Local symmetry by Ciro Santilli 37 Updated 2025-07-16
Appears to be a synonym for: gauge symmetry.
A local symmetry is a transformation that you apply a different transformation for each point, instead of a single transformation for every point.
TODO what's the point of a local symmetry?
Bibliography:
Added this basic but fundamental protection layer to the website.
The email setup will of course be reused when notifications are eventually implemented.
Currently using SendGrid as the email provider. Very easy to setup, and has a free plan.
Adding reCAPTCHA immediately after email is a must otherwise an attacker could send infinitely many emails to random addresses, which would lead to the domain being marked as spam. I was pleasantly surprised about how easy the integration ended up being.
"Magic star" can refer to several different concepts, depending on the context. Here are a few possible interpretations: 1. **Mathematics**: In number theory, a magic star is similar to a magic square. It consists of points arranged in a star shape where the sums of the numbers in a specific formation (such as lines or diagonals) all yield the same total.
Video 1.
Fabry Perot Interferometer by JFC UCL (2016)
Source. Description only, reasonable animations. Considers the case of two nearby beam splitters.
Video 2.
Fabry-Perot Introduction by Williams College Physics (2020)
Source.
Shows a working device. Confocal optical cavity, one of the mirrors scans back and forward moved by a piezoelectric motor, this is called a "scanning Fabry-Perot interferometer".
Does not produce an interference pattern, only an on/off blob, which is then fed into an oscilloscope for analysis. The oscilloscope shows both the mirror displacement (which is given by a voltage) and the light detector output.
Video 3.
Aligning a Scanning Fabry-Perot Interferometer by University of South Florida (2016)
Source. Very detailed, and shows of some nice equipment and techniques.
Conda by Ciro Santilli 37 Updated 2025-07-16
Conda is like pip, except that it also manages shared library dependencies, including providing prebuilts.
This has made Conda very popular in the deep learning community around 2020, where using Python frontends like PyTorch to configure faster precompiled backends was extremely common.
It also means that it is a full package manager and extremely overbloated and blows up all the time. People should just use Docker instead for that kind of stuff: www.reddit.com/r/learnmachinelearning/comments/kd88p8/comment/keco07k/

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 5. . 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.
  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