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Hey there everyone, Julian here for DNews. Have you ever wondered how long a second is?
You’re probably thinking it’s a second. A second is a second. But how did we come
up with that? The exact length of a second? After all it’s an important measurement
because so much depends on it. Everyone has to agree on how long a second is to accurately
measure speed, frequency, and of course, time itself. And as it turns out the second has
gone through a few minute but important definition changes over its history.
When defining just how long a second is it’s tempting to start with the length of a day
and break it up. 24 hours in a day, 60 minutes to an hour and 60 seconds to a minute means
a there are 86,400 seconds in a solar day. Solar day meaning the amount of time it takes
the sun to come back to the same spot in the sky. And for a while this was indeed the definition,
until the 1950s when people realized that the Earth’s rotation wasn’t uniform enough
to consistently measure seconds. So rather than define a second by how long it took the
earth to spin around, it’s more accurate to measure seconds as a subdivision of a year,
or how long it takes the earth to orbit the sun.
That exact amount of time can vary slightly from year to year as well so in 1960 it was
decreed by the Eleventh General Conference on Weights and Measures that seconds would
be based off the year 1900. Yep, there are people who represent dozens of countries and
their job is to get together every so often and figure out how to measure everything.
I bet no one is ever late to those meetings.
Anyway, 1900 was calculated to be 365.242198 days long, which means the second was officially
defined by the conference as 1/31,556,925.9747 of the year.
But even while this new definition was being ratified, people were already working on defining
a second even more accurately. The thought: maybe time could be based on atoms. The element
cesium 133 has just one electron in its outermost shell, and in 1958 it was discovered this
electron switches from one possible spin to the other and back again 9,192,631,770 times
every second. There’s still some uncertainty here, as the cesium electron can give or take
20 oscillations per second, but being off by 20 hz for every 9 billion means that atomic
clocks are off by only a nanosecond each month. The 13th General Conference on Weights and
Measures changed the definition of a second to this atomic standard in 1967 and it’s
been the same ever since.
Now though an even more precise standard is on the horizon. Cesium’s electron vibrates
in the microwave range, so scientists rely on microwave clocks, not to be confused with
the clock on your microwave. But some atoms like strontium have measurable oscillations
100,000 times faster than cesium, in the optical range. These so called optical clocks have
been known about for some time but it’s difficult to keep them running reliably. Now
though Dr Christian Grebing and a research team from the National Metrology Institute
of Germany have made them a bit more practical by using a microwave laser to keep track of
time when the optical clock is down.
This may all sound confusing, but basically, a clock like this could tick for 14 billion
years and only be off by 100 seconds. Something this accurate could make gps satellites precise
down to the centimeter, or make financial transactions on global stock markets faster
and more numerous. Grebing still thinks optical clocks are another 10 years away from being
implemented. But after that it sounds like the General Conference on Weights and Measures
won’t have to bring up seconds in their minutes for a long long time.
If learning about what a second is piqued your interest, head over to our sister show
DNews+ where Trace will tell you exactly how days, weeks, months and years came to be.
It’s their own “brief history of time.”
A
lot can happen in a second. What was the best second of your life?