September 26, 2022

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The super-clocks that define what time it is

So, at laboratories like NPL, scientists are now experimenting with new optical technology, with the hope that within the next decade or so, the second will get a new definition.

Much more testing is needed first though. “You need to create a definition that’s usable, that’s practical, and realisable for all of the different national metrology labs around the world,” says Curtis. “So it can’t be just some bespoke thing that only one group can do. And if they do it really well, it has to be something that we can universally call a redefinition.”

Time as a construct

So what should the rest of us make of all this? For one, it illustrates an extraordinary truth: there is no clock on Earth that can ever be perfectly stable or run at exactly the right rate. This was true when people used sundials, and it’s still true today – even with atomic timekeeping.

The second, for instance, is defined according to the technology we have available, and what a group of metrologists charged with making the decision choose it to be. Atomic clocks, no matter how accurate, still need “steering”. And when metrologists do things like add leap seconds to the timescale, they are adjusting time to human needs: to make sure some things stay the same, like the enjoyment of the sunrise in the morning.

Clock time is what we agree; it’s not the true time.

However, this agreement is a necessity for living and working within modern societies. If we went back to the days when all time was defined locally, many of our technologies would stop working, trains would crash, and financial markets would collapse. Like it or not, the world is built on clock time.

It can be illuminating, though, to consider what the foundations of this construct actually are. When you think about time like a metrologist does, time becomes something different.

Back at NPL, as I read the “do not touch the maser” sign, I ask one of the scientists showing me around if he himself is a good timekeeper: is he personally punctual, for example?  “Oh, I only think in nanoseconds,” he replies.

*Richard Fisher is a senior journalist for BBC Future and tweets @rifishHe writes the newsletter The Long-termist’s Field Guide, and is the author of an upcoming book called The Long View (Wildfire/Headline).

If you want to dig deeper into timekeeping, the UK National Physical Laboratory offers a free e-learning course called Introduction to Time and Frequency Measurement.

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