The Biggest Ideas in the Universe | 11. Renormalization by Sean Carroll (2020)
Source. Gives a very quick and high level overview of renormalization. It is not enough to satisfy Ciro Santilli as usual for other Sean Carroll videos, but it goes some way.Can you do anything with it? What's the license?
Basically a synonym of Lorentz covariance?
No chat only? .... community.jitsi.org/t/chat-function-only/79067
As of 2020: end-to-end encryption optional and turned off as default, and marked as experimental...
Appears to be based on XMPP: community.jitsi.org/t/jitsi-users-is-jitsi-a-regular-xmpp-server/13211
Not end-to-end encrypted by default, WTF... you have to create "secret chats" for that:
You can't sync secret chats across devices, Signal handles that perfectly by sending E2EE messages across devices:This is a deal breaker because Ciro needs to type with his keyboard.
Desktop does not have secret chats: www.reddit.com/r/Telegram/comments/9beku1/telegram_desktop_secret_chat/ This is likey because it does not store chats locally, it just loads from server every time as of 2019: www.reddit.com/r/Telegram/comments/baqs63/where_are_chats_stored_on_telegram_desktop/ just like the web version. So it cannot have a private key.
Allows you to register a public username and not have to share phone number with contacts: telegram.org/blog/usernames-and-secret-chats-v2.
Has Reproducible builds on Android and iOS: core.telegram.org/reproducible-builds
Self deleting messages added to secret chats in Q1 2021: telegram.org/blog/autodelete-inv2
Can delete messages from the device of the person you sent it to, no matter how old.
Not really dedicated to open source course material, nor to free courses...
The "Open" in its name only made sense in the 60's, when it was founded, nowadays, there isn't much about this institution that is very different compared to traditional Oxbridge. "Cheap more online university" would be a more adequate name for it.
A system that would truly live up to the name "Open" in the year 2020 is the one described at the ideal university by Ciro Santilli.
Wikipedia even says that the initial focus was on broadcasting learning material on television and radio, so what happened to that now that we have an even more powerful on-demand tool called Internet!
They even created their own MOOC website, FutureLearn. But www.freecodecamp.org/news/massive-open-online-courses-started-out-completely-free-but-where-are-they-now-1dd1020f59/ mentions:OMG. God why.
The course content is still free to access, but it’s only available for the duration of the course, and for two weeks after it ends.
A few open sources at: www.open.edu/openlearn/free-courses. The 5-hour course on particle physics says it all. Stated as of 2023 at www.open.ac.uk/about/open-educational-resources/openlearn/free-learning:
The OU provides around 5% of its formal course materials as free open educational content every year on OpenLearn
www.youtube.com/watch?v=Pj0rbafFBak What's an Open University Degree Like? by Luke Cutforth (2021) mentions that it is more autodidactic/online, and it encourages part time learning.
youtu.be/rsWwffX-u0A?t=99 Open University - How does it work? by Matt Greg Vlogs (2017) shows that they do have their own custom institutional material. And it is not open???? Please. youtu.be/rsWwffX-u0A?t=222 mentions that there is no entry exam, and you can change your courses at any time, that is good at least.
Israel apparently also created their own version in the 70's inspired by the British one: Open University of Israel. Same story it seems.
LaTeX subset that output nicely to HTML.
Too insane though due to LaTeX roots, better just move to newer HTML-first markups like OurBigBook Markup or markdown.
Derivation of the Klein-Gordon equation by 
Ciro Santilli 35 Updated 2025-01-10 +Created 1970-01-01
Ciro Santilli 35 Updated 2025-01-10 +Created 1970-01-01The Klein-Gordon equation directly uses a more naive relativistic energy guess of squared.
But since this is quantum mechanics, we feel like making into the "momentum operator", just like in the Schrödinger equation.
But we don't really know how to apply the momentum operator twice, because it is a gradient, so the first application goes from a scalar field to the vector field, and the second one...
So we just cheat and try to use the laplace operator instead because there's some squares on it:
But then, we have to avoid taking the square root to reach a first derivative in time, because we don't know how to take the square root of that operator expression.
So the Klein-Gordon equation just takes the approach of using this squared Hamiltonian instead.
Since it is a Hamiltonian, and comparing it to the Schrödinger equation which looks like:taking the Hamiltonian twice leads to:
We can contrast this with the Dirac equation, which instead attempts to explicitly construct an operator which squared coincides with the relativistic formula: derivation of the Dirac equation.
TypeScript is good. It does find errors in your JavaScript. But it is a form of "turd polishing". But Ciro Santilli would rather have a polished turd than a non-polished one.
Part of the reason TypeScript became popular is due to the universality of asset bundlers. Once you are already using an asset bundler, changing the
.js extension into .ts to get a less shitty experience is an easy choice.The other big reason is that JavaScript is so lose with type conversions, notably undefined happily converting to strings without problems, and any missing properties of Object happily being undefined. We should actually use ES6 Map everywhere instead of using Objects as maps.
Since TypeScript is not the default form of the language however, it inevitably happens that you need to add external types for a gazillion projects that are using raw JavaScript, and sometimes fight a lot to get things to work. And so we have: github.com/DefinitelyTyped/DefinitelyTyped. Not sure if this is beautiful, or frightening.
But in the end, as with other type of static linters, TypeScript generally transforms a few hard to debug runtime issues, into a bunch of stupid to solve compile time issues, which is generally a good thing.
The fact that this it parses comments JSDoc comments in JavaScript files is quite amazing.
Examples under typescript. Run each one of them with:Helper:
npx tsc example.ts
node example.jstsr() (
# ts Run
f="$1"
npx tsc "$f"
node "${f%.*}.js"
)
tsr example.ts- typescript/inferFromInit.ts. Should fail with:since TypeScript infers the type of
hello.ts:2:1 - error TS2322: Type 'string' is not assignable to type 'number
ifrom first assignment asstring, and we then attempt anumberassignment later on - typescript/inferAfterInit.ts. Does not fail, as the first assignment cannot be computationally determined at runtime without breaking computer science.
- typescript/js-from-ts/main.ts: call JavaScript file typescript/js-from-ts/notmain.js from TypeScript.TODO we are unable to make it typecheck that require, i.e. make that fail, but we've seen cases in complex codebases where that did happen and www.typescriptlang.org/docs/handbook/intro-to-js-ts.html has infinite information on supporting it. So... how to make it fail??
npx tsc jsFromTs.ts && node jsFromTs.js - typescript/functionArgument.ts: basic argument tests
- typescript/functionOptionalArgument.ts:
f(n?: number)
- typescript/functionOptionalArgument.ts:
- typescript/functionOptions.ts:
f({n, s}: {n: number, s: string})
Some major annoyances of TypeScript:
- destructuring assignment in function arguments requires repeating all arguments:
- stackoverflow.com/questions/12710905/how-do-i-dynamically-assign-properties-to-an-object-in-typescript how to dynamically assign properties to objects without defining explicit interfaces? We really need a syntax of type:
const myobj = { i: 2, [s string], } if (something) { myobj.s = 'asdf' }
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