David Papp Blog

What Are Leap Seconds and Why Are They Being Scrapped?

In 1972, atomic clocks showed that a day is not exactly 86,400 seconds long, which can cause problems for timekeeping. To fix this problem, leap seconds were introduced. A leap second is a one-second adjustment made at the end of December and/or June to keep Coordinated Universal Time (UTC) close to Universal Time (UT1).

However, with the rise of digital technology, leap seconds have become a problem because they can break the assumptions used in software to represent time. When billions of interconnected networked computers try to execute a leap second jump at the same time, many of them fail in a wide variety of ways, which can lead to significant outages and impacts on critical infrastructure such as electricity grids, telecommunications systems, and financial systems.

To address these problems, the International Telecommunications Union, which governs leap seconds, has decided to abandon leap seconds for 100 years or so, starting in 2035. During this time, the discrepancy between UTC and UT1 may grow to as much as a minute. Dropping the leap second now can prevent its dangers and allow plenty of time to work out less disruptive ways to keep time aligned.

The elimination of leap seconds will bring several benefits to timekeeping. First, it will simplify the calibration of timekeeping devices and systems since they will no longer have to account for leap seconds. Second, it will reduce the potential for errors and disruptions in computer systems and networks, which will improve their reliability and performance. Third, it will make timekeeping more accurate and reliable since atomic clocks are much more precise and stable than the Earth’s rotation.

The decision does not mean abandoning the idea of keeping time aligned with Earth, but recognizing that the disadvantages of the current leap second system are too high and getting worse.

An extreme approach would be to fully adopt an abstract definition of time or to make larger adjustments than a second, but far less frequently and with better preparation to limit the dangers. The next meeting of the Bureau International des Poids et Mesures, which will decide how far we’re willing to let things drift before a new approach is decided upon, is set for 2026.

So remember to make every second count and seize the day!