# Basic epidemic math

We are living in an epidemic of armchair epidemiology, and far be it for me to contribute by giving my own feverish take as an expert of an unrelated field. Therefore, I solemnly swear that I will make no predictions about the present pandemic. I am not paid enough to make such predictions–and if you did pay me I would consider it my professional duty to find you a better expert.

What I can do for free, is read up on basic epidemiology, and digest the maths for you, dear reader. My sources: Wikipedia’s article on mathematical modeling and compartmental models, and some lecture notes I found. My expertise: during my PhD in physics, I frequently worked models like the one I’m about to discuss, only with electrons instead of people.

The SIR Model

The very first epidemiological that one learns about, is the so-called SIR model. This model divides the population into three groups (“compartments”): susceptible (S), infected (I), and recovered (R). Susceptible people are those who could be infected; infected people are those who are currently infectious; recovered people are those who are no longer infectious, and are immune to infection. “Recovered” can be a bit euphemistic, since one method of “recovery” is dying. Another method of “recovery” is by developing symptoms strong enough that the victim knows to quarantine themself (becoming less infectious).

# I read popular physics: The Milky Way

It’s time for another entry in my series where I read through physics articles in Scientific American, now through the eyes of a former physicist. It’s a gratifying exercise because I used to struggle through these when I was in high school. Now, if I struggle, I know it’s not my fault!

Today’s article is “New View of the Milky Way” by Mark J. Reid and Xing-Wu Zheng in the April 2020 issue. Oddly the titles in the print version never seem to match the titles in the online version–also the online version is paywalled this time, that means no images, sorry folks!

The main thrust of the article is that they used radio astronomy to map out the Milky Way galaxy. Now you might think that since we’re inside the Milky Way, we have an especially clear idea of its shape. But it’s surprisingly difficult, because determining the distance of stars is hard, and there are dust clouds in the way. If you’ve ever seen an image of the Milky Way as viewed from the outside, those are all artists’ conceptions and we don’t know what it actually looks like.

So the first thing I see in this article, is an image of the Milky Way, as viewed from outside. At first I thought, this is really neat, finally an image that’s more than just an artist’s conception. But nope, it’s just another artist’s conception. Created to be consistent with the study’s results, but still just art.

# Spinning Box experiment

For my monthly repost, I thought I’d reach way back to bring you this post from 2008.  I was a physics undergrad back then!

Here’s a physics experiment that you can try yourself right now. It’s fun, I promise.

First, you have to find a small rectangularly-shaped object. Nothing valuable or breakable. A box works fine. A book works too, but you may have to tape the book shut for best results. It is important that there are no square sides on the object. All sides must be rectangles!

Here’s my 3-d model of the box (created with Mathematica). Your own box might differ slightly in its shape, but it should be more or less the same. What are those sticks, you ask? They’re just imaginary lines I drew to mark the three principal axes. If you have an object like a cube or a sphere, one axis is as good as another. But for an object shaped like above, there are three special axes of rotation, called the principal axes.

Now, take the box and toss it up into the air. Give it some spin as you toss it. First, make it spin around the blue line, then the green line, and then the red line.* Observe any differences between the three. I will wait.

# Factorial experiments

cn: It’s math

When I was an experimental physicist, one of the difficulties was the sheer number of different knobs you could tune… the power of the laser, the rate of laser pulses, the angle of the laser, the material being measured, the temperature, and numerous other knobs more difficult to explain. The search space was too large, and I had to judiciously choose what things to measure.

But in some ways, it’s easier in physics. I had a lot of physics theory to inform my expectations. Suppose you’re designing a website for a personal business, there isn’t quite as much theory to tell you what design features will drive business. You might be stuck trying everything, throwing stuff at a wall until something sticks.

It turns out there’s some interesting math behind this. If you throw everything at a wall, that’s an awful lot of things. But there are ways to throw fewer things at the wall and get about the same information from your experiment.

I tried to make so that not all my links were COVID-19-related… so I have one thing.  Yeah, the problem with virus links is not just that we’re tired of them, it’s that they get out of date too quickly for a monthly link roundup.

Why Avatar has the Most Ironic Soundtrack of All Time | Sideways (video) – Avatar was a thing, I guess it must have had a soundtrack?  Apparently the director wanted the aliens to have totally alien music, blending all sorts of traditions, like nothing we’ve ever heard before.  So the composer consulted with an ethnomusicologist, and they made what was requested.  But the director rejected it over and over, and the movie got a bland soundtrack that I for one cannot remember.  The guy who made this video though, he’s just so unreasonably optimistic about this rejected soundtrack.  Does he think that if they made a soundtrack unlike anything anyone’s heard and put it in a blockbuster film, people would like it?  It was a fool’s quest from the start.  Gosh, I’m sure I would like it, but I also like pop songs where the vocals are a half-step out of key.

For those who don’t like video, the story is also in an article written by the ethnomusicologist.

The rest are coronavirus.

I Can’t Stop Watching Contagion | Folding Ideas (video) – Content warning: anxiety-inducing.  Dan Olson talks about a 2011 film about a pandemic, sort of like how I wrote earlier about Doomsday Book, but he does it better.

# Working out

Another thing I have been doing while stuck at home, is weight training. That’s out of character for me. I’ve never “worked out” in my life, never gone to a gym, or otherwise made a deliberate plan to exercise. Not since P.E. classes in middle school. I used to go hiking occasionally, but stopped several years ago as I decided I wasn’t fond of the activity (in retrospect this may have been asthma-related).

The story goes that my husband goes to the gym on a regular basis. All the gyms are closed. So he bought some gym equipment, which we store on the balcony. I proposed I could join him, so this happened.

Each day, we start with some jumping jacks to warm up, and a few stretches. Then my husband picks out some exercises from a book or youtube, focusing on a particular group of muscles. For each exercise we repeat the motion for several sets, and around 10 repetitions per set. The next day we work on a different group of muscles.

It’s completely different from my P.E. classes from when I was a kid.

# Heaven’s Vault, Disco Elysium

My blog has hit a bit of a slump–the coronavirus has taken the wind out of everything that isn’t itself. But if I were to examine the more direct causes for the slump, I’d have to look at video games. Yes, I’m playing video games instead of blogging. Well why don’t I blog about video games?

In the past month, I played two narrative video games: Heaven’s Vault and Disco Elysium.  These are my brief reviews.

Heaven’s Vault is a game about an archaeologist trying to understand the collapse of an ancient civilization. It takes place in a low-tech sci-fi environment where people sail between the “moons” of a nebula, but only really through the use of ancient tech. This game features four main gameplay loops: sailing between moons, exploring sites, dialogue trees, and translating ancient text.