# Atomic time boffins build better second-watcher

US researchers recently named the atomic clock at the UK's National Physical Laboratory (NPL) in London the most accurate atomic timepiece on the planet. Experts from the University of Pennsylvania found that NPL-CSF2 loses just one nanosecond every two months. It's a badge of honour for NPL, the birthplace of the first …

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#### >"or more precisely A1+"

Ironically less precise owing to typo!

This may seem a silly question, but: How do you prove that your clock is more accurate than someone elses ?

#### Surely

How do you prove that a clock is more accurate than everybody else's ?

#### So, how do they do that?

How can you tell if the most accurate clock in the world is losing time?

By definition wouldn't you be measuring it with an ever-so slightly less accurate one?

"A man with one watch knows the time, a man with two is never sure"

#### Probably built in someones shed.

Is it just me, or is the CSF2 held together with that old stalwart of British engineering -- string?

#### as opposed

The stalward of merkin engineering is duct tape.

#### Goon Show

Eccles: I know the time - I asked a man once and he wrote it down for me on a piece of paper

#### Stable Time

Eccles was right. I too have a piece of paper from the same show in 1957 and it still says 8 o'clock! Hasn't lost or gained at all.

#### Circular reference

Erm, is it me, or does the theory behind atomic time have a circular reference in it. Namely that to measure a second they have to excite atoms until they do something so many times a second?

#### re. Circular reference

No circular reference; all clocks work by having something happen "many times a second", the "something" (like a pendulum swing for example) will have a known frequency and the clock mechanism just counts how many cycles have occurred.

The tricky bit is working out the frequency of the thing you're using to "measure time" (most "real world" clocks are calibrated against a known accurate time source).

I'm fairly sure that Hz is defined as cycles per second, and as these atomic clocks are "more accurate" than any other clock, they don't have a "known accurate time source" to measure against, thus the comment about them having a circular reference. IMO this will become increasingly true if they ditch UTC, as they won't even have the 24/60/60 breakdown of the solar day.

Wouldn't it be better for them to define a second as x number of y event that occurs when z quantity of material has been heated up to temperature t?

#### The second is already precisely defined

as the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.

So, you just have to count cycles, until you get enough to make up a second.

The issue is how to count and average the radiation. It's the error in generating and detecting the radiation that's key.

Since 1967 the Second has been defined as 9,192,631,770 wobbles of a Caesium 133 atom.

Which is handy if you happen to have a clock uses wobbling Caesium atoms as its reference.

However in the article/attached documentation, didn't they refer to the act of exciting said caesium 133 atoms using microwaves until they get the requisite number of wobbles/second? This would infer that if you put more or less energy in they will wobble at a different frequency...

It is more like a filter, you pump in radiation at around the right frequency and tune it until the cesium atoms wobble the most.

#### Measuring time

don't they use pulsars ?

#### Oh look

another witless downvote.

Seems a perfectly valid comment to me. And the OP did use a "?" implying he was seeking knowledge rather than imparting it.

It's a pity the NPL can not be relied upon for time. I remember not too long ago their NTP server failed, and the first they knew about it was when I phoned them up.

#### How do you know?

You compare your time with the average of a bunch of other clocks around the world.

Some individual clocks drift faster or slower - if yours stays at the average you are the winner.

You have to love the NPL attitude, leap seconds will become unworkable in only 1700years and if a massive comet hit the earth everyone would have to adjust their watches.

#### One leap second per month?

In 1700 years, the Earth's rotation will be slowing at such a rate as the lengthen the the year by 12 seconds? If that rate is maintained the year will be more than one hour longer in 2000 years.

Outrageous! The Vogons will hear of this!

#### Not fast enough.

I'd be happier with 1 rotation every 32 hours. That way I could get more work done, have a longer leisure time and get more sleep.

#### and not only that

but because the atomic time is disconnected from the UTC, approximately 528000 years after that, a new Pope Gregory will have to re-adjust our dates by 11 days again.

#### Somehow ...

I thought an atomic time boffin would be much more imposing.

The is just his 3 dimensional projection for god sake!

#### From Sundials to Atomic Clocks: Understanding Time and Frequency

NIST (the US National Institute of Standards and Technology) has a pdf booklet named "From Sundials to Atomic Clocks: Understanding Time and Frequency" available at http://www.boulder.nist.gov/timefreq/general/pdf/1796.pdf

NIST has a good description of NIST-F1 which is a cesium fountain atomic clock at http://www.nist.gov/pml/div688/grp50/primary-frequency-standards.cfm

Does he get his jeans from Tesco?

#### But what difference will it make ?

Nice article, but it's a pity that despite there being so many accurate time sources out there, nobody bothers to use them.

My VoIP desk phone, which presumably gets its time from an NTP server somewhere, is always showing a different time to my laptop connected to the same network...

#### I'm gobsmacked...

...at the amount of technology required to calculate beer-o-clock.

(icon for the humour-free among us)

#### Man at a bar...

Man at a bar asks another man what the time is.

He replies; "Time to buy a watch."

#### WHERE is Fort Collins??

Well, their time might be accurate, but the height of a foot (at El Reg!) is way off.

"NPL is at an elevation of 79 feet above sea level and suffers more from the effects of gravity on its results than Fort Collins, which is more than 3,315 ft, above sea level in the Rocky Mountains in Boulder Colorado, where the effect of gravity is less."

Wow. Fort Collins is in Boulder?? at 3315 feet?? REALLY?!?

(Is somebody, used to sea level, getting dizzy from the altitude?)

Denver, Colorado is famous as "The Mile-High City" (statue mile, of course, so 5280 ft.).

Boulder Colorado is just a bit higher - 5430 ft above sea level (at City Hall). It has the Univ of Colorado - and the NIST Time and Frequency Division. Don't know the elevation at their clocks, but it should be close.

( http://www.nist.gov/pml/div688/staff.cfm )

Fort Collins, Colorado, is NOT in Boulder, Colorado. It's not even in the same county. It's about 32 miles further north than Boulder, and is the home of Colorado State Univ. -- as well as NIST "time" radio stations WWV & WWVB, and an Internet time server. It's also lower -- 5003 ft at City Hall.

( the 10 MHz antenna is at: 40° 40' 47.8" N 105° 02' 25.1" W - to within 10 feet or so )

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