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Costruire l'orologio definitivo 17.11.14

NPR racconta come è stato costruito l'orologio atomico, basato sullo stronzio, più preciso del mondo, capace di non perdere neppure un secondo in 5 miliardi di anni e come questo incidentalmente risulti essere un problema proprio per la misurazione del tempo. C'entra la gravità e la nozione stessa di tempo.

The relative nature of time isn't just something seen in the extreme. If you take a clock off the floor, and hang it on the wall, Ye says, "the time will speed up by about one part in 1016."

That is a sliver of a second. But this isn't some effect of gravity on the clock's machinery. Time itself is flowing more quickly on the wall than on the floor. These differences didn't really matter until now. But this new clock is so sensitive, little changes in height throw it way off. Lift it just a couple of centimeters, Ye says, "and you will start to see that difference."

This new clock can sense the pace of time speeding up as it moves inch by inch away from the earth's core.

That's a problem, because to actually use time, you need different clocks to agree on the time. Think about it: If I say, 'let's meet at 3:30,' we use our watches. But imagine a world in which your watch starts to tick faster, because you're working on the floor above me. Your 3:30 happens earlier than mine, and we miss our appointment.

This clock works like that. Tiny shifts in the earth's crust can throw it off, even when it's sitting still. Even if two of them are synchronized, their different rates of ticking mean they will soon be out of synch. They will never agree.

The world's current time is coordinated between atomic clocks all over the planet. But that can't happen with the new one.

"At this level, maintaining absolute time scale on earth is in fact turning into nightmare," Ye says. This clock they've built doesn't just look chaotic. It is turning our sense of time into chaos.

Ye suspects the only way we will be able to keep time in the future is to send these new clocks into space. Far from the earth's surface, the clocks would be better able to stay in synch, and perhaps our unified sense of time could be preserved.