Mediocre physics teachers who are trying to explain the concept of entropy often say that entropy is a sort of measure of chaos, with increases in entropy meaning increased chaos. I found that claim confusing from the first time I heard it; once I got a grip on the concept of entropy, I realized that it’s simply false: entropy has little to do with chaos. Consider, for instance, a bucket into which different-color paints have been slopped, forming a chaotic mess of colors. That mess has less entropy than it will after you mix it to a orderly uniform color, which is the opposite of the way the entropy-means-chaos idea would have it. Likewise, a room filled with a chaotic mixture of air at different temperatures has less entropy than it will after the temperatures all equilibrate to the same value. Or take a situation in which you have two cylinders, one filled with air and the other evacuated, and connected by a pipe with a valve. Once you open the valve, half the air will rush from the full cylinder to the empty; this will increase the entropy. But which situation is more chaotic than the other? Relative to the everyday meaning of chaos, it’d be hard to say.

Buypartisan, adj. As of, or pertaining to, a situation in which the partisans have been bought. Commonly misspelled.

Over the years, I’ve seen entirely too much confusion surrounding the electrical quantity known as power factor. Even its definition is often confused. Roughly half the sources I’ve encountered define it to be the cosine of the phase difference between current and voltage – a definition that was adequate sixty years ago when waveforms were almost all sinusoids of the same frequency, but which is entirely inadequate now that both current and voltage are commonly chopped up using silicon. The “phase” of a non-sinusoidal signal can have many definitions, and probably none of those definitions yields a meaningful number for power factor. The old formula is still fine as a formula for the power factor in the case that one is dealing only with sine-wave power supplying old-fashioned devices, but fails as a general definition.

“Hmm, I shouldn’t be going anywhere with the car making a noise like that.”

The weblog software that people seem to choose by default these days is Wordpress. Wordpress has a lot of features, is widely used and liked, and is offered as a free single-click install by a lot of web hosting providers. But several of the Wordpress blogs I follow have been hacked at some point. When I looked into blogging software, the reason became clear: Wordpress is a large piece of software, written in PHP, a language which originally was designed arose in a world where security concerns were much less significant, and which has addressed those security concerns (and other evolving needs) by adding things, not by a fundamental redesign. (UPDATE: it appears I was being far too generous to PHP in saying that it had been ‘designed’.) The result is a rather large, complicated language, which is hard to learn well enough to master all the security issues. Also, Wordpress uses an SQL database to store weblog entries, comments, and such, which opens up possibilities of SQL injection attacks. The single-click install is easy, but upgrading is not so easy; and if one runs the software for any length of time, one has to upgrade much more often than one has to install.

This blog quite intentionally has very little formatting. “Quite intentionally”, because not only does it save my effort, but also lets mobile devices with tiny screens format the text the way they want, without having to fight my formatting. But there’s one piece of formatting code I use: limiting the width of the text column. That is a principle of typesetting that I disliked at first, but eventually accepted: long lines are just too hard to read; the eye too easily loses its place when scanning back to the left to get to the start of the next line.

There are a number of things which I’ve accumulated, as being good to write, but which I either haven’t written or have written for a very limited audience. They cover a wide variety of topics, and range in scope from technical details to the largest of questions. Here they come…