Keeping Time with a Mercury Atom

Roland Piquepaille writes "The National Institute of Standards and Technology (NIST) has announced that a new experimental atomic clock based on a single mercury atom is now at least five times more precise than NIST-F1, the U.S. standard clock. This mercury atomic clock 'would neither gain nor lose a second in about 400 million years' while it would take 'only' 70 million years to NIST-F1, based on a 'fountain' of cesium atoms, to gain or lose a second. But even if this new kind of optical atomic clock is more accurate than cesium microwave clocks, it will take a while before such a design can be accepted as an international standard. A ZDNet summary contains pictures and more details about the world's most precise clock."

Comments

unfortunately

[legallyillegal]

syncing to time.singlemercuryatom.nist.gov doesn't work yet.

Re:unfortunately

[uglydog]

maybe it's been /.ed?

Re:400 million years

[gardyloo]

Pfft. You'll regret saying that when the readers of the future see the article's 3.56*10^12th dupe.

Great news for D-Link

[GreggBz]

Great news for those mission critical D-Link routers!

Only problem is...

[mrjb]

They're treating time as if it were something absolute.

Re:Only problem is...

[Umbral Blot]

Relativity doesn't make clocks less useful, in fact it makes them more useful (because you can use them to figure out how fast you are going as well). And assuming that the clock remains under constant acceleration there is no reason to believe that relativity would make it less accurate.

Re:Only problem is...

[Lumpy]

That an it will help prove my Theory that there is a black hole in time here on the planet earth. AS we age we accelerate towards the black hole and therefore experience time distortion. Think about it. As a child summer took F-O-R-E-V-E-R. As a Teen it took about what felt like the right amount of time. As a Young Adult in college it seems like summer was shorter than normal. A person in their 40's summer feels like about 3 weeks and other effects of time distortion take effect.... Week-ends feel like they last ony a single day. And the inconsistancies also start showing as the time gravitional waves pass by you. A work week seems like it took a day to pass while a co-worker next to you in the same age bracket feels like it took much longer.

As you get near your 80's the gravity of the black hole starts tugging not only at your time harder by at you in physical ways. Your skin starts sagging, you break bones easier because of the greater gravity in the physical dimensions.. How many people have heard old people complain it's hard to walk?? Huh! Observable proof!

Mercury clocks would help here. We attach one to every newborn for a decade and then look at the time distortion as it happens so we can figure out how to defeat this terror.

Re:One small problem...

[enrevanche]

i'm sure that they use a stable isotope.

the isotope you mention (194) is synthetic anyways

Re:How much accuracy do you need?

[gardyloo]

See this page: http://www.sciencemuseum.org.uk/on-line/atomclocks /page6.asp

The only problem arises...

[viking2000]

...from the Heisenberg uncertainly principle:

The more precisely
the MOMENTUM is determined,
the less precisely
the POSITION is known

So this clock is unfortunately missing. And when it is found, it is not so accurate anymore.

Re:400 million years

[evilviper]

It's easy to make impressive statements like that when you know nobody will be around to prove you wrong!

Complete nonsense. This isn't a "prediction", it's a mathematical number/time. Like any other number/time, you can easily convert it into shorter time-frames.

1 sec in 400 million years is ==
    1/2 sec in 200 million years
    1/4 sec in 100 million years
    1/8 sec in 50 million years
    etc.

That means it is accurate to 0.000000025ths of a second in 10 years... A more partical time-frame, which can be tested fairly easily.

I Know I'm Missing Something Here...

[stuffman64]

I'm just curious about something here. If a second is defined to be 9,192,631,770 oscillations of a Caesium-133 atom, then why is it said atomic clocks are accurate to within a second over 70 million years? Isn't that lost/gained second itself defined by the Caesium atom's transitions? I hope this question makes sense...

Re:I Know I'm Missing Something Here...

[oskay]

The trick is that the second is defined to be the frequency of an unperturbed cesium atom, which is about as real as that "frictionless plane" that you might have had in high-school physics.

An example of the problem is this: for technical reasons, a small magnetic field is needed inside a cesium clock. Magnetic fields change the spacing between all atomic energy levels to some degree. For cesium, the relevant change is very small, but it is still there. What you need to do is measure the magnetic field, calculate how much it affects the frequency of the atomic transition, and correct your output frequency by the required amount. What ultimately sets the accuracy level of a given clock is how well the magnetic field shift (and dozens of others) can be corrected for.

The same is true for the mercury clock. The difference is that the systematic frequency shifts that can affect accuracy of the clock are now understood, and controllable, at a higher level of precision.

Re:400 million years

[evilviper]

Only test that I can think of would be to build two of these, plus a control of some sort, and leave them right next to each other for ten years. Only the control will be less accurate than the device you're measuring...

The same way they've been doing it for many years with current atomic clocks... You don't just have a single clock, you have a BANK of numerous atomic clocks, and use statistical sampling to correct drift. And establish a very, very accturate time base.

wristwatch

[elmartinos]

Can't wait to have a wristwatch with this. My atomic wristwatch is a bit too bulky.

Re:How accurate is accurate enough?

[rwwh]

Scientific American once had a nice paper about time. I remember these two facts:

• At an accuracy of 10^-17, the earths gravity makes that two identical clocks, one of which is 5cm higher up than the other one, will start deviating from each other (i.e. time really IS different 5 cm up, at this accuracy)
• At an accuracy for 10^-17, relativistic effects start playing a role at walking speeds (i.e. time really IS different at walking speed than at rest, at this accuracy).

I think 5cm and 5km/hour are reasonable usability limits, hence an accuracy of better than 1:10^17 would not make much sense to me.

Re:One small problem...

[oskay]

The clock is based on mercury-199. Yes, it's a stable isotope.

Re:How accurate is accurate enough?

[oskay]

The 400-million year figure is still limited by technical issues, not fundamental physics. It is expected that once a few more calibration methods are tried out, that it will be able to reach its theoretical limit, which actually does turn out to be pretty close to one second in five billion years. In any case, these millions-of-years figures are not really practical-- they're just the way that clock people phrase things so that they sound good in the popular press. What really matters is that the precision that can be obtained in a much shorter period of time is much higher. Right now the mercury clock has errors at the level of about a second in 400 million years-- but a second is a lot of timing error! Perhaps a more useful (but equivalent) figure would be 2.3 ns per year, or perhaps you would rather use 44 picoseconds per week.

Re:400 million years

[Das Modell]

It's easy to make impressive statements like that when you know nobody will be around to prove you wrong!

This man begs to differ.