As the world prepares to gain an extra second of time on June 30 at precisely 23:59:59 GM, computer experts fear the extra ‘leap second’ could crash the internet.
Scientists say the reason for adding the extra second is to compensate for the slowing Earth rotation, thus allowing the discrepancy between ‘Earth’ time and ‘atomic’ time to be fixed.
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The extra second is needed because the Earth’s rotation is gradually slowing down by around two-thousandths of a second per day, and it needs to catch up with atomic time.
Atomic time uses vibrations within atoms to measure time and is said to be the most reliable because atoms resonate at extremely consistent frequencies.
To keep them in sync, it is necessary to occasionally jump Earth’s time back – for mathematical reasons similar to adding leap years.
The decision to do so is made every time Earth time is slower by about half a second, making it about half a second quicker instead.
‘At the time of the dinosaurs, Earth completed one rotation in about 23 hours,’ says Daniel MacMillan of Nasa’s Goddard Space Flight Center.
‘In the year 1820, a rotation took exactly 24 hours, or 86,400 standard seconds. Since 1820, the mean solar day has increased by about 2.5 milliseconds.’
This year will be the 26th time since 1972 that a leap second will have been added.
When asked about keeping computer clocks synchronised, John Engates, chief technology officer at Rackspace, said: ‘Time gets complicated fast.’
This is because not everyone will add the leap second in the same way, or at same time.
In some systems, the computer clock shows 60 seconds instead of rolling over to the next minute – or shows the 59th second twice.
As a result, the computer sees a leap second as time going backward, causing a system error and the central processing unit (CPU) to overload.
In 2012, problems arose when subsystems got confused by the time change and caused hyperactivity on certain servers.
Many companies, including Reddit, Yelp and LinkedIn, reported crashes as their systems struggled to cope.
This time around, the major firms say they are prepared.
Companies such as Google add fractions of a second over the preceding year so they don’t need to make a sudden jump – known as a ‘leap smear’.
‘We have a clever way of handling leap seconds,’ wrote Google site reliability engineers Noah Maxwell and Michael Rothwell in a blog.
‘Instead of repeating a second, we ‘smear’ away the extra second.’
But this might cause its own problems. Harlan Stenn, chief maintainer of the Network Time Protocol, told Information Week he doesn’t like the smear.
‘At noon on June 30, clocks of smear implementers will be off by a half second,’ he said.
It means processes based on precise timing – such as the amount of time a valve opens to add a chemical to a mix – will be off by half a second.
‘What if you’re getting radiation treatment? Do you want your radiation dose to be off by a half-second or more?’ said Stenn.
However, some nations, including the US, have supported a change to get rid of leap seconds. They want to simply let the clocks run out-of-sync instead.
Were such a decision to be made, it’s unlikely we could ever go back to a leap second system and keep the clocks in sync.
This is because the clocks would be out of sync by several minutes, or maybe hours eventually, which would be virtually impossible to add to systems without disastrous consequences.
Without leap seconds, there would be a slip of two to three minutes by the year 2100 – and half an hour by 2700.
Other countries, like Britain, want to keep leap seconds to preserve certain regularities – such as Greenwich Mean Time, which is the time when the sun crosses the Greenwich Meridian.
A vote is due to take place by the Radiocommunication Assembly and the World Radiocommunication Conference later in the year to decide the leap second’s fate.