Most people are vaguely aware that the year is not exactly 365 days long, and, every fourth year, we add a leap day to make up for lost time. Not as many know that the length of the 24-hour day itself is also hard to pin down at exactly 86,400 seconds.

The time it takes for the Earth to spin one full rotation on its axis is affected by the seasonal changes of the trade winds, the changing ocean currents, and over longer time frames, the buildup of glaciers and mountains, earthquakes, and the movement of the Earth’s liquid core. Even the building of a large reservoir can change the length of a day by an instant.

On June 30, 2015, the second hand of the clock will essentially strike midnight twice.

The changes add up–on average, Earth’s rotation slows by two-thousandths of a second a day–which is why, since the first leap second in 1972, the world’s timekeepers at the International Earth Rotation Service in France add a “leap second” to the year every so often. The world’s 26th leap second ever will be added this year, on June 30, 2015, when the second hand of the clock will essentially strike midnight twice.

According to the Telegraph, this poses major hassles for software and computing companies that rely on precise time keeping. Usually, systems around the world stay in sync with each other using a system called the Network Time Protocol, which is programmed to stay within a few milliseconds of Coordinated Universal Time–the official scientific time for the world as measured by atomic clocks. But the protocol doesn’t deal well with leap seconds. The last leap second in 2012, for example, caused sites like Mozilla, Yelp, and Reddit to crash and problems with Linux operating systems–like a mini-version of the Y2K bug.

Behind all of this is a fascinating philosophical debate over whether to have leap seconds at all. The Unites States argued for their elimination at a 2012 conference because of the trouble they cause today’s precise navigation, communication, and financial systems. That may be true, but getting rid of them means accepting that humanity’s version of time will forever be out of sync with Earth’s astronomical reality. As the Telegraph reports:

But Britain opposes the change, saying that it would forever break the link between our concept of time and the rising and setting of the Sun. Experts also fear that once this link is broken it could never be restored because although Earth’s timekeeping systems are built to accommodate the occasional leap second, adding a leap minute or hour to global time would be virtually impossible.

Untethering our society from the physical world seems like humanity’s ultimate hubris, and people who rely on technology should probably just figure out a way to deal. After all, Y2K wasn’t all that bad, was it?