Lorentz gauge condition Updated +Created
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.
Lorentz transformation Updated +Created
The equation that allows us to calculate stuff in special relativity!
Take two observers with identical rules and stopwatch, and aligned axes, but one is on a car moving at towards the direction at speed .
When both observe an event, if we denote:
It is of course arbitrary who is standing and who is moving, we will just use the term "standing" for the one without primes.
Then the coordinates of the event observed by the observer on the car are:
where:
Note that if tends towards zero, then this reduces to the usual Galilean transformations which our intuition expects:
This explains why we don't observe special relativity in our daily lives: macroscopic objects move too slowly compared to light, and is almost zero.
Freedom of speech Updated +Created
Ciro has the radical opinion that absolute freedom of speech must be guaranteed by law for anyone to talk about absolutely anything, anonymously if they wish, with the exception only of copyright-related infringement.
And Ciro believes that there should be no age restriction of access to any information.
People should be only be punished for actions that they actually do in the real world. Not even purportedly planning those actions must be punished. Access and ability to publish information must be completely and totally free.
If you don't like someone, you should just block them, or start your own campaign to prepare a counter for whatever it is that they are want to do.
This freedom does not need to apply to citizens and organizations of other countries, only to citizens of the country in question, since foreign governments can create influence campaigns to affect the rights of your citizens. More info at: cirosantilli.com/china-dictatorship/mark-government-controlled-social-media
Limiting foreign influence therefore requires some kind of nationality check, which could harm anonymity. But Ciro believes that almost certainly such checks can be carried out in anonymous blockchain consensus based mechanisms. Governments would issues nationality tokens, and tokens are used for anonymous confirmations of rights in a way that only the token owner, not even the government, can determine who used the token. E.g. something a bit like what Monero does. Rights could be checked on a once per account basis, or yearly basis, so transaction costs should not be a big issue. Maybe expensive proof-of-work systems can be completely bypassed to the existence of this central token authority?
Some people believe that freedom of speech means "freedom of speech that I agree with". Those people should move to China or some other dictatorship.
Free university Updated +Created
Related projects:
Frobenius theorem (real division algebras) Updated +Created
From first principles Updated +Created
Los Alamos From Below by Richard Feynman (1975) Updated +Created
Amazing talk by Richard Feynman that describes his experiences at Los Alamos National Laboratory while developing the first nuclear weapons.
Video 1.
Los Alamos From Below by Richard Feynman (1975)
Source.
GF(4) Updated +Created
Ciro Santilli tried to add this example to Wikipedia, but it was reverted, so here we are, see also: Section "Deletionism on Wikipedia".
This is a good first example of a field of a finite field of non-prime order, this one is a prime power order instead.
, so one way to represent the elements of the field will be the to use the 4 polynomials of degree 1 over GF(2):
  • 0X + 0
  • 0X + 1
  • 1X + 0
  • 1X + 1
Note that we refer in this definition to anther field, but that is fine, because we only refer to fields of prime order such as GF(2), because we are dealing with prime powers only. And we have already defined fields of prime order easily previously with modular arithmetic.
Over GF(2), there is only one irreducible polynomial of degree 2:
Addition is defined element-wise with modular arithmetic modulo 2 as defined over GF(2), e.g.:
Multiplication is done modulo , which ensures that the result is also of degree 1.
For example first we do a regular multiplication:
Without modulo, that would not be one of the elements of the field anymore due to the !
So we take the modulo, we note that:
and by the definition of modulo:
which is the final result of the multiplication.
TODO show how taking a reducible polynomial for modulo fails. Presumably it is for a similar reason to why things fail for the prime case.
Git design rationale Updated +Created
The fundamental insight of Git design is: a SHA represents not only current state, but also the full history due to the Merkle tree implementation, see notably:
This makes it so that you will always notice if you are overwriting history on the remote, even if you are developing from two separate local computers (or more commonly, two people in two different local computers) and therefore will never lose any work accidentally.
It is very hard to achieve that without the Merkle tree.
Consider for example the most naive approach possible of marking versions with consecutive numbers:
  • Local 1:
  • Local 2:
    • 0: root commit
    • 1: commit 1
    • 2: commit 2 by local 2
    • 3: commit 3 by local 2
  • Remote
If Local 1 were to push to Remote first, how could Local 2 notice that when it tries to push itself? The navie method of just checking: "does Remote have commit "2"" does not work, because Local 2 has a different version of commit 2 than local 1.
GitHub's replacement of master branch with main (2020) Updated +Created
By GitHub around Black Lives Matter, due to a possible ludicrous relationship with slavery of black people:For the love of God, the word "master" is much more general than black slavery. If you are going to ban it, you might as well ban the word "evil".
Several software projects followed the purge from their codebases, maybe GitHub followed someone else's lead, it's hard to say.
The words "whitelist" and "blacklist" were also targeted.
GitLab Updated +Created
GitLab was very important to Ciro because he wanted to base Booktree on it.
Git tips / diff3 Updated +Created
diff3 conflict is basically what you always want to see, either by setting it as the default as per stackoverflow.com/questions/27417656/should-diff3-be-default-conflictstyle-on-git:
git config --global merge.conflictstyle diff3
or as a one off:
git checkout --conflict=diff3
With this, conflicts now show up as:
++<<<<<<< HEAD
 +5
++||||||| parent of 7b0f59d (6)
++3
++=======
+ 6
++>>>>>>> 7b0f59d (6)
7b0f59d is the SHA-2 of commit 6.
instead of the inferior default:
++<<<<<<< ours
 +5
++=======
+ 6
++>>>>>>> theirs
We can also observe the current tree state during resolution:
* b4ec057 (HEAD, master) 5
* 0b37c1b 4
| * fbfbfe8 (my-feature) 7
| * 7b0f59d 6
|/
* 661cfab 3
* 6d748a9 2
* c5f8a2c 1
so we understand that we are now at 5 and that we are trying to apply our commit 6
So it is much clearer what is happening:
  • master changed the code from 3 to 5
  • our feature changed the code from 3 to 6
and so now we have to decide what the new code is that will put both of these together.
Let's say we decide it is 5 + 6 = 11 and continue rebasing:
git add .
git rebase --continue
We now reach:
++<<<<<<< HEAD
 +11
++||||||| parent of fbfbfe8 (7)
++6
++=======
+ 7
++>>>>>>> fbfbfe8 (7)
and the tree looks like:
* ca7f7ff (HEAD) 6
* b4ec057 (master) 5
* 0b37c1b 4
| * fbfbfe8 (my-feature) 7
| * 7b0f59d 6
|/
* 661cfab 3
* 6d748a9 2
* c5f8a2c 1
So we understand that:
  • after the previous step we added commit 6 on top of 5
  • now we are adding 7 on top of the new 6 (which we decided would contain 11)
and after resolving that one we now reach:
* e1aaf20 (HEAD -> my-feature) 7
* ca7f7ff 6
* b4ec057 (master) 5
* 0b37c1b 4
* 661cfab 3
* 6d748a9 2
* c5f8a2c 1
Git tips / git mergetool with meld or kdiff3 Updated +Created
These are good free newbie GUI options:
sudo apt install meld
git mergetool --tool meld

sudo apt install kdiff3
git mergetool --tool kdiff3
https://raw.githubusercontent.com/cirosantilli/media/master/meld.png
https://raw.githubusercontent.com/cirosantilli/media/master/kdiff3.png
Let's make a more interesting conflict:
git-tips-2.sh
#!/usr/bin/env bash

set -eux

add() (
  rm -f f
  for i in `seq 10`; do
    printf "before $i\n\n" >> f
  done
  printf "conflict 1 $1\n\n" >> f
  for i in `seq 10`; do
    printf "middle $i\n\n" >> f
  done
  printf "conflict 2 $2\n\n" >> f
  for i in `seq 10`; do
    printf "after $i\n\n" >> f
  done
  git add f
)

rm -rf git-tips-2
mkdir git-tips-2
cd git-tips-2
git init

for i in 1 2 3; do
  add $i $i
  git commit -m $i
done

add 3 4
git commit -m 4

add 5 4
git commit -m 5

git checkout HEAD~2
git checkout -b my-feature

add 3 6
git commit -m 6

add 7 6
git commit -m 7
Good targets for amateur astronomy Updated +Created
Looking at most astronomical object through a telescope is boring because you only see a white ball or point every time. Such targets would likely only be interesting with spectroscopy analysis.
There are however some objects that you can see the structure of even with an amateur telescope, and that makes them very exciting.
Some good ones:
Good video game to watch Updated +Created
This is a list of video games that are good to watch other people playing, even if you don't play yourself. And often they are better to watch than to play as you don't have to waste your time as much!
Google Passwords Updated +Created
When they disabled this from Chromium, it was one of the things that prompted Ciro Santilli to switch to Proton Pass.
Google X Updated +Created
Wikipedia reads:
Any contributor could create and own new Knol articles, and there could be multiple articles on the same topic with each written by a different author.
so basically exactly what Ciro Santilli wants to do on OurBigBook.com. Ominous.
Like any closed source "failure", everything was deleted. wiki.archiveteam.org/index.php/Knol
Gordon Linoff Updated +Created
Infinitely many SQL answers.
As mentioned at Ciro Santilli's Stack Overflow contributions, he just answers every semi-duplicate immediatly as it is asked, and is therefore able to overcome the Stack Overflow maximum 200 daily reputation limit by far. E.g. in 2018, Gordon reached 135k (archive), thus almost double the 73k yearly limit due to the 200 daily limit, all of that with accepts.
This is in contrast to Ciro Santilli's contribution style which is to only answer questions as he needs the subject, or generally important questions that aroused his interest.
2014 Blog post describing his activity: blog.data-miners.com/2014/08/an-achievement-on-stack-overflow.html, key quote:
For a few months, I sporadically answered questions. Then, in the first week of May, my Mom's younger brother passed away. That meant lots of time hanging around family, planning the funeral, and the like. Answering questions on Stack Overflow turned out to be a good way to get away from things. So, I became more intent.
so that suggests his contributions also take a meditative value.
www.data-miners.com/linoff.htm mentions he's an SQL consultant that consulted for several big companies.
LinkedIn profile: www.linkedin.com/in/gordonlinoff/ says he now works at the New York Times.
2021 Reddit thread about him: www.reddit.com/r/programming/comments/puok1h/a_single_person_answered_76k_questions_about_sql/ mentions that by then he had:
answered 76k questions about SQL on StackOverflow. Averaging 22.8 answers per day, every day, for the past 8.6 years.
History of quantum mechanics Updated +Created
The discovery of the photon was one of the major initiators of quantum mechanics.
Light was very well known to be a wave through diffraction experiments. So how could it also be a particle???
This was a key development for people to eventually notice that the electron is also a wave.
This process "started" in 1900 with Planck's law which was based on discrete energy packets being exchanged as exposed at On the Theory of the Energy Distribution Law of the Normal Spectrum by Max Planck (1900).
This ideas was reinforced by Einstein's explanation of the photoelectric effect in 1905 in terms of photon.
In the next big development was the Bohr model in 1913, which supposed non-classical physics new quantization rules for the electron which explained the hydrogen emission spectrum. The quantization rule used made use of the Planck constant, and so served an initial link between the emerging quantized nature of light, and that of the electron.
The final phase started in 1923, when Louis de Broglie proposed that in analogy to photons, electrons might also be waves, a statement made more precise through the de Broglie relations.
This event opened the floodgates, and soon matrix mechanics was published in quantum mechanical re-interpretation of kinematic and mechanical relations by Heisenberg (1925), as the first coherent formulation of quantum mechanics.
It was followed by the Schrödinger equation in 1926, which proposed an equivalent partial differential equation formulation to matrix mechanics, a mathematical formulation that was more familiar to physicists than the matrix ideas of Heisenberg.
Inward Bound by Abraham Pais (1988) summarizes his views of the main developments of the subjectit:

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