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Keeping Time with a Mercury Atom

Zonk posted more than 7 years ago | from the nice-watch dept.

153

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."

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153 comments

unfortunately (5, Funny)

legallyillegal (889865) | more than 7 years ago | (#15727035)

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

Re:unfortunately (5, Funny)

uglydog (944971) | more than 7 years ago | (#15727293)

maybe it's been /.ed?

Re:unfortunately (1)

Sillygates (967271) | more than 7 years ago | (#15727410)

I'm just waiting for the wristwatch [leapsecond.com] version.

400 million years (2, Insightful)

gfody (514448) | more than 7 years ago | (#15727047)

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

Re:400 million years (3, Funny)

gardyloo (512791) | more than 7 years ago | (#15727054)

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

Re:400 million years (4, Insightful)

evilviper (135110) | more than 7 years ago | (#15727123)

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.

Re:400 million years (2, Insightful)

Planesdragon (210349) | more than 7 years ago | (#15727233)

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.

How, exactly?

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...

Re:400 million years (4, Informative)

evilviper (135110) | more than 7 years ago | (#15727248)

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.

Re:400 million years (0, Troll)

pacinpm (631330) | more than 7 years ago | (#15727394)

And what happens when ALL those clocks loose second per million years at the same rate? You will not catch such error.

Re:400 million years (1)

Niffux (824706) | more than 7 years ago | (#15727457)

Some gain a second, some lose a second. It'll all even out in the end, I hope.

Re:400 million years (1)

Shimmer (3036) | more than 7 years ago | (#15727509)

Think about it. If they all drift at the same rate, it's not drift.

Re:400 million years (1)

alexhs (877055) | more than 7 years ago | (#15727378)

What matters is that it's a clock with a 10^-16 s precision. Now I'm not sure how quantum physics needs that much precision.

Re:400 million years (4, Funny)

Das Modell (969371) | more than 7 years ago | (#15727453)

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

This man [wikipedia.org] begs to differ.

Open Season (-1, Troll)

Frankie70 (803801) | more than 7 years ago | (#15727052)

I officially throw open this whole topic to be used for
bitching about Roland Piquepaille.

Closed Season (1, Offtopic)

Doc Ruby (173196) | more than 7 years ago | (#15727074)

Roland is back with the accepted stories you wish you'd submitted, and no one is wasting time with any bullshit about how he's robbing us with his good editing.

Re:Closed Season (1)

1u3hr (530656) | more than 7 years ago | (#15727696)

no one is wasting time with any bullshit about how he's robbing us with his good editing.

Because the lazy editors at Slashdot don't care how he's gaming the system with his regurgitated stories. And he links to his personal blog, describing it as "a ZDNet summary". Could I link to my home page and describe it as a "Yahoo summary"?

He's sleazy, but Slashdot deserves no better.

Great news for D-Link (5, Funny)

GreggBz (777373) | more than 7 years ago | (#15727059)

Great news for those mission critical D-Link routers! [slashdot.org]

One small problem... (0)

creimer (824291) | more than 7 years ago | (#15727060)

So you're going to trust a single mercury atom [wikipedia.org] to keep time acurate for 400 milliion years even though the half-life is only 444 years? Oh, wait a minute. The planet Mercury is being used for this new clock. For a split second, I thought we had a serious technical problem.

Re:One small problem... (4, Informative)

enrevanche (953125) | more than 7 years ago | (#15727090)

i'm sure that they use a stable isotope.

the isotope you mention (194) is synthetic anyways

Re:One small problem... (1)

scapermoya (769847) | more than 7 years ago | (#15727211)

congratulations, you fail high school chemistry regressively.

Re:One small problem... (3, Interesting)

oskay (932940) | more than 7 years ago | (#15727304)

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

Only problem is... (5, Funny)

mrjb (547783) | more than 7 years ago | (#15727063)

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

Re:Only problem is... (5, Insightful)

Umbral Blot (737704) | more than 7 years ago | (#15727077)

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... (1)

DigiShaman (671371) | more than 7 years ago | (#15727138)

A clock in only accurate within its own space and time. For example, moving this clock to another area of the universe may slow or speed it up. However, say you are in the same area as this clock...would you notice the change in pace? No. The only way to measure change is against another point of reference such as another clock located in another part of the universe.

Don't you just love relativity? ;) It's a topic which defines nothing being absolute.

Re:Only problem is... (1)

Umbral Blot (737704) | more than 7 years ago | (#15727152)

I didn't say you could do it with a single clock. And it's "frame of reference" not "space and time" there are many frames of reference, and only one space-time.

Re:Only problem is... (-1, Troll)

brian0918 (638904) | more than 7 years ago | (#15727255)

Yes, you understand the buzz words. Now take a course or two for a real understanding :) (and no, a generic wishy-washy book with pretty pictures for the layman doesn't count)

Re:Only problem is... (1)

Umbral Blot (737704) | more than 7 years ago | (#15727270)

ha ha ha! Would you like me to give you a lecture about distance in Minkowskian geometry? Or perhaps a quick introduction to Riemann manifolds? Take a class ... you make me smile, I have been to way too many classes as it is.

Re:Only problem is... (3, Insightful)

Lumpy (12016) | more than 7 years ago | (#15727664)

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.

How much accuracy do you need? (2, Interesting)

tylernt (581794) | more than 7 years ago | (#15727071)

So... at what point do you say that a clock is accurate enough? I mean, yeah maybe this thing is more accurate than current technology, but if it turns out to be way more expensive, why bother? How often do you need the accuracy that current technology can't provide?

Re:How much accuracy do you need? (1, Redundant)

cyko500 (315074) | more than 7 years ago | (#15727239)

Bogart: Thugtor, why make rocks pointy? Waste too much time. Rocks already makes things dead good 'nuff.

Thugtor spears Bogart.

Re:How much accuracy do you need? (1)

PatrickThomson (712694) | more than 7 years ago | (#15727393)

I was surprised it took the "why bother?" people this long to flourish out of the woodwork. I'm no physicist, but if it was pointless they wouldn't do it or it'd be some poorly-funded "just because" research project in a closet somewhere. See my sig for further details.

Re:How much accuracy do you need? (2, Interesting)

Detritus (11846) | more than 7 years ago | (#15727485)

We can always use more accuracy. Many communications systems rely on accurate clocks to keep the transmitters and receivers in synchronization. Frequency stability is also important for communications systems and test and measurement equipment. Any defects in the clock will degrade the performance of the equipment.

Why? (2, Interesting)

mh101 (620659) | more than 7 years ago | (#15727076)

Can someone explain why we even need this sort of precision?

Re:Why? (1)

ComradeSnarky (900400) | more than 7 years ago | (#15727085)

Scientific experiments, etc. etc.

Re:Why? (0)

Anonymous Coward | more than 7 years ago | (#15727150)

Can somebody explain to me why this is modded Flamebait? It's a perfectly good question, to answer to which also interests myself. It seems impractible for use by the general public, let alone the scientific community. Anyone know?

Re:Why? (1)

Lazbien (788979) | more than 7 years ago | (#15727191)

Obligatory: Me Too!

What's the practical application for something like this? Is this a "win" in the science category, or is this just another way of doing the same thing?

Re:Why? (1)

(negative video) (792072) | more than 7 years ago | (#15727419)

What's the practical application for something like this?
Radar and lidar. The more accurate the instrument's clock, the more accurate its distance measurements.

Also, gravity affects time, so you can use clocks and radios to measure the relative gravitational potential between two points in space. By sending a sufficiently good clock into deep space, we might be able to see if the solar system contains any dark matter.

Re:Why? (2, Informative)

bmo (77928) | more than 7 years ago | (#15727498)

Like the other guy said, radar, lidar, but also add navigation and land surveying. Longitude is determined by time difference between UTC and local time. If you make this clock small enough, and replace the current constellation of GPS satellites with new ones based on this type of clock, you increase the resolution.

--
BMO

Re:Why? (1)

KDR_11k (778916) | more than 7 years ago | (#15727321)

If we forget the length of a meter we can use that clock to measure the speed of light accurately enough to know how large a 299792458th of the distance it travels per second is?

Re:Why? (1)

E++99 (880734) | more than 7 years ago | (#15727699)

Can someone explain why we even need this sort of precision?
GPS for one. Others are mentioned in the article.

How accurate is accurate enough? (1)

Finnegar (918643) | more than 7 years ago | (#15727105)

While a 70 million to 400 million jump is quite exceptional, how long will this continue? Will anyone really want to use a clock that won't lose a second until AFTER the sun has expanded and burnt up the earth (~5 billion years)?

Re:How accurate is accurate enough? (0)

Anonymous Coward | more than 7 years ago | (#15727130)

Re : Will anyone really want to use a clock that won't lose a second until AFTER the sun has expanded and burnt up the earth (~5 billion years)?

The current caesium clock would have drifted by 71 seconds while the mercury clock would have drifted by 12.5 seconds before the sun swallowed the earth.

Re:How accurate is accurate enough? (1)

dtfinch (661405) | more than 7 years ago | (#15727169)

If the error is random, without skew, it may be more like 8.4 seconds vs 3.5 seconds.

Re:How accurate is accurate enough? (4, Interesting)

rwwh (989154) | more than 7 years ago | (#15727291)

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:How accurate is accurate enough? (3, Informative)

oskay (932940) | more than 7 years ago | (#15727322)

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.

How did they make the clock, and will it break? (1)

aersixb9 (267695) | more than 7 years ago | (#15727113)

Why is it that cars break in 15 years, and most other things are extremely fragile, but this clock can last 40 billion years? Is it made from some kind of super-dense material? Why is the quality of this timepiece so great, and how is it made? It would be nice to have some technical information on how an ordinary person could manufacture a timepiece of this exact precision. Are the materials from a very deep mine? Are they hydrogen materials? Why is this clock so accurate?

Re:How did they make the clock, and will it break? (1)

gardyloo (512791) | more than 7 years ago | (#15727127)

It would be nice to have some technical information on how an ordinary person could manufacture a timepiece of this exact precision. Are the materials from a very deep mine? Are they hydrogen materials? Why is this clock so accurate?

      *sob*

Re:How did they make the clock, and will it break? (2, Insightful)

voice_of_all_reason (926702) | more than 7 years ago | (#15727159)

Actually, the logical design of the clock will last 40 billion years until it produces an error. I'm quite sure we will never design any sort of mechanical device can actually last that long to find out.

//unless you socket it with a zod rune...

Re:How did they make the clock, and will it break? (1)

Frozen Void (831218) | more than 7 years ago | (#15727363)

Someone played too much Diablo II.
What if someone removes the zod,cubing hel+tp scroll with the zod socketed item? (this is like asking if immortals can commit suicide,will they do it eventually?)

Re:How did they make the clock, and will it break? (1)

Ramble (940291) | more than 7 years ago | (#15727495)

"this is like asking if immortals can commit suicide,will they do it eventually?" As shown in season 2 episode 18 "Death Wish" of ST: Voyager, an immortal being (Q) will eventually commit suicide.

Re:How did they make the clock, and will it break? (0)

Anonymous Coward | more than 7 years ago | (#15727176)

You build several clocks, and replace them as they fail.

Re:How did they make the clock, and will it break? (0)

Anonymous Coward | more than 7 years ago | (#15727331)

It all sounds so technical and yet so dumb. So how can I make one too? the clock.

AC

Re:How did they make the clock, and will it break? (0)

Anonymous Coward | more than 7 years ago | (#15727418)

oh my GOD, you are a moron. Not only did you get the numbers wrong, you have no concept of this issue whatsoever!

Re:How did they make the clock, and will it break? (1)

Lumpy (12016) | more than 7 years ago | (#15727685)

I do have an answer for you. Most things break in a specific time span because of lack of maintaince + abuse.

There are many cars from the 60's, 70's, and 80's on the road now that look fantastic and work great. While I can point at about 5-6 around here that are less than 4 years old that are on their last leg. Cars specifically suffer from the "what? I change the oil and put gas in it" syndrome. Cars need around $400-$1000US in maintaince every year and they do not get it. Most cars on the road do not get their proper service performed only oil changes at the cheapest place and gas added when needed. This significantly degrades the lifespan of the vehicle. Also not changing the service intervals compared to driving conditions. In areas of extreme temperature changes you should cut the time in 1/2 for oil changes. Michigan,Minnesota,etc... need the oil changed newrly twice as much in the winter months as the oil is cycling from 200 degrees to 30 degrees twice a day. transmission fluid and filter changes almost never happen in cars until something is wrong. etc...

Cars fail because people do not know the real cost of ownign a vehicle. Now my mint condition 1986 Fiero GT will last about 2 weeks in the hands of my daughter. but I also suspect that a 2006 Corvette Z06 would last only 1 week in her hands, simply because of abuse. (Yes wrapping it around a tree is abuse)

Laptops- Abuse causes failure. My daughter and I both have Dell D800 Laptops. Mine is still in near perfect condition except for shiney keys from use. Hers is missing keys, has a broken hinge, her trackpad has a dent in it, headphone jack is busted.... Simple abuse is causing hers to have problems while mine still looks new.

Now, this clock CANT last 400 million years. It can keep time that accurate so that way it will not lose a picosecond in a decade which at that accuracy will give you the ability to have GPS systems that without DGPS equipment can deliver millimeter accuracy at every location on the planet. That is the use not something to see if the clocks are still accuate in 400 million years, but really accurate navigation for us here and spacecraft at the edge of the solar system. At least until someone start smashing the clocks, dropping them, spilling coke on them and not changing the oil.

The only problem arises... (5, Funny)

viking2000 (954894) | more than 7 years ago | (#15727114)

...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:The only problem arises... (1)

pdxdada (684092) | more than 7 years ago | (#15727508)

It gets worce than that. How long to you think it'll take for that single atom to tunnel out of there. How embaracing would that be: scientists are finally on the verge of proving string theory in a spectacular, multinational, high precision experament when:
Scientist1 "Sir the clock stopped, we seem to have lost the atom."
Scientist2 "Well look around, it has to be here somewhere."

I'm registering domain names now (2, Funny)

shidarin'ou (762483) | more than 7 years ago | (#15727115)

400 million years in the future, my descendents will profit unthinkable amounts from their ownership of y400002k.com

Just in case the religious right get a further hold on our country in the future, I've also registered jesuswillreturn400002k.com and (hedging my bets) spaghettimonsterwillreturn400002k.com

but we all know that by that time, humanity will simply be slaves to the powerfully accurate mercury clock.

So, I for one welcome our new mercury atom overlords, and remind them that mercyatomoverlords.com can be had for the steal of 6.7 billion dollars, should cover the cost of registering the domain up to that point.

Re:I'm registering domain names now (1)

gardyloo (512791) | more than 7 years ago | (#15727131)

You forget that COBOL will once again become the language of the future, and all the clocks will think it's year ** by then.

Re:I'm registering domain names now (1)

gardyloo (512791) | more than 7 years ago | (#15727139)

Goddamn slashdot's filtering crap. Insert witty comment between the asterisks.

Re:I'm registering domain names now (1)

More_Cowbell (957742) | more than 7 years ago | (#15727369)

Dude ... spaghettimonsterwillreturn400002k.com is still available [toothpastefordinner.com]

At school (1)

tsa (15680) | more than 7 years ago | (#15727119)

Teacher: What! You're 15 attoseconds late! Again! Go stand in the corner!

Re:At school (1)

maxwell demon (590494) | more than 7 years ago | (#15727348)

But it's not my fault! I was running so fast that time dilation made my clock go out of sync, so I didn't notice that I was late!

but will it (2, Funny)

p51d007 (656414) | more than 7 years ago | (#15727120)

Fit on my wrist??????????

Re:but will it (1)

kfg (145172) | more than 7 years ago | (#15727154)

Yes, but the device to enable you to see it won't.

KFG

Re:but will it (1)

p51d007 (656414) | more than 7 years ago | (#15727189)

Drat! Where's my X-Ray glasses?

Re:but will it (1)

pontifier (601767) | more than 7 years ago | (#15727235)

It might, but if you move your arm at all you might as well just have a regular cesium clock on your wrist because you'll be losing any advantage you gain to relativistic effects.

Re:but will it (1)

oskay (932940) | more than 7 years ago | (#15727325)

Of course not! It's an atomic clock, not an atomic watch! (Actually, the entire atom trap is only about 1 cm across. The problem is the three rooms full of support equipment.)

Re:but will it (0)

Anonymous Coward | more than 7 years ago | (#15727432)

like this???

http://www.leapsecond.com/pages/atomic-bill/ [leapsecond.com]

Neat (1)

dtfinch (661405) | more than 7 years ago | (#15727125)

How do you calibrate a new atomic clock, if you have nothing more accurate to compare it against? And if we have clocks that won't lose or gain a second in 70 million years, why do we need to develop one that won't lose or gain a second in 400 million years?

Re:Neat (1)

oskay (932940) | more than 7 years ago | (#15727335)

Calibration is a process that evaluates the possible sources of frequency shifts, measuring how strong each type of stimulus and response is. For example, how strongly is the transition frequency affected by magnetic fields, and how much magnetic field is there?

It's actually the same procedure that's already used for the best cesium clocks-- there's isn't (or wasn't anyway) anything better to compare those to, and yet they've been making great strides forward for fifty years now.

As for the second question, we're not running a clock for 400 million years-- what counts is that it's that much more accurate in the lab today.

Re:Neat (1)

Guppy06 (410832) | more than 7 years ago | (#15727709)

"How do you calibrate a new atomic clock, if you have nothing more accurate to compare it against?"

A combination of the metric of fuckload of cesium clocks the world uses for official timekeeping and of known astronomical events. In other words, the same way we figure out UTC.

"And if we have clocks that won't lose or gain a second in 70 million years, why do we need to develop one that won't lose or gain a second in 400 million years?"

Because it takes 70 million years to lose an entire second. If, for example, you're trying to keep track of something that lasts for a billionth of a second (say, your CPU cycles), you miss one of them over the course of about 26 days.

Is it just me... (0, Redundant)

Stompp (987549) | more than 7 years ago | (#15727133)

or should I even care how many MILLIONS of years it takes a clock to get thrown off by an entire second?

70 million years is more than enough time for me... Sounds like somebody needs more grant money to me!

Recent findings from the GNAAU prove that Dr. Mart (-1, Offtopic)

MasterofGS (989146) | more than 7 years ago | (#15727134)

Recent findings from the GNAAU prove that Dr. Martin Luther King Jr. was gay
Recent findings from the GNAAU prove that Dr. Martin Luther King Jr. was gay
Monday January 16, 2006

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"These findings were how I, and my colleagues, had originally hypothesized. We have determined that Dr. Martin Luther King Jr., of civil rights fame, was not only a gay nigger, but a gay nigger of great magnitude. His homosexuality and niggerdom exceeded that of any average gay nigger.

"Many findings have proved our theory. Our research began in 1998, during the trial to determine his cause of death." The professor went on to explain how he, and his colleagues, were requested to perform an autopsy on King in order to determine a cause of death.

"Our first clue was that his anus was irregularly torn and bruised. From there, we hypothesized that he took nigger dong inside him on a regular basis. We then took a DNA sample, which showed an enormously large similarity to that of lesser primates, known commonly as apes. The DNA sample also showed that he was stricken with GRIDS, the leading killer of Gay Niggers everywhere. At this point, my colleague, head of the Law Department at GNAAU, dj28, investigated further."

In a classified report by dj28, released publicly today, The Gay Nigger Investigative Unit reported that not only had they determined that King had a harem of Gay Niggers, but that they had met and spoke with several of them. Only to learn that the rest had died of GRIDS, and that Dr. Martin Luther King Jr, was a great Gay Nigger; Possibly the greatest of all gay Niggers.


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Re:Recent findings from the GNAAU prove that Dr. M (-1, Troll)

Rahl Fagdick (989152) | more than 7 years ago | (#15727314)

All niggers are indeed faggots

I Know I'm Missing Something Here... (3, Interesting)

stuffman64 (208233) | more than 7 years ago | (#15727155)

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...

Because there are limits to measuring cesium (1, Interesting)

Anonymous Coward | more than 7 years ago | (#15727262)

For any definition of a fundamental unit, there are (quantum-mechanical or practical) limitations on how accurately the specified measurement can be made. Thus, there is a small but finite spread in the effective values used by different laboratories. As long as the new standard is within that range, it is "exactly the same" in the sense of being indistinguishable, but nonetheless better, because its measurement uncertainty is smaller.

Whenver the definition is revised, the new proposed standard is compared to the old accepted standard as precisely as anyone has ever done. For example, Louis Essen measured the frequency of the Cesium hyperfine transition as 9,192,631,770 +/- 20 Hz relative to the old tropical year definition. Thus, 9,192,631,770 was picked as the definition.

However, there are quantum mechanical limitations on our ability to measure that. In particular, when we examine the atoms for a time t, there is an uncertainty proportional to 1/t in the frequency. With cesium atoms, which are electrically neutral, gravity poses a problem. There's no way to hold them up without disturbing them, so they fly through cesium beam clocks in a fraction of a second, giving a small uncertainty in the measurement frequency. Suppose this is +/-1 Hz; that then leads to an uncertainty of +/- 1/9192631770 in the duration of a second.

Cesium fountains slow the cesium atoms down as much as possible and thereby extend the measuring time and reduce the uncertainty. However, for any given measuring time, a higher frequency will always lead to a smaller relative uncertainty. The problem is that 9 GHz is accessible to fast electronics. The mercury clock generates a frequency of 1,064,721,609,899,143 Hz (+/-10 Hz as of current measurements) - that's 1.065 Petahertz! There's no electronics that can keep up, so the challenge of building such a clock is measuring its output frequency. Nonetheless, it should be obvious that with a base frequency some 100,000 times higher than the base frequency of a cesium clock, the potential measurement uncertainty is 100,000 times lower.

If the standard second is ever redefined, it will be to a value that is indistinguishable from the old one using any cesium clock ever built.

It's like drawing a line. Suppose you have a line in pencil, and need to know where it is as precisely as possible. After a while the width of the pencil gets annoying, so you sit down with a magnifying glass and measure it as precisely as possible, and draw a line with a super-sharp pen through the middle of the pencil line. But then that's too wide and fuzzy, so you use a microscope and score a line with a diamond-tip probe. But then that's too wide, so you use an atomic-force microscope and push individual atoms around. Then the atoms are too fuzzy, so you cryogenically cool it to reduce their motion. Etc. etc. Each standard is equal to the old one because it's inside the range of uncertainty of measurement.

Re:I Know I'm Missing Something Here... (1)

Planesdragon (210349) | more than 7 years ago | (#15727271)

Sure it does. You just need to realize that what they really mean is "a second is that unit of time that we can measure by counting 9,192,631,770 occilations of a Caesium-133 atom", with the emphasis on the WE.

Let's take another absurdly re-defined measurement, the meter (you know, the basis of the entire metric system). It was originally defined, by the French Academy of Sciences, as one ten-millionths the distance from the north pole to the equator, in a line around the curve of the earth. The fact that the earth really is slightly different than 40,000 meters in north-south circumfrance doesn't change this definition, becasue the inferred component in the "1/10,000,000th" definition is "as measured by the French Academy of Sciences circa 1791."

Another example, which is a personal favorite, is to parse exactly what the "fact" is when you see a temperature. The real fact is "what the operator stated the thermometer to read." Which means that if the temperature doesn't seem right, it can be because the operator was mistaken, the thermometer didn't work, there's something off-kilter with the thing being measured, or our basic understanding of thermodynamics is flawed. Since (1) and (2) are easy to control for (insert additional tech, with seperate thermometer), most of the time we just worry about (3) -- since we can only talk about (4) if we also rule out (3).

(I really don't get why folk get all hung up on "definitions" of our units of measurement. An inch is an inch is an inch, if it's "the line on a ruler", "the length between the hashes on a particlar bar in the Smithsonian", "0.0254 meters", or "the distance light travels through a vaccum in 1/11,802,852,677.16... seconds".)

Re:I Know I'm Missing Something Here... (1)

rwwh (989154) | more than 7 years ago | (#15727278)

Yes, you are missing something. The vibrations have to be counted, but this is not trivial. In fact, such clocks make use of a separate electronic oscillator and then try to keep it in sync with the atoms vibrations. Sometimes a cycle can be missed, offsetting the clock.

Re:I Know I'm Missing Something Here... (5, Informative)

oskay (932940) | more than 7 years ago | (#15727377)

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.

Upper Limit? (2, Insightful)

NexFlamma (919608) | more than 7 years ago | (#15727158)

At what point do people simply say that our time keeping methods are good enough?

We already have a clock that only loses 1 second every 70 million years! The odds of the current time keeping system (or mankind, for that matter) continuing in it's current form for the next 70 million years are rather low, so why do we really need one that only loses a second every 400 million?

Sure, it's nice to be able to improve, but can't the research money go to something more useful? Like, maybe cancer research or studies into how we can build giant robots that transform into dinosaurs...

Re:Upper Limit? (1)

eobanb (823187) | more than 7 years ago | (#15727280)

At what point do people simply say that our time keeping methods are good enough?

Well, quantum theory says that there is in fact a smallest possible period of time, called Planck time.

I assume that would be the limit. Not even the practical limit, but The Limit.

--Eoban

Re:Upper Limit? (1)

Jedi Alec (258881) | more than 7 years ago | (#15727312)

Well, quantum theory says that there is in fact a smallest possible period of time, called Planck time.

I assume that would be the limit. Not even the practical limit, but The Limit.


Indeed, and as soon as a suitable thunderstorm comes past and Igor raises the lightning rod, we shall be able to measure it.

Re:Upper Limit? (0)

Anonymous Coward | more than 7 years ago | (#15727569)

Well, I am no expert in physics but maybe they don't plan to use this clock to see if it is time for their lunch break. And the fact that they give a precision of one second in 400 million years may be to give to the public an idea of how precise it is and not indicate that they plan to look the time on it in 400 million years.

What if they need to keep time for interactions that evolve in the nano/femtosecond time scale?

Not to mention that time is with length and mass, one of the fundamental unit of the Système International (SI) and more precision in the mesure of time can allow more precision in the mesure of almost anything such as length, current etc.

It's Saturday Night (0)

Anonymous Coward | more than 7 years ago | (#15727178)

I'm keeping time with empties.

Accuracy (2, Insightful)

thorndt (814642) | more than 7 years ago | (#15727193)

I'm suspecting that this level of accuracy would be quite useful in high-end scientific experiements--not so much for general wall-clock settings.
For example, measuring the duration of extremely short events--like in particle accelerators.

Re:Accuracy (0)

Anonymous Coward | more than 7 years ago | (#15727351)

I demand you tell me why we need such dumb stupid stuff. Hell, my Timex keeps great time as far as I know.

(seriouly - funding will be cut off for projects like this because of the 'whut the?' reaction, unless it has a military application)

Universal clock? (1)

CCFreak2K (930973) | more than 7 years ago | (#15727195)

This reminds me of that one clock that someone wanted to stick into a New Mexico cave or something. It was big, mechanical (IIRC) and had a foot pedal that you stepped on to update the display.

The details in my head are sketchy, but I think there was a Slashdot article on it. Maybe it wasn't. Anyway, this reminds me of it.

How do you know the percision? (1)

mechaman (898770) | more than 7 years ago | (#15727219)

How do you determine that it will gain or lose a second in 400 million years instead of 70 million years if:

A.)It hasn't been around long enough to find out.
B.)There are no timepieces more accurate to base this estimate on.

wristwatch (3, Funny)

elmartinos (228710) | more than 7 years ago | (#15727251)

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

Completely Accurate? (1)

hussain (579409) | more than 7 years ago | (#15727308)

Alright, so if we have a clock that loses a single second every seventy million years, why not just move it a second every 70 million years and end up with a clock that (should) be 100% accurate?

Question (0)

Anonymous Coward | more than 7 years ago | (#15727318)

So why does the page say:
"Jim Bergquist's optical clock team produced the first optical atomic clock based on a transition of a single mercury (Hg+) ion in 2001. The newest single-ion clocks, using either Hg+ or aluminum (Al+) ions, show the best time-keeping performance ever measured, neither gaining nor losing a second in a billion years."

I'm confused...

Erroneous pictures (1)

oskay (932940) | more than 7 years ago | (#15727355)

The first picture in the ZDNet article is not actually of the mercury clock, it's of the strontium atomic clock under development at JILA. JILA is associated with NIST, but they are not even on the same campus. The strontium clock uses a competing technology and is at a much earlier stage of development-- and performance-- when compared to the mercury clock!

Looks like Roland Piquepaille failed to RTFA?

Missing the point (1)

pdxdada (684092) | more than 7 years ago | (#15727494)

I hear a lot of people asking why we need this much accuracy. I'll give you a hint, it's not so we'll know the time in 700 million years, it's so we'll know it now. Some years ago an expirament was carried out where an atomic clock was loaded on a plane and flown around for hours. When it landed again the clock on board was compared with a clock on land and the limit of the accuracy of clocks showed a difference predicted by relativity. Now imagine if we could add some decimal points to that difference, not just substantiate current theory, but look for subtle differences. It's a hell of a lot cheeper than building giant ring accelerators or firing off expencive rockets which the nerds (a term of affection) here seem to support.

Re:Missing the point (2, Informative)

Teancum (67324) | more than 7 years ago | (#15727703)

To add a more practical real world example to this line of thought....

Clock accuracy is one of the key components of GPS systems and other navigational equipment. By having a much more accurate clock, you would be able to build devices that can determine with higher precision exactly where you are on the Earth... or for that matter in space even.

If you aren't aware of the "data" that is streamed out of GPS satellites, all that is transmitted is a clock signal that simply says what time it is right now, and along with some identification information. When compared to other satellites and applying some fairly straight-forward mathmatics (that includes some relativity equations), you get your current position.

In fact, while you might be able to determine within about 20 feet where you are at with current GPS technology and think that is "good enough" for the purposes of using that technology, navigation in the Solar System is going to need even higher clock accuracy in order to plot accurate trajectories to Mars and not get the current 30% failure rate of spacecraft trying to get there and accidentally crashing into the surface or other navigational mistakes caused by inaccurate plotting of the motion of both Mars and the Earth.

In short, you life someday (perhaps even now) might litterally depend on the navigation equipment of the vehicle you are in (read airliner) knowing precisely where you are at, and a more accurate clock will give that vehicle better accuracy to keep you alive.

Confusion ... (1)

jolshefsky (560014) | more than 7 years ago | (#15727639)

Wait, so the White Rabbit is always in a hurry, but it's the Mad Hatter who has the accurate clock?

Leap Year ? (1)

Joebert (946227) | more than 7 years ago | (#15727641)

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.

Do we really need a more precise clock ?
I mean, can't we just bury some notes about Leap Years somewhere for anyone that's around in 70 million years ?
The dinosaurs are about 65 million years older than us right ? Look how far the world has come. Hell, I'll bet whatever is living here 65 million years from now will have built-in clocks in their brains anyway.
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