Ciro Santilli @cirosantilli 37

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Position representation Updated 2025-07-16

A way to write the wavefunction

ψ (x)

such that the position operator is:

x

(1)

i.e., a function that takes the wavefunction as input, and outputs another function:

x ψ (x)

(2)

If you believe that mathematicians took care of continuous spectrum for us and that everything just works, the most concrete and direct thing that this representation tells us is that:

the probability of finding a particle between $x_{0}$ and $x_{1}$ at time $t$

equals:

\int_{x_{0}}^{x_{1}} x ψ x, t d x

(3)

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Protein complex Updated 2025-07-16

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Proton Pass Updated 2025-07-16

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proton.me/pass

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Quantum LC circuit Updated 2025-07-16

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A quantum version of the LC circuit!

TODO are there experiments, or just theoretical?

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Raspberry Pi 3 Updated 2025-07-16

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Model B V 1.2.

SoC: BCM2837

Serial from cat /proc/cpuinfo: 00000000c77ddb77

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Cutoff energy Updated 2025-07-16

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Cython Updated 2025-07-16

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Energy-momentum relation Updated 2025-07-16

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GFP tagging Updated 2025-07-16

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Using green fluorescent protein as a protein tag.

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How many logical qubits are needed to run Shor's algorithm? Updated 2025-07-16

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quantumcomputing.stackexchange.com/questions/5048/how-many-logical-qubits-are-needed-to-run-shors-algorithm-efficiently-on-large

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Room temperature and pressure superconductor Updated 2025-07-16

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LK-99:

www.tomshardware.com/news/superconductor-breakthrough-replicated-twice

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Ruby on Rails React integration Updated 2025-07-16

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Integrations React integration:

github.com/shakacode/react_on_rails: webpack and server-side rendering
github.com/reactjs/react-rails Official on the React side only. Demo app linked from package: github.com/BookOfGreg/react-rails-example-app and how it fails: github.com/BookOfGreg/react-rails-example-app/issues/30... The related projects section has some good links:
shakacode/react_on_rails
github.com/hyperstack-org/hyperstack transpiles Ruby to JavaScript + React. What could possibly go wrong? :-)

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Selected Papers on Quantum Electrodynamics by Julian Schwinger (1958) Updated 2025-07-16

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Julian Schwinger's selection of academic papers by himself and others.

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Time-independent Schrödinger equation for a free one dimensional particle Updated 2025-07-16

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\frac{\partial ^{2}}{\partial x ^{2}} ψ (x) = - \frac{2 m E}{ℏ ^{2}} ψ (x)

(1)

so the solution is:

ψ (x) = e^{\frac{2 m E i x}{ℏ}}

(2)

We notice that the solution has continuous spectrum, since any value of

E

can provide a solution.

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Project Gutenberg remove line breaks Updated 2025-07-16

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ubuntuforums.org/archive/index.php/t-1132578.html

Their txt formats are so crap!

E.g. for;

wget -O pap.txt https://www.gutenberg.org/ebooks/1342.txt.utf-8

a good one is:

perl -0777 -pe 's/(?<!\r\n)\r\n(?!\r\n)( +)?/ /g' pap.txt

The ( +)? is for the endlessly many quoted letters they have, which use four leading spaces per line as a quote marker.

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Proton-to-electron mass ratio Updated 2025-07-16

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Proton VPN Updated 2025-07-16

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God, I love this company so much.

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Python classes Updated 2025-07-16

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Richard Feynman Quantum Electrodynamics Lecture at University of Auckland (1979) Updated 2025-07-16

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Talk title shown on intro: "Today's Answers to Newton's Queries about Light".

6 hour lecture, where he tries to explain it to an audience that does not know any modern physics. This is a noble effort.

Part of The Douglas Robb Memorial Lectures lecture series.

Feynman apparently also made a book adaptation: QED: The Strange Theory of Light and Matter. That book is basically word by word the same as the presentation, including the diagrams.

According to www.feynman.com/science/qed-lectures-in-new-zealand/ the official upload is at www.vega.org.uk/video/subseries/8 and Vega does show up as a watermark on the video (though it is too pixilated to guess without knowing it), a project that has been discontinued and has has a non-permissive license. Newbs.

4 parts:

Part 1: is saying "photons exist"
Part 2: is amazing, and describes how photons move as a sum of all possible paths, not sure if it is relativistic at all though, and suggests that something is minimized in that calculation (the action)
Part 3: is where he hopelessly tries to explain the crucial part of how electrons join the picture in a similar manner to how photons do.
He does make the link to light, saying that there is a function $P (A, B)$ which gives the amplitude for a photon going from A to B, where A and B are spacetime events.
And then he mentions that there is a similar function $E (A, B)$ for an electron to go from A to B, but says that that function is too complicated, and gives no intuition unlike the photon one.
He does not mention it, but P and E are the so called propagators.
This is likely the path integral formulation of QED.
On Quantum Mechanical View of Reality by Richard Feynman (1983) he mentions that $E$ is a Bessel function, without giving further detail.
And also mentions that:
$E = f (1, 2, m) P = f (1, 2, 0)$
(1)
where m is basically a scale factor.
such that both are very similar. And that something similar holds for many other particles.
And then, when you draw a Feynman diagram, e.g. electron emits photon and both are detected at given positions, you sum over all the possibilities, each amplitude is given by:
$c \times E (A, D) \times E (D, B) \times P (B, C)$
(2)
summed over all possible $D$ Spacetime points.
This is basically well said at: youtu.be/rZvgGekvHes?t=3349 from Quantum Mechanical View of Reality by Richard Feynman (1983).
TODO: how do electron velocities affect where they are likely to end up? $E (A, D)$ suggests the probability only depends on the spacetime points.
Also, this clarifies why computations in QED are so insane: you have to sum over every possible point in space!!! TODO but then how do we calculate anything at all in practice?
Part 4: known problems with QED and thoughts on QCD. Boring.