To balance out a very gradual slowing of the Earth’s rotation, scientists are adding an extra second to the day on Tuesday.
The so-called leap second is imperceptible to humans — there have been 25, most of them uneventful, since 1972 — but lately it has been known to throw many of the systems we use out of sync.
For some people in science and technology, the practice of adding extra seconds to the day with relatively little advanced warning is more disruptive than helpful. At its most harmless, the practice is criticized as anachronistic. (If humans can’t tell the difference and it will be thousands of years until a shift is noticed, is it really necessary? a writer at Quartz argued.) At its worst, the leap second can disrupt entire computer systems that were not made to account for flexibility in time.
For many computers, even a small wrinkle in time, like an additional second, can shut down an entire operation. During the last leap second, in 2012, sites including Foursquare, Reddit and LinkedIn reported service interruptions. Travelers flying Qantas Airways experienced delays when a global airline reservation system failed.
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This year, a few big plans are in place to prevent any Y2K-style havoc. Since roughly $4.6 million is traded on global exchanges in any given second, the markets are looking to prevent any glitches: Stock markets in the United States will end after-hours trading early, and markets overseas are resetting their clocks well in advance. And since 2011, Google has been developing a technique referred to as “leap smear,” in which the extra second is divided into even tinier bits of time spread over the course of the day.
The decision on whether to add a leap second is made by a group of scientists who make up the International Earth Rotation and Reference Systems Service. The group decides whether to adjust the length of a day based on changes in the Earth’s rotation.
“In the short term, leap seconds are not as predictable as everyone would like,” Chopo Ma, a member of the group’s directing board, told NASA.
Some scientists say the relatively short lead time from I.E.R.S. can lead to more glitches. Others say making sure time is precisely coordinated with computers is the right thing to do. Udo Seidel, who was working at Amadeus Software when its reservations system crashed at Qantas, is now working to simulate the effects of leap seconds on computer systems.
“If we cannot manage to make our systems handle a leap second,” Mr. Seidel told Wired, “then we have bigger problems.”
As scientists spent the day keeping a wary eye out for the glitch that could undo the Internet, nonscientists were using the Internet to fritter the time away. The crew at the HBO show “Last Week Tonight” built a website of one-second videos — one clip includes Nicolas Cage in a bear suit — called Spend Your Leap Second Here. In another corner of the Internet, people posted one-second selfies. And on Twitter, people shared their ideas for how to spend the extra time: