Ciro Santilli @cirosantilli 37

This is a good first concrete example of a Lie algebra. Shown at Lie Groups, Physics, and Geometry by Robert Gilmore (2008) Chapter 4.2 "How to linearize a Lie Group" has an example.

We can use use the following parametrization of the special linear group on variables $x$, $y$ and $z$:

Every element with this parametrization has determinant 1:Furthermore, any element can be reached, because by independently settting $x$, $y$ and $z$, $M_{00}$, $M_{01}$ and $M_{10}$ can have any value, and once those three are set, $M_{11}$ is fixed by the determinant.

To find the elements of the Lie algebra, we evaluate the derivative on each parameter at 0:

Remembering that the Lie bracket of a matrix Lie group is really simple, we can then observe the following Lie bracket relations between them:

One key thing to note is that the specific matrices $M_x$, $M_y$ and $M_z$ are not really fundamental: we could easily have had different matrices if we had chosen any other parametrization of the group.

TODO confirm: however, no matter which parametrization we choose, the Lie bracket relations between the three elements would always be the same, since it is the number of elements, and the definition of the Lie bracket, that is truly fundamental.

Lie Groups, Physics, and Geometry by Robert Gilmore (2008) Chapter 4.2 "How to linearize a Lie Group" then calculates the exponential map of the vector $x{M}_x+y{M}_y+z{M}_z$ as:with:

TODO now the natural question is: can we cover the entire Lie group with this exponential? Lie Groups, Physics, and Geometry by Robert Gilmore (2008) Chapter 7 "EXPonentiation" explains why not.

Given the function $\psi$:the operator can be written in Planck units as:often written without function arguments as:Note how this looks just like the Laplacian in Einstein notation, since the d'Alembert operator is just a generalization of the laplace operator to Minkowski space.

The fact that you cannot have trailing commans in lists or dicts as in 3, at:is one of the most infuriating design choices of all time!!!

If you shine microwave radiation on a Josephson junction, it produces a fixed average voltage that depends only on the frequency of the microwave. TODO how is that done more precisely? How to you produce and inject microwaves into the thing?

It acts therefore as a perfect frequency to voltage converter.

The Wiki page gives the formula: en.wikipedia.org/wiki/Josephson_effect#The_inverse_AC_Josephson_effect You get several sinusoidal harmonics, so the output is not a perfect sine. But the infinite sum of the harmonics has a fixed average voltage value.

And en.wikipedia.org/wiki/Josephson_voltage_standard#Josephson_effect mentions that the effect is independent of the junction material, physical dimension or temperature.

All of the above, compounded with the fact that we are able to generate microwaves with extremely precise frequency with an atomic clock, makes this phenomenon perfect as a Volt standard, the Josephson voltage standard.

TODO understand how/why it works better.

One of the least evil of the big tech companies of the early 21st century, partly because Sergey Brin's parents fled from the Soviet Union and so he is anti censorship, although they have been tempted by it.

Google only succeeds at highly algorithmic tasks or at giving infinite storage to users to then mine their data.

It is incapable however of adding any obvious useful end user features to most of its products, most of which get terminated and cannot be relied on:

This also seems to extend to business-to-business: twitter.com/MohapatraHemant/status/1343969802080030720 ex-Googler tells how they lost the cloud to Amazon.

More mentions of that:

Too many genius engineers. They need some dumber people like Ciro Santilli who need to write documentation to learn stuff.

Ciro Santilli actually attempted two interviews to work at Google in the early 2010's but very quickly failed both on the first phase, because you have to be a fast well trained coding machine to pass that interview.

Ciro later felt better about himself by fantasizing how he would actually do more important things outside of Google and that they would beg to buy him instead.

He was also happy that he wouldn't have to use Google crazy internal tools: someone once said that Google's tools make easy tasks middle hard, and they also make impossible tasks middle hard. TODO source.

But whatever the case: Ciro will not, ever, spend his time drilling programmer competition problems to join a company.

www.wired.com/story/google-shakes-up-its-tgif-and-ends-its-culture-of-openness/ "GOOGLE TGIF 1999 video". TGIF is the weekly all hands meeting abolished in 2019: www.wired.com/story/google-shakes-up-its-tgif-and-ends-its-culture-of-openness/

Haven't found the one yet:

Optional but really ideal:

The state of messaging is ridiculous as of 2020.