what’s the secret to comedy? 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 hasto agree on how long a second is to accurately measure speed, frequency, and of course, timeitself. and as it turns out the second has gone through a few minute but important definitionchanges over its history. when defining just how long a second is it’stempting to start with the length of a day and break it up. 24 hours in a day, 60 minutesto 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 thesky. and for a while this was indeed the definition, until the 1950s when people realized thatthe earth’s rotation wasn’t uniform enough to consistently measure seconds. so ratherthan define a second by how long it took the earth to spin around, it’s more accurateto measure seconds as a subdivision of a year, or how long it takes the earth to orbit thesun. that exact amount of time can vary slightlyfrom year to year as well so in 1960 it was decreed by the eleventh general conferenceon weights and measures that seconds would be based off the year 1900. yep, there arepeople who represent dozens of countries and
their job is to get together every so oftenand figure out how to measure everything. i bet no one is ever late to those meetings. anyway, 1900 was calculated to be 365.242198days long, which means the second was officially defined by the conference as 1/31,556,925.9747of the year. but even while this new definition was beingratified, 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 outermostshell, and in 1958 it was discovered this electron switches from one possible spin tothe other and back again 9,192,631,770 times every second. there’s still some uncertaintyhere, as the cesium electron can give or take
20 oscillations per second, but being offby 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 secondto this atomic standard in 1967 and it’s been the same ever since. now though an even more precise standard ison the horizon. cesium’s electron vibrates in the microwave range, so scientists relyon microwave clocks, not to be confused with the clock on your microwave. but some atomslike strontium have measurable oscillations 100,000 times faster than cesium, in the opticalrange. these so called optical clocks have been known about for some time but it’sdifficult to keep them running reliably. now
though dr christian grebing and a researchteam from the national metrology institute of germany have made them a bit more practicalby 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. somethingthis accurate could make gps satellites precise down to the centimeter, or make financialtransactions on global stock markets faster and more numerous. grebing still thinks opticalclocks are another 10 years away from being implemented. but after that it sounds likethe general conference on weights and measures won’t have to bring up seconds in theirminutes for a long long time.
if learning about what a second is piquedyour interest, head over to our sister show
penn state 3d printing club,dnews+ where trace will tell you exactly howdays, 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 bestsecond of your life?
