Not about saving daylight

We’ve just gone through the annual ritual of Falling Back, shifting our clocks by an hour to conform to Standard Time. It’s the regular opportunity for scientists to point out, with either smugness or exasperation, that all summer we haven’t really been Saving Daylight; that there is exactly the same amount of daylight regardless of what our clocks read. Sometimes they wander off into explanations of Local Solar Time, Standard Time Zones and, if not quickly stopped, bring up atomic clocks.

Here we will avoid that sort of thing. In the interests of understanding other people, or at least building character, we’ll look at time from the standpoint of non-scientists. It’s not the same time as we understand, and translation is in order.

To a scientist, time is a coordinate, like the lines of latitude and longitude you find on a map of the Earth. Those lines aren’t actually there, in the sense that driving across Kansas you would see a blue-ink north-south line labeled “100º West Longitude” running through the wheat fields. More importantly, you could start your longitude from Paris instead of Greenwich; 100º West Longitude would go through different wheat fields, but you’d still calculate the same number of miles between Los Angeles and New York. No physical thing you can figure can depend on your choice of coordinate system.

To any modern person, time is much less tractable. It’s a somewhat mysterious thing displayed by clocks, smartphones, watches—though sometimes imperfectly (especially by microwave ovens). It has an objective existence: you have to be at work by 9am, get the kids to soccer at 7pm, be in line for the restaurant by 8:30 or they’ll cancel your reservation. You are not at liberty to shift your time by an hour, fifteen minutes, half a day, something that to a scientist is a trivial coordinate translation. He may get the same answer in his calculation; you won’t.

And social time is asymmetric: you don’t get your eight hours of sleep evenly before and after midnight (who turns in at 8pm and rises at 4am?). The standard 9 to 5 working day is not quite centered on noon, but more importantly leisure time activities are heavily weighted toward the evening. School sports (most of them), prime time TV, going out for dinner and a movie happen in the later part of the waking day.

This is the rationale for Daylight Savings Time (DST): rather than have the extra summertime hours of daylight fall evenly before and after noon, the whole structure of social time is shifted so that more of them occur in the later, leisure-time part of our day. In principle things like kids’ soccer games and Sunday outdoor barbeques could shift their schedules individually to take the time of sundown into account; in practice, it’s far easier just to shift the whole interconnected mass of social time at once.

It’s not actually a very convincing rationale. In the first place, applied nationwide it’s pretty crude. The time of sunset at Seattle, without DST, is something like 3 ½ hours later in midsummer than in midwinter; which is a bigger difference than San Diego (in the same time zone) enjoys with DST. As it is, Halloween falls in Daylight Savings Time in the US—exactly when you’d rather have the trick-or-treating darkness happen earlier, so the kids could be home at a decent hour.

And it only really holds for activities we do outside without artificial light, which are getting pretty rare nowadays. Even Little League fields mostly have lights. At the other end of the year, it completely ignores the fact that there are things we do in the winter for which a bit of extra daylight would be welcome: walking home from football practice, say.

So—perhaps we should just admit that social time has come unstuck from the Sun, and stay on Daylight Savings Time all year? Our astronomer, surprisingly, was not appalled at the idea. “It has darkness later in the morning, which means there’s more of a chance that people out early will notice the sky. If someone out walking their dog, in the quiet before things have started happening, looks up and notices Venus or Mercury as a morning star—well, it might just be worth it.”