Instead of 11:59:59 leading to midnight, the clocks on June 30 will add an extra second: 11:59:60 as atomic time catches up to the Earth's rotation.
Atomic time is perpetual, but the Earth's rotation has been slowing by two thousandths of a second per day, according to The Times of India. The Earth's rotation could be slowed by planetary wobble or given a boost by a geological event like an earthquake. In order to catch up with real time, atomic clocks will "hold their breath" on June 30.
Australian authorities are concerned that the stock market - set to open during the extra second - will fall into chaos. The ASIC has issued a warning to financial market stakeholders to be ready. In 2012, large companies and popular websites, including Reddit, Mozilla and LinkedIn, faced technical problems when time was added, according to the Telegraph. Qantas flights were delayed due to problems with its check-in system.
"Is it going to be the end of the world as we know it?" Suelette Dreyfus, computer security expert, told Australian Broadcasting Corporation News. "Probably not, but for companies that haven't actually spent some time thinking through what it might mean for their systems, there is a risk that things could go astray."
Google released a statement on its blog explaining how "smearing" a second means they won't have any issues. "During a 20-hour 'smear window' centered on the leap second, we slightly slow all our servers' system clocks (by approximately 14 parts per million). At the end of the smear window, the entire leap second has been added, and we are back in sync with civil time. ... Twenty hours later, the entire leap second has been added and we are back in sync with non-smeared time."
The first leap second was added in 1972, and it will be the 26th time it has been added to clocks in history.
"The Earth is slowing down a little bit," said Nick Stamatakos, the chief of Earth Orientation Parameters at the U.S. Naval Observatory, according to The Times of India. "They add an extra second to something called UTC (Coordinated Universal Time) in order to make sure the rate of UTC is the same as atomic time."
"For that day [June 30] there'll be 86,401 seconds, instead of 86,400 seconds. The length of the day for you and I and everyone on the Earth will have an extra second," Stamatakos added.