The bizarre, quasi-regular global event known as the leap second is the product of a somewhat discomforting power struggle between modern society and our planet. It comes down to this: our hyperconnected world requires timekeeping to maintain a level of precision and consistency that our ever-so-slightly-irregularly spinning planet's natural timescale just can't deliver.
The leap second "is an attempt to keep the rotational location of the Earth in sync with the rest of the solar system," according to John Lowe, leader of the Time and Frequency Services Group at the National Institute of Standards and Technology (NIST).
That sounds pretty grand and important — so why is its existence going up for a vote by an international body in charge of setting time standards in Geneva this fall? Because what it's really about is keeping the clock in the sky in sync with the clock in Boulder, Colorado (or wherever your nation's atomic clock of reference is located).
"It's what humans have always done — we've used the sun as our clock," Lowe said. But by this measure, the days are getting longer, because Earth's spin slows down by about a few milliseconds each year. That's where the leap second comes in. Adding one second every couple of years keeps our atomic clock from straying too far from the solar clock.
Every time a leap second gets instituted, however, software engineers must make adjustments to the many programs that keep the world-as-we-know-it running. And doing that opens up opportunities for errors.
The next leap second event will occur at the very last second of the day on June 30 of this year. The last one occurred in 2012, and caused temporary outages among web giants including Reddit, LinkedIn and Gawker. Some warn that the leap second may be a ticking time bomb that will wreak havoc upon more serious systems, such as air traffic control.
Lowe is not particularly worried about this, mostly because the other 25 leap seconds that have been implemented since 1972 worked out fine for the most part, but opinions are mixed.
To make matters more difficult, Earth's spin doesn't even slow down at a regular rate. As a result, it has to be implemented on a case-by-case basis — unlike the leap day, which is known years and years ahead.
Everybody's already got the leap day written into their software, but "the leap second has to be manually inserted," Lowe said. Software engineers only ever have about six months to prepare for a leap second event.
Generally, we just ignore the "extra" time that the planet randomly inserts into our days. We forgo this intuitive natural clock in favor of a far less intuitive – but more precise – natural clock: the atomic clock. Just as there's a hunk of metal sitting in a vault in France that defines the kilogram, the cycling of cesium atoms between two different energy levels provides a physical standard for the second. Every 9,192,631,770 cycles marks the passing of a single second.
If we were to simply follow the time set by cesium atoms and ignore the slight slowing of Earth's spin, the discrepancy between the two clocks would be nearly imperceptible. Over the course of the next millennium, this slowing might require more frequent leap seconds — but as Lowe said, "we're still only talking minutes over the course of any individual's lifetime." He added that it is, however, "a big deal for astronomers." In keeping track of the timing for a lunar eclipse or a comet, astronomers would have to adjust to accommodate for that small discrepancy.
But ultimately, the issue is the buildup of many leap seconds. By the time the year 2500 rolls around, we may be an hour out of sync.
"I would call that a problem," said Lowe. High noon by the sun would creep away from 12 p.m. Sundials would slowly be rendered obsolete.
It's also important to stay in sync with natural day and night cycles for reasons beyond tradition and sentimentality. Keeping track of time by this cycle is so basic that it is ingrained in our biology – and that of most living things – as the orchestrator of many physical, behavioral and mental changes. The increased risk of serious health conditions including heart disease and diabetes observed among shift workers starkly demonstrates why we can't ignore this natural clock altogether.
Still, going through all of this effort to correct for a one-second inaccuracy seems overkill. Plus, we already do that ridiculous thing called daylight saving time, which deliberately throws our atomic clock-based time off the solar clock for half the year.
Instituting a less frequent "leap minute," or something to that effect, would seem like a reasonable compromise. The problem Lowe sees with that solution is that it would increase the chance of having an even more chaotic "mini Y2K," because "no one would be prepared for it when we finally got around to the leap minute." At least the leap second keeps software engineers on their toes.
As the technical difficulties following the leap second in 2012 demonstrate, however, a lot of software systems aren't well-adapted to work with leap seconds, either. They still only happen every couple of years or so, which is a fairly long time, relative to the lifespan of a lot of software.
So the vote over the leap second this fall will be all-or-nothing. Unless it gets postponed again, of course. The scientific community has been arguing over this issue for over a decade. The issue is trivial enough that NIST – the organization that dictates time across the United States – "does not have a position on it," according to Lowe. Yet at the same time, it demands a deep and strangely unsettling decision between keeping the peace in the computerized world and keeping in sync with the cosmos.
The vote could go either way. But we can be sure that even if we get rid of the leap second, we can never really break free from the solar clock. In the end, the cosmos always wins.
