# I tried microtonal music and liked it

The pitch of a note is determined by its frequency, and frequency can vary within a continuous spectrum. And yet, in the western music tradition, we only use frequencies with discrete values. That’s not a bad thing, but it implies a whole world of possibilities not explored. Microtonal music, also known as xenharmonic music, sets out to make use of the unused frequencies.

I recently tried listening to a lot of microtonal music, because I discovered that you can find lots of it through the microtonal tag on Bandcamp. Sure, a lot of it isn’t very good because anyone can put music on Bandcamp, but there were enough gems that I continued to peruse the tag. I’ll share just two examples. First, I selected Brendan Byrnes, because I think his music has the most pop appeal, while also being unapologetically microtonal.

# An altruistic Prisoner’s Dilemma

This is a repost of an article I wrote in 2015, with a short postscript added.

Jeff Kaufman talks about an ethics trade that he sometimes does with a friend.

I have a friend who is vegan for animal welfare reasons: they don’t think animals should be raised for food or otherwise suffer for our benefit. On the other hand, they used to really enjoy eating cheese and miss it a lot now that they’re vegan. So we’ve started trading: sometimes I pass up meat I otherwise would have eaten, and in exchange they can have some cheese.

This is a win-win for the vegan, since they get to have some cheese, and there is no net harm to animal welfare.  It is not clear what’s in it for Jeff though, except for his idiosyncratic preference to have such trades.  I am not sure this is an interesting scenario by itself, since, in general, any trade is possible with sufficiently idiosyncratic preferences.

Therefore, I propose a similar scenario, which I’ll call the vegan/omnivore dilemma.

# Tessellation symmetry

This is (the last) part of my series about symmetry in origami.

A tessellation is a set of tiles that fill up a 2D plane. And I do mean the entire 2D plane, infinite in extent. When we talk about origami tessellations, these are models that could hypothetically fill a 2D plane, if we had an infinite amount of paper. In practice, an origami tessellation is finite, but for the purposes of discussing symmetry, we will imagine them to be infinite.

An example of an origami tessellation, the Rectangular Woven Design by David Huffman

Previously, I only discussed two kinds of symmetry transformations: rotation, and reflection. However, many tessellations have repeating patterns, and this in itself is another form of symmetry. Are there other kinds of symmetries that we forgot? Let’s take an inventory of all the possible kinds of symmetry transformations.

# Symmetrical coloring theorem

This is an appendix to my series about symmetry in origami. Here I will provide a proof that my construction of symmetrical colorings works.

While I try to make the series accessible to people who do not know much about math, I don’t think there’s much point in trying to make this proof broadly accessible. This is intended as a reference for people with some experience with group theory. (You need to know about cosets at the very least.)

# One: the universe’s favorite digit

This is a repost of an article I wrote way back in 2011.  I’m still proud of figuring this one out.

Out of all the digits, from zero to nine, one is the most common.  This has to do with the log scale.

The log scale captures an important fact that is true of many quantities in life.  Take money for instance.  If you have one dollar, then earning another dollar is great because you’ve doubled your money!  If you have a million dollars, earning another dollar does not make much of a difference.  Small changes matter less the more you already have.

This is true on a log scale too.  On a log scale, 1 is the same distance from 2 as 100 is from 200.  The higher you go up, the more the numbers all get smooshed together.  What does that mean for the digits from zero to nine?

In the above picture, I show a log scale.  And on that scale, I highlighted in blue all the regions where 1 is the first digit of the number.  You should see that the blue regions cover more than one tenth of the log scale.  In fact, they cover about 30%.  And so, if we pick numbers randomly on the log scale, about 30% of those numbers will have 1 as their first digit.

Just for fun, let’s apply this concept on the fundamental constants of nature.  I will compare two hypotheses: [Read more…]

# How to make symmetric colorings

This is the fourth part of a series about symmetry in origami.

Given an origami model, what are the possible symmetric colorings?

This is a question I posed in an earlier post, and I said I didn’t know the solution.  I thought about it a lot, and I found the solution. I will write up a mathematical proof in a later post.  Here I will just explain the result.

A brief review: Each origami model has an associated shape symmetry group, which is the set of all transformations (rotations and reflections) which leave the shape unchanged. There is also an associated color symmetry group, which leaves the shape and colors unchanged. Then there is the pattern symmetry group, which may swap the identities of some of the colors, but leaves the color patterns unchanged. In this post, C is the color symmetry group, and P is the pattern symmetry group.

I defined a “symmetric coloring” to be one where P is “large” and C is “small”. I didn’t say how large P needed to be, or how small C needed to be, but it doesn’t matter. I found a method that can construct any and all symmetric colorings.

### Fundamental domains

Suppose we want to find a symmetrical coloring of a cube. First question: Are we assigning a color to each face, each vertex, or each edge? We want to find a general solution that will work in all three cases, as well as any more complicated case. So the first thing we need to do is divide the cube into fundamental domains.

Each triangle on the cube’s surface represents a fundamental domain. In total, there are 48 fundamental domains.

# The impossible symmetry

This is the third part of a series about symmetry in origamiPreviously, I established the idea of a symmetry group, a set of transformations that leaves a model’s shape unchanged.  Next, I talked about how the colors of a model define a subgroup.  In this post, I will explain the concept of a normal subgroup.

### First illustration: The Umulius

We begin with a case study of one of my favorite models, Thoki Yenn’s Umulius.  “Umulius” is a Danish insult meaning “impossible person”.

Ignoring the colors, the Umulius nearly has cubic symmetry.  Here I have a series of diagrams “cleaning up” the details to make the underlying cubic symmetry clear.