User talk:Sbyrnes321/Archives/2018

Your help desk question

Did you get an answer to your question about template syntax? No one responded at the Help Desk. It's not something I would know about, but it sounds appropriate for WP:VPT.— Vchimpanzee • talk • contributions • 22:34, 17 January 2018 (UTC)

No, I didn't get an answer, thanks for the suggestion. :-D --Steve (talk) 00:43, 18 January 2018 (UTC)

List of unsolved problems in physics (Talkpage)

There is currently a discussion at Wikipedia:Administrators' noticeboard/Incidents regarding an issue with which you may have been involved. Arianewiki1 (talk) 07:53, 1 February 2018 (UTC)

Effective mass (solid-state physics)

The template to which you previously linked in this article is at the top of the now-linked electronic band structure article (it being the title article). I'm not sure if you still wanted to reference it. 87.254.80.110 (talk) 02:53, 11 April 2018 (UTC)

On further consideration, I guess it's not a big deal either way, you're welcome to set it up however you see fit and it's fine with me. :-D --Steve (talk) 16:31, 11 April 2018 (UTC)

Your last edit to the article "Fresnel equations"

There seem to be four problems with your edit.

1. The Poynting vector has the units of intensity, not power.
2. In the definition of that intensity, "per unit area" refers to the area of a surface normal to the Poynting vector, not the area of the interface between two media.
3. The distinction that needs to be drawn is between the normal component and the magnitude of the Poynting vector.
4. Two occurrences of the term "intensity vectors" remain in the paragraph. There may be a better expression than "intensity vector" that the reader would understand at this point, but I'm pretty sure that "power flow vector" isn't it.

Working on the theory that you knew what you meant to say, but didn't quite manage to say it, I ask you to make a second attempt.

— Gavin R Putland (talk) 14:32, 24 April 2018 (UTC).

Well, the Poynting vector has units of watts/m². What do we call that? I would personally feel pretty comfortable calling it a "power" (...if the context of areal density was sufficiently clear), or "power density" in other cases. I wouldn't normally call it "intensity", which I think of as either J/m³ or W/steradian or various other things depending on context. The Poynting vector article calls it "directional energy flux" at the top, and "power flow" in a different part of the article.

I had not previously heard of "intensity" being used as a vector quantity, and google books suggests that this usage is pretty rare in electromagnetism, though not unheard of (...and reasonably common for acoustic waves). I've always seen intensity used as a scalar, and the words "intensity vector" immediately struck me as a mistake, motivating me to edit. (And sorry I missed other instances.) Well, I guess on reflection that that was an overreaction, and also that "power flow vector" was little improvement if any. OK, well, I now vote for sticking with "Poynting vector", the only term with essentially zero risk of being misunderstood, out of the possibilities mentioned above.

If you want R+T=1, then you better define T and R in relation to "the component of the Poynting vector which is normal to the material interface". Do you agree with that? If we use that kind of language, then the "per unit area" phrase should not come up in the first place, I think.

Thanks, and you're doing a fine job editing that article, --Steve (talk) 16:55, 24 April 2018 (UTC)

@Sbyrnes321: Thank you. Since your reply, the article "Fresnel equations", including your paragraph, has received much attention from User:Interferometrist, who is a bit more adventurous than I am, and may yet incur the displeasure of User:Srleffler for that reason. So the following is probably moot, but...

Interferometrist prefers "irradiance" to "intensity". And yes, it did belatedly occur to me that one could speak of irradiance or intensity as the (scalar) component of the Poynting vector in a given direction.

Yes, I agree concerning "the component of the Poynting vector which is normal to the material interface". Fortunately, so does Interferometrist.

FYI, I recently expanded the article "Fresnel rhomb". Following a suggestion from Interferometrist (see talk:Fresnel rhomb), I was planning to move some of that material (with modifications) to a "Derivation" section in the article "Fresnel equations", and some of it to the article "Total internal reflection". But perhaps I should wait for some of the dust to settle.

— Gavin R Putland (talk) 06:25, 25 April 2018 (UTC).

It's all looking fine to me, thanks again.

As for putting in a derivation, it can be a good thing but can easily become overwhelming, making the article potentially intimidating for novices and potentially hard-to-navigate for everyone. My friendly advice is: (1) Think of it more like "outline of derivation", not "derivation", i.e. the high-level inputs, assumptions, and procedures, with the details left to references. For example, My paper section 3, 2nd paragraph is more-or-less the extent of what I personally would put into a derivation section for Fresnel equations, though reasonable people can differ on how much more detail is appropriate. (2) Think hard about whether to use a show/hide box, or maybe even a separate article Derivation of Fresnel equations.

For example, the sections Faraday's law of induction#Proof of Faraday's law or Angular momentum operator#Derivation using ladder operators are examples of mine that I think are good illustrations of both (1) and (2). :-D --Steve (talk) 14:05, 25 April 2018 (UTC)

I disagree with you revert at Fourier transform infrared spectroscopy in Conceptual introduction

I really understand what you mean but the problem is that viewing a Michelson interferometer as a wavelength filter is not right at all. In fact, that is how a spectrometer works. More over the usual mistake about the Michelson interferometer is to compare it to a spectrometer which it is not. You must know that all wavelengths are passing through a Michelson interferometer and that what you see on one of the output ports is the sum of the interference pattern of each wavelength for a certain optical path difference. I know that the way a Michelson interferometer works is not easy to understand but it may be better to avoid false description (I am sorry for my poor english). This is a description taken from Michelson interferometer : "The Michelson interferometer's detector in effect monitors all wavelengths simultaneously throughout the entire measurement, increasing the integration time and the total number of photons monitored"

Oh, I already wrote a message at Talk:Fourier_transform_infrared_spectroscopy#Conceptual_introduction ... I will copy this message and we can keep talking there :-)

atan2-pic

Thank you for trimming the lead section, I hope my tweaking does not annoy you. In any case, I am bold enough to ask you to perhaps trim the new pic on the left and the bottom, but in any case to repair the truncation of the coordinates. Respectfully, Purgy (talk) 12:09, 1 July 2018 (UTC)

I beg pardon, the truncation is at least in part caused by my screen scaling (110%). Purgy (talk) 13:06, 1 July 2018 (UTC)

Great! I'm not annoyed, and ditto since I am tweaking too. :-)

I like having the origin at the center of the figure to better evoke "Euclidean plane" associations / memories and not evoke "positive x vs positive y graph" associations / memories, if you know what I mean.

Just to be clear, are you saying that there's no truncation problem after all, or is there still something to fix? --Steve (talk) 14:18, 1 July 2018 (UTC)

Sorry, I do not know where the truncation problem with the pic resides. In my browser? When I newly open the atan2 page the pic renders fine(!), if I then open the History of the page and from there any comparision, then the right side of the pic is truncated roughly at the half of the "x" in the argument list of the atan(y,x) there. Increasing the scaling on my screen from 110% upwards does not change the rendered range, but decreasing the scale to 100% lets the pic appear again in full beauty. I have seen such effects already with specific pixel specs, but this here has the thumb-default. I am rather clueless.

My "perhaps" anticipated already your intention to have the origin in the center. Take my suggestion as my horror vacui.

I corrected the intervals of the codomain, returned to the capital Arctan to emphasize the principal branch also in the notation, and removed some vagueness.

Finally, let me, please, deposit my strong aversion in using myself anything like "orientation" within texts for non-experts. I perceive this concept to be a very delicate topic, seducing to be considered as easily and intuitively accessible, but to my perception this is hard to formulate, and hardly understood in a resilient way (fully alternating volume form???). I do not suffer too much from reading e.g. "ccw", but I avoid anything like right-hand-rules for myself as much as possible. Happy pseudoscalars. Purgy (talk) 19:22, 1 July 2018 (UTC)

I'm looking into the image issue at village pump technical; I reproduced it in wikipedia beta android app.

Thank you for correcting my embarrassing typos :-D

I had never before seen anyone use a capitalization-based distinction (atan vs Atan) between multi-valued and principal branch definitions. How common is that, and in what subfields / contexts?

If I look at the sentences:

(A) The angles are signed, with counterclockwise angles being positive, and clockwise being negative.

(B) Points in the upper half-plane (y ≥ 0) deliver values in [0, π], points with y < 0 return values from (-π, 0).

I personally am not be capable of understanding (B) except by mentally translating it into (A), and likewise I personally would not be able to speak the sentence (B) except by starting with (A) and working through the cases. Is this not the case for you? Are you the opposite—where if you read (A) you find it nonsensical, and then you spend 10 seconds to mentally translate it into the form (B), and then say, "Oh, now I get it!"? I mean, I appreciate that different minds work in different ways, but I would find that awfully surprising. You'd have to be a very non-visual thinker, I reckon, to find (B) more understandable and memorable than (A). Are you?

And I'm still not seeing any way to start with (A) and wind up misunderstanding anything later on. Yes I am familiar with pseudovectors and pseudoscalars and much else. I have never seen anything that makes me think that envisioning signed angles like (A) is a bad idea...

Thanks again! --00:59, 2 July 2018 (UTC)

Thanks for taking care about this technicality (would you mind to provide a link, please?), and, of course, you are very welcome. Re the capitalizing I have to admit that I am a bad WP-n: I ruthlessly spread things, which I have seen in my life in academic textbooks, even when I have no citable bibliographic data at hand, and this even more, if I saw it in WP (complex Log, at least), not introduced by myself. For my excuse: I do not edit-war for these things, not even when I am firmly convinced about their usefulness and formal applicability.

Enjoying a chat about orientation: I consider the angles, enclosed by +X and the rays through (1,1) and (1,-1) to have the same size, but their return values of atan2 to have signs according to the sign of y. Personally, I intentionally prefer to dispose of the intuitive notion signed angle a priori, but rather would introduce it for this special case based on atan2. For this very reason I talk about "angles between", and not about "angles from ... to" (cf. definition of angles in linear algebra/Clifford algebra).

As alluded to above, I am not on a crusade against using the concept of "orientation", but I believe that this is a concept involving far more pitfalls than obvious at first glance. Orientation in 1D is just a sign, but already here the alternative solution, the opposite assignment, is swept under the rug for its minuscule importance. In 2D, including the complex, there are again two equivalence classes (i is ONE square root of -1, there are TWO quotient algebrae, ...) and, for isomorphism, only one is talked about. As I see it, the trouble increases with higher dimensions, perhaps not really in math, but in intuition. The mentioned right-hand-rule from 3D is still manageable for people being aware of screwing in left and right (perhaps not at the outer wings ;) ), but here already the end of the cross-product lingers, to be substituted by some more elaborate construct, satisfying math needs. How about "ccw rotation in 4D"?

I am contemplating whether relying on a not fully understood concept (orientation) in some luckily accessible special case (angles in flat 2D) pays the rent, or should rather be avoided. In any case I fully agree that your preferred access via signed angles is intuitive, popular, and, of course, not wrong.

I hope that I could mediate some understanding for my POV. Cheers, Purgy (talk) 09:03, 2 July 2018 (UTC)

Discussion was here, and I think the image issue is fixed now, thanks again for pointing it out. --Steve (talk) 03:05, 3 July 2018 (UTC)

Question: Your latest edit suggests that Arg has range 0 to 2pi, but that Atan2 has range -pi to pi, so you need to translate between them by sometimes adding or subtracting 2pi. Wouldn't it be simpler to say that Arg has range -pi to pi, and Atan2 has range -pi to pi, and then Arg and Atan2 have a direct and very simple relation? The arg article currently says that -pi to pi is the "usual" definition of Arg's principal branch, and that 0 to 2pi is less common but not unheard of. That is also consistent with my experience in physics and engineering, and with the implementations of Arg in all the programming languages that I regularly use, i.e. that it goes -pi to pi. Or sorry if I'm misunderstanding something. :-D --Steve (talk) 03:17, 3 July 2018 (UTC)

If you don't object to signed angles in this particular case, that's good enough for me, and there's no need to discuss further, but it's fun so I will anyway. :-D

I guess I would suggest to not forget that, as a matter of pedagogy, most smart people can take concrete ideas and special cases and pictures and build an abstract concept on top of them, but only utter geniuses can understand an abstract concept starting from nothing whatsoever. Maybe not even utter geniuses, if you take a longer view of what concrete ideas and special cases and pictures the utter geniuses might be drawing on.

So, I read a good textbook in high school that said "What if someone sneaks in at night and replaced i with -i in every line of every math textbook on earth?" After pondering that I eventually became very comfortable saying "obviously cos(x*) = (cos x)*" and so on, and when I later learned about quotient algebras and Galois theory etc. it built on that foundation. Later on, a physics textbook had an analogous troublemaker sneaking in and replacing "right-hand rule" with "left-hand rule" and vice-versa everywhere in physics textbooks. I pondered that and was enlightened, and a decade later I was helping all my friends manipulate pseudotensors in their grad school homework. Again, in both these examples, I feel like I started with something simple and concrete (complex numbers), then learned nuances and manipulations of the concrete thing (what if we swap i with -i?) to get something richer, learned and manipulated more examples, built up abstractions, related them to symbolic manipulations, saw which aspects don't generalize, and on and on. It's a whole process, there's no way around that, but the concrete simple visual starting points, when we're lucky enough to have them available, are essential foundations to be cherished. :-D --Steve (talk) 03:50, 3 July 2018 (UTC)

I really cherish your view on fun!

• Thanks for repairing and for the technicalities, too. I love to learn how much we rely on automatic selection from abundant alternatives/rerendering, so that less skeptical suppose we approach AI. BTW, I should have suspected the rendering of fonts myself, and, as another BTW, let me give you an ancient Chinese curse: "I tell you about "kerning", so you never again will enjoy any printed writing." >ref< XKCD?>/ref< (e.g. LONGINES) :D
• I think I remedied the atan2 re your question. Well, I am used to [0,2pi) as Arg-standard, and even the first pic in this article may be seen as suggesting it (by signed angles, of course :) ), and, as said, I am a bad WP-n in relying on self-acquired disinformation, instead of looking for eternal truth in the Sources, qualified as reliable by holy consensus (Flies eat shit - billions can't err; Fake news - so sad; .... :| ). Continuing with BTWs, I do not consider writing Atan2, because I take atan2 as a function $\operatorname {atan2} :\;\mathbb {R} ^{2}\smallsetminus \{(0,0\}\to (-\pi ,\pi ]$, discontinuous along $\{(x,0):x<0\},$ not supplying any possibility for selecting a non-exhaustive principal branch.
• When mulling over your question I noticed parts in the arg-article, which are related to the information I tagged as "cn" and removed from the atan2 article. I am severely disinterested in all things numerical, and I think that the algebraically identical expressions for the Arctan-arguments do not suggest themselves a different behaviour in numerical stability (blow-ups?). The removed versions in atan2 were definitely rubbish to my judgement. Any periodicity must be introduced by wanton polar coverings (see pics in atan2). In contrast to this, I believe that the rationale for "2arctan" saving cases in the atan2-definition, which I included there, would deserve mentioning. After all, any principal branch of arctan is just the half of the atan2 codomain.

See you. Purgy (talk) 10:22, 3 July 2018 (UTC)

Sounds good to me! :-D --Steve (talk) 01:11, 4 July 2018 (UTC)

I thought a while about your (A) and (B) and came up with this. I do use both metaphors, the half planes mostly when thinking about collections of points (and angles as magnitudes located in half planes), and the rays, rotating in some sense, mostly when thinking about one point. And here comes my hammer, why I think that half planes are the access, that is way much easier to formalize:

How do you establish a signed angle as a scalar field (vs. a pseudoscalar)?

I do not know which one is the more practicable, but I am quite sure that half planes are simpler than both. I also do not know about a simpler introduction of signed angles that holds across arbitrarily investigative minds. I hope I could convey my reservation to signed angles without hurting any feelings. I do not editorially object to signed angles, but uphold my efforts to avoid them at lower levels for the time being. Cheers. Purgy (talk) 07:50, 4 July 2018 (UTC)

Density matrix in quantum chemistry

Hi! I wanted to follow up on your revert of my edit to density matrix. I agree that my addition was superficial and inaccurate, but I do think there should be some mention there of the use of the idea in quantum chemistry. In the Hartree-Fock method and molecular orbital theory, a "density matrix" is used the numerics to hold the products of basis function coefficients for molecular orbital pairs. This can then be used to compute electron density, which I believe is basically a 1-electron reduced density matrix (other spatial coordinates integrated out). In other cases two electron RDM are used. So it is a pure state, but the coefficients are unknown and vary during the computation. I wonder if you have suggestions as to how to incorporate this link into the current density matrix article? Karol (talk) 10:50, 5 July 2018 (UTC)

Hi Karol, thanks for the message. I'm happy to chat about this. I'm afraid my molecular orbital theory is a bit rusty, and the Hartree-Fock and molecular orbital theory wiki articles don't mention the density matrix at all. Can you suggest any textbooks / articles / lecture notes elaborating on what you just said? Maybe I'll understand better after reading something like that. But I'll elaborate anyway based on my current understanding.

Practically everything in quantum mechanics can (and often is) calculated using density matrices. Density matrices are an alternative formalism to pure states, so they'll show up wherever pure states do. If a person is calculating anything whatsoever about atoms, or molecules, or particle beams, or atom-photon interactions, or quantum cryptography, or quantum computers, or whatever, I would not be remotely surprised to see them to be using density matrices rather than pure states for some or all of that calculation; in fact I would be quite surprised to see them not use density matrices at least occasionally.

Sure, you can write in the Density matrix article that density matrices are involved in electronic structure models in quantum chemistry. Just like you can write in the Quantum state article that quantum states are involved in electronic structure models in quantum chemistry. And you can write in the Angular momentum operator article that angular momentum operators are involved in electronic structure models in quantum chemistry. And on and on. Do you see what I mean? Yes of course they come up, these are some of the most basic tools in quantum mechanics and obviously anyone doing quantum mechanics is going to use them. So I'm not sure I see why their involvement in quantum chemistry electronic structure models should be called out specifically, unless it's leading up to a more specific and important point. Or sorry again if I'm misunderstanding :-D --Steve (talk) 13:21, 5 July 2018 (UTC)

Hi Steve, thanks for the response. You make a good point and I wasn't thinking that way when I made the edit. There are tons of textbooks, but a concise definition of what I was referring to can be found in equation (69) and section D of this chapter. I think what spurred me was that density functional theory is linked to from the "see also" section of density matrix, and that has a strong presence in quantum chemistry. It does seem other fields where density matrices come up are linked to (like decoherence theory), and physics pages often have sections listing applications, but in the end I guess it's always some sort of balance between relevance and verbosity. Anyway, no need to go into this further. Karol (talk) 16:18, 5 July 2018 (UTC)

An "Applications" section is a fine idea. It could start by saying that you can use density matrices in practically any QM calculation if you want, but they're especially helpful and common in situations like ... and then listing major examples. Also, thanks for the links, I look forward to reading them. --Steve (talk) 16:48, 6 July 2018 (UTC)

I had a go at adding an Example Applications section. My description of what density matrices are doing there is maybe a little bit different than what you wrote above, but it's based on your link and I'm moderately confident that I understood the PDF. Do you agree with my description? I now see that I was wrong, it is in fact a different use of density matrices than any of the others in the article—instead of a statistical ensemble of various different pure states, you have various different pure states which are all simultaneously occupied by different electrons! :-D --Steve (talk) 18:39, 8 July 2018 (UTC)

Thanks! I think that's an excellent start. And yes, you're right that a key difference is that it's being used for multiple particles described by uncorrelated wavefunctions. There's also some related bits in electronic correlation, which I see you've edited in the past. See you around! Karol (talk) 12:11, 10 July 2018 (UTC)

See you! BTW I haven't really edited electronic correlation, I only fixed a broken link once 10 years ago. --Steve (talk) 16:02, 10 July 2018 (UTC)

"Quantum violation of local realism"

I was late to the move discussion at Talk:Quantum nonlocality (didn't know it was happening until after it closed). I like "Quantum violation of local realism" as a title much more than "Quantum nonlocality", and I even prefer it a little over plain "local realism", since I think "quantum" really needs to be in there somewhere. I'd be happy to support the move when you officially propose it. XOR'easter (talk) 13:45, 13 July 2018 (UTC)

Thanks! --Steve (talk) 23:51, 13 July 2018 (UTC)

Could you make another couple of figures for atan2?

Hi Steve,

You made this nice clean drawing. Could you do two more, but with the point in the second quadrant and other with the point in the first quadrant and its reflection in the third quadrant.

I am going to try to really clean up the intro to that article and the definition. I s'pose I could make drawings but I want them to look consistent and clean. I dunno that mine will be as good as yours. Bestest, 50.47.108.245 (talk) 19:08, 26 July 2018 (UTC)

Sorry, I'm too busy right now. --Steve (talk) 00:05, 27 July 2018 (UTC)

Quiz Question

A quiz just claimed that copper was the 3rd most conductive element. I was at Electrical resistivity and conductivity and it’s 2nd, but the list doesn’t state it’s comprehensive - though I expect the Top5 are. I can’t think of another element to check. Can you tell me? I would’ve asked on Talk, but I don’t know if the article needs a “definite” Top10?

PS. Nifty images on the top page. There’s really something magical about half-lives: I reckon the atoms “talk” to each other somehow. MBG02 (talk) 04:08, 8 September 2018 (UTC)

I don't know, sorry. --Steve (talk) 14:25, 8 September 2018 (UTC)

Resistivity article

I know you deleted your note on the talk page, but you were totally right about the over-technicality of presenting the most complex definition first. I got wrapped up in the fact the section labeled "general definition" was actually a simplification. Thanks for being frank. Forbes72 (talk) 11:09, 16 September 2018 (UTC)

No problem, glad we're on the same page on that! :-D --Steve (talk) 22:41, 16 September 2018 (UTC)