SCOTT SIMON, HOST:
One day, one full rotation of the Earth takes exactly 24 hours, right? Well, not exactly. The Earth's spin has slowed down ever so slightly so that one rotation is 24 hours and some number of microseconds. Since 1972, we have been adding leap seconds every few years to make up that difference, but that is about to change. We're joined by Philippe Richard from Bern, Switzerland. He's director of the Swiss Federal Institute of Metrology. Thank you for being here. And metrology, that's the study of measurement?
PHILIPPE RICHARD: Yes. Sure. Thank you for inviting me.
SIMON: What does it matter if we're off a few microseconds?
RICHARD: It's not so big, but maybe - you made a great introduction. But if you agree, I want to tell you a short story of two watches to introduce the concept.
SIMON: Sure.
RICHARD: Imagine you have two watches, a nice, old Swiss mechanical watch and a modern, precise quartz watch. If you compare them, you will soon realize that the time difference will probably increase with time, and if you want your quartz watch to follow your old Swiss watch, you will have to correct your quartz watch by some seconds or maybe by some minutes. So let's now imagine your old Swiss mechanical watch is the Earth, which rotates on its axis in 24 hours. So the necessary correction to follow the Earth's rotation is what we call a leap second.
SIMON: So there's been a vote recently by an international committee of which you are a part to no longer use leap seconds?
RICHARD: Exactly. There was the General Conference on Weights and Measure last week in Versailles, close to Paris, and member states decided to abandon the concept of leap second. They introduced a leap hour, so we can wait much longer before initiating a change.
SIMON: Like, a thousand years longer, right?
RICHARD: It's a lot, yes. The leap seconds were starting in 1972, and we have introduced since that time 27 leap seconds, so one every two year in average. So you will have to wait really long, probably between 4,000 or 7,000 years in order to reach one hour. Just to put it very simply, introducing a leap hour instead of a leap second is to pass the problem on the future generation.
SIMON: Ha. Well, we've done that in a few different cases. Yeah. Will we notice the difference?
RICHARD: So basically not. It's not a real problem in everyday life.
SIMON: Yeah.
RICHARD: Because the 27 leap second in the past were totally unnoticed. Nobody will notice any potential increase of the gap between these two watches, the astronomical and the atomic timescale. If you ask how will this decision affect our daily life. Not at all. We will not realize the change.
SIMON: Keeping track of the exact time is important in many features of everyday life, isn't it?
RICHARD: Yes, it is. Yes. Yeah, yeah. The precision is extremely important and is becoming increasingly important also for the synchronization of power grids for electricity networks, for computers networks, satellite positioning. It's very important because this is all technical issues of everyday life, and everyone is happy when everything works correctly. But the infrastructure behind this is related to metrology and very precise measurements.
SIMON: Philippe Richard is director of the Swiss Federal Institute of Metrology. Thanks for spending so much time with us.
RICHARD: You're welcome.
(SOUNDBITE OF JAMES ASHER'S "ROBOTTOM") Transcript provided by NPR, Copyright NPR.
NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.
