A clearer view of what matters

While the time shown on a clock passes steadily, the Earth’s rotation does not remain perfectly constant. To account for that difference, an extra second is sometimes added. That adjustment is known as a leap second. But as concerns grow that this can place a burden on computer systems, a move to phase out leap seconds is now underway.

The Verge reported that the International Bureau of Weights and Measures (BIPM) has decided to bring forward the timeline for ending leap seconds, and that the new plan will take effect starting May 20 next year. Under the previous plan, leap seconds were to be phased out no later than 2035. The schedule change was explained by the possibility that, as the Earth’s rotation changes, future adjustments may require subtracting time rather than adding it. While adding a second has already been done before, there are concerns that subtracting a second would be unprecedented.

Leap seconds are a device for narrowing the gap between atomic time and astronomical time. Atomic time is measured with extreme precision based on the vibrations of atoms, while astronomical time is based on the Earth’s rotation and the movement of the sun. Because the Earth’s rotation changes slightly over time, these two time standards can drift apart in the long run, and leap seconds have served to correct that gap.

The problem is that computers and communication systems that handle time may not smoothly process such irregular one-second adjustments. The report noted that several online services experienced disruptions when leap seconds were added in the past. It also added that major technology companies such as Meta, Google, Microsoft, and Amazon have supported the move to abolish leap seconds.

According to the report, one proposed alternative to leap seconds is to let the difference between atomic time and astronomical time grow gradually, then apply a much larger unit called a “leap hour.” The next time an hour would be added is estimated to be around 3,000 years from now. In other words, the key change is not about suddenly moving clocks forward by an hour in daily life, but about changing how the international time standard is managed.

Even if changes to the time system are not obvious, they can still affect synchronization across communications and computer systems. That is why the actual implementation process and operational details matter. This timeline and these details have been summarized based on The Verge’s report, and the abolition of leap seconds is a reminder that timekeeping standards and digital infrastructure are closely intertwined.