Kitchen: 2021-04: nine-volt battery battery at 8.79V. Not sounding.

Haven't found the one yet:

Optional but really ideal:

The state of messaging is ridiculous as of 2020.

Largest programs ever written:

It gets the job done, but cannot make a large codebase DRY without insanity.

As of 2020, C is like Latin, and we are in the Middle Ages, where it has become a lingua franca.

It is interesting to note how late C appeared: 1972, compared e.g. to Fortran which is from 1957. This is basically because C was a "systems programming language", i.e. with focus on pointer manipulation, and because early computers were so weak, there was no operating system or many software layers in the early days. Fortran however was a numerical language, and it ran directly on bare metal, an application that existed before systems programming.

Examples under c.

The key question is: why is this not symmetrical?

One answer is: because one of the twin accelerates, and therefore changes inertial frames.

But the better answer is: understand what happens when the stationary twin sends light signals at constant time intervals to each other. When does the travelling twin receives them?

By doing that, we see that "all the extra aging happens immediately when the twin turns around":

Another way of understanding it is: you have to make all calculations on a single inertial frame for the entire trip.

Supposing the sibling quickly accelerates out (or magically starts moving at constant speed), travels at constant speed, and quickly accelerates back, and travels at constant speed setup, there are three frames that seem reasonable:

If you do that, all three calculations give the exact same result, which is reassuring.

Another way to understand it is to do explicit integrations of the acceleration: physics.stackexchange.com/questions/242043/what-is-the-proper-way-to-explain-the-twin-paradox/242044#242044 This is the least insightful however :-)

Bibliography:

The default feathers-chat app runs on NeDB (local filesystem JSON database).

Ciro Santilli managed to port it to Sequelize for PostgreSQL as shown at: github.com/cirosantilli/feathers-chat/tree/sequelize-pg

Amazingly confirms the wave particle duality of quantum mechanics.

The effect is even more remarkable when done with individual particles such individual photons or electrons.

Richard Feynman liked to stress how this experiment can illustrate the core ideas of quantum mechanics. Notably, he night have created the infinitely many slits thought experiment which illustrates the path integral formulation.

Ubuntu 23.04 install:

Hello world:

Install a package, e.g. Bookdown:

Do electrons spontaneously jump from high orbitals to lower ones emitting photons?

Explaining this was was one of the key initial achievements of the Dirac equation.

Yes, but this is not predicted by the Schrödinger equation, you need to go to the Dirac equation.

A critical application of this phenomena is laser.

See also:

TODO understand better, mentioned e.g. at Subtle is the Lord by Abraham Pais (1982) page 20, and is something that Einstein worked on.