Unit circle by Ciro Santilli 37 Updated 2025-07-16
The unitary group is one very over-generalized way of looking at it :-)
Gamma ray by Ciro Santilli 37 Updated 2025-07-16
Most commonly known as a byproduct radioactive decay.
Their energy is very high compared example to more common radiation such as visible spectrum, and there is a neat reason for that: it's because the strong force that binds nuclei is strong so transitions lead to large energy changes.
Gamma rays are pretty cool as they give us insight into the energy levels/different configurations of the nucleus.
They have also been used as early sources of high energy particles for particle physics experiments before the development of particle accelerators, serving a similar purpose to cosmic rays in those early days.
But gamma rays they were more convenient in some cases because you could more easily manage them inside a laboratory rather than have to go climb some bloody mountain or a balloon.
The positron for example was first observed on cosmic rays, but better confirmed in gamma ray experiments by Carl David Anderson.
The orthogonal group has 2 connected components:
It is instructive to visualize how the looks like in :
  • you take the first basis vector and move it to any other. You have therefore two angular parameters.
  • you take the second one, and move it to be orthogonal to the first new vector. (you can choose a circle around the first new vector, and so you have another angular parameter.
  • at last, for the last one, there are only two choices that are orthogonal to both previous ones, one in each direction. It is this directio, relative to the others, that determines the "has a reflection or not" thing
As a result it is isomorphic to the direct product of the special orthogonal group by the cyclic group of order 2:
A low dimensional example:
because you can only do two things: to flip or not to flip the line around zero.
Note that having the determinant plus or minus 1 is not a definition: there are non-orthogonal groups with determinant plus or minus 1. This is just a property. E.g.:
has determinant 1, but:
so is not orthogonal.
If we didn't have GUIs, terminal multiplexers would be our desktop environments. E.g. they handle stuff like:
  • window switching
  • copy pasting across windows
  • screen locking
  • clock on the status bar (same one that holds tabs)
It is a thing of beauty.
We can then immediately see that the matrix is symmetric, then so is the form. We have:
But because is a scalar, we have:
and:
Ciro Santilli likes this.
He doesn't have the patience to actually watch full episodes with rare exceptions, rather just watching selected scenes from: www.youtube.com/channel/UCdeIGY2DIjpGf0A2m9GSE3g, but still, it is interesting.
What appeals to Ciro in this series is how almost nothing is solved by violence, almost everything is decided in the bridge, at the "cerebral" level of the command structure. This reminds Ciro of a courtroom of law sometimes.
Maybe there's also a bit of 90's nostalgia involved too though, as this is something that would show on some random cable channels a bored young Ciro would have browsed during weekends, never really watching full episodes.
One crime of many episodes is being completely based on some stupid new scientific concept, which any character to back it up.
Another thing that hurt is that due to their obsession with the senior members of the crew, sometimes those senior members are sent in ridiculously risky operations, which is very unrealistic.
Episodes that Ciro watched fully and didn't regret:
Semi worth it:
Not worth it:
  • Cause and effect
TODO
  • s06e11 Chain of command
Monster group by Ciro Santilli 37 Updated 2025-07-16
Video 1.
Group theory, abstraction, and the 196,883-dimensional monster by 3Blue1Brown (2020)
Source. Too basic, starts motivating groups themselves, therefore does not give anything new or rare.
react/hello.html by Ciro Santilli 37 Updated 2025-07-16
Minimal React hello world example. As you click:
  • one counter increments every time
  • the other increments every two clicks
By opening a web inspector, you can see that only modified elements get updated. So we understand that JSX parses its "HTML-like" into a tree, and then propagates updates on that tree.
By looking at the terminal, we see that render() does get called every time the button is clicked, so the tree of elements does get recreated every time. But then React diffes thing out and only updates things in the DOM where needed.

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