Ciro Santilli @cirosantilli  40

What is my phone breaks? What if I don't want to have a fucking phone? What if I move countries and have to change the fucking number? Also evil but less because done by all: chat programs that can't send you an email if you don't see the message in X minutes.

European Union, time to force those evil companies to use support open standards like XMPP?

The solution to "how to prevent spam" is simple: your ID is a public key that you own the private key for. If you start getting spammed, generate a new public key, and send it to all contacts, and dump the previous ID.

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Serverless browser P2P chat Updated 2025-07-16

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stackoverflow.com/questions/2463665/how-create-a-p2p-web-chat-without-any-server

It seems impossible to avoid the signaling server. With signaling server:

Games:

github.com/rameshvarun/netplayjs

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Email Updated 2025-07-16

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Ciro Santilli's email can be found by cloning one of his repositories on GitHub. It is also given at: Section "How to contact Ciro Santilli".

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Instant messaging Updated 2025-07-16

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C++ memory model Updated 2025-07-16

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stackoverflow.com/questions/6319146/c11-introduced-a-standardized-memory-model-what-does-it-mean-and-how-is-it-g

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How to reference a book in Wikipedia markup? Updated 2025-07-16

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Their reference markup is incredibly overengineered, convoluted, and underdocumented, it is unbelivable!

Use the reference:

This is a fact.{{sfn|Schweber|1994|p=487}}

Define the reference:

===Sources===
{{refbegin|2|indent=yes}}
*{{Cite book|author-link=Silvan S. Schweber |title=QED and the Men Who Made It: Dyson, Feynman, Schwinger, and Tomonaga|last=Schweber|first=Silvan S.|location=Princeton|publisher=University Press|year=1994 |isbn=978-0-691-03327-3 |url=https://archive.org/details/qedmenwhomadeitd0000schw/page/492 |url-access=registration}}
{{refend}}

sfn is magic and matches the the author last name and date from the Cite, it is documented at: en.wikipedia.org/wiki/Template:Sfn

Unforutunately, if there are multiple duplicate Cites inline in the article, it will complain that there are multiple definitions, and you have to first factor out the article by replacing all those existing Cite with sfn, and keeping just one Cite at the bottom. What a pain...

You can also link to a specific page of the book, e.g. if it is a book is on Internet Archive Open Library with:

{{sfn|Murray|1997|p=[https://archive.org/details/supermenstory00murr/page/86 86]}}

For multiple pages should use pp= instead of p=. Does not seem to make much difference on the rendered output besides showing p. vs pp., but so be it:

{{sfn|Murray|1997|pp=[https://archive.org/details/supermenstory00murr/page/86 86-87]}}

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Faraday's law of induction Updated 2025-07-16

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Lorentz force Updated 2025-07-16

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force_density = ρ E + J \times B

(1)

Equation 1.

Lorentz force

A little suspicious that it bears the name of Lorentz, who is famous for special relativity, isn't it? See: Maxwell's equations require special relativity.

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Explicit scalar form of the Maxwell's equations Updated 2025-07-16

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For numerical algorithms and to get a more low level understanding of the equations, we can expand all terms to the simpler and more explicit form:

\frac{\partial E _{x}}{\partial x} + \frac{\partial E _{y}}{\partial x} + \frac{\partial E _{z}}{\partial x} = \frac{ρ}{ε _{0}} \frac{\partial B _{x}}{\partial x} + \frac{\partial B _{y}}{\partial x} + \frac{\partial B _{z}}{\partial x} = 0 \frac{\partial E _{z}}{\partial y} - \frac{\partial E _{y}}{\partial z} = - \frac{\partial B _{x}}{\partial t} \frac{\partial E _{x}}{\partial z} - \frac{\partial E _{z}}{\partial x} = - \frac{\partial B _{y}}{\partial t} \frac{\partial E _{y}}{\partial x} - \frac{\partial E _{x}}{\partial y} = - \frac{\partial B _{z}}{\partial t} \frac{\partial B _{z}}{\partial y} - \frac{\partial B _{y}}{\partial z} = μ_{0} (J_{x} + ε_{0} \frac{\partial E _{x}}{\partial t}) \frac{\partial B _{x}}{\partial z} - \frac{\partial B _{z}}{\partial x} = μ_{0} (J_{y} + ε_{0} \frac{\partial E _{y}}{\partial t}) \frac{\partial B _{y}}{\partial x} - \frac{\partial B _{x}}{\partial y} = μ_{0} (J_{z} + ε_{0} \frac{\partial E _{z}}{\partial t})

(1)

Equation 1

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Coulomb's law Updated 2025-07-16

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Static case of Maxwell's law for electricity only.

Is implied by Gauss' law if Maxwell's equations: physics.stackexchange.com/questions/44418/are-the-maxwells-equations-enough-to-derive-the-law-of-coulomb

The "static" part is important: if this law were true for moving charges, we would be able to transmit information instantly at infinite distances. This is basically where the idea of field comes in.

Video 1.

Coulomb's Law experiment with torsion balance with a mirror on the balance to amplify rotations by uclaphysics (2010)

Source.

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Solutions of Maxwell's equations Updated 2025-07-16

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Video 1.

Understanding Electromagnetic Radiation! by Learn Engineering (2019)

Source. Shows animations of a dipole antenna which illustrates well how radiation is emitted from moving charges and travels at the speed of light.

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Maxwell's equations in 2D Updated 2025-07-16

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TODO it would be awesome if we could de-generalize the equations in 2D and do a JavaScript demo of it!

Not sure it is possible though because the curl appears in the equations:

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Existence and uniqueness of solutions to Maxwell's equations Updated 2025-07-16

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TODO: I'm surprised that the Wiki page barely talks about it, and there are few Google hits too! A sample one: www.researchgate.net/publication/228928756_On_the_existence_and_uniqueness_of_Maxwell's_equations_in_bounded_domains_with_application_to_magnetotellurics

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Electric field Updated 2025-07-16

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Hall effect Updated 2025-07-16

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The voltage changes perpendicular to the current when magnetic field is applied.

Figure 1.
Hall effect experimental diagram
. Source. The Hall effect refers to the produced voltage $V_{H}$ , AKA $V_{y}$ on this setup.

An intuitive video is:

Video 1. Source.

The key formula for it is:

V_{H} = \frac{I _{x} B _{z}}{n t e}

(1)

where:

$I_{x}$ : current on x direction, which we can control by changing the voltage $V_{x}$
$B_{z}$ : strength of transversal magnetic field applied
$n$ : charge carrier density, a property of the material used
$t$ : height of the plate
$e$ : electron charge

Applications:

the direction of the effect proves that electric currents in common electrical conductors are made up of negative charged particles
measure magnetic fields, TODO vs other methods

Other more precise non-classical versions:

quantum Hall effect

Bibliography:

hyperphysics.phy-astr.gsu.edu/hbase/magnetic/Hall.html

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Electromagnetic four-potential Updated 2025-07-16

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A different and more elegant way to express Maxwell's equations by using the:

instead of the:

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 There are unlisted articles, also show them or only show them.