Weighing whether to wait a second, scientists put off decision for three years

I’m sure you are all as relieved as I am that Thursday’s meeting of the International Telecommunications Union postponed its scheduled vote on whether to drop the leap second:

http://www.bbc.co.uk/news/science-environment-16625614

The next planned one-second adjustment to Universal Time, at the end of June, will go ahead. And delegates will return home for consultations before the issue arises again at the World Radio Conference in 2015.

The Americans, French and Japanese are reportedly leading the charge for abolition, while China, the U.K. and Canada are among those opposed. Me too, although I don’t get to vote.

We need to keep the leap second because otherwise we begin to lose contact with, and understanding of, what we set out to measure in the first place: time as a measure of human experience. Not to get too hyperbolic, the cycles of day and night, spring, summer, fall and winter, life and death.

Up till the 1950s, Greenwich Mean Time set the world standard for precisely measuring time, and it did so through direct observation of Earth’s rotation and motion relative to the sun. Then atomic clocks were developed that could keep time very consistently around the world, independent of actual solar observations. In 1967, the length of the second was defined as a precise number of “transitions” (no, I have no clue either) of a caesium atom.

The problem that emerged (and that people knew existed before adopting the atomic standard) is this: the yardstick was more precise than what we were trying to measure. Earth’s rotation varies very slightly year to year, due to things like tides, glacial rebound and earthquakes, and in any case has been slowing down since the planet’s formation. The leap second was introduced in 1972 as a way to keep Universal Time (atomic time) synced with GMT (till then, purely solar time). An extra second would be inserted (or dropped) in any year calculated as running long (or short). The resulting adjustable measure was called Co-ordinated Universal Time (UTC), for all purposes now interchangeable with GMT.

One argument cited at this week’s ITU meeting for wanting to drop leap seconds is that they occur whenever the difference between UTC and mean solar time nears a full second -- in other words, at irregular, unpredictable intervals. (Eleven seconds were added in the period from 1972 to 1983, but none in the period 199-2004. Messy.)

That adds unwanted complexity and (theoretical) possibility of error to some navigation or communication systems, like satellites in orbit or interplanetary probes. GPS and its Russian counterpart, GLONASS, for example, ignore leap seconds in their internal operations. (But having already opted out, the global positioning providers aren’t the ones pushing for a change.)

Agreed, skipping leap seconds would have virtually no affect on anyone. At the current rate of slippage, it would take about a century to accumulate a minute’s divergence from observed solar time, roughly 6,000 years to total one hour. Proponents of the change have seriously suggested that we simply wait for that to happen, then insert a “leap hour.” In 6,000 years or so!

I have my own suggestion for the time-masters: you can drop the leap second if you first redefine the length of the second. Otherwise, stick with the status quo.

As of June, there will have been a total of 25 seconds inserted in the 40 years we’ve followed the current atomic definition; not one second has been removed. That’s an upward adjustment every two out of three years. Pretty clearly, the baseline used to initially calculate the length of the second was decades out of date; most of the correcting that’s now being done is for slowing that had already occurred by the 1960s.

Build that two-thirds of a second per year (or half that much if you’re chicken) into a recalculated atomic definition. Don’t even worry if it ends up proving high. Earth’s rotation is inexorably slowing down; eventually it will fall into sync. Just wait a century or two or three and you’ll look like geniuses.

My bottom line is this: yes, in this e-linked world we need consistency and accuracy in timekeeping. And yes, defining the second as 9,192,631,770 cycles of a caesium 133 transition does give consistent, repeatable results. But unlike, say, distance – which we can and do assign arbitrary measuring sticks to – time on Earth comes with its own built-in measures: the day, the year.

And by built-in I mean built into us humans. The week, the hour, the minute and the second may seem arbitrary, but they are just names for divisions or multiples of those natural measures.

We’ve decided to call one-86,400^th of a day a second – and that real definition has to take precedence over a half-century-old (and apparently low-balled) estimate of how many times a caesium atom can undergo a particular change in that amount of time. Sorry, but the cycles of Sun and Earth, even if they are fuzzy and changeable, must define time on this planet. Thinking that its measurement can be decoupled from them is simply perverse.

(Apologies if this post ran a bit long. I arbitrarily inserted a couple of leap paragraphs.)