Wikipedia talk:Articles for deletion/Philosophical interpretation of classical physics
Ħ :Section that is the most problematical. Any insights into what Ingham is trying to say would be greatly appreciated. To me, the crux of the matter appears to be Ingham's failure to explain, precisely, what he means by bringing things up to human (or macro) scale. Trying to use my intuition, when all else has failed, it seems that he is saying that there are only utterly determinative processes going on in quantum-scale interactions, but that when we "bring them up" they become probabilistic in nature. The fact that, e.g., single electrons put through a double-slit device show up at various places in various concentrations on a detection screen, is "probabilistic" to us because we cannot do the calculations necessary to predict when they will show up here and when they will show up there; nevertheless, in each case there is a definite reason why the electron took one path to the screen rather than any other path. Somehow that information is "there" on the quantum scale, but it gets splattered somehow in the process of "bringing it up." If that is what he means, it would be of great help if he would actually say so.
Any process of measurement requires that the object being measured be subjected to forces external to it, as when photons are directed at something and the paths of the photons are subsequently noted.
- Ħ :No problem.
This step demands that procedures be used that inevitably spoil the coherence of the isolated pure quantum state that is the subject of the experiment.
- Ħ :Unclear since no experiment has been explicitly mentioned. Ingham’s intention may be to describe an attempted measurement of an electron by directing one or more photons at it.
Phase information in the quantum description cannot be represented classically, and is lost.
- Ħ :Unclear. The expression “phase information” comes completely out of the blue. Why make the reader guess?
If some photons, electrons, or other quantum-scale entities used in the measurement process are described quantum mechanically and included in a quantum calculation, then the result is a deterministic quantum description, i.e., a description that contains no probabilities.
- Ħ :Big if. Getting the numbers to crank through the equations this way implies that there are determinate numbers, and that they can be gotten. And what happened to probability densities?
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.
- Ħ :This sentence is incomprehensible to me. The process of by which “the information” is “brought to the human scale” must be given an operational definition or else the above statement is meaningless.
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, so the experimental result must be in classical form.
- Ħ :I'm stumped. What “devices” is he talking about? What information? Stored where? I guess he is just saying that computers store and compute information taken from macro-scale instruments. Anything we compute or write or just think about depends on electrons or photons or whatever showing up on detection screens such as our retinas or photographic film, and, e.g., a photon “in flight” by definition hasn’t shown up anywhere yet. The whole problem is that we expect the photon to behave like a macro-scale particle (ball bearing propelled out of a slingshot, for instance), and the fact is that we can’t see the ball bearing, we can only get hit in the eye by it.
- Ħ :The reference to quantum computers seems irrelevant, at least as I understand quantum computers. Information is entered into quantum computers by “classical” processes like users sitting at keyboards. What Ingham writes sounds as though he thinks that information could pass from a closed quantum “box” (experimental apparatus) to a quantum computer, that said information would retain its micro status, that the quantum computer would process it “quantumly”, i.e. without losing anything by moving to macro scale, and then could report answers to the macro level without losing data. Somehow. But all is my wild speculation built on guesses about a fundamentally incomprehensible assertion.
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.
- Ħ :Is that saying that, e.g., there is an uncertainty in where the photon is between emitter and target, but that the uncertainty disappears when the photon shows up on the detector? Or what? The uncertainty principle indicates that there is a definite limit to the precision of simultaneous measurement of two characteristics. That uncertainty comes up whenever we use measurement tools to try to pin a micro-scale entity down. There is no problem with representing the limits on the measurement in the language of macro-scale physics. Is he really trying to say that the electron has an exact position but that measuring it messes the position up?
- Ħ :Or maybe he is saying that neither the photons nor the electron have exact positions, so it is pointless to ask for them? So we come up with statements about the probability of where something is?
- Ħ :As you can see, I, the “average well-informed reader,” come up with two antithetical guesses pertaining to one murky sentence.
From a quantum perspective, this non-physical information in the classical description of the original quantum system comes from the unknown phases of particles and devices used in the experiment but known and described only classically.
- Ħ :What does he mean by “unknown phases”? Unknown psi-function information? It sounds like he is admitting that we cannot know the actual values of the psi-functions because electrons and photons don’t broadcast private information about themselves, so we have to bounce electrons in approximate directions and then check out where they show up on detector screens and argue from there.
Viewed classically, it appears to be random.
- Ħ :But, he seems to imply, "it" (unknown phases of particles and devices?)is actually not random or probabilistic.
- Ħ :What appears to be random? Is Ingham saying that, e.g., electrons can show up in unexpected places, as in quantum tunneling? Is he saying that photons can show up at various positions on a screen even though classical physics would have them show up at a single point?
One example of such a process might involve measuring the position of an electron with light.
- Ħ :Maybe it will be possible to determine for sure what he means by “such a process.” This whole article would be vastly improved by the provision of operational definitions for all processes and components of experiments.
If the light's wave function is not known and hence cannot be included in the system wave function, then neither the quantum state of the electron plus photon system nor the prediction of the electron's classical position can be stated except in terms of probabilities, because the light photons exchange amounts of momentum with the electron that are unknown.
- Ħ :The light’s wave function is unknowable. We have no justification for assuming that the light leaves the emitter in a determinate direction. The covert assumption here may be that the light has a wave function such that it has a determinate direction of propagation, i.e., that its terminal point on the detector is determinate even if we cannot know what the determinate answer to any calculations might be.
It is the requirement for extra information (beyond that specified by the uncertainty principle), in a classical description, that makes probabilities inevitable.
- Ħ :What, precisely, is this extra information? I can ‘’’guess’’’ that it means things like “the actual position where a photon appears on the detection screen of an experimental apparatus such as a double-slit device.” Where the photon appears is definitely a matter of probability. But the statement above suggests that there is something other than “probability density” in the actual quantum scale event, as though the photon had a deterministic position that was disturbed “probabilistically” when a classical description was made. How can a verbal description be made? What difference does it make if a verbal description is made? The key event is not the making of a verbal description, but the showing up of something observable on the macro scale, e.g., the showing up of an electron on the detection screen of some apparatus. All that I have said may be irrelevant to what Ingham was trying to say because I cannot get clear on his words.
From this point of view, this information does not describe reality.
- Ħ :What information does not describe reality? The information that the uncertainty principle does not provide is where, within the range of uncertainty, something is. If we state the position and momentum of, e.g., an electron to be within such and such limits, we do not fail to describe reality. We describe it more accurately than otherwise by stating limits of accuracy. If Ingham is actually talking about predictions based on the Shrödinger equation, the results are not “unreal” but probabilistic.
The experimenter is simply asking more than there is to know.
- Ħ :Regrettably, it is not even clear what Ingham thinks the experimenter is asking.
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