Quantum number by Ciro Santilli 40 Updated 2025-07-16
However, it very cool that they are actually discovered before the Schrödinger equation, and are present in the Bohr model (principal quantum number) and the Bohr-Sommerfeld model (azimuthal quantum number and magnetic quantum number) of the atom. This must be because they observed direct effects of those numbers in some experiments. TODO which experiments.
E.g. The Quantum Story by Jim Baggott (2011) page 34 mentions:
As the various lines in the spectrum were identified with different quantum jumps between different orbits, it was soon discovered that not all the possible jumps were appearing. Some lines were missing. For some reason certain jumps were forbidden. An elaborate scheme of ‘selection rules’ was established by Bohr and Sommerfeld to account for those jumps that were allowed and those that were forbidden.
This refers to forbidden mechanism. TODO concrete example, ideally the first one to be noticed. How can you notice this if the energy depends only on the principal quantum number?
Video 1.
Quantum Numbers, Atomic Orbitals, and Electron configurations by Professor Dave Explains (2015)
Source. He does not say the key words "Eigenvalues of the Schrödinger equation" (Which solve it), but the summary of results is good enough.
Determines energy. This comes out directly from the resolution of the Schrödinger equation solution for the hydrogen atom where we have to set some arbitrary values of energy by separation of variables just like we have to set some arbitrary numbers when solving partial differential equations with the Fourier series. We then just happen to see that only certain integer values are possible to satisfy the equations.
The direction however is not specified by this number.
To determine the quantum angular momentum, we need the magnetic quantum number, which then selects which orbital exactly we are talking about.
Fixed quantum angular momentum in a given direction.
Can range between .
E.g. consider gallium which is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p1:
The z component of the quantum angular momentum is simply:
so e.g. again for gallium:
Note that this direction is arbitrary, since for a fixed azimuthal quantum number (and therefore fixed total angular momentum), we can only know one direction for sure. is normally used by convention.
Spectroscopic notation by Ciro Santilli 40 Updated 2025-07-16
This notation is cool as it gives the spin quantum number, which is important e.g. when talking about hyperfine structure.
But it is a bit crap that the spin is not given simply as but rather mixes up both the azimuthal quantum number and spin. What is the reason?
Video 1.
Spectroscopic notation by Andre K (2014)
Source.
TODO. Can't find it easily. Anyone?
This is closely linked to the Pauli exclusion principle.
What does a particle even mean, right? Especially in quantum field theory, where two electrons are just vibrations of a single electron field.
Another issue is that if we consider magnetism, things only make sense if we add special relativity, since Maxwell's equations require special relativity, so a non approximate solution for this will necessarily require full quantum electrodynamics.
As mentioned at lecture 1 youtube.com/watch?video=H3AFzbrqH68&t=555, relativistic quantum mechanical theories like the Dirac equation and Klein-Gordon equation make no sense for a "single particle": they must imply that particles can pop in out of existence.
Bibliography:
KCNK2, also known as K2P2.1 or TREK-1, is a gene that encodes for a member of the two-pore domain potassium channel family. This channel plays a significant role in regulating the electrical activity of neurons and other cells by allowing potassium ions to flow across the cell membrane, which is crucial for maintaining the resting membrane potential and contributing to the repolarization phase of action potentials.
The Ainu creation myth is part of the indigenous Ainu culture of Japan, particularly associated with the northern regions such as Hokkaido. The Ainu have a rich oral tradition, and their mythological stories illustrate their understanding of the world, nature, and their relationship with the divine. In Ainu creation myths, the world is often described as being formed from the sea. One notable myth starts with the god of the sea, who created the first land.
The Aircraft Reactor Experiment (ARE) was a project developed by the United States in the late 1950s to explore the feasibility of using nuclear power for aircraft propulsion. Conducted by the Los Alamos National Laboratory and the Atomic Energy Commission, the primary objective of the experiment was to determine if a nuclear reactor could be designed for use in an aircraft engine and if it could provide sufficient thrust and power for sustained flight.
Visual math HTML book by Ciro Santilli 40 Updated 2025-07-16
When you see some tagged examples, you will immediately know what this means.
An intransitive game is a type of game or sport where the relationship between the players or strategies does not follow a simple transitive order. In a transitive game, if Player A defeats Player B and Player B defeats Player C, then Player A is expected to defeat Player C. However, in an intransitive game, this pattern does not hold; the outcomes can be cyclical or non-linear.
Gelenbevi Ismail Efendi, also known as Gelenbevi Ismail or simply Ismail Efendi, was a prominent figure in the late Ottoman Empire, particularly noted for his contributions to the field of education, especially in relation to modernizing and reforming the educational system in Turkey. He is particularly associated with the title of "Gelenbevi," which refers to his origins in the town of Gelenbe in present-day Turkey.
The Atiyah conjecture on configurations is a mathematical statement concerning the representation theory of algebraic structures, specifically related to bundles of vector spaces over topological spaces. It is named after the British mathematician Michael Atiyah, who has made significant contributions to several areas of mathematics, including topology, geometry, and mathematical physics.

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!
We have two killer features:
  1. 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-calculus
    Articles 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/derivative
  2. 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.
    Figure 2.
    You can publish local OurBigBook lightweight markup files to either https://OurBigBook.com or as a static website
    .
    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.
  3. https://raw.githubusercontent.com/ourbigbook/ourbigbook-media/master/feature/x/hilbert-space-arrow.png
  4. Infinitely deep tables of contents:
    Figure 6.
    Dynamic article tree with infinitely deep table of contents
    .
    Descendant pages can also show up as toplevel e.g.: ourbigbook.com/cirosantilli/chordate-subclade
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