phys.libretexts.org/Courses/University_of_California_Davis/UCD%3A_Physics_9HE_-_Modern_Physics/06%3A_Emission_and_Absorption_of_Photons/6.2%3A_Selection_Rules_and_Transition_Times has some very good mentions:
So it appears that if a hydrogen atom emits a photon, it not only has to transition between two states whose energy difference matches the energy of the photon, but it is restricted in other ways as well, if its mode of radiation is to be dipole. For example, a hydrogen atom in its 3p state must drop to either the n=1 or n=2 energy level, to make the energy available to the photon. The n=2 energy level is 4-fold degenerate, and including the single n=1 state, the atom has five different states to which it can transition. But three of the states in the n=2 energy level have l=1 (the 2p states), so transitioning to these states does not involve a change in the angular momentum quantum number, and the dipole mode is not available.So what's the big deal? Why doesn't the hydrogen atom just use a quadrupole or higher-order mode for this transition? It can, but the characteristic time for the dipole mode is so much shorter than that for the higher-order modes, that by the time the atom gets around to transitioning through a higher-order mode, it has usually already done so via dipole. All of this is statistical, of course, meaning that in a large collection of hydrogen atoms, many different modes of transitions will occur, but the vast majority of these will be dipole.It turns out that examining details of these restrictions introduces a couple more. These come about from the conservation of angular momentum. It turns out that photons have an intrinsic angular momentum (spin) magnitude of , which means whenever a photon (emitted or absorbed) causes a transition in a hydrogen atom, the value of l must change (up or down) by exactly 1. This in turn restricts the changes that can occur to the magnetic quantum number: can change by no more than 1 (it can stay the same). We have dubbed these transition restrictions selection rules, which we summarize as:
Kind of a synonym for hydrogen emission spectrum not very clear if fine structure is considered by this term or not.
A line set for hydrogen spectral line.
Non-anomalous: number of splits matches predictions of the Schrödinger equation about the number of possible states with a given angular momentum. TODO does it make numerical predictions?
www.pas.rochester.edu/~blackman/ast104/zeeman-split.html contains the hello world that everyone should know: 2p splits into 3 energy levels, so you see 3 spectral lines from 1s to 2p rather than just one.
It also mentions that polarization effects become visible from this: each line is polarized in a different way. TODO more details as in an experiment to observe this.
Well explained at: Video "Quantum Mechanics 7a - Angular Momentum I by ViaScience (2013)".
Experimental physics - IV: 22 - Zeeman effect by Lehrportal Uni Gottingen (2020)
Source. This one is decent. Uses a cadmium lamp and an etalon on an optical table. They see a more or less clear 3-split in a circular interference pattern,
They filter out all but the transition of interest.
- youtu.be/ZmObNFAqkBE?t=165 passes the lines through a polarizer, which shows how orbital angular momentum is carried by photon polarization
- youtu.be/ZmObNFAqkBE?t=370 says they are looking at 1D2 to 1P1 changes.
Exist because double bonds don't rotate freely. Have different properties of course, unlike enantiomer.
Key exmaple: d and L amino acids. Enantiomers have identical physico-chemical properties. But their biological roles can be very different, because an enzyme might only be able to act on one of them.
Nothing personal, just Ciro Santilli strongly disagrees with the moderation philosophies of these users.
One particular type of user Ciro particularly dislikes are those who do more moderation than content. Ciro finds it very hard to understand why some people spend so much time moderating. Maybe that's how politicians exist, some people just like that kind of activity.
The moderators tend to have lower intermediate rep. They spend too much time moderating and too little time coding.
- Users who are publicly against the ability to criticize the character of politicians, shown after "I think Trump is disgusting as a person" was removed from Ciro's profile: cirosantilli.com/china-dictatorship/stack-overflow-forbids-criticizing-the-character-of-genocidal-political-leaders-like-xi-jinping
- Journeyman Geek:
- is also against political speech against the CCP in Stack Overflow
- deletionism: single handedly deletes opposing answers without giving any explanation TODO example;
- closurism: superuser.com/questions/248517/show-keys-pressed-in-linux
- Journeyman Geek:
- Yvette Colomb deleted a few of Ciro's answers, related: Ciro Santilli's Stack Overflow suspension for vote fraud script 2019.
- chrisF: envorces Stack Overflow no duplicate answers policy: stackoverflow.com/questions/9242135/how-to-force-rsync-to-create-destination-folder/72178249#72178249
- meta.stackexchange.com/users/361484/luuklag meta.stackexchange.com/questions/18614/style-guide-for-questions-and-answers/326746?noredirect=1#comment1283471_326746Fair comment, but do you need to flag before comment, and downvote? That answer was clearly a labour of love, on a subject that will never ever make anyone any money (markup style). Too much meta rep, too little programming rep.
Flagged as spam, there obviously is affiliation between the first link and the poster, which is not disclaimed.
- Cody Gray
- Charcoal bot people: charcoal-se.org/
- askubuntu.com/users/10616/thomas-ward Thomas Ward deletionism:
- e.g. convert here's a bug report answer to comment: askubuntu.com/questions/1464992/cant-drag-clip-to-timeline-in-kdenlive-in-ubuntu-23-04/1469359#comment2575312_1464992
- askubuntu.com/questions/524242/how-to-find-out-which-nvidia-gpu-i-have/1469351#1469351 deleted a perfectly valid "Settings -> Details -> About" GUI answer
- Machavity stackoverflow.com/users/2370483/machavity.Deletionism: stackoverflow.com/questions/13714454/specifying-and-saving-a-figure-with-exact-size-in-pixels/64632093#64632093. Edit: reverted.
- askubuntu.com/users/10616/thomas-ward Thomas Ward deletionism:
- Dharman
- security.stackexchange.com/users/6253/schroeder: deletionism security.stackexchange.com/questions/231637/signal-contact-people-or-have-people-contact-me-without-revealing-phone-numbe/245665?noredirect=1#comment591690_245665
TBD:
- webapps.meta.stackexchange.com/users/88163/rubén: possible deletionist webapps.stackexchange.com/questions/149933/why-does-the-archive-org-of-most-youtube-videos-fail-with-sorry-the-wayback-mac, but: might reconsider: webapps.meta.stackexchange.com/questions/4502/why-were-not-customer-support-for-your-favorite-company/4503?noredirect=1#comment5167_4503. Didn't: archive.ph/wip/EyZS7
Not so strong, but bad experience:
- Zac67 networkengineering.stackexchange.com/users/36720/zac67: you cannot mention any specific device, even if it is for illustrationa purposes...That's like, the opposite of reproducibility...
Deleted answers are dumped at: github.com/cirosantilli/cirosantilli.github.io/issues
Basic component in spintronics, used in both giant magnetoresistance
Leads to the Dirac equation.
The Dirac equation, OK, is a partial differential equation, so we can easily understand its definition with basic calculus. We may not be able to solve it efficiently, but at least we understand it.
But what the heck is the mathematical model for a quantum field theory? TODO someone was saying it is equivalent to an infinite set of PDEs somehow. Investigate. Related:
The path integral formulation might actually be the most understandable formulation, as shown at Richard Feynman Quantum Electrodynamics Lecture at University of Auckland (1979).
Quantum electrodynamics by Lifshitz et al. 2nd edition (1982) chapter 1. "The uncertainty principle in the relativistic case" contains an interesting idea:
The foregoing discussion suggests that the theory will not consider the time dependence of particle interaction processes. It will show that in these processes there are no characteristics precisely definable (even within the usual limitations of quantum mechanics); the description of such a process as occurring in the course of time is therefore just as unreal as the classical paths are in non-relativistic quantum mechanics. The only observable quantities are the properties (momenta,
polarizations) of free particles: the initial particles which come into interaction, and the final particles which result from the process.
Pinned article: Introduction to the OurBigBook Project
Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
Intro to OurBigBook
. Source. We have two killer features:
- topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculusArticles of different users are sorted by upvote within each article page. This feature is a bit like:
- a Wikipedia where each user can have their own version of each article
- a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.Figure 1. Screenshot of the "Derivative" topic page. View it live at: ourbigbook.com/go/topic/derivativeVideo 2. OurBigBook Web topics demo. Source. - local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
- to OurBigBook.com to get awesome multi-user features like topics and likes
- as HTML files to a static website, which you can host yourself for free on many external providers like GitHub Pages, and remain in full control
Figure 3. Visual Studio Code extension installation.Figure 4. Visual Studio Code extension tree navigation.Figure 5. Web editor. You can also edit articles on the Web editor without installing anything locally.Video 3. Edit locally and publish demo. Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.Video 4. OurBigBook Visual Studio Code extension editing and navigation demo. Source. - Infinitely deep tables of contents:
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact





