#PhysicsFactlet
I had to redo an old animation about quantum tunnelling in the time domain, so why not post it here?
#QuantumMechanics #ITeachPhysics
A few details:
* The incident and reflected waves interfere, creating fringes in the wavefunction modulus when it hits the barrier.
* Even when far away from the barrier, the wavefunction of the "free" particle is slowly broadening.
#PhysicsFactlet
It's a foggy day here in Albion, so let's talk about light (multiple) scattering!
Fog is composed of micrometre sized water droplet that can scatter light. This has two main effects: some of the light that was supposed to reach your eyes don't (because it is scattered away), and some of the light that was not supposed to reach you gets scattered into your eyes.
The denser is the fog and the further an object is from you, the more likely light is to be scattered away before it reaches your eyes. The amount of unscattered light (i.e. the one your eyes can use to form a sharp image) goes down exponentially (Lambert-Beer law), so an object in the fog gets dimmer pretty quickly. On the other hand there is a chance that light that was never meant to reach you is now scattered into your eyes, but since it arrives from a largely random direction, mixed up with a lot of other scattered light, your brain perceived it as a white blur on top of everything else. And since far away object were already dim, this white halo can easily overpower them, so you can't see them anymore.
#PhysicsFactlet
Do you want an interpretation of quantum mechanics that doesn't really work that well in practice, but that would look fantastic for your Sci-Fi novel? I have for you "Many interacting words" (not to be confused with the similarly named "Many worlds interpretation").
In this interpretation the universe is 100% classical, but instead of being one universe there is a VERY large number of them, all classical and weakly interacting with each other. In particular each particle is classical, but is repelled by its "copies" in the other universes. This is able to replicate a lot of the most weird effects of quantum mechanics. For instance, classically a particle is not able to overcome a potential barrier if it doesn't have enough energy to do so, but in this interpretation the particle would be repelled by its copies, so it has a non-zero chance of getting enough of a kick to jump on the other side of the barrier, producing the phenomenon we usually call "quantum tunnelling".
Another effect replicated by this model is the "zero point energy" i.e. the fact that the lowest energy a particle can have is not zero, but a bit higher than that. In this interpretation this comes to be because the particle (which is classic) would like to sit at zero energy, but so do all of its "copies", and they repel, so none of them can really sit at zero energy.
If you want, in this interpretation the very fact we see quantum effects is evidence of parallel universes!
https://journals.aps.org/prx/abstract/10.1103/PhysRevX.4.041013
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Schematic of the epicycle model, as requested by @johncarlosbaez (see https://mathstodon.xyz/@johncarlosbaez/113652794327730499 for his thread on the topic).
Apart from having (hopefully) more colorblind-friendly colors, this one is in the #PublicDomain instead of being copyrighted.
#Physics #Astronomy
#PhysicsFactlet: The "Ashcroft/Mermin Project" Chapter 7: Crystal systems
As a Bravais lattice must be invariant under discrete translations, there are only a small number of possible types of Bravais lattices (5 in 2D and 14 in 3D).
#Physics #ITeachPhysics
#PhysicsFactlet: The "Ashcroft/Mermin Project" Chapter 6: Diffraction from a crystal
A wave with a wavelength comparable with the interatomic spacing of a crystal will diffract, resulting in intensity peaks at different angles, that act as a "fingerprint" of the crystal structure.
#PhysicsFactlet
A work in progress (trying to show diffraction by a crystal, but right now the whole thing is way too messy).
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Not a great animation, but I made it for a lecture, so I am sharing it 
Electric (red line) and magnetic (black lines) fields of the TE₁,₁ mode propagating in a rectangular waveguide.
#PhysicsFactlet: The "Ashcroft/Mermin Project" Chapter 5: The reciprocal lattice
Every crystal plane is perpendicular to a combination of the reciprocal lattice vectors. The (integer) coefficients of these combinations are known as "Miller Indices".
#PhysicsFactlet: The "Ashcroft/Mermin Project" Chapter 5: The reciprocal lattice
The "reciprocal" of a Bravais lattice is the set of k-vectors that yield a plane wave with the same periodicity of the Bravais lattice (i.e. effectively the Fourier transform of the lattice).
#PhysicsFactlet: The "Ashcroft/Mermin Project" Chapter 4: Crystal Lattices
Once we have the Bravais lattice, we can fully describe a crystal structure by specifying how the atoms are arranged around the lattice points (i.e. the "basis").
#PhysicsFactlet: The "Ashcroft/Mermin Project" Chapter 4: Crystal Lattices
The "Wigner-Seitz" primitive cell is the region of space that is closer to a given point in the lattice. It has the advantage of being a primitive cell with the same symmetries as the Bravais lattice.
#PhysicsFactlet: The "Ashcroft/Mermin Project" Chapter 4: Crystal Lattices
A Bravais lattice is an infinite array of points generated by discrete translations, so that every point can be written as a (integral) linear combination of the basis vectors.
#PhysicsFactlet: The "Ashcroft/Mermin Project"
Chapter 2: Sommerfeld model
Electrons in a metal can be approximated as a Fermi gas, where only one electron can occupy a given state. At low temperature most of them are difficult to excite, because there is no free state available.
#PhysicsFactlet: The "Ashcroft/Mermin Project"
Chapter 1: The Drude Theory of metals
Electrons in a metal are accelerated by an electric field, but they keep bouncing on the metal defects/impurities. The resulting diffusion-like motion produces a roughly steady current.
#PhysicsFactlet: The "Ashcroft/Mermin Project"
I will try to (likely very slowly) go through the classic textbook "Solid State Physics" by Ashcroft and Mermin and make one or more animation/visualization per chapter.
This will (hopefully) help people digest the topic and/or be useful to lecturers who are teaching about it. As with all my animations, feel free to use them.
The idea is that the animations are a companion to the book, so I will give only very brief explanations here.
* You have my blessing to use my animations (#PhysicsFactlet) for your lectures etc. Just let me know when you do 
* I tried to explain how I make them here: https://www.youtube.com/watch?v=2zOUZlHKKbs
* I release almost all of my scientific visualizations in the public domain, and upload them (with the code used to generate them) on Wikimedia Commons. The only exceptions are those that I consider not interesting enough. You can find them here: https://commons.wikimedia.org/w/index.php?title=Special:ListFiles/Berto&ilshowall=1
