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How should time be defined?

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By Hamish Johnston

For most people there are 86,400 seconds in a day – but astronomers have known for some time that days are getting longer thanks to sudden shifts in the Earth’s rotation.

While most of us will live our entire lives oblivious to this tiny warping of time, it does mean that the time kept by super-accurate atomic clocks and the astronomical time calculated from Earth’s motion are drifting apart by up to one second per year.

To solve this problem, the International Telecommunications Union (ITU) maintains Coordinated Universal Time (UTC). The length of the second in UTC is defined as a certain number of beats of an atomic clock, whereas the actual time of day is defined astronomically. This is done by adding or subtracting “leap seconds” to UTC when necessary.

For the past decade, however, various groups have been calling for the abolition of the leap second and the adoption of pure atomic time. The ITU will be meeting in Geneva over the next few weeks and the abolition of the leap second is on the agenda. Indeed, the first debate is scheduled for today.

If the ITU does do away with the leap second, it will end tens of thousands of years of astronomical timekeeping by humans. This bothers some scientists – including Markus Kuhn of the University of Cambridge in the UK. You can read more about the leap second, and Kuhn’s arguments, here.

What do you think? You can have your say by participating in this week’s Facebook poll, where the question is:

How should time be defined?

By the Earth’s rotation
By an atomic clock

In last week’s poll we found ourselves in rather gloomy territory following the news that the famous Doomsday Clock had swung one minute closer to midnight. We asked you to choose from a list of scenarios the one you believe is most likely to lead to the end of civilization as we know it.

Runaway climate change emerged as voters “favourite” choice by picking up 49% of the votes. In second place was a nuclear world war, receiving 27% of votes. In third place was an asteroid impact with 12% of votes. Fourth place went to an act of bioterrorism with 10% of votes. And just 6% of voters believe that we will meet our end at the hands of an alien invasion.

Once again, the poll attracted a lot of comments from our fans on Facebook, despite its rather depressing theme. And a lot of people appeared to have given the doomsday scenario some serious thought. That includes Bill Dortch, who warned “I would say an act of bioterrorism, especially now that not one, but two researchers, with NIH funding, have demonstrated how very easy it would be.”

Cathy McHale Albano also believes that our fate will ultimately lie in our own hands. “I’m guessing it’s got to be something caused by humanity, so it’s runaway climate change, bioterrorism or nuclear world war,” she says. “The insidious nature of climate change makes it more likely, in my mind, although all it takes is one wrong move by one of the world’s wackos for the other two to happen.”

However, there were plenty of others who answered the poll in jest, including Lynette Fitch Blair: “Since there is no category for zombie apocalyse, then I guess alien invasion is the next best choice.” And Paul Tangney, who chipped in early to point out that we were offering “some post-festive cheer from the physics community”.

Thank you for all of your votes and comments, and we look forward to hearing from you again in this week’s poll.

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