Merkle tree Updated 2025-07-16
Paul Allen Updated 2025-07-16
PCI Updated 2025-07-16
Video 1.
PCIe computer explained by ExplainingComputers (2018)
Source.
Personalized learning Updated 2025-07-16
Inferior compared to self-directed learning, but better than the traditional "everyone gets the same" approach.
Video 1.
Project SOCRATES at Illinois University Urban-Champaign (1966)
Source. It is 2020, and we are not there yet. God!
Phi Updated 2025-07-16
Two lower case variants... both used in mathematical notation, and for some reason, in LaTeX \varphi is the one that actually looks like the default standard modern lowercase phi, while \phi is the weird one. I love life.
C3 Updated 2025-07-16
Year 4 Updated 2025-07-16
Sylvain Poirier Updated 2025-07-16
Ciro Santilli feels a bit like this guy:
singlesunion.org/ so cute, he's looking for true love!!! This is something Ciro often thinks about: why it is so difficult to find love without looking people in the eye. The same applies to jobs to some extent. He has an Incel wiki page: incels.wiki/w/Sylvain_Poirier :-)
Figure 1.
Sylvain's photo from his homepage.
Source. He's not ugly at all! Just a regular good looking French dude.
Video 1.
Why learn Physics by yourself by Sylvain Poirier (2013)
Source.
Physics journal Updated 2025-07-16
The strongest are:
Sylvester's law of inertia Updated 2025-07-16
The theorem states that the number of 0, 1 and -1 in the metric signature is the same for two symmetric matrices that are congruent matrices.
For example, consider:
The eigenvalues of are and , and the associated eigenvectors are:
symPy code:
A = Matrix([[2, sqrt(2)], [sqrt(2), 3]])
A.eigenvects()
and from the eigendecomposition of a real symmetric matrix we know that:
Now, instead of , we could use , where is an arbitrary diagonal matrix of type:
With this, would reach a new matrix :
Therefore, with this congruence, we are able to multiply the eigenvalues of by any positive number and . Since we are multiplying by two arbitrary positive numbers, we cannot change the signs of the original eigenvalues, and so the metric signature is maintained, but respecting that any value can be reached.
Note that the matrix congruence relation looks a bit like the eigendecomposition of a matrix:
but note that does not have to contain eigenvalues, unlike the eigendecomposition of a matrix. This is because here is not fixed to having eigenvectors in its columns.
But because the matrix is symmetric however, we could always choose to actually diagonalize as mentioned at eigendecomposition of a real symmetric matrix. Therefore, the metric signature can be seen directly from eigenvalues.
Also, because is a diagonal matrix, and thus symmetric, it must be that:
What this does represent, is a general change of basis that maintains the matrix a symmetric matrix.
Obsidian (software) Updated 2025-07-16
Good:
Bad:
Figure 1.
Obsidian demo
. Source.
It good to think about how Euclid's postulates look like in the real projective plane:
Unlike the real projective line which is homotopic to the circle, the real projective plane is not homotopic to the sphere.
The topological difference bewteen the sphere and the real projective space is that for the sphere all those points in the x-y circle are identified to a single point.
One more generalized argument of this is the classification of closed surfaces, in which the real projective plane is a sphere with a hole cut and one Möbius strip glued in.
Telecommunication Updated 2025-07-16
Communicating at a distance, from Greek "tele" for distance!
A very cool thing about telecommunication is, besides how incredibly fast it advanced (in this sense it is no cooler than integrated circuit development), how much physics and information theory is involved in it. Applications of telecommunication implementation spill over to other fields, e.g. some proposed quantum computing approaches are remarkably related to telecommunication technology, e.g. microwaves and silicon photonics.
This understanding made Ciro Santilli wish he had opted for telecommunication engineering when he was back in school in Brazil. For some incomprehensible reason, telecommunications was the least competitive specialization in the electric engineering department at the time, behind even power electronics. This goes to show both how completely unrelated to reality university is, and how completely outdated Brazil is/was. Sad stuff.
Telegram (software) Updated 2025-07-16
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.
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.
Telephone-based system Updated 2025-07-16
This section is about telecommunication systems that are based on top of telephone lines.
Telephone lines were ubiquitous from early on, and many technologies used them to send data, including much after regular phone calls became obsolete with VoIP.
These market forces tended to eventually crush non-telephone-based systems such as telex. Maybe in that case it was just that the name sounded like a thing of the 50's. But still. Dead.
Video 1.
Long Distance by AT&T (1941)
Source. youtu.be/aRvFA1uqzVQ?t=219 is perhaps the best moment, which attempts to correlate the exploration of the United States with the founding of the U.S. states.

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