Oliver Steele

These are some hard questions my kids asked me when they were very young, with answers below:

• Why are far away things small?
• Why is it easier to pull a stroller (along a driveway with large gravel) than to push it?
• Why can we breath air but not dirt?

The challenge in answering this kind of question is to create an answer that’s comprehensible to anyone capable of framing the question. So, for example, the answer to the first question doesn’t have to do with ratios and similar triangles: this is a fine computer graphics explanation for undegraduates, but is (to use a metaphor) the assembly language version of an answer that can be written in Java. (Or the Java version of an answer that can be written in Haskell

Sometimes the process of constructing an answer means porting an answer back from a mathematical formulation, to an implementation on top of common-sense physics; a process that must be similar to translating a work between languages.

Some attempts at answers:

Why are far away things small?
So that they’ll fit. You can see many more far away things than near things; their images have to be smaller so that they’ll all fit in your eye.

Why is it easier to pull a stroller than to push it (over a rough surface)?
Because there’s many ways away from you, but only one way towards. When the gravel turns the wheels ithe stroller tends to change direction, but if you’re pulling it, there’s only one way that matches up with force from your hands.

This is similar to the well-known reason that it’s harder to pull into a parking space than out of one: there’s fewer ways for the car to be out of the space than in it. This is a useful principle to remember when you’re deciding whether to back into a space now or back out of it: back out of it later, because the rest of the task is easier. (This doesn’t apply when you’ve got extra time when you park, but you’ll be leaving in a hurry.)

Why can we breath air but not dirt?
(A dead-end answer is that air has free oxygen. But even if dirt enough too, our lungs couldn’t extract it.)

Our lungs can squeeze out air but not dirt because air is a gas. When you press on a gas, it goes wherever there’s less of it. When you press on a solid, it goes in the direction you press it. This means that squeezing a gas from all sides, like our lungs do, moves it out. Squeezing dirt from all sides would just compact it.

I’ve been reading about Col John Boyd’s OODA Loop — Observe, Orient, Decide, and Act — and I realized that some of the thinking based on this theory articulates intuitive reasons I’d had for liking zero defect milestones. Strategies such as “shortening your loop” and “getting inside” the enemy’s loop are those that zero defect milestones facilitate. If “Act” is the process of shipping a release, keeping the software in a shippable state preserves the ability of an organization to change the length of its loop based solely on external schedule requirements, without added constraints due to the accumulation of quality and other technical debts.

It’s notable how often MBA types use military analogies to justify business processes. I used to think this was to play up the glamour of business competition. Having learned something about the military from books such as Cognition in the Wild , it’s apparent that there’s another reason too. It’s not because business is war, but because war is business. The armed forces are the largest test field for the study of management, administration, and the creation and maintenance of institutional knowledge. Many of the processes for performing these tasks are independent of the line work that is being managed.

In the early nineties, On Technologies released a wonderful product, called Instant Update, which allowed multiple workers to view and edit a shared rich text document. Many authors could edit the document at once, changes to separate paragraphs were resolved automatically, and a simple dialog box let you choose how to resolve each conflict. Each paragraph was marked as to who last modified it when.

Unlike Microsoft Word, which now does some of this (but didn’t then), publishing your changes was as simple as pressing the “Update” button.

At Apple Cambridge, we used this to collaborate on design discussions within the office, and between Cambridge and California. (Larry Tesler was a frequent contributor from there.)

I’ve missed this tool for a long time. Lately, at Laszlo we’ve been using a wiki for technical and planning discussions. This seems to be the fad in engineering organizations, and justly so.

A wiki is just Instant Update without the wysiwyg interface, without the line-by-line conflict resolution, but implemented as a web application, so that it can be universally deployed.

Double Trouble

In four months Miles will be twice Charlotte’s age. (He will be 10; she will still be 5.) A year ago, he was also twice Charlotte’s age. (He was 8; she was 4.) A year from now, he will have spent exactly one year at twice her age (if you truncate ages to the year), but that year will have been distributed into two intervals, at the beginning and end of a two-year period. See the gray portion of the illustration.

Back to the Future

Miles was recently twice Charlotte’s age (and will be again). But there was a time at which Charlotte’s age was twice Miles’s age. (But there wasn’t any time at which Charlotte wasn’t twice as old as Miles.)

A Family of Squares

Until today I was the product of my children’s ages, and we are all perfect squares.

A wedding is a coercion operator from a state, to an event that marks the beginning of the state. (The English word “marriage” denotes either.) The advantage of an event over a state, is that it can be used as a reference for other events, symbolizing happiness, community, fertility, ,etc., by placing these other events at the same time and location. This is analogous to time binding in linguistics.