闰秒在计量学界引发了三十年的激烈争论。如今，这场争论终于尘埃落定：闰秒正式被废除。
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.
取消普通人一直浑然不知的晦涩指标可能看起来是件新鲜事，但废除闰秒对你每天依赖的技术有着重大影响。它还能避免可能出现的危险时刻：即世界上首次出现负闰秒的可能性。
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.
国际计量局（以其法语缩写BIPM著称）周四表示，将于2027年5月停止发布闰秒，以调整所谓的协调世界时（UTC），自1972年以来已累计添加了32个闰秒。
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 to adjust what’s known as Coordinated Universal Time (UTC), 32 of which have been added since 1972.
世界在1972年实施闰秒，是因为原子钟测量的时间与地球自转所基于的时间之间出现了日益扩大的差距。这种差异的原因是什么？后者主要由于月球引起的潮汐摩擦以及地球自转不同步而减慢。地球的熔融核心、海洋和大气层也会影响自转速率。
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.
闰秒是让由原子钟驱动的协调世界时（UTC）与天文保持的世界时（UT1）保持同步的一种方式。可以把它想象为给火车添加一点额外的轨道，使其能够精确地与另一列火车保持平行运行。闰秒并不是按固定间隔发生的——就像闰年一样——而是BIPM利用全球数百个原子钟的平均值，将它们的时间计算与天文时间进行比较，以确定何时需要闰秒。最近一次添加闰秒是在2016年。
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.
当然，添加闰秒并非易事，看起来可能只是为了多出一秒而费尽周折。但UTC对各种技术至关重要，因为众多API和数据库都依赖于它。引入闰秒有助于使UTC和UT1保持同步，但也给运行在UTC上的各种系统造成了混乱，迫使公司们想办法应对每隔几年添加一次的闰秒。
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.
美国国家标准与技术研究院研究员犹大·莱文在一封电子邮件中写道，谷歌和Meta等多家科技公司采用了一种“ smearing（摊开）”的方法来处理闰秒。简而言之，他们将闰秒分散到一天左右的时间里，以微小的增量进行调整。但闰秒也导致其他系统出现问题；例如，澳洲航空在2012年曾因闰秒导致其预订系统崩溃。
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.
添加闰秒本身就已经够棘手了。但由于近年来地球因气候变化而加快了自转速度，需要添加负闰秒的概率一直在上升。（总是离不开气候因素。）根据2024年《自然》杂志的一项研究，冰川融化导致行星重力发生了极端变化，以至于负闰秒可能早在2029年就需要被加入。放弃闰秒 altogether（彻底取消闰秒）的部分考量正是因为采用负闰秒所带来的风险不值得冒险。
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 the 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.
莱文表示：“即使过去50年里，正闰秒仍然带来持续问题，但人们担心负闰秒会更为严重，因为其影响从未经过测试。”
“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.
BIPM 时间部门主任帕特里夏·塔维拉在给《WIRED》的一封电子邮件中证实了这些担忧。她写道：“负闰秒的概率让我们确定了在2027年实施的日期。”她补充说，在工业标准组织进行测试后，情况更加紧迫，因为测试“显示出负闰秒导致的几次故障”。塔维拉表示，该组织将等到2027年5月20日才实施，因为这一天是1875年《米制公约》签署的纪念日——该公约促成了BIPM的成立，也是计量学日。换句话说，这是标记时间流逝——或者更准确地说，标记其缺失——的完美时机。
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.”Tavella says the group is waiting until May 20, 2027 to implement it because it's the anniversary of 1875g 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.
闰秒的终结让每个人的生活变得更简单了。“好消息是我们什么都不用做！”塔维拉说。“只需继续累积秒数和‘正常’的60秒一分钟。”莱文也同意这一观点，他写道：“生活将少一份麻烦。”
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.”Levine concurs, writing that “life will have one less hassle.”
但推迟添加闰秒并不意味着原子时间和天文时间不会继续分离。这就是为什么BIPM还同意设立闰小时。考虑到闰秒累积所需的时间，闰小时还相距千年。（毕竟，一小时有3600秒。）“我们目前尚未讨论闰小时，”塔维拉说。“如果系统依赖于UTC，它们什么都不用做。如果它们依赖于UT1，它们必须能够使用UT1-UTC的信息，而在未来，该信息将大于1秒。”换句话说，这不是我们的问题，祝愿未来世代好运！
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.)“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.”In other words, not our problem, and good luck to future generations!