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Atomic Clocks

nist.gov

51–60 of 89 posts

Re: Atomic Clocks

#51
post #17

What, Exactly, Is a Clock? To understand atomic time, we must first understand something about clocks. A clock is, at its core, a marriage of two components: a mechanism that oscillates, or ticks with a steady beat, and a device that counts those beats and displays the time Yeah but more deeply time is a property of the universe that the clock including atomic clocks are tracking. Kant said it is 'schema' i.e. withou…

> Yeah but more deeply time is a property of the universe that the clock including atomic clocks are tracking.

I'll quote Einstein who said "time is what the clock says".

Re: Atomic Clocks

#52
post #15

Long before most of you were born there was a special number you could call to get the time here in the USA. It would give you a localized time every 10 seconds. It was considered an authoritative value, but I knew that normal analog clocks drifted a fair amount, and I was fascinated by the Time voice. There was also a special number to dial that was called Information. When I was about 12, I suddenly thought that’s…

The one we used is still active JU-55961 (area code 502), only difference is it plays an ad first. It had a little jingle used to memorize it, so I still remember it today. I searched the internet for that number, and apparently there were hundreds of these JU numbers for different services.

Re: Atomic Clocks

#53
post #42

Earlier quoted context omitted.

That “all around the world” leaves significant gaps: https://hagensieker.com/2019/11/17/multiband-6-what-is-it/ I had a weather station with an external antenna that could never sync, even during the night, even placed outside in the "best" side of the house on my neck of the EU. A solar powered, low battery wristwatch that's never outside in the middle of the night will fare much worse. It's interesting old school t…

Syncing directly from a 4G signal would be a lot more practical than VLF or HF time signals, but I haven't found a wall clock that does so.

On the one hand, yes. On the other, my country has just shut down 3G and 2G only stays because it's still used by emergency services. How long will 4G last? Longer than bluetooth and the Casio app?

It'd be nice if something like this could be maintained long term. The US, UK and Germany signals have been working since the ~1960s.

Re: Atomic Clocks

#54
It's still relative. I think...

If you could have a atomic wristwatch and you travel around the world with it, you will have a very precise time for you, but you'll end up out of sync with almost every other atomic clock.

If you sync two atomic clocks and put one at the surface of the arctic ocean and another one on top of Mount Nevado in Peru, and leave them there for one million years, the clock in Peru will be 1.88 years ahead of the clock in the arctic.

That is a difference of 0.44 nanoseconds per day.

Don't quote me on that though.. I'm not a physicist.

Re: Atomic Clocks

#55
post #36

Earlier quoted context omitted.

Moving objects don't emit gravitational waves though. They have to be orbiting.

First, that claim is patently false. Two objects with size accelerating directly towards each other (i.e. zero orbital angular momentum hence zero "orbit") will produce waves. A moving object will produce detectable changes in gravity so arguing about "waves" in the context of atomic clocks detecting gravity is irrelevant.

I don't GR but I'm fairly certain dipole does not work for gravitational waves (i.e. two objects accelerating straight at each other). Supposedly, there's a specific definition of "gravitational wave" here. You can, of course, detect the change in gravity though, regardless of "gravitational wave" or not.

Re: Atomic Clocks

#57

Fun fact, two (very expensive) wristwatches have actual atomic timekeeping in them, instead of just receiving a radio time signal: the Bathys Hawaii Cesium 133, and a few different shaped from Hoptroff London. All released 2013-2015. Not sure what happened then for there to be suddenly two.

[deleted]

Re: Atomic Clocks

#58

Earlier quoted context omitted.

Symmetricom (now owned by Microchip) released the first Chip Scale Atomic Clocks in 2011. It probably took some time for them to become available to watch designers and for them to be integrated into watch designs. https://www.nist.gov/noac/success-story-chip-scale-atomic-cl... I'm guessing the watches sold poorly and the chip packages are still large compared to a watch movement, so no new designs.

Sadly, no major miniaturization breakthroughs since. And those CSACs still eat up a lot of power (as do good OCXOs), making them rough for battery powered wearables.

Surely a good opportunity to tout your recent wristware Jeff? :D

Re: Atomic Clocks

#60

> Today’s best atomic clocks are billions of times more accurate and precise than any other type of clock. If they had been running since the Big Bang, 13.8 billion years ago, they would have lost or gained less than a second. Absolutely incredible, but then confused by the next assertion that is made without context: > New kinds of clocks may soon open up capabilities that previous generations could only dream about…

Cost, size, weight, and power are definitely things that can be improved on. The atomic clocks you can buy for a lab are big 3U boxes but shrinking it down to something portable is the future.

I actually work with one of those chip scale atomic clocks. The goal is to put it in space. If you need precise timing in space, the current state is to lock to a GPS reference clock (just for timing, don't care about position), train an OCXO, and let it drift for a day or two before you require GPS again. OCXOs (and crystal oscillators in general) can be very accurate but the stability is easily affected by temperature swings. So as your satellite goes in and out of the sunlight or as components inside turn on and off, the surrounding temperature changes and can make the clock drift. This isn't a problem on earth since you can always have a GPS receiver running but on a power constrained satellite, this is not ideal. The CSAC gets 100x better thermal stability than even some of the best space-qualified OCXOs. This means you could potentially run for 100x longer before you need to reacquire GPS, assuming the same environment and performance requirements. The CSAC also has a brain inside so potentially you can do all of your characterization on the ground and not even need a GPS receiver onboard. It also requires much less time to become stable after powering on than a normal crystal oscillator.

You get the same benefits on the ground, super precise timing for the processors and modems without necessarily needing a GPS receiver. The modern assumption (and pretty much proven in Ukraine) is that GPS will be completely unavailable on a battlefield. Anything portable or battery-powered will likely not be able to make use of newer anti-jam features of GPS (very power hungry) so you need something small, precise, and quick to come online.

Modern waveforms often require very tight timing to properly demodulate so having a pocket sized atomic clock solves a lot of problems.

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