There are several choices of electromagnetic four-potential that lead to the same physics.
E.g. thinking about the electric potential alone, you could set the zero anywhere, and everything would remain be the same.
The Lorentz gauge is just one such choice. It is however a very popular one, because it is also manifestly Lorentz invariant.
OurBigBook Web by Ciro Santilli 40 Updated 2025-07-16
The website system that runs OurBigBook.com. For further information see:Relies on the OurBigBook Library to compile OurBigBook Markup.
This single experimental observation/idea is the basis for all of special relativity.
Special relativity is the direct result of people bending their backs to accommodate for this really weird fact.
Basically everything that applies to the blogs section also applies here, but university lecture notes are so important to us that they deserve a bit more talk.
It is arguable that this is currently the best way to learn any university subject, and that it can already be used to learn any subject.
We basically just want to make the process more efficient and enjoyable, by making it easier:
  • to find what you want based on an initial subject hit across the best version of any author
  • and to publish your own stuff with one click, and get feedback if people like it or not, and improvement suggestions like you do you GitHub
One major problem with lecture notes is that, as the name suggests, they are merely a complement to the lecture, and don't contain enough detail for you to really learn solely from them without watching the lecture.
The only texts that generally teach in enough depth are actual books, which are almost always commercial.
So in a sense, this project can be seen as a path to upgrade free lecture notes into full blown free books, from which you can learn from scratch without any external material.
And a major way in which we believe this can be done is through the reuse of sections of lecture notes by from other universities, which greatly reduces the useless effort of writing things from scratch.
The intended mental picture is clear: the topics feature docs.ourbigbook.com/#ourbigbook-web-topics will is intended to act as the missing horizontal topic integration across lecture notes of specific universities, e.g:
MIT calculus course             UCLA calculus course

* Calculus                <---> * Calculus
  * Limit                 <--->   * Limit
    * Limit of a function
    * Limit of a series   <--->     * Limit of a series
  * Derivative            <--->   * Derivative
                                    * L'Hôpital's rule
  * Integral              <--->   * Integral
Figure 1.
Example topics page of OurBigBook.com
.
One important advantage of lecture notes is that since they are written by the teacher, they should match exactly what "students are supposed to learn to get good grades", which unfortunately is a major motivation for student's learning weather we want it or not.
One big open question for this project is to what extent notes written for lectures at one university will be relevant to the lectures at another university?
Is it possible to write notes in a way that they are naturally reusable?
It is our gut feeling that this is possible. But it almost certainly requires an small intentional effort on the part of authors.
The question then becomes whether the "become famous by getting your content viewed in other universities" factor is strong enough to attract users.
And we believe that it might, it just might be.
Bibliography:
Luminiferous aether by Ciro Santilli 40 Updated 2025-07-16
Can you just imagine what if luminiferous aether was one single fixed rigid body? This is apparently what Maxwell believed, Subtle is the Lord by Abraham Pais (1982) page 111 quoting his entry to Encyclopedia Britannica:
There can be no doubt that the interplanetary and interstellar spaces are not empty but are occupied by a material substance or body, which is certainly the largest, and probably the most uniform, body of which we have any knowledge.
Then it would provide a natural space coordinate for the entire universe!
Apparently Einstein was the first to completely say: let's just screw this aether thing completely then, it's getting too complicated, and we don't really need it. As Wikipedia puts it well, in very unencyclopedic tone[ref]: Aether fell to Occam's razor.
The geometry of divisors is a topic in algebraic geometry that deals with the study of divisors on algebraic varieties, particularly within the context of the theory of algebraic surfaces and higher-dimensional varieties. A divisor on an algebraic variety is an algebraic concept that intuitively represents "subvarieties" or "subsets", often associated with codimension 1 subvarieties, such as curves on surfaces or hypersurfaces in higher dimensions.
Crush the current grossly inefficient educational system, replace today's students + teachers + researchers with unified "online content creators/consumers".
Gamify them, and pay the best creators so they can work it full time, until some company hires for more them since they are so provenly good.
Destroy useless exams, the only metrics of society are either:
  • how much money you make
  • how high is your educational content creator reputation score
Reduce the entry barrier to education, like Uber has done for taxis.
Help create much greater equal opportunity to talented poor students as described at free gifted education.
Give the students a flexible choice of what to learn, which basically implies that a much large proportion of students get a de-facto gifted education.
In some ways, Ciro wants the website to feel like a video game, where you fluidly interact with headers, comments and their metadata. If game developers can achieve impressively complicated game engines, why can't we achieve a decent amazing elearning website? :-)
Aether drag hypothesis by Ciro Santilli 40 Updated 2025-07-16
Given experiments such as the Fizeau experiment and the Michelson-Morley experiment that couldn't really detect the Earth's movement across aether, people started to wonder if the Earth wasn't dragging the luminiferous aether.

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