Atomic Clocks Compared With Astounding Accuracy

The remarkable accuracy of atomic clocks makes them excellent instruments for timekeeping and other precision measurements. From a report: Writing in Nature, the Boulder Atomic Clock Optical Network (BACON) Collaboration reports extremely accurate comparisons of three world-leading clocks in Boulder, Colorado, housed at the National Institute of Standards and Technology (NIST) and the JILA research institute. The authors show how their clock comparisons provide insights into fundamental physics and represent substantial progress towards redefining the second in the International System of Units (SI). Atomic clocks 'tick' at a rate determined by the frequency of light that is emitted or absorbed when an atom changes from one energy state to another. Clocks based on different atoms run at different rates, and the term 'optical clock' refers to one that runs at an optical frequency. Three of the worldâ(TM)s best optical clocks are the aluminium-ion and ytterbium clocks at NIST and the strontium clock at JILA. The measured frequencies of all three clocks are estimated to be correct to within a fractional uncertainty of 2 parts in 10^18 or better.

This level of uncertainty could, in principle, allow the clocks to keep time so accurately that they would gain or lose no more than one second over the age of the Universe. Such optical clocks would be 100 times more accurate than caesium clocks. There is therefore a desire to redefine the SI second in terms of an optical-clock frequency and to move away from the current definition based on caesium. But before such a redefinition is possible, scientists must build confidence in the reproducibility of optical clocks through a series of clock comparisons. The target accuracy for these comparisons is at the level of parts in 10^18 to clearly demonstrate the superiority of optical clocks over caesium clocks.

Comparison

[lazarus]

So in summary, when comparing clocks it seems clear that it's not the size that matters as much as the way it moves.

It depends

[Roger W Moore]

So in summary, when comparing clocks it seems clear that it's not the size that matters

That depends: if your clock is large enough and accurate enough then its gravitational field will cause a measurable time dilation effect.

Re:

[Admiral Krunch]

So in summary, when comparing clocks it seems clear that it's not the size that matters

That depends: if your clock is large enough and accurate enough then its gravitational field will cause a measurable time dilation effect.

So outside observers think you lasted longer than you really did, compared to a local partner?

Re:

[Roger W Moore]

It will be interesting. However, if they can reduce the size of these clocks to the size of a bedside alarm clock then it will suddenly become possible to do table-top demos of relativity which will be fun!

Time...travel.

[Ostracus]

No more excuses for being late for work.

Fabric of space-time

[Tim12s]

I'm sure I read a scifi short story of these wondrous technology/military advances which were fantastic until the fabric of space&time broke down rendering the military technologies useless and unable to talk to one another during impending assault and war. Thus resulting in the failure and loss to a fundamentally simpler/weaker technological force with rudimentary military that.... just worked.

Re:

[invid]

One of the rules on the Evil Overlord list is to give your high tech minions low tech backup weapons, so that when the hero deactivates the high tech weapons (which always need a central node to run properly, which I used to think was stupid watching these kinds of shows in the 80s, but which I now know was a prescient reference to WiFi), the minions can pull out their revolvers and kill the hero.

Re:

[Beryllium Sphere(tm)]

That may have been Arthur Clarke's "Superiority". The losing side kept coming up with one superweapon after another but all had hidden flaws while the other side successfully pursued a policy of "quantity has a quality all its own".

Specifically, what you mention sounds like the shielding technology that stretched space so that the shielded ship was an infinite distance from the enemy. The problem was that every time you stretched space, it ruined the calibration of all the equipment including communications

Re:

[Agripa]

https://en.wikipedia.org/wiki/... [wikipedia.org]

Long winded

[chill]

That's a long winded way of saying they're all going to synchronize their watches.

Re:

[alvinrod]

It's not so much saying they're going to synchronize their watches as it is saying that they're going to conduct some experiments to show that a one type of clock is far less likely to be out of sync with other clocks of the same type as opposed the type of clock that's been used for official purposes up until this point. If they are unable to conclusively show that, then there's no reason to change from the type of clock being used now.

Re:

[Admiral Krunch]

There's potentially a lot more to it than that. [gossipum.com] With more accurate clocks we might be able to tell if physical constants are actually constant. Or detect dark matter passing through a network of such clocks.

Fixed clock

[backslashdot]

Even an atomic clock can be wrong once every 10^18 seconds.

Re:

[sconeu]

So over the lifetime of the universe, it's been off by 4 seconds. Fire the guy who built such a crappy device! /s

If they're both so accurate...

[WoodstockJeff]

... why not define a second in terms of the available (to the user) hardware?

Re:

[hackertourist]

The second IS defined in terms of available hardware, specifically, cesium-based atomic clocks [nist.gov].

Re:

[John Allsup]

The issue is whether we should redefine the second based on newer (and more accurate) optical atomic clocks, rather than sticking with the caesium clocks that have been around for a while.

Re:

[hackertourist]

The research described in TFA is to determine if they can do that without causing issues.

You know the old saying ...

[fahrbot-bot]

Three of the world's best optical clocks are the aluminium-ion and ytterbium clocks at NIST and the strontium clock at JILA. The measured frequencies of all three clocks are estimated to be correct to within a fractional uncertainty of 2 parts in 10^18 or better.

This level of uncertainty could, in principle, allow the clocks to keep time so accurately that they would gain or lose no more than one second over the age of the Universe.

Someone with one optical atomic clock knows the age of the Universe, someone with two is never sure ...

But

[rossdee]

You still need to adjust it twice a year for daylight saving. standard time

What do we want?! Unicode!

[superposed]

It is troubling when a tech website can’t even manage to display run-of-the-mill non-ASCII characters on its front page: “the worldâ(TM)s best optical clocks”.

Gravitational time dilation

[John Allsup]

The effects of gravity upon time have been observed for height differences of only a metre. The more accurate clocks get, the more significant gravitational issues become as a source of error. (I do not know, however, the actual amount of time dilation observed since the paper on it is paywalled.)

Re: Gravitational time dilation

[As_I_Please]

https://www.nist.gov/news-even... [nist.gov]

Described in the Sept. 24 issue of Science,* the difference is much too small for humans to perceive directlyâ"adding up to approximately 90 billionths of a second over a 79-year lifetimeâ"but may provide practical applications in geophysics and other fields.

Re:

[joe_frisch]

I think they are not getting close to the point where random fluctuations in the earths gravitational potential (due to density changes) will become a limit and measurements will need to be done in deep space in order to do better

They can claim the longitude award prize

[140Mandak262Jamuna]

https://en.wikipedia.org/wiki/... [wikipedia.org]

But the British gov is likely welsh on the promise. I mean, when they stiff Robert Hooke, the president of the royal society, there is no level too low for them to steep down to....

Speechless

[arnach]

The only time I ever heard Science Friday host Ira Flatow actually speechless (he's usually quite chatty) was when one of the NIST optical clock researchers told him that the Flatiron mountains on the southwest edge of Boulder significantly affect the accuracy of these clocks.
So, my question is: Where in the universe do you take them to decide the final calibration? Maybe Boulder CO USA is the center of the universe...

ain't nobody got time for that

[mad7777]

lose one second in 10^18, but then lose an hour because of DST madness, and all that work goes out the window!