Talk:Introduction to quantum mechanics/Archive 4

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New comment on the opacity of the article

Surely a better job can be done to express ideas easily and clearly at the following key point in the tale. It doesn't mean anything to the layman. As a layman who's trying to understand these matters, I know roughly what needs to be said here, but the following doesn't communicate it. - "He modelled the thermal radiation as being in equilibrium, using a set of harmonic oscillators. To reproduce the experimental results he had to assume that each oscillator produced an integral number of units of energy at its one characteristic frequency, rather than being able to emit any arbitrary amount of energy." The first sentence is particularly opaque.

~~ deschreiber —Preceding unsigned comment added by Deschreiber (talk • contribs) 20:45, 22 May 2011 (UTC)

I understand your frustration. It is matched by a counterpart frustration of my own: Many attempts that I have tried to make to keep the article comprehensible to somebody who has not had a couple years of college physics have been attacked by readers who have said that they feel that I am talking down to them. Writers such as Einstein and Heisenberg have a facility for writing in simple language. They can represent as clearly as possible what they mean without using the concise symbolic manipulations given in higher math, and, at the same time, they can very successfully preclude readers from drawing inappropriate conclusions from what they have written. Preventing readers from jumping to false conclusions is a great art. Lesser writers, such as I, can write things that can be defended as being correct, but that may not convey the desired information to readers who take it in some way other than was intended. If I were to try to improve that passage, my first thought would be to make a schematic diagram showing how Planck was imagining the production of energy in a "black body." The diagram would likely be called lacking in esthetic merit, and also criticized for lacking any academic citations.

"He modeled the thermal radiation...using a set of harmonic oscillators," sounds like it should be parallel in meaning to "He modeled the clay...using a set of bamboo knives and spatulas," -- but that idea is wrong. The writer probably was trying to convey the idea that Planck made a mental model of the production of radiation. In his model the black body contained a set of things (which were not described) that could oscillate, and that each had is own dimensions and, consequently, had its own characteristic frequency. I would guess that Planck saw a black body producing radiation as being analogous to a xylophone with a very extended range. Elecro-magnetic frequencies would be analogous, then, to sound frequencies. The intensity of sound at any one frequency is a sort of xylophone orchestra is dependent on how many times during a short interval a certain vibrating bar on the xylophone or xylophones is hit. If there are one thousand xylophone bars that vibrate at A (440 hertz) and only one that vibrates at 44000 hertz, the strength of that very high sound frequency will be much lower than the 44 hertz A.

Some editors would not accept a long, drawn-out discussion such as I have produced, and would argue that Wikipedia is an "encyclopedia" and not some kind of "boy's guide to how the world works."

I agree with you that the passage you have quoted is not suitable. Perhaps other editors will provide suggestions on how it might be improved.P0M (talk) 22:06, 22 May 2011 (UTC)

I think an introduction to QM through matrix theory would be more appropriate. The example of light polarization can be used as the leading example throughout the article. QM is the math of complex vector spaces, so we should present it as such. The "physics stuff" and the infinite dimensional hilbert spaces (wave functions) are perhaps too complicated for an introductory article -- the reader is left with the vague understanding and still vulnerable to all the quantum non-sense in popular culture. I volunteer a rewrite, but I am not sure what is the policy on this. — Preceding unsigned comment added by Ivan.Savov (talk • contribs) 19:20, 17 June 2011 (UTC)

I got to the point of trying to reproduce the calculations that Heisenberg would have used in working out his paper of 1925. Unfortunately, my own life imposed some time restraints on me and I chickened out. I think it would be useful to have as concrete an example providing that our target audience (let's say good high school mathematics but no calculus) could understand.

One of the things that you could do would be to make a "sandbox" file in your own userspace and then draft your idea of what the article should do with the matrix discussions. If you could work these ideas out as far as the math goes, working out discussions to coordinate with them would be relatively easy.P0M (talk) 04:39, 18 June 2011 (UTC)

Question on intended meaning

The text currently says:

And the traditional mechanisms for generating photons are classical devices, in which the energy output is regulated by varying the frequency. But Einstein proposed that although a particular frequency is tied to a specific energy level, the frequency is dependent on the energy level, not vice versa (contrary to the tenets of classical physics). This formed his solution to the photoelectric effect, even though it was counter-intuitive.

The way this passage is written makes it seem that the energy delivered by a brown dwarf star should be less than the energy delivered by a blue laser pointer. The energy output of a campfire is regulated by the amount of wood burning and the relative availability of oxygen.

The frequency of a photon is the energy of the photon. For a description given in an appropriate system of units, E = f. In a black body, enough thermal energy must be available to raise electrons to orbitals sufficiently high that when those electrons fall to a lower energy level they will lose enough potential energy to result in the production of high frequency photons. If there is not enough thermal energy in the system, then the highest level of photon production will be at an appropriately lower frequency and the flux of photons of higher frequencies will rapidly drop as we look at higher and higher frequencies, i.e, the graph of energy delivered per unit time against frequency will spike at an appropriately low frequency.

In instances of the photoelectric effect, it is the frequency of the individual photons, not the intensity of the beam of light, that determines whether electrons will be driven and an electrical potential be produced. The photo cell constructed of appropriate metals will not produce a flow of electricity no matter how much low frequency light is directed at it. It could sit quietly in and come to thermal equilibrium with an oven set at 500 degrees fahrenheit. But a single photon of a frequency higher than some characteristic value will produce a current flow, and a blue laser would produce a current of a certain voltage (but of low amperage if it's a laser pointer).

I do not believe the passage quoted above conveys the correct information.P0M (talk) 08:00, 31 August 2011 (UTC)

If nobody can see anything wrong with what I have stated above, I'm going to change the article. P0M (talk) 01:49, 2 September 2011 (UTC)

Exclusion principle

The section on the exclusion principle currently has the following content:

He developed the exclusion principle from what he called a "two-valued quantum degree of freedom" to account for the observation of a doublet, meaning a pair of lines differing by a small amount (e.g. on the order of 0.15 Å), in the spectrum of atomic hydrogen. The existence of these closely spaced lines in the bright-line spectrum meant that there was more energy in the electron orbital from magnetic moments than had previously been described. In early 1925, Uhlenbeck and Goudsmit proposed that electrons rotate about an axis in the same way that the earth rotates on its axis. They proposed to call this property spin. Spin would account for the missing magnetic moment, and allow two electrons in the same orbital to occupy distinct quantum states if they, "spun" in opposite directions, thus satisfying the Exclusion Principle. A new quantum number was then needed, one to represent the momentum embodied in the rotation of each electron.

The average reader is not going to be able to figure out what is being said. To me it sounds like walking in to the middle of a debate where everybody else knows the personalities and facts, but the listener only hears "he said" or "she said" and has no idea of either what is being alleged to have a connection or of what the nature of the connection is.

Whew. Not exactly introductory, is it? RockMagnetist (talk) 05:55, 30 November 2011 (UTC)

The favorite zinger of some physicists, and I'm not sure how far back it goes, is: "It is not even wrong." If I knew what the writer had been trying to say I'd find it far easier to fix it. If the quotation was cited it would be easy to find the context and maybe whatever was being paraphrased. Actually I think I sort of remember the concrete details, starting with people seeing a pair of bright lines where theory said there should be one line, but I was too tired and it was too late to start working on it last night.P0M (talk) 15:00, 30 November 2011 (UTC)

Actually, I have rewritten it already. RockMagnetist (talk) 15:27, 30 November 2011 (UTC)

Great! Thanks. P0M (talk) 16:11, 30 November 2011 (UTC)

Here's a nice coincidence - the "not even wrong" quote is attributed to Pauli. RockMagnetist (talk) 16:15, 30 November 2011 (UTC)

Pauli was a neat guy. Wasn't he the one who was exiled from all physics experiments in progress because with him in the lab room they always went out of kilter? The idea that some supposed theory is so incoherent, logically at least, that it could not be shown by experiment to have failed is essential to the philosophy of science. The short "lug" that Pauli used seems to be characteristic of his personality—willing to take issue with anybody, but not ever doing so in an unfriendly way.

I'm not sure, but I think that I can understand all of this article now. Thanks for your help!P0M (talk) 16:41, 30 November 2011 (UTC)

You're welcome, and thanks for your improvements to the article. According to one story, Pauli heard that there had been an explosion in a lab, and he wrote the lab to tell them that he must have caused it because he had been in a nearby train station at the time. RockMagnetist (talk) 16:46, 30 November 2011 (UTC)

Merger discussion

The result of the discussion for Basic concepts of quantum mechanics was to merge it with this article. I have copied over the main content from Basic that was missing from this article. RockMagnetist (talk) 06:45, 1 December 2011 (UTC)

I'll be bold and redirect the page to here. IRWolfie- (talk) 20:28, 3 December 2011 (UTC)

Tricky wording. Check my reasoning.

Einstein explained the effect by postulating that a beam of light is a stream of particles (photons), and that if the beam is of frequency f then each photon has an energy equal to hf.[1] An electron is likely to be struck only by a single photon, which imparts at most an energy hf to the electron[1] (in point of fact, it logically cannot be struck by more than one photon, since the first it absorbs will cause it to eject). Therefore, the intensity of the beam has no effect;[note 1] only its frequency determines the maximum energy that can be imparted to the electron.[1]

Technically I think this paragraph is correct only because it contains the hidden premise that the beam of incident light of frequency f is capable of ejecting electrons. If we treat the quoted paragraph strictly, and say that we are talking about any beam of light and/or any frequency of that light, then it is certainly possible that an electron can absorb a photon without being ejected because the frequency of that photon is simply too low. The electron that wss affected will take a higher orbit, and it is possible that some other photon might be absorbed and cause it to be ejected.

By false reasoning this paragraph derives a conclusion that may in itself at least reflect the mass effect of the beam that will be observed. The most important fact is that electrons will ordinarily return to their equilibrium state in a relatively short time if they are not ejected from their atoms. So two conditions would have to be met within that brief time span to make an ejection by lower energy photons possible. First, the electron must in that short span of time consecutively absorb two photons. Second, the energies of the two photons must sum up to an appropriate value to cause ejection of the electron. So an electron can logically be struck by more than one photon, but the chances are slim that any ejections would be produced in that way.P0M (talk) 10:21, 1 December 2011 (UTC)

Logic doesn't follow

I'm sure there are other sections in the article like this, but this one caught my attention first since it's close to the introduction:

In the late 19th century, thermal radiation had been fairly well-characterized experimentally. The wavelength at which the radiation is strongest is given by Wien's displacement law, and the overall power emitted per unit area is given by the Stefan–Boltzmann law. Therefore, as temperature increases, the glow colour changes from red to yellow to blue to white. Even as the peak wavelength moves into the ultra-violet, enough radiation continues to be emitted in the blue wavelengths that the body continues to appear blue. It never becomes invisible—indeed, the radiation of visible light increases monotonically with temperature.[3] Physicists were searching for a theoretical explanation for these experimental results.

The concluding sentence of this paragraph, "Physicists were searching for a theoretical explanation for these experimental results.", doesn't fit into context well. The sentence implies, to at least the uninitiated reader, that something about those results didn't make sense alongside the previous discoveries of physics, but what it was is never mentioned.

Clarification of what about the properties of the observation of wavelength-emittance required explanation is required. Being an uninitiated reader myself, I don't have the facility to do that. 69.116.250.211 (talk) 13:59, 11 December 2011 (UTC)

Good point. The physicists were simply trying to come up with a theory that would predict the frequencies that would be most strongly associated with a given temperature. The classical theory got more and more off the higher the temperature went, which indicated clearly that the physicists did not know what was going on. P0M (talk) 17:48, 11 December 2011 (UTC)

I have changed things around a bit so that the historical development is clearer and the question being answered is explained better. In doing so I have removed some details (originally copied from an other Wikipedia article) that do not seem to me to be relevant to explaining what Planck was up to. See if the current way of explaining things works better for you.P0M (talk) 18:56, 11 December 2011 (UTC)

Ah, I see. That's much better. 69.116.250.211 (talk) 23:35, 12 December 2011 (UTC)

Quantum mechanics in science fiction?

I am interested in creating a new article on this topic. Or perhaps it belongs in this article. Or maybe still, an article in the Quantum mechanics main article. I was wondering what everyone thinks. I want to make sure this is addressed in the appropriate forum. Sunshine Warrior04 (talk) 05:30, 5 April 2012 (UTC)

The purpose of both articles is to explain to the reader what quantum mechanics says. To the extent possible these articles avoid getting into just the interpretations of quantum mechanics offered by the scientists who work in this field. The equations of quantum mechanics do not say in an unambiguous way what "actually happens" in the real world. So we get talk about wave functions that "collapse" here rather than there, but there is no telling before the fact where they will collapse. and there is no explanation for why one possible result of the equations is "chosen" rather than any of the others. But we also get talk about multiple universes being created, one for every quantum decision, so that everything always goes all ways. The whole thing begins to resemble scholastic angels dancing on pin heads, but at least the interpretations reveal how physicists try to put things through their own heads.

To go beyond even that level of connectedness to talk about the fictional uses that people have put the interpretations to would, in my opinion, only serve to confuse readers who are trying to find some scrap of recognizable fact to hang onto, some coherent picture that explains how the universe can appear to be so crazy.

Why not consider fitting your idea into the article(s) on science fiction? For one thing, you would not have to defend yourself against physicists while you are trying to explain a science fiction article that may not involve a brand of physics that is acceptable to physicists.P0M (talk) 05:57, 5 April 2012 (UTC)

Point well taken. This is why I did not just jump in with my own article. I happen to be a student of physics and an lover of science fiction so I really see no problem with adding something here. But I can understand a lot of serious minded people getting upset. Well just a link at the end of this article would suffice. Cheers mate! Sunshine Warrior04 (talk) 06:42, 6 April 2012 (UTC)

Would you like to supply a link? P0M (talk) 01:47, 11 June 2012 (UTC)

Also, I agree that adding to one of the science fiction articles might be a good way to go. I say give it a try. If its not a good fit don't worry because any such error can be corrected. Or you can simply supply a link and we can see if it is appropriate for this article or some other. ---- Steve Quinn (talk) 07:13, 11 June 2012 (UTC)

Bertelmann's socks

The article says "Even more disconcerting, pairs of particles can be created as entangled twins — which means that a measurement which pins down one property of one of the particles will instantaneously pin down the same or another property of its entangled twin, regardless of the distance separating them." . This is not disconcerting at all. Put a pink and a blue pingpong ball in two identical boxes. Send one, chosen at random, to Beijjing; send the other to Washington. Take a peek in the box in Washington: the ball is pink! Far away, the box in Beijing suddenly contains a blue pingpong ball!!!

Whatever it is that's odd about entanglement, it's not what the article says it is. Richard Gill (talk) 18:20, 9 June 2012 (UTC)

How would you advocate clarifying the matter? P0M (talk) 01:38, 11 June 2012 (UTC)

I think this phenomenon is indeed disconserting. It is anti-intuitive. In contrast, the two ping pong balls are objects that are not related to this, and they are not really related to each other. The position or movement of one ping pong ball does not affect the other. ---- Steve Quinn (talk) 07:21, 11 June 2012 (UTC)

Exactly. But why do you think that what is said about entanglement implies that one particle is affecting the other? The consequence of entanglement that from measuring one particle you can predict the outcome of the same measurement on the other particle, however far away it is, is not counter-intuitive at all. It does not imply that your measurement on one of the particles is influencing the other, as the ping-pong ball example shows. If the reader wants to know what is weird about entanglement, they should read the article on Bell's theorem.

But I'm sorry, I admit I don't have a short fix to the problem.

Einstein, Podolsky, Rosen used the entanglement property to argue that quantum mechanics was incomplete. You could measure position on one particle, and then you would know the outcome of measuring position on the other. You could measure momentum on one particle, and then you would know the outcome of measuring momentum on the other. Therefore both particles have simultaneously definite values of both position and momentum, while quantum mechanics only predicts probability distributions of measurements of just one.

Bell however later turned this argument on its head. By analysing a slightly more complicated version of the story, he showed that the predictions of quantum theory could not be true under any theory of the kind called "local realist". Richard Gill (talk) 12:31, 11 June 2012 (UTC)

unindent

I agree that you have stated the crux of the matter. We just need to get the current version fixed so that it is not misleading anymore. P0M (talk) 06:58, 12 June 2012 (UTC)

I started to draft something, but it's gotten to be too long for the lead. I'm too tired to see whether it can be tightened up and shortened enough to fit into the lead. So I'll put it here, and in the interim I'll truncate discussion of entanglement in the lead.

Even more disconcerting, pairs of particles can be created as entangled twins. It is difficult to talk about this phenomenon in ordinary language because it throws our usual ideas of causality into confusion. For instance, a subatomic object such as an electron can sometimes have the potential to display a clockwise spin or a counterclockwise spin. In quantum mechanics this condition is described by saying that the electron has a superposition of a wave function that accords with its having clockwise spin and this same wave function also accords with its having counterclockwise spin. Humans have grown up under conditions in which something that is spinning either goes one way or the other, so even the fact that the electron is in some analogical sense "spinning in both directions at once" goes against all ordinary experience. Such an electron is known empirically to have spin only after it interacts with some other particle or system of particles in such a way that it has to manifest spin. The "fact" that such an electron has the simultaneous potential to spin either way comes out of the mathematics of quantum mechanics because the equations do not include any factor that determines which spin an electron might have. One might easily assume that just because quantum mechanics does not inform us of which spin the electron has, it must in fact have one spin or the other. But experiments show otherwise, as will be explained below.

When two electrons interact under certain circumstances, they thereafter share the same quantum state. As a consequence, the two electrons have the same quantum state that includes the potential to spin. However, the consequence of this sharing of a potential to spin in a clockwise way or in a counterclockwise way is that if one of them enters into an interaction and thereupon manifests a clockwise spin, then the other electron of this pair can thereafter only manifest a counterclockwise spin. As suggested above, one might assume that from the beginning one had a hidden but real clockwise spin and the other had a similar coumterclockwise spin. But John Bell has shown that this idea is falsified by experiment.

The magnitude of weirdness of the phenomenon called entanglement becomes clearer when another consequence of theory is examined and then proven by experiment: The distance between the two electrons when an experimental measurement of the spin of one of them is performed is irrelevant. The electrons might be separated by any distance and yet if one of them had its spin measured and was found to be, e.g., counterclockwise, then even though prior to that time the other electron had the potential to manifest spin of either sense, after that time the other electron must manifest the kind of spin that is opposite to that of the first electron.

This theoretical and empirical finding confounds our ideas of causation. Ordinarily we mean by "cause" that something such as an electron was behaving in one way and then a force interacted with it and changed what it was doing. Perhaps an electron was heading in a straight line through a vacuum tube until a magnetic field was applied to cause it to change its trajectory. But in the case of the entangled electrons, contriving to have the first electron interact with some other system so that the first electron has to show itself as having one kind of spin will result in the other electron becoming limited to manifesting only the other kind of spin, and yet no force has been applied to it. Because the speed of light limits the minimum time it would take for any force (such as a magnetic field) to travel from the first electron to its entangled twin, it is certain that if the second electron's spin is measured before a light signal could have reached it, then no force from afar could have influenced it. Therefore, it is affirmed that doing something to make the first electron show one spin or the other does not cause the other electron to be required to show the opposite spin. However, if action on the first electron had not been taken, then the second electron would have been free to manifest either spin. So something has changed, and it has changed as though there were no intervening distance between the two electrons.

Prior to the discovery of this phenomenon, nobody doubted the idea that things have to be in touch with each other in some sense for there to be an interaction between them. Swinging a bat will do nothing to a bsseball unless the bat makes contact with the ball. Sound from a distant thunderbolt will affect one's ears only after sound waves have traveled over the intervening distance. The light of a nova will be seen only after photons from that cosmic explosion have traveled for many years to reach observers on earth. Nevertheless, if entangled electron twins were sent off in opposite directions and one were examined when the two were one light year apart, somehow the other would instantly "know" how it was supposed to manifest its spin.

More later.P0M (talk) 08:21, 12 June 2012 (UTC)

Just a comment on the revised lead. It is not common to refer to the body of the article in the lead, and should not be necessary because the lead is a summary of the article. RockMagnetist (talk) 14:18, 12 June 2012 (UTC)

My thought, which may not have been clear, was to head off attempts to say very much more in the lead and to get future contributors to look at and/or modify the section. I'll take that part out, but we all will need to be aware of future alterations that may muddy the water. I don't know where the stuff that Dr. Gill complained about came from. I missed it. P0M (talk) 17:02, 12 June 2012 (UTC)

I think that one of the confounding issues is what to name what Einstein called "spooky action at a distance." The idea of action involves the application of some force over some amount of time, and our ordinary idea of "causing something" involves exerting force on some system to influence its behavior. But entanglement is exhibited without the lag that would be required were interactions at a velocity ≤ c, so something is going on that is not "causal" in the usual sense. On the other hand, before one or the other entangled twin particles is measured, they both have the freedom or the potential to manifest either spin, and after one of them is measured and must manifest a spin then the other no longer has the freedom or potential to manifest any spin other than the opposite of the one that was first measured. So something has changed, and it strikes me as creating an intellectual smokescreen to say that there is only some kind of abstract "correlation" involved. Like the "collapse" of a wavefunction, we have no idea of what is going on or how to describe it. All we know is that it happens. It also strikes me as possibly significant that the time sequence may not be clear. From my frame of reference, electron A is observed first, and electron B is observed second. Someone else, in another frame of reference, may see electron B as being observed first and electron A as being observed second. There are also phenomena within the same frame of reference that we call retrocausal. We have no way of knowing that the discovery of the polarity of photon B at time T+n determines, retrocausally, the polarity of photon A at time T. If we say that these changes are not local, that must (I think) mean that they are not local in space-time. So, in a sense, I end up arguing against my own discomfort with the idea that there is "only" a correlation between the discovered states of any entangled twins.

If you are finding what I just wrote confusing, imagine what the whole discussion will do to someone who has just heard an intriguing mention of quantum physics on TV and has come to Wikipedia for more information. We need to be very careful to make our vocabulary and explanations such that our article can be processed by such readers. Lack of appropriate words is a big challenge.P0M (talk) 18:22, 12 June 2012 (UTC)

It's true that something interesting is happening but whatever it is, it does not violate any principle of causality. There is no "action at a distance". Observation of electron A does not give any information at all about what is happening to electron B. We only appear to see spooky effects on things which are parts of our mathematical description, not on the real things. For instance, the wave function. But who says the wave function is something out there, in physical reality?

The EPR - Bell story does lead to phenomena which can be used by distributed decision makers to collaborate with one another, in ways which we cannot imagine possible in classical physics. Any classical explanation would involved instantaneous communication over large distances. All these phenomena are about achieving correlations which are extreme relative to one another.

Let me give an example. We have two teams of players. Alice and Bob are playing against Xander and Yolanda. Repeatedly, Xander and Yolanda are each going to give one "bit" to Alice and Bob respectively. So Alice and Bob together receive 00, 01, 10 or 11, but neither knows the bit of the other. Alice and Bob's job is to each output one "bit" in such a way that their two output bits are different if their input bits are 00, 01, or 10; but equal if their input bits are 11. Thus in each of the first three cases they are to output 01 or 10 while in the last case they are to output 00 or 11.

They are not allowed to communicate in any way while making their decisions!

It's not difficult to see that if Xander and Yolanda choose their bits independently and completey at random (fair coin tosses), then whatever Alice and Bob do, they are sure to give a "wrong" answer at least 1 time in 4, in the long run. ie error rate 25%. On the other hand, if they have each got a quantum computer stored with entangled quantum systems, they can decrease their down to almost 15%.

One can give examples with more exciting gains, but they are more complicated; this is the easiest one to explain. All of the examples involve randomness, they involve differences between correlations. Richard Gill (talk) 07:29, 13 June 2012 (UTC)

Maybe we can use one thing that you said, "Any classical explanation would involved instantaneous communication over large distances." The person who has not encountered this stuff in the lab needs concrete details to hang onto while trying to absorb more abstract aspects of a presentation.P0M (talk) 19:48, 13 June 2012 (UTC)

I have added one sentence, and one citation, to the lead. I hope that this way of saying things will not be misleading or incorrect.P0M (talk) 20:48, 13 June 2012 (UTC)

Section "Wave function collapse"

Couple of points:

1. "Wave function collapse is a forced term for whatever happened when it becomes appropriate to replace ..."

What does "forced term" mean here?

2. "for instance in the CCD of an electronic camera" ... " In its place some physical change in the detection screen has appeared, e.g., an exposed spot in a sheet of photographic film."

Obviously, CCD cameras don't have film. Gwideman (talk) 12:17, 28 August 2012 (UTC)

Changed to remove ambiguity. P0M (talk) 16:58, 29 August 2012 (UTC)

Any comment on what "forced term" means? Thanks. Gwideman (talk) 22:57, 31 August 2012 (UTC)

I don't know any any more customary way to name the situation in which you are forced to use some awkward or otherwise unsuitable expression that you know is not very good. The counterpart of "forced term" is "whatever happened." Nobody has come up with a good explanation for what a photon "chooses" to do. It has x probability of showing up here, y probabily of showing up there.... all these probabilities, but it only shows up at one place and you can never tell which one it will be. The waveform is sort of everywhere at once, and the photon could show up with fairly high probability as many places, so what goes on? Physics doesn't tell us, at present anyway. We say this very widespread waveform just disappears and a photon shows up. What does it mean "disappears" or "collapses"? In my imagination it is like a soap bubble that gets picked by a needle and when that happens the bubble disappears and all that is left is a little globule of soapy water. The trouble is that we do not have the needle in reality. P0M (talk) 19:43, 25 April 2013 (UTC)

Would "forced expression" be better for you?P0M (talk) 19:48, 25 April 2013 (UTC)

Too close to a chronology?

I think that this structure of this article is currently too close to the historical development of quantum mechanics. I think that a proper introduction to QM should start with concepts. I think the proper starting point is the physical significance of the Planck constant. If we can just convince that read the the Planck constant is real and relevant and give them some notion of its implications, then they will have some sense of intuition of QM rather than just its historical chronology.--180.183.41.215 (talk) 00:23, 13 February 2013 (UTC)

Agreed- the current article's order and content does not serve its purpose. Mcplums (talk) 13:51, 9 May 2013 (UTC)

Partial agreement. Such a discussion may be appropriate, but not in the first paragraph - see Talk:Introduction to quantum mechanics#This article is far too complicated for the layperson. RockMagnetist (talk) 14:37, 9 May 2013 (UTC)

Come to think of it, this is a better history of quantum mechanics than History of quantum mechanics. Maybe the histories should be merged. If a more conceptual approach is taken, it should start with simple observations like the double-slit experiment. There may be a place for discussing the action, but much later in the article. RockMagnetist (talk) 15:00, 9 May 2013 (UTC)

I absolutely agree. As an "introduction" to quantum mechanics this article has some deficiencies - why should nontechnical people who just want the modern theory explained to them, have to wade through historical matters such as blackbody radiation and the obsolete Bohr theory of the atom? However it is a better historical overview than History of quantum mechanics. I suggest this article's content be merged into History of quantum mechanics and a new article be written from the ground up. --Chetvorno^TALK 16:42, 9 May 2013 (UTC)

Emission spectrum of a gas

The text here says that for a gas its emission spectrum consists of a few distinct colours identified by their wavelengths, but it's hard to understand how this is possible in real numbers. The text seems to suggest that wavelengths are actually represented not as reals, but as integers multiplied by a very small real constant, the same for all colours; is my understanding true? The emission lines on the picture look so thick... (Thank you for the article, of course!) - 89.110.8.148 (talk) 05:46, 25 April 2013 (UTC)

I just learned the reason for the physical width of the lines -- it's the uncertainty principle at work again. Some physical processes involve relative clarity on momentum and so produce relatively greater uncertainty on frequency, hence a broader band. Astronomers need to be very clear on light frequencies from different objects when they are looking at red-shifts and trying to determine how fast something is going away from us, so they like one particular hydrogen frequency that is characterized by a very sharp line.

The wavelength that we see is subject to Doppler effects. In the same reference frame, frequencies are stable within uncertainty limits as determined by the events producing the photons.

I'm not sure what you mean by "real numbers." "Real" as opposed to "imaginary numbers"?P0M (talk) 19:31, 25 April 2013 (UTC)

See The Quantum Challenge, by Greenstein and Zajonic, p. 59 for the sharp line calculations, etc.P0M (talk) 20:22, 25 April 2013 (UTC)

chopping block

I finally squeezed out some time to take out the intense math section. (See the complaints above.) I don't think I've left anything that needs to be drawn more tightly together. P0M (talk) 06:38, 6 June 2013 (UTC)

Dirac wave equation

I just realized that somebody put in a hairy equation with no indication of what all the letters and symbols mean.

c is the speed of light

αk and β are 4 × 4 matrices

p is momentum so what is p with hat?

m is the rest mass of the electron.

Why somebody would put in such an equation in the first place beats me. Should we just delete this section?P0M (talk) 07:51, 6 June 2013 (UTC)

I think the text in the section is fine, but I have removed the boxed equation. Adding a full explanation would take up too much space and is not appropriate to an introduction article, showing the equation without an explanation is pointless, and details are in the linked Dirac equation article anyway. Gandalf61 (talk) 08:37, 6 June 2013 (UTC)

I agree with removing the equation. I think the text is OK for the general reader The pargraph has a nice surprise ending, "Dirac's equations sometimes yielded a negative value for energy, for which he proposed a novel solution: he posited the existence of an antielectron and of a dynamical vacuum." However, I am not sure we need "dynamical vacuum" in that sentence, or "the many-particle" before the "quantum field theory" wiki-link. I don't think the general reader will understand what is a "dynamical vacuum" and why the adjective-phrase "the many-particle" is there. I suggest removing "dynamical vacuum" and "the many particle". However leave in "quantum field theory" as a wiki-link. ----Steve Quinn (talk) 21:22, 6 June 2013 (UTC)

Sounds good to me.P0M (talk) 23:22, 6 June 2013 (UTC)

Diffraction: Wrongly labeled/identified picture

The picture claimed to show a double-slit diffraction pattern shows clearly a single-slit diffraction pattern. This misidentification is already present in the material on Wikimedia.59.189.171.128 (talk) 05:02, 17 November 2013 (UTC)

I'm not sure I entirely agree with your diagnosis (I never liked the old picture but it did seem to me to show variation on more than one length scale) but with a bit of clicking through to related articles I found a much better image in the Double-slit experiment article, so I have replaced the problematic image. Djr32 (talk) 12:33, 17 November 2013 (UTC)

I just noticed the claim that by 59.189.171.128. I made both pictures using the same double-slit device (blocking one slit for the simple diffraction pattern). Some people might claim that the single-slit picture is wrong because it shows a couple of side bands. A picture made about 70 years ago shows a main band and three pairs of side bands. (Sears, Optice, opposite p. 222) MIT had much better equipment than I had, but their best diffraction image doesn't look a bit like my double-slit image. For what can be done with a "hardened laser" and a single pinhole (just verified the details with Petrov Victor) take a look at this:

Petrov Victor