matter of experiment" basically what you wanted to say? That it is essentially a matter of a conceptualization that fails so badly to fit the reality it was intended to describe that it produces only nonsense?

I am thinking that this should drive home the point that one should not seriously think in such a way. David R. Ingham 03:53, 11 October 2005 (UTC)

What is the intended referent for "this"? What is the intended referent for "such a way"? Sorry if I appear thick-headed, but I have found that assuming I can guess what somebody else intended to say is a fairly reliable way to get myself even more confused. P0M 08:41, 11 October 2005 (UTC)

[edit] Request for citation

The article currently says, "One of Messiah's examples involves measuring the position of an electron with light. If the light's wave function is not known and hence cannot be included in the system wave function, then the predictions of the electron's position can only be stated in terms of probabilities, because the light photons exchange amounts of momentum with the electron which would then be unknown." Where does he say that? Thanks. P0M 01:17, 13 October 2005 (UTC)

You don't mean the discussion starting on p. 45 that discusses how the wavelength of light that would be useful in such an attempt would be in the x-ray range, and then discusses the difficulty of measurement purely in terms of how strong a perturbation would be produced on an electron by that radiation, do you? P0M 02:37, 13 October 2005 (UTC)

[edit] http://en.wikipedia.org/w/index.php?title=Philosophical_interpretation_of_classical_physics&curid=2690589&diff=25388356&oldid=25323074

I don't think "implies" is the right word. David R. Ingham 03:15, 15 October 2005 (UTC)

Fixed. P0M 01:03, 18 October 2005 (UTC)

[edit] Point by point (1)

(archived)

[edit] Point by point (2)

The expression "brought to the human scale" needs an operational_definition. P0M 06:52, 30 September 2005 (UTC)

This statement, too, needs to be redone. As it stands it does not have any clear meaning. P0M 20:27, 8 October 2005 (UTC)

My intention is that it help to guide understanding of the rest of the phagraph. David R. Ingham 23:08, 19 October 2005 (UTC)

I understand what your intent is, however, I do not know what the statement means. If you know what it means then it should be possible to explain what it means to other people. As it stands it cannot guide understanding. It serves only to obfuscate the discussion. P0M 23:24, 19 October 2005 (UTC)

[edit] Point by point (3)

Failing to find any place in Messiah's book that actually fits the statement that "One of Messiah's examples involves measuring the position of an electron with light. If the light's wave function is not known and hence cannot be included in the system wave function, then the predictions of the electron's position can only be stated in terms of probabilities, because the light photons exchange amounts of momentum with the electron which would then be unknown," I have decided to track through the literature in more-or-less historical sequence to discover where there might be an actual assertion that is at least close to what has been claimed in the article.

  • The Revolution in Physics, Louis de Broglie. Nothing even close.
  • Atomic Physics and Human Knowledge, Niels Bohr. Chapter on "Discussion with Einstein on Epistemological Problems in Atomic Physics." This article is very well written, but difficult to comprehend unless one has thoroughly learned the exact definitions of many terms. It does not appear to support David's specific contentions, however.
  • The Nature of the Chemical Bond, Linus Pauling, pp. 10-11:

The stationary quantum states of a molecule or other system are states that are characterized by definite values of the total energy of the system. These states are designated by a quantum number, represented by the number n, say, or by a set of two or more quantum numbers, each of which can assume any one of certain integral values. The system in the nth stationary quantum state has the definite energy value W[n] and is represented by the wave function ψ[n]. Predictions can be made about the behavior of the system known to be in the nth quantum state by use of the wave function. These predictions, which relate to the expected results of experiments to be carried out on the system, are in general not unique, but instead statistical in nature. For example, it is not possible to made a definite prediction of the position of the electron relative to the nucleus of a normal hydrogen atom; instead, a corresponding probability distribution function can be found.

The bold print is mine. --P0M
I believe that the above quotation is illustrative of a more general characteristic of the problems involved in locating an electron or other quantum domain entity by causing a second quantum domain entity to impinge upon it, and, subsequently, determining the location at impact of the second object on a detection screen. Neither the electron nor the photon has a location or a trajectory in the sense of the words as used in macro-scale discourse. Each has its ψ function. When the photon and the electron interact with each other, their ψ functions are both changed in some way. The energy of the light can be known because we can arrange an experimental apparatus that reliably emits light of a certain frequency. The direction of the line between the light source and the target can only be determined (when there is no intervening electron or other light blocker) by observing its point of arrival on the target. So if it hits the electron we can only be approximately aware of its "line of flight" because we do not know where the electron is except in a general way. Then the electron will strike the detection screen at some point at some verifiable point. That means that we have only two points out of three defined clearly. The "orbit" (to once again use figurative language from the macro world) of the electron will be changed by the impact of the photon. That is to say, its ψ function will be changed. So the ψ function of the electron, which originally had to have been unknown, has now been changed by the impact of the photon, which originally had an unknown ψ function. The resultant ψ function now has two unknown components. If we haven't hit it too hard with the photon, then we know what its orbital is, so we know what its frequency and energy are, but we do not know its position. Its position was precisely what we were trying to determine in the first place, and it seems that the one thing we can know for sure is that we have jarred it to someplace it wouldn't be if we had left it alone. I'm doing this in first-draft mode, thinking at the keyboard. Please correct what I have written if needed. P0M

Failure to give a citation may necessitate removing the statement quoted above. Emended,P0M 00:28, 17 October 2005 (UTC)

I know that I am not following my sources closely, but that is all in there somewhere. Just worry about making it correct and clear.

I cannot help make it correct and clear unless you will tell me the source in Messiah or somebody who writes equally clearly like Francis Sears. I have scanned the two volumes of this text and looked in the obvious places. I have looked through the index. I have searched the other physics texts that I have on hand. Nowhere do I find a trace of the kind of discussion you mention. P0M 02:46, 20 October 2005 (UTC)

I think your paragraph above is correct but don't see how to use it yet. The uncertainty principle garantees that one must make enough random phase approximations for the unspecified phases to supply the extra information for the classical description.

Incidentally, Linus Pauling said that his appointment was as professor of physics as well as of chemistry but the chemistry department head was his boss and wouldn't let him teach the nature of the chemical bond in a physics class. David R. Ingham 23:33, 19 October 2005 (UTC)

One note: the statement above: "Neither the electron nor the photon has a location or a trajectory in the sense of the words as used in macro-scale discourse. Each has its ψ function. When the photon and the electron interact with each other, their ψ functions are both changed in some way." is not the way QM works. To understand how two particles interact, one generally must construct a single wave function that describes both. There are special situations where one can simplify things. For example in solving the hydrogen atom, one normally ignores interactions with the proton and just calculates a single electron moving in the proton's static coulomb field. In general, however, you can't do that. For two entangled photons you need a wave function that includes both. The case of an electron and a photon gets even messier because photons can be created and destroyed in the process. --agr 10:56, 6 November 2005 (UTC)
Thank you very, very much. At last some light on this subject. P0M 16:22, 6 November 2005 (UTC)

[edit] Point by point (4)

The article claims: "The Copenhagen interpretation holds back from declaring quantum mechanics primary and from downgrading classical physics to the status of an approximation that uses terms for which there are no true referents." (Emphasis is mine.) What terms without true referents does it use? P0M 01:01, 18 October 2005 (UTC)

Does my addition fix it? David R. Ingham 23:41, 19 October 2005 (UTC)

No. If you are going to claim that there are terms (words) without true referents, then you have to be willing to say what those words are. What words that classical mechanics uses have no true referents? Mass, energy, momentum, position in space, position in time? Name a few, please. P0M 02:41, 20 October 2005 (UTC)

[edit] Moving forward

I have been getting no answers to my questions, only reactions to changes that I actually make, so I have started to restate the most problematic section on the basis of my "intuitive" understanding of the intended meaning.

(I have also archived the first half of the discussion. Nothing has been lost. If anybody wants anything, please cut and paste to bring it back in at the top of this page.) P0M 22:34, 18 October 2005 (UTC)

Maybe my "Analogy to Lamarckianism" comment was too outlandish to stay up top. David R. Ingham 23:49, 19 October 2005 (UTC)

Archiving old talk pages need involve no judgments on the material archived. Some users need to conserve bandwidth and as files grow over 32 k they may take too long to load and/or be too big for older browsers to edit. Generally when talk pages are archived the decision is a simple one: archive all discussion before a certain date. But if the talk page has "forked" into several discussions growing at the bottom of several sections then archiving can be a problem. From experience I know that it is important to cut information from the archive file and paste to the current discussion file when restoring portions of archived material for continuing discussion. If you don't do it that way you end up with much duplication and much confusion.
Another principle that can be used to archive discussions is simply to archive all discussions that seem to have reached a natural stand-still. I am at the point of archiving my "point 1" for instance, because it's already been resolved. P0M 00:36, 20 October 2005 (UTC)

[edit] Point by point (5)

The article says:

Because the classical approximation does not conform to the uncertainty principle, it must make mention of information that the quantum system, which does conform, cannot supply. This non-physical information is generated randomly.

How can nature make mention of something. This way of saying things seems almost solipsistic. Maybe that is not quite the right word except that human intelligence seems to be implicitly pictured as behind the change from the quantum physics picture to the Newtonian physics picture. The quantum system has no information on X (whatever that is). The classical system needs an X for some reason, so "it" plucks an X out of a random number generator somehow. Without knowing what the author of these words had in mind it is hard for me to imagine how to make them less vague. But let me try to provoke a correction:

We have set up a double-slit apparatus. Our X in this case is the measured physical position of a photon. We have done a good job setting up and testing our apparatus, so we know that we can kick off one photon from some emitter of photons. We've done that job enough times with no barrier between the LED and the detection screen that we can be pretty sure that we will get a good run of the experiment often enough to be useful. We put in the double slit barrier. At t[0] we fire off one photon. "It" "goes through" the two slits resulting in a superposition of two ψ waves. Between t[0] and t[1] (when a photon shows up on the detection screen) we have no information on the position of the photon. When the photon interacts with the screen we must have a single position. Photons in this apparatus show up at points that are statistically in accord with quantum theory, but the order in which they hit the various positions on the screen is totally random. P0M 04:14, 19 October 2005 (UTC)

Sounds good to me. Much clearer than the original. WhiteC 20:28, 19 October 2005 (UTC)

I don't see why you think nature makes approximations. That sounds "Lamarckian" to me. I think the paragraph does need work, but that sentence seems nearly right as it stands. It needs the actual source of the random information, which is what the "hidden variables" people need. David R. Ingham 21:42, 19 October 2005 (UTC)

I don't think nature makes approximations. You are the one who wrote: "This non-physical information is generated randomly." I was trying to paraphrase the text that I quoted. I'm not a mind reader, so I may have paraphrased it the wrong way, but when you write unclearly then that is the risk that you incur. You are also the one who spoke of nature "making mention" of something, which seems even more questionable to me.
If your last sentence above means that the paragraph in question needs to indicate the actual source of the randomness, then I agree. And, by the way, on what page does Messiah discuss measuring the location and momentum of an electron? P0M 23:43, 19 October 2005 (UTC)

Several places, I think.

I have asked several times. Please tell me where. P0M 00:40, 20 October 2005 (UTC)

Yes, it doesn't occur to me when I am writing that people might read it in ways like that.

Trying to write from a quantum mechanical point of view, it was incorrect or misleading of me to say simply that the extra information is generated randomly. In principle, if the whole laboratory and physics journal were described quantum mechanically, there would be no probabilities in the prediction and that description would closely correspond to a particular classical description of the result and the journal article. The outcome only seems random when the experiment is viewed classically. It comes from the assumption that the apparatus is known, when really the classical description includes no phases. David R. Ingham 00:18, 20 October 2005 (UTC)

[edit] Explanation

This section is, of course, why I, perhaps optimistically, deleted the "too technical" symbol. Probably, for most readers who make any sense of the article at all, this will be the understandable part.

Perhaps it might be more conventional to put the easiest part at the top, but I like getting to the point first and explaining it below, as is done now.

In this context, the statistical mechanics paragraph is a bit technical and not essential, but I like it because it makes the point that it was the classical description of nature itself that first failed, not just its incompatibility with the accurate dynamical forces. This seems to me to drive home the theme of the article. -- Ingham

I know where I got the information that I put in this section and can easily add citations. As a matter of fact, most of what I added is so much a commonplace of the discussions on quantum mechanics that multiple citations could be provided. But we have to be willing to try to live up to the standards of someone like Greene who can write about these matters with perfect clarity, and we have to be able to give accurate citations. P0M 02:56, 20 October 2005 (UTC)

[edit] Difficult to understand

Not only is this page difficult to understand but it is original research as the essay does not provide verifiable sources for the claims that are made, etc. I think this article should be deleted, but I am willing to see if it can be improved to something that is both understandable and verifiable. Trödel|talk 00:44, 20 October 2005 (UTC)

Thanks for the suggestion. I can easily supply citations for the garden variety stuff I have tucked in here and there. Do you have suggestions for citation style? I think there is a way to make regular footnote superscript numbers and have them pop the reader down to a section of notes at the bottom of the article. P0M 03:00, 20 October 2005 (UTC)

No, it is certainly not original research, unless you mean educational research. It follows the sources listed and other standard sources but presents it in a way that is more oriented toward philosophy and depends less on mathematics. Perhaps we should list more sources, but Messiah is really all that is needed, as he devotes so much space to the subject. He is not always easy to understand either and can't be read in short sections. What are you having trouble verifying? If you are really worried about the content, I suppose you should put in disputed flags.

An article that "presents it in a way" that has an orientation other than the neutral point of view is by definition a work of original research. Encyclopedic articles should present the information available on a subject not provide a new orientation to the subject at hand. If Messiah is the only source then there should be an encyclopedic article on him where this is one of the items discussed. Trödel|talk 03:27, 20 October 2005 (UTC)

My opinion is that the point of view of quantum mechanics texts must be considered the neutral point of view on quantum mechanics. Messiah is by no means unusual in this point of view, only in the space devoted to it. It is the observation that this most conventional point of view was under-represented in Wikipedia that motivates this article. As we find relevant parts of other sources we will add references.David R. Ingham 16:02, 20 October 2005 (UTC)

What originally motivated me is that people are still putting quantum mechanics on the defensive after a century of uninterrupted verification. The things that were originally considered absurd are nearing the engineering stage. More specific is that people are still thinking as though nature continually generated probabilities by converting back and forth between quantum and classical descriptions of itself. That is clearly contradictory to what Messiah says.

I just now have been working on the Explanation section, which is our attempt to make it understandable. Of course no-one should expect the subject to be easy to understand, no matter how it is presented. I understood some of these things very early in life and am trying to remember how to look at them without using much mathematics. I took off my "too technical" flag because it seemed we are doing as well as can be expected, not because it wouldn't be good to further increase the potential readership. You are welcome to put it back if you like. 03:06, 20 October 2005 (UTC)

I am of the opinion that if something can not be explained well to an educated person (in my case an educated college graduate with a B.S. in Physics) then it needs more editing. However, I am not sure that this article would survive a AfD vote since it is too much like original research. Thus I am not willing to invest the time in trying to more clearly articulate the ideas for intelligent non-scientists unless it will survive a challenge to its verifiability (and generally one source is not enough to create an article on). Trödel|talk 03:27, 20 October 2005 (UTC)
When there is only one reputed source, and repeated requests for page numbers are met with claims that it "is all in there somewhere. Just worry about making it correct and clear," then there does not seem to be any way to go forward. P0M 16:39, 20 October 2005 (UTC)

[edit] Footnote style

I looked up footnotes. The one I just added seems good to me. I hope Interpretation of quantum mechanics will adopt the same style. Or are there other suggestions?David R. Ingham

[edit] The measurement process

There is not yet a clear division, here, between the quantum and classical descriptions of the measurement process. The classical description must have been studied closely, in the dawn of quantum physics, to argue the uncertainty principle, but is less interesting now. The quantum description may be an active subject of research, because of its complexity and its relevance to entanglement and to quantum computing.David R. Ingham

[edit] Toward agreement on a neutral point of view

Suppose we rename Interpretation of quantum mechanics to History of the interpretation of quantum mechanics, rename this article to "Subtleties of the relation between quantum an classical descriptions of nature]], and archive this entire article and re-write it, closer to its text book sources but without plagiarizing?

There is good historical material in that other article, but its title, as it is, is misleadingly outdated. Its category would change from physics to history of physics.

Part of the objective for the new article should be to help understand entanglement, if possible.

Text book authors work hard to make it believable to people who did not grow up understanding quantum mechanics, and maybe there is much more of that quality that can be taken without adhering too closely. This would allow this article to be checked sentence by sentence against its sources, as people here want, but would still be representative of a modern view. David R. Ingham 10:50, 26 October 2005 (UTC)

As I mention on the Wikipedia:Articles for deletion/Philosophical interpretation of classical physics page, this article is mis-named, as it fails to mention any topic that is normally discussed when the "philosophy of classical mechanics" is discussed. This article seems to be enitrely about quantum. I would think the the Stanford encyclopedia of philosophy might provide a good example of what this article should look like. linas 15:17, 26 October 2005 (UTC)
For example [2] and [3] and [4] and [5] for a 'mainstream' view of classical physics philosophy.linas 15:25, 26 October 2005 (UTC)

[edit] Introduction

There were problems with the old introduction, but this one fails to identify the central point that the classical description includes more information than can be observed.David R. Ingham

Trying to fix that, I see that we have deviated from the issue. Sorry if I don't always have time or express myself clearly enough to keep things on track.

The subject is not just the verbal representation of classical physics, it is that the mathematical form itself contains untestable information. This is the point that is philosophical in nature. (Quantum mechanics does not suffer from this problem, in this case.) The uncertainty principle is a failure of classical physics and not of quantum physics. (Perhaps my previous sentence is all that is needed for than introduction.) As Feynman puts it, the fact that the information is not testable does not in itself condemn classical physics to the status of an approximation, what does is that its predictions are wrong. The statistical mechanics examples show that some of these failures follow directly from the classical description itself.

  • page 2-9 of The Feynman Lectures on Physics, Vol. III
  • Albert Messiah, Quantum Mechanics, English translation by G. M. Temmer of Mécanique Quantique, 1966, John Wiley and Sons, p. 45

David R. Ingham 21:23, 30 October 2005 (UTC)


Ħ: re:Messiah, 45-50

Ħ: Messiah says that the old quantum theory contained mention of things for which there are no observations, for instance: the orbit of an electron (because any measurement of low orbit electrons would distort their orbits beyond recognition, like trying to locate a fly with a fly swatter). He agrees with many others that our expectations should not be carried over from our everyday experience and make us expect or demand that electrons be discrete entities with planet-like orbits.

Ħ: This kind of situation is one that the philosophy of science deals with as almost a matter of course. We must always guard our thinking against unconscious assumptions, preconceptions, prejudices, etc., and philosophy is the category where we put analytical tools that we have designed for this kind of serious housekeeping task.

Ħ: The problem implicit in this part of Messiah's book, as in many others, is that familiarity with the macro scale phenomena successfully described in classical physics prepares us to misunderstand micro scale phenomena successfully described in quantum physics. The title "Philosophical interpretation of classical physics" does not prepare the average well-informed reader for the contents of the article that Ingham wants to present. Something like "Pitfalls of the classical mindset" would come closer to what is being discussed.

Ħ: It is a practical mistake to say that classical physics descriptions "include more information than can be observed". Readers will interpret that statement to mean that there is true information known and included in the descriptions of classical physics, but it happens to be information that is learned by some means other than by direct observation. The truth is that classical physics descriptions sometimes allege to be reports on things like planetary electron orbits for which there is no evidence.

Ħ: In the Interpretation_of_quantum_mechanics article, there is a chart of several interpretations. Ingham seems to me to want to take the Bohm position as the correct one and claim hidden variables, variables that are there and that determine, e.g., in which position a photon "show up" in a double-slit experiment. To prefer one of those several viewpoints fails to meet the requirement that we maintain a neutral point of view.

Ħ: As Messier says in a footnote on the fourth page of chapter 2,

After violent controversies, [the Copenhagen interpretation] has finally received the support of the great majority of physicists. However, it had (and still has) a number of die-hard opponents, among which one should notably list Einstein, Schrödinger, and de Broglie. The controversy has finally reached a point where it can no longer be decided by any further experimental observations; it henceforth belongs to the philosophy of science rather than to the domain of physical science proper.

Surely the Bohm or any other interpretation is no more sacrosance.P0M 23:21, 30 October 2005 (UTC)

I think you may be starting to learn some physics, POM. That introduction may be an improvement. I am not sure why we were both looking at the same page in Messiah at the same time.

The section on the measurement process is in need of help too. Please see the discussion page for the rfd where I have listed problems. P0M 04:45, 31 October 2005 (UTC)

I agree that we should end up with a different title, but I started with this one to balance "Interpretation of quantum mechanics", because a poor fit between a theory and its approximation belongs to the approximation and not to the theory. As I said, somewhere, we should talk about the history of when physicists still thought classically and talk about physics from a contemporary point of view. I want this article to permanently do the latter but also at present to lead people away from seeing viewpoints as contemporary, when they are not.

Of course there must be current philosophical discussion of physics, but I can't see how that can be interesting until we already know enough physics to understand entanglement and quantum computing. From what I am reading in Physics Today, that will not reach an encyclopedia soon.

If I find some historical evidence, I would like to include that Einstein's failure to "understand" quantum mechanics was caused by people putting things too conservatively for him to see the leap. I don't remember much talk about the "interpretation of curved space". He simply said that was how it is and the experiments confirmed it. There was no putting it softly to keep from disturbing people. David R. Ingham 03:24, 31 October 2005 (UTC)

[edit] 68.127.179.177

I may have failed to log on.

[edit] Physics and the Real World (is that a tv show?)

I looked this up :"Physics and the Real World" by George F. R. Ellis, Physics Today, July, 2005 I don't see what the error you refer to is. Maybe you could write one of your essays and post it to your personal website , or to wikinfo.org where original research is ALLOWED (along with an unmangled version of this Phil Interp. of Cl Phys. page while you're at it.) GangofOne 03:14, 3 November 2005 (UTC)

[edit] Point by point (6)

[edit] Point by point (6)

The current text says:

The Copenhagen interpretation was formulated while quantum mechanics was new and no one was used to it, so it describes quantum mechanics in terms of classical physics in a way that is adequate for practical purposes. The Copenhagen interpretation holds back from declaring quantum mechanics primary and from downgrading classical physics to the status of an approximation that uses terms for which there are no true referents at the micro scale. That is, it still spoke as though the uncertainty principle were a part the the quantum theory itself rather than part of nature.

After reviewing Heisenberg's Physics and Philosophy, among other early works, I believe the above statement does not correctly reflect the facts. Note that no citations have been provided. The passage consists of groundless assertions made in support of one point of view. P0M 08:10, 3 November 2005 (UTC)

[edit] Afd failed

Per Wikipedia:Articles_for_deletion/Philosophical_interpretation_of_classical_physics. Most were for delete, but could not agree on what form of deletion. --Woohookitty(cat scratches) 11:42, 5 November 2005 (UTC)

So what now?Karol 09:05, 28 November 2005 (UTC)
We need to decide what the article is intended to explain, and then we need to find a title that is clear.P0M 15:06, 28 November 2005 (UTC)

[edit] New material

I have not had new sources to add recently, but here is a very good one.

Physics Today, April 2006, "Weinberg replies", p. 16, "... but the apparatus that we use to measure these variables—and we ourselves—are described by a wave function that evolves deterministically. So there is a missing element in quantum mechanics: a demonstration that the deterministic evolution of the wave function of the apparatus and observer leads to the usual probabilistic rules."

In principle the answer is given by the correspondence principle, but the details are very complicated, so there is not a clear derivation of "the usual probabilistic rules". Theorists tend to be more often quoted than experimentalist and less involved with this issue. David R. Ingham 05:57, 10 May 2006 (UTC)

This quote clearly supports the thesis of this article, that it is classical physics that requires explanation in terms of quantum physics. David R. Ingham 06:26, 10 May 2006 (UTC)

[edit] Entangled cat

[edit] Entangled cat

To avoid repeating the same text again, I am putting a link to my comment about Schrödinger's cat: [[6]].

This is another example of how it is dangerous to think of our classical picture as real. It is only an approximation to QM, and the rules about when it is valid can be subtle. David R. Ingham 20:49, 23 August 2006 (UTC)

[edit] Toward a quantum interpretation of Copenhagen

In doing an experiment, one naturally intends to obtain results that are as stable as possible. The fundamental advantage of digital data is that it is stable: on paper there is too much ink or graphite to wander away. Especially, in electronics, the feedback stabilizes the state of the memory. Signals are re-shaped to stay within reliable bounds by each stage of the circuitry. When doing an experiment the result might be a continuous variable in analog form, but it must be stored stably. The physical "collapse" that then must occur in an experiment consists of reaching a region of positive feedback and falling into a stable state of some sort. This is typically one or more bits in a computer, or more traditionally a number in a notebook. The requirement that the system be in the bottom of a well does not necessarily imply that which well is unique. In rare cases, the best description may be a linear combination of stable states. That is still a good experiment, as long as all of the components of the state vector that have non-vanishing amplitude are themselves stable.

The essence of the Copenhagen Interpretation is that this physical (describable in QM) collapse occurs at the same time that a classical approximation is used. Of course, without a quantum computer, the result must be expressed classically. When these two things can be described as happing at the same time, they are called "wave function collapse". What Einstein was attacking was QM with the Copenhagen Interpretation, as no other form was clear at that time. He appears to have won, in the sense that one cannot understand an EPR experiment in terms of Copenhagen without giving up things like locality.

A century later, we see that he should have attacked the over-simplified rules for doing experiments and not the mathematical theory. David R. Ingham 04:16, 27 August 2006 (UTC)

[edit] So where's the CLASSICAL physics?

Where's action at a distance? Point particles? The three body problem? 1Z 22:56, 29 October 2007 (UTC)