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Device That Revolutionized Timekeeping Receives an IEEE Milestone (ieee.org)
An anonymous reader writes: The invention of the atomic clock fundamentally altered the way that time is measured and kept. The clock helped redefine the duration of a single second, and its groundbreaking accuracy contributed to technologies we rely on today, including cellphones and GPS receivers. Building on the accomplishments of previous researchers, Harold Lyons and his colleagues at the U.S. National Bureau of Standards (now the National Institute of Standards and Technology), in Washington, D.C., began working in 1947 on developing an atomic clock and demonstrated it to the public two years later. Its design was based on atomic physics. The clock kept time by tracking the microwave signals that electrons in atoms emit when they change energy levels. This month the atomic clock received an IEEE Milestone. Administered by the IEEE History Center and supported by donors, the milestone program recognizes outstanding technical developments around the world.
https://en.wikipedia.org/wiki/Big_Ben
Just sayin'.
Me thinks you don't understand atomic clocks at all.
I think you have the wrong story....
I think he/she knows SOMETHING about atomic clocks. The OP probably knows that caesium is a key ingredient in many atomic clocks, but have just confused the 133-weight stable isotope used in clocks with the 137-weight radioactive isotope, or the like.
"Atomic clocks are based on the periodic decay of radioactive isotopes."
No, they aren't. Radioactive decay is random and would make a terrible clock. The second is defined in terms of a electron transitions of the cesium-133 atom, which is the only stable isotope. Hydrogen maser clocks are even more stable timekeepers, but again, not based on a radioactive isotope.
"National Security is the chief cause of national insecurity." - Celine's First Law
Well, I was going to mod you up +1 Informative, but then I notice the goatse link... Now, since I'm writing this, I can't mod you down either. But at least I can warn others to check the links before clicking. (Note: The rest of the links appear to be legit.)
XML is like violence. If it doesn't solve your problem, you're not using enough of it. --AC
Did they just use whatever the "reference time" was for some existing highly accurate clock? Or did they do a bunch of astronomical measurements and then set the atomic clock based on some astronomical reference that defined some specific time?
Or his knowledge is limited to Rb(87) clocks, although he's still incorrect about the timekeeping being based on radioactive decay. Rb(87) is radioactive, but has an extremely long half-life, like 50 gigayears.
"National Security is the chief cause of national insecurity." - Celine's First Law
dunno how promptly these milestones seek to record technological change but in this case, 70 years down the road, we've jumped in the teritory of ;-)
* overflowed unsigned 32bit integers, if measured in seconds!
Makes sense. Caesium's half-life is about 30 years. You're sharper than I thought, Beau.
Hmmm... Carbon-12 is a stable isotope. Carbon-14, on the other hand, undergoes radioactive decay.
What do they do with it? Is it just for getting packets passed off to different towers in the correct order or something? Just for billing? For keeping track of where you where when? I've heard a lot people complain while traveling about the time on their phone being off, by timezones or just by minutes, so it doesn't seem like the system NEEDS it. :)
The Second option is how they "set" an atonic clock, but it's only really setting the local offset to what the astronomical TIME it is...
TIME is defined by astronomical references, the passage of time is MEASURED by clocks. So when you ask "What time is it?" you are asking an astronomical question. If you are asking "How long has it been since..?" then you are needing a clock to be measuring how much time has passed..
By the Way... Astronomical time is not governed by the passage of time. Where they are generally related (the earth generally rotates 1 time every 24 hours) the relationship is not exact because one day isn't always the same length as the day before.
Not just accuracy but redefinition. Originally the second was based on astronomical measurements which would vary. With this redefinition it's also easier for scientists to create their own accurate clock. The kilogram is still waiting for its redefinition.
Atomic clocks have noting to do with radioactive decay.
Accurate time is needed by cell phones (and all digital networks) for a number of purposes. Accurate time is needed to clock high speed data circuits. When you're talking about billions of bits per second, a small error loses lots of bits. Accurate time is needed for seamless handoffs of signals between cell sites. It is needed for enhanced 911 location systems to work. It is used in radio frequency systems to keep transmitters on frequency which becomes more and more important as channels get closer together. It is used to keep TDMA and CDMA systems in sync.
For information about the history of the definition of a second as measured by the first cesium clock, see https://en.wikipedia.org/wiki/....
Could've just left it to be modded down to -1, after which hardly anyone will see it. Instead, here's your post at +4, drawing more attention to it...
I laughed IRL
Hydrogen maser clocks are even more stable timekeepers, but again, not based on a radioactive isotope.
Don't forget rubidium! - much cheaper than cesium or hydrogen, but also not as accurate. (Also not radioactive)
Hydrogen masers become unstable and drift ('aging effect') while Cesium is consistent. Applications where very accurate time over both the short and long term are required (such as Galileo GNSS) use a combination of Hydrogen and Cesium standards, using each to overcome the weakness of the other.
Cesium also benefits from the fact its oscillation is literally the definition of a second.
-- Sometimes you have to turn the lights off in order to see.
You're assuming this is the first TIME (trying to tie in to the story this is posted under) that they have been found in violation of the TOS. If this is the SECOND or other subsequent warning then this action seems appropriate.
Errr... why is this -1? It's two vintage videos about quartz crystal manufacture. Seems legit to me?
Thanks, don't know how that happened.
Knowledge is how to play a game, intelligence is how to win, wisdom is knowing what game to play.
you're a complete fucking idiot. Congrats!
The GPS receiver in your phone (and GPS/GNSS systems in general) utterly depend on hyper-accurate timekeeping to work. In a nutshell, the orbiting satellites are transmitting perfect "true" time continuously, as well as information on its orbit. Your GPS receiver uses that information to work out the precise local time, and using that it can calculate the exact position of the satellite around the earth, the distance to each of the satellites, and thus its own position.
The ephemeris data (precise information on its orbit) transmitted by the satellites is only good for about 6 hours, before it has to be updated both on the satellite and on your phone, and takes time to download. In the GPS world, this is known as a "Warm Start" and can take up to a few minutes. If you've moved your device more than a few hundred km while off, or left it powered off for several days, it needs to download an entirely new Almanac, which takes up to 12 minutes (a cold start).
With assisted GPS, as used on cell networks, the phone will get the almanac and relevant ephemeris from the cell network, greatly improving the time to fix.
That's just the GPS side of things though... As others have mentioned, the actual radio interface is utterly dependent on precise timing in order to function. The cheapest and most reliable way to achieve this is with timing derived from GPS.
Of course, the software clock on a phone is completely independent of these two things, it's just that normally it gets its settings from GPS or the network.
...si hoc legere nimium eruditionis habes...
The other links are actually informative. Why throw out the good with the bad? You might choose to do it otherwise, but I chose to do it this way. Have a nice day.
XML is like violence. If it doesn't solve your problem, you're not using enough of it. --AC
Many years ago, I wound up doing a small contract/visit at the Naval Research Labs at the Navy Yards in DC. Partly by tradition, partly by necessity, the Navy has a healthy obsession with accurate time keeping, and I was working with the Navy's time geeks. They were a fascinating group of guys to work with, their equipment and clocking was accurate enough to measure the (electrical) distance to a satellite in geosynchronous orbit to within half an inch.
Anyhow, I was having lunch in his office and there on the shelf is this oddly shaped piece of metal. I ask him about it, and basically he goes "oh, that's the prototype atomic clock I built for the first GPS satellite." and hands it to me. It was about the size of a football, and pretty damned cool. :)
...si hoc legere nimium eruditionis habes...
Rb(87), which is used for clocks, is radioactive, although not much.
"National Security is the chief cause of national insecurity." - Celine's First Law
Ohhhhhh. I didn't think about it being used for keeping the data in sync. I was just thinking about the handoffs. Cool. Those guys are smart.
I keep getting logged out... The GPS needing the timing I got. I just couldn't think of what else. I was thinking the phone could just get the timing from there, but I guess phones didn't always have GPSs and you can't get a GPS signal indoors. And the whole "warn start" thing. We use a lot of GPS receivers in the field and it's really annoying when the internal battery has quit and you have to wait for a cold start every time. Ugh. Thanks!
The first atomic clock, developed near this site by Harold Lyons at the National Bureau of Standards, revolutionized timekeeping by using transitions of the ammonia molecule as its source of frequency. Far more accurate than previous clocks, atomic clocks quickly replaced the Earth’s rotational rate as the reference for world time. Atomic clock accuracy made possible many new technologies, including the Global Positioning System (GPS).
and posted it in a park in Washington DC near where the original work was done.
Move along, no sig to see here.
The company that makes, pretty much, all the atomic clocks that most people use nowadays (They bought the business from HP who was the big player, as well as a bunch of smaller players) has an atomic clock standard IN A SMD CHIP.
https://www.microsemi.com/products/timing-synchronization-systems/embedded-timing-solutions/components/sa-45s-chip-scale-atomic-clock
They are $1600 from Digi-Key. The dedicated, old, repuroposed GPS I use to keep my computers time-sync'd is now not good enough. I want one of these. Must.. have.. needlessly.. accurate AND precise time...
Never change slashdot, never change.
20 years of the sginer
Like any clock, they just count predicable periodic events. You don't 'set' the clock. It just counts upwards forever since the time it was turned on. Mapping those counts to human-readable time that everyone agrees on is a different exercise.
But considering out calendar is based off of solar events.. The answer is yes.
Before the advent of accurate clock we would just check the stars and planets a lot because that was the only good way to keep time.. And since the advent of atomic clocks we've found out the earth's orbit varies and slows a little over the decades and we keep having to add and subtract seconds from the official "Time"
This causes trouble for things like satellites, missles, very secure servers, telecoms, and scientific experiments because keeping everyone on the same page is a pain when the official "Time" keeps changing willy-nilly. So there are proposals for a "Scientific" time that never changes relative to our orbit around the sun and instead relies on the counts and consensus of many very accurate clocks synced up all around the globe.
Inattentive carelessness would be my guess as to how it happened.
"So long and thanks for all the fish."
it is too bad that, in practice, the referential synchronized atomic clocks in paris and counterpart locations around the free world have all observed significant drift from each other. so, cesium as the standard is under review while other potentially more predictable choices are being researched. sorry i forget the leading alternate solutions under consideration. and i offer no references, because i am picking up my child at the moment. ...and time for me stands still momentarily just before transitioning to toddler-lightning fast speed. :-P
Simple, they googled it.
Table-ized A.I.