NIST's New Atomic Clock Is So Precise Our Ability To Measure Gravity Constrains Its Accuracy (vice.com) 92
dmoberhaus writes: Researchers at the National Institute for Standards and Technology (NIST) have developed an atomic clock that is so precise that our models of Earth's gravity aren't accurate enough to keep up with it. As detailed in a paper published this week in Nature, the atomic clock could pave the way for creating an unprecedented map of the way the Earth's gravity distorts spacetime and even shed light on the development of the early universe. "The level of clock performance being reported is such that we don't actually know how to account for it well enough to support the level of performance the clock achieves," Andrew Ludlow, a physicist at NIST and the project lead on the organization's new atomic clock, told me on the phone. "Right now the state of the art techniques aren't quite good enough so we're limited by how well we understand gravity on different parts of the Earth."
Great! (Score:2)
So now it's device that can measure not just time, but gravity too.
Re: (Score:1)
i dunno, how accurate is a device we cant actually accurately measure?
Re: (Score:1)
The standard thing to do is to build another one and compare the two: the stability of a single clock should be sqrt(2) smaller. If you have three clocks, then you can determine the stability of each clock. This doesn't tell you about systematic errors but physics comes to the rescue there because the influences that cause systematic frequency errors (magnetic fields, collisions, black body radiation ...) can be characterised and controlled.
So is it hooked up so we can sync our PC clocks? (Score:3)
Sure internet lag, and performance of our PC especially in terms of the time clock wouldn't matter... But darn it, I want my PC to have accurate time.
Re: (Score:3)
Because I want my clock to be accurate.
It is like having speakers that go to 11
Re: (Score:2)
Because I want my clock to be accurate.
It's a security feature. It allows you to require krb5_deltat < .000000000000000001
Less than 1 microsecond network time with PTP (Score:2)
You can get time accurate to within about a thousand to a millionth of a second with PTP, using network time as your reference. That's the time standard used by thr vast majority of people, network time aka ntp time aka internet time, which is closely synced to GPS time.
So which time do you want to consider "correct" - the time used by 98% of the precision clocks, or the time used by one clock in Boulder?
NTP is super easy to use and pretty darn accurate as well. PTP is quite a bit more accurate, with micros
Re: (Score:2)
That's not what offset means. Good news though (Score:2)
I have good news and bad news for you.
The offset value we log isn't the actual difference between your clock and the peer clock, and the logged value is seconds, not milliseconds. If you see 0.08 in the log, that means we're *assuming* that you're about 0.08 *seconds* off from that peer.
If you ping a server "thousands of miles away", you'll notice each ping takes a different number of milliseconds. That difference in ping times, or jitter, is pretty much a hard limit on sync accuracy with the NTP protocol.
More about network distance (Score:2)
The reason for choosing the closest server may merit more explanation. If you're on the west coast and you query a server on thr east coast, your accuracy suffers with every router and switch along that path, so you end up with some unknown offset from the NTP server's time. ISPs and geographically disperse companies don't have that problem. Here's why.
Comcast will have a DNS server / ntp server in Houston. It may have a GPS, tdma, or LTE reciever locally connected, but most importantly it peers with their
Re: (Score:2)
Re: (Score:2)
>> Logs are showing an average offset of 0.08ms and max of 5ms.
> I'm not looking at logs.
As my friend would say, "you do you, Beau". :)
Re: (Score:2)
> . I use a bunch of public strata 1 and strata 2 with similar offsets to the strata 1 from around the USA.
FYI that's considered rude. If, as it seems, we're talking abour your house. The reason it's considered rude is because it is selfish, you're taking up slots that should be going to tier 2 servers with ten of thousands of users.
It would be more polite to use the pool for your continent:
https://www.ntppool.org/zone/@ [ntppool.org]
Our pool servers are pretty well synced. Any that go out of sync are kicked out the p
Re: (Score:2)
But darn it, I want my PC to have accurate time.
The optical lattice clocks they're talking about "would take longer than the age of the universe (13.8 billion years) to lose a second." (from: Scientists Build Atomic Clocks Accurate Enough to Measure Changes in Spacetime Itself [gizmodo.com]). If you think your PC will last that long, I want to know more about it than the clocks... :-)
Re: (Score:2)
The accuracy would only be valid for its own time frame, though. As soon as you need to send the time anywhere else, and you have to, even if it's just to a circuit to read the time from, the accuracy depends on stability of the environment. Any kind of change in acceleration, including but not limited to gravity, will cause a cumulative difference over, well, time, for lack of a better word.
Someone storing large amounts of metal in a nearby building, or Boring a tunnel underneath might be enough to cause
Re: (Score:2)
But darn it, I want my PC to have accurate time.
You can buy an atomic clock on a chip, such as the SA.45S from microsemi.
A dev kit version with serial output runs just under a thousand bucks for quantities of one, and would give you a legit strata-0 time source.
It's not as accurate as this new atomic clock NIST has, this one will drift by 10^-11 seconds per day, but it's far far cheaper.
Re: (Score:1)
Not quite. How do you set time of day? It's only a frequency reference, not a time reference. For time references, there's really only GNSS, dialup time services like ACTS and the various radio services (and maybe Iridium). The value of the CSAC, synchronised with GNSS, is that it will give you better holdover than the very ordinary crystal oscillator in your PC if GNSS is unavailable.
As for the frequency offset, the CSACs 'age,' that is their frequency offset increases with time, so that the time offset in
Re: (Score:1)
I know you were just joking but ... it's not a clock. It's a frequency reference. A clock needs to run continuously and the state of the art 'clocks' like lattice clocks are not reliable enough to do this yet. Very good frequency references can be used to correct the frequency of less accurate clocks and this is what happens in the computation of Coordinated Universal Time. Time of day is computed from 400 or so continuously running hydrogen masers and caesium beam standards and then a very small correction
Re: (Score:2)
He'll figure it out.
More like his daughter will.
New, extremely accurate altimeter? (Score:2, Interesting)
Since you can measure gravity extremely accurately, and gravity varies with height, does that mean they've just invented an extremely accurate altimeter?
Re:New, extremely accurate altimeter? (Score:5, Interesting)
Yes, but it must be locally calibrated. I was talking to a guy that used to work at WWV, he said that moving an older clock up one story would make a very noticeable change in it's tick time - this one might be sensitive to inches.
Re: (Score:3)
Sensitive to about a centimeter actually, with a sustained observation.
Re: New, extremely accurate altimeter? (Score:2)
This is an extremely accurate Dark Matter detector. We are either measuring Earthâ(TM)s distortion as the moon revolves around us, as the solar system revolves around the sun, or as we enter a region of space where we are swimming in dark matter.
Re: (Score:2)
Finally, I can accurately tell people both how high they are, as well as exactly how long I've been waiting to tell them that. And they say science is a waste of money.
Re: (Score:2)
One time I flew with a Geiger counter and noticed that radiation level was (somewhat) correlated with what my gps said the altitude was, probably more practical than using a clock ;-)
Nice clock you have there (Score:2)
If you pay us a couple million a year, we probably won't create any black holes around it. Just insurance ya know? /s
And behind Door #2 time is running out for (Score:5, Informative)
And behind Door #2 time is running out for WWVB.
The low frequency WWVB standard and short wave clock time standards seem have time running
out for them.
https://www.voanews.com/a/time... [voanews.com]
It may simply be that we will know with more precision when infrastructure has its plug pulled.
GPS time is likely better than NTP time for computers.
Clocks like this may allow for the elimination of almost all Olympic timing errors and ties.
I can see headlines... runners fail to best Usain Bolt's best time by one Picosecond +/- 2.7 Femtoseconds.
Re:And behind Door #2 time is running out for (Score:5, Funny)
I can see headlines... runners fail to best Usain Bolt's best time by one Picosecond +/- 2.7 Femtoseconds.
No fair! You changed the outcome by measuring it!
Re: (Score:2)
Precision doesn't gain you anything when accuracy is the actual problem. Why thousandths of seconds are significant where the bulk activity of a human is concerned baffles me. At this level of precision, the outcome is basically arbitrary.
Re: (Score:2)
Truth is stranger than fiction, but it is because Fiction is obliged to stick to possibilities; Truth isn't. Mark Twain..
+1.
Also, I just want to confess that I will be stealing your Mark Twain quote for use at some other venue.
First World Problems (Score:2)
So get cracking on that spacetime gravity problem!
It's just a theory (Score:1)
"our models of Earth's gravity aren't accurate enough to keep up with it."
It's just a theory.
It's not like it was a law or something.
Next up: The first watch to become inaccurate... (Score:2)
Interesting new problems (Score:2)
Imagine if you had a array of these clocks spread out in a 2d grid, level with each other to within less than a millimeter, It is possible some would run faster or slower than the others because of subterranean variations in density, and thus slightly different amounts of gravity.
Interesting stuff, thanks for sharing.
FINALLY! (Score:2)
Now we will FINALLY know what time it really is!
A man with two watches (Score:2)
A man with a watch can tell you what time it is.
A man with two watches is never really quite sure.
This new clock demonstrates a sort of high-tech version of this problem. Two of these clocks might not agree because they are in different locations, where gravity is stronger or weaker. At least in this case, the clock can help solve its own problem by helping refine the map that it needs to be more accurate.
Re: (Score:2)
A man with a watch can tell you what time it is.
A man with two watches is never really quite sure.
A man with a properly configured NTP server with more than 8 peers or GPS locks can smugly tell both of the other men their clocks are wrong.