The Leap Second Is No More

Leap seconds have driven a raging debate in the metrological community for three decades. Now, that argument has been put to rest: The leap second is officially dead.

在过去的三十年里，闰秒问题在计量学界引发了激烈的争论。如今，这场争论终于尘埃落定：闰秒正式成为历史。

Doing away with an obscure metric the average person has been blissfully unaware of may seem like a novelty, but killing the leap second has major ramifications for technology you rely on every day. It also helps stave off what could’ve been a dangerous moment in time: The possibility of the world’s first negative leap second.

废除一个普通人几乎察觉不到的冷门指标看似新鲜，但取消闰秒对你每天依赖的技术有着重大影响。这也帮助避免了一个可能出现的危险时刻：全球首次出现负闰秒的可能性。

The International Bureau of Weights and Measurements (known by its French acronym BIPM) on Thursday said that in May 2027 it would stop issuing leap seconds, 32 of which have been added since 1972 to adjust what’s known as Coordinated Universal Time (UTC).

国际计量局（BIPM）周四表示，将于2027年5月停止发布闰秒。自1972年以来，为了调整协调世界时（UTC），人类已经增加了32个闰秒。

The world implemented the leap second in 1972 due to a growing gap between time measured with atomic clocks and time based on the Earth’s rotation. The reason for the discrepancy? The latter is slowing down due in large part to tidal friction caused by the moon and Earth’s rotation not lining up. The molten core of the Earth as well as oceans and the atmosphere also affect the spin rate.

世界在1972年引入闰秒，是因为原子钟测量的时间与基于地球自转的时间之间的差距日益扩大。造成这种差异的原因是什么？主要是由于月球引起的潮汐摩擦以及地球自转的不对齐，导致地球自转速度减慢。此外，地球熔融地核、海洋和大气层也会影响自转速度。

Leap seconds are a way to keep atomic-clock-driven UTC in line with astronomically kept Universal Time (UT1). Think of it like adding a little extra track for a train to keep running exactly parallel with another one. Rather than happening on a set interval—like a leap year—BIPM uses the average of hundreds of atomic clocks around the world and compares their time calculations to astronomical time to determine when a leap second is necessary. The most recent one was added in 2016.

闰秒是一种使原子钟驱动的UTC与天文观测的世界时（UT1）保持一致的方法。可以把它想象成给火车增加一小段轨道，以确保它能与另一列火车完全平行运行。与闰年不同，闰秒并非按固定间隔发生；BIPM通过全球数百个原子钟的平均值，并将其计算结果与天文时间进行对比，来决定何时需要增加闰秒。最近一次增加闰秒是在2016年。

Of course, adding track is no small effort, and it may seem like a lot of hassle for a measly second. But UTC is vital for all sorts of technology given the number of APIs and databases that rely on it. Introducing a leap second helped keep UTC and UT1 aligned, but it also wrought havoc on various systems running on UTC and forced companies to figure out how to deal with them when they were added every few years.

当然，增加轨道并非易事，为了区区一秒钟似乎显得过于麻烦。但考虑到大量依赖UTC的API和数据库，UTC对各类技术至关重要。引入闰秒有助于保持UTC与UT1的同步，但也给运行在UTC上的各种系统带来了混乱，迫使企业在每隔几年增加闰秒时，必须设法应对。

A number of tech companies like Google and Meta use “a ‘smear’ method of dealing with leap seconds,” Judah Levine, a fellow at the US National Institute of Standards and Technology, writes in an email. In essence, they spread a leap second out over the course of a day or so in tiny increments. But leap seconds have thrown off other systems; the airline Qantas, for example, saw its booking system borked by a leap second in 2012.

美国国家标准与技术研究院的研究员犹大·莱文（Judah Levine）在一封电子邮件中写道，谷歌和Meta等许多科技公司使用“平滑法”来处理闰秒。本质上，他们将一秒钟分散在一天左右的时间里，以微小的增量进行调整。但闰秒也曾导致其他系统瘫痪；例如，澳洲航空（Qantas）的预订系统就在2012年因闰秒而出现故障。

Adding a leap second is hard enough as it is. But the odds of having to add a negative leap second have been rising in part because Earth has picked up rotational speed in recent years due to climate change. (There’s always a climate angle.) Melting ice has caused a shift in the planet’s gravity so extreme that a negative leap second may have been required as soon as 2029, according to a 2024 Nature study. Part of the calculus of ditching the leap second altogether was that going negative isn’t worth the risk.

增加闰秒本身就已经够难了。但由于气候变化导致地球近年来转速加快，需要增加“负闰秒”的可能性也在上升。（总离不开气候因素。）2024年《自然》杂志的一项研究显示，冰川融化导致地球重力发生剧烈偏移，最早可能在2029年就需要引入负闰秒。彻底废除闰秒的部分考量在于，冒着风险去执行负闰秒并不值得。

“There are continuing problems with positive leap seconds even after 50 years, and the concern was that the negative leap second would be much more serious because its effects had never been tested,” Levine says.

莱文表示：“即便实施了50年，正闰秒仍存在持续的问题，人们担心负闰秒会带来更严重的后果，因为其影响从未经过测试。”

BIPM time department director Patrizia Tavella confirmed those concerns in an email to WIRED. “The probability of a negative leap second convinced us [to] set the application date in 2027,” she wrote, adding that there was added urgency following tests by an industry standards group that “showed several failures with a negative leap.”

BIPM时间部门主任帕特里齐亚·塔维拉（Patrizia Tavella）在给《连线》杂志的邮件中证实了这些担忧。她写道：“负闰秒的可能性促使我们决定将实施日期定在2027年。”她补充说，行业标准组织进行的测试显示“负闰秒会导致多次故障”，这增加了紧迫性。

Tavella says the group is waiting until May 20 2027 to implement it because it’s the anniversary of 1875 signing of the Metre Convention, creating BIPM, as well as Metrology Day. In other words, it’s the perfect time to mark the passing of time—or more accurately, the lack thereof.

塔维拉表示，该组织之所以等到2027年5月20日才实施，是因为那天是1875年《米制公约》签署（BIPM由此成立）的纪念日，也是世界计量日。换句话说，这是纪念时间流逝——或者更准确地说，是纪念不再流逝——的最佳时机。

The death of the leap second makes life easier for everyone now. “The nice fact is that we have nothing to do!” Tavella says. “Just continue to accumulate second[s] and ‘normal’ minutes of 60 seconds.”

闰秒的终结让每个人的生活都变得更轻松。“好消息是我们什么都不用做了！”塔维拉说，“只需继续累积秒数，保持每分钟60秒的‘正常’节奏即可。”

Levine concurs, writing that “life will have one less hassle.”

莱文对此表示赞同，他写道：“生活将少了一件麻烦事。”

But kicking the can on adding leap seconds doesn’t mean atomic time and astronomical time won’t continue to drift apart. That’s why BIPM also agreed to create a leap hour. Given how long it takes leap seconds to add up, a leap hour is millennia away. (There are, after all, 3,600 seconds in an hour.)

然而，推迟增加闰秒并不意味着原子时间和天文时间不会继续产生偏差。因此，BIPM也同意设立“闰小时”。考虑到闰秒累积所需的时间，闰小时的出现还需要数千年。（毕竟，一小时有3600秒。）

“We do not speak of leap hour yet,” Tavella says. “If systems rely on UTC, they have nothing to do. If they rely on UT1, they have to be able to use the information UT1-UTC which, in [the] future, will be larger than 1 second.”

“我们现在还不谈论闰小时，”塔维拉说，“如果系统依赖UTC，它们什么都不用做。如果它们依赖UT1，就必须能够使用UT1与UTC之间的差值信息，而这个差值在未来将超过1秒。”

In other words, not our problem, and good luck to future generations!

换句话说，这不是我们要操心的问题，祝后代好运！