Ciro Santilli @cirosantilli 37

Ciro Santilli used to read books when he was younger (Harry Potter up to the 4th, Lord of the Rings), but once you are reading code, technical articles and news the whole day, you really just want to watch videos of people doing useless things on YouTube to rest, enough text.

Books are slow. No patience. Need faster immediate satisfaction.

Paradoxically Ciro feels like he's becoming a writer of sorts though, one semi independent section/answer/piece of knowledge at a time.

Writing is not just giving out information. It is re-feeling it.

TODO. I think this is the key point. Notably, $U(1)$ symmetry implies charge conservation.

More precisely, each generator of the corresponding Lie algebra leads to one separate conserved current, such that a single symmetry can lead to multiple conserved currents.

This is basically the local symmetry version of Noether's theorem.

Then to maintain charge conservation, we have to maintain local symmetry, which in turn means we have to add a gauge field as shown at Video "Deriving the qED Lagrangian by Dietterich Labs (2018)".

Forces can then be seen as kind of a side effect of this.

Bibliography:

Subgroup of the Poincaré group without translations. Therefore, in those, the spacetime origin is always fixed.

Or in other words, it is as if two observers had their space and time origins at the exact same place. However, their space axes may be rotated, and one may be at a relative speed to the other to create a Lorentz boost. Note however that if they are at relative speeds to one another, then their axes will immediately stop being at the same location in the next moment of time, so things are only valid infinitesimally in that case.

This group is made up of matrix multiplication alone, no need to add the offset vector: space rotations and Lorentz boost only spin around and bend things around the origin.

One definition: set of all 4x4 matrices that keep the Minkowski inner product, mentioned at Physics from Symmetry by Jakob Schwichtenberg (2015) page 63. This then implies:

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 $+x$ direction at speed $v$.

TODO image.

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 $\frac{v}{c}$ 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 $\frac{v}{c}$ is almost zero.

The name makes absolutely no sense in modern terms, as nor colors nor light are used directly in the measurements. It is purely historical.

Best ones:

What an awesome list the dude compiled. Contains many of the features we care the most about of the sky, since of course, apparent magnitude is a big determinant of that.

Highly radioactive isotope of caesium with half-life of 30.17 y. Produced from the nuclear fission of uranium, TODO exact reaction, not found in nature.

The fucked thing about this byproduct is that it is in the same chemical family as sodium, and therefore forms a salt that looks like regular table salt, and dissolves in water and therefore easily enters your body and sticks to things.

Another problem is that its half-life is long enough that it doesn't lose radioactivity very quickly compared to the life of a human person, although it is short enough to make it highly toxic, making it a terrible pollutant when released.

This is why for example in the goiânia accident a girl ended up ingesting Caesium-137 after eating an egg after touching the Caesium with her hands.

Many devborads require a 5V power supply.

This is common on wall transformers and USB, but not in batteries.

For battery power you need a transformer.

This is the kind of mind-bending argument twists that Ciro Santilli loves. If we take out the "a real child is hurt" aspect, does it still make sense to make it illegal?

Of course, hentai of young-looking girls has already existed since forever. Bit with newer image generation methods in the 2020s used for computer generated child pornography, especially sometimes photorealistic text-to-image generation, things are taken to another level.

They actually carry atomic clocks in them.

This is a good book.

It has some overlap with Surely You're Joking, Mr. Feynman, which it likely takes as primary sources of some stories.

However, while Surely goes into a lot of detail of each event, this book paints a more cohesive and global picture of things.

In terms of hard physics/mathematics, this book takes the approach of spending a few paragraphs in some chapters describing in high level terms some of the key ideas, which is a good compromise. It does sometime fall into the sin of to talk about something without giving the real name to not scare off the audience, but it does give a lot of names, notably it talks a lot about Lagrangian mechanics. And it goes into more details than Surely in any case.

$L^p$ is:

And then this is why quantum mechanics basically lives in $L^2$: not being complete makes no sense physically, it would mean that you can get closer and closer to states that don't exist!

TODO intuition