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WikiProject Time assessment rating comment
Needs more cites to be a B.
Want to help write or improve articles about Time? Join WikiProject Time or visit the Time Portal for a list of articles that need improving. -- Yamara 15:54, 17 January 2008 (UTC)
Atomic Travel Alarm Clock Video
Discussion
"The most accurate time scales are moderated by precise astronomical measurements and the insertion or removal of leap seconds. " seems to be wrong since TAI is just as accurate as anything else, in fact, you could argue that it's more "accurate" than UTC since you can use a precise TAI time in the future and know how long from now that is. With UTC you can't.
How did they set the first atomic clock? Did they use astronomical measurements or some other source?
--haavis 12:15, 5 Nov 2004 (UTC)
A: Using astronomical measurements. Does the last paragraph in caesium standard explain it well enough?
--tdunc 8:29,10 May 2007
"When the electrons are attracted back closer by the opposite charge of the nucleus, the electrons wiggle before they settle down in their new location. This moving charge causes the light, which is a wave of alternating electricity and magnetism."
This explaination is unacceptable. The author either needs to elaborate or change it all together, why the electron jumps to a lower level. I have reason to believe it is not because of attraction due to charge (which would be constant), rather the electron emits a photon thus lowering its energy level, which could by coincidence mimick charge attraction but I dont feel its the same concept. If so it needs to work both ways, we cant for instance say a repeling charge is responsible for an electron going into a higher energy level. What is with the word "wiggle" anyway?
There is also a transit delay of approximately 1 ms for every 300 kilometers (186 mi) the receiver is from the transmitter. When operating properly and when correctly synchronized, better brands of radio clocks are normally accurate to the second.
Don't you mean millisecond instead of second ? 1 ms for every 300 kilometers means you must be 300,000 (300 x 1000) kilometers from the source to cause a 1 second delay, since the circumference of the earth is ~40,000 km, this does not make much sense.
Accurate compared to what?
"National standards agencies maintain an accuracy of 10-9 seconds per day"
So I set up my brand new atomic clock, go away for 3 million years, and come back to find out it is off by one second. Compared to what? Another atomic clock? I don't see what else it could be if, by definition, an atomic clock is the standard. --Chauncey27 19:21, 24 December 2005 (UTC)
Radioactivity?
How radioactive are small atomic clocks? Is it safe to make handheld devices with them?
atomic clocks are not based on radioactivity or decay but on electromagnetic wave frequencies, and the materials used (such as cesium 133) are stable, otherwise the clock wouldn't work well.81.206.145.191 21:43, 13 May 2007 (UTC)
Cesium-133 is a stable isotope and is not dangerous in a radioactive sense. Rubidium-85 is also a stable isotope, where as Rubidium-87 is vaguely radioactive, decaying with beta-radiation (electron) with half-life of 4.88E10 years, which isn't directly lively. For all practical uses it is safe. Being alkali metals, they would be seriously bad if in contact with skin or water for that matter. Maybe a small text should state what needs to be said: "atomic clocks does not use radioactivity as a mechanism for measurement of time". It is a common misconception and clearly pointing this fact out should be helpful. Cfmd (talk) 00:43, 24 January 2011 (UTC)
Synchronization
How are Atomic clocks synchronized across the world, or are they not? Do they have to be in the same place to be synchronized off each other sort of thing? Even then how do they set them with such prescison accuracy? --The preceding unsigned comment was added by 90.192.138.193 (talk) 21:02, 22 December 2006 (UTC).
they can be synched to each other 1: over a symmetric latency connection (such as radio waves), or 2: by using GPS as a reference. a location can tell how it's time compares to GPS, or a single GPS satellite, say 50 nanoseconds ahead. then another place can use that information.81.206.145.191 21:43, 13 May 2007 (UTC)
Or you can pop a portable atomic clock with a battery backup on a plane. Jim77742 01:25, 20 June 2007 (UTC)
Using airplanes would be unpractical, because Einstein learned us that clocks run slower the faster their speed and the higher their altitude (or the lesser the gravitational field). See [1] and [2] for explanation and experiment with cesium clocks at moderate altitude. Jaho 00:16, 5 July 2007 (UTC)
An answer to the synchronization issue can be found on http://tycho.usno.navy.mil/twstt.html. Jaho 00:29, 5 July 2007 (UTC)
While the clocks may not need to be synchronized, they are often coordinated to roughly have the same time. Use of GPS, GLONASS and TWSTT for such synchronisation is being used. Caesium beam clocks is then usually allowed to count freely and unsteered and then GPS, GLONASS and TWSTT is used for comparison between clocks not being local to each other. Such comparison forms the base of the EAL, TAI and UTC time as being maintained by BIPM. For clocks with not requirement to be part of the BIPM network, they are usually synchronised once and for all using a GPS receiver and then set alone for itself. Many telecom applications does not require the network clock to even have Time of Day but only to give a very stable 2,048 MHz clock to the network. Cfmd (talk) 00:50, 24 January 2011 (UTC)
Travel Atomic Clock Sync
I have a very small travel global Atomic Clock and alarm clock. It is Atomic Radio Controlled. It has to be manually set to: US, UK, Japan and EU via a button on the back. It does not change on its own as I fly from time zone to time zone.
If I am out of range of: England, Switzerland, Japan or the US will the clock no longer sync? In the US the clock wants to sync to Mountain Time due to the Atomic Clock is located in Colorado. Colorado is on Mountain Time.
How does a travel Atomic Clock differ from a stationary clock? My stationary clock updates on its own when it unplugged and plugged in again. If the power goes out the clock resets on its own. A travel clock requires a manual reset, selecting the country for the Atomic Clock and sometimes changing Daylight Savings Time.
Why does the page on Atomic Clocks not cover the small travel version as well? Bree25 (talk) 02:47, 30 April 2013 (UTC)
Mercury Atomic Clock Keeps Time with Record Accuracy
www.nist.gov/public_affairs/releases/mercury_atomic_clock.htm --The preceding unsigned comment was added by 218.102.23.117 (talk) 14:30, 8 January 2007 (UTC).
picture of HP 5071A
i think the article about atomic clocks needs a picture of a HP/Agilent/Symmetricom 5071A, because it is the most common/famous atomic clock (caesium based primary frequency standard) in existence and it has most weight in maintaining UTC - every country's time keeping lab has them.81.206.145.191 21:43, 13 May 2007 (UTC)
Early work: discussion of dubious fact
I tagged the reference to a 1949 NBS atomic clock as 'dubious' and 'citation needed': because I can't find it in the histories. Terry0051 (talk) 01:10, 25 February 2009 (UTC)
By the way, be sure to look at Louis Essen's own recollections on this history, on the excellent website here: [3]. The section on "Atomic Clock" gives a good history of what was happening in the USA and UK in the 1950s. DonPMitchell (talk) 16:35, 11 August 2009 (UTC)
Radio clocks
"Atomic clocks" for less than $50: This marketing term "atomic clock" refers to a radio controlled device receiving a time signal from one or more transceivers connected to real atomic clocks. Examples at: koolatrononline(dot)stores(dot)yahoo(dot)net/hummer-multi-bank-automatic-clock(dot)html www(dot)ehow(dot)com/how_2099664_buy-atomic-clock(dot)html --Preceding unsigned comment added by 131.130.249.17 (talk) 09:07, 16 February 2010 (UTC)
Ytterbium atomic clocks
Someone should add something to this article about the new ytterbium atomic clocks under development. I don't know a lot about them, and, if no one else does it, may end up doing it myself after I read into it more, but if not, at least a mention should be added. --Preceding unsigned comment added by 99.249.74.84 (talk) 21:27, 15 December 2010 (UTC)
Maser
The following passage from this article:
"The first atomic clock was an ammonia maser device built in 1949 at the U.S. National Bureau of Standards (NBS, now NIST)."
seems to conflict with the passage from the "maser" article:
"Theoretically, the principle of the maser was described by Nikolay Basov and Alexander Prokhorov from Lebedev Institute of Physics at an All-Union Conference on Radio-Spectroscopy held by USSR Academy of Sciences in May 1952. They subsequently published their results in October 1954. Independently, Charles H. Townes, J. P. Gordon, and H. J. Zeiger built the first maser at Columbia University in 1953."
Some explanation to harmonize the dates in these two passages would be helpful. Psalm 119:105 (talk) 09:58, 17 January 2011 (UTC)
Applications
Atomic clocks can also be used as sensors for gravitational and magnetic fields. See: http://www.wired.com/science/discoveries/news/2007/12/time_nist?currentPage=2 72.221.84.128 (talk) 14:56, 11 January 2012 (UTC)
Lord Kelvin reference
The statement that Kelvin proposed a clock based on atomic transitions seems a bit misleading. He proposed using the known distinct spectral frequencies of atoms, but wasn't he about 30 years too early to know about atomic transitions? -- Preceding unsigned comment added by 173.206.4.23 (talk) 03:41, 1 November 2012 (UTC)
I noticed that as well. I thought the sentence went beyond misleading to just wrong. --Davefoc (talk) 08:30, 29 April 2015 (UTC)
Assessment
Found the following undated assessment in comment on this page. --Kvng (talk) 19:11, 6 September 2012 (UTC)
Accuracy vs precision
A number of places in the article include references such as "accurate to one second". These should actually read "precise to one second". Accuracy refers to the central tendency of a measurement, whereas precision refers to the possible range of deviation. -- Preceding unsigned comment added by 108.68.83.101 (talk) 03:00, 22 October 2013 (UTC)
NIST's mercury ion clock
So, if that's the standard by which new clock technology is measured, why do we hear no more of it? Jim.henderson (talk) 21:08, 2 January 2015 (UTC)
Diagrams
The section Physics package realisations needs several diagrams added to improve clarity. RJFJR (talk) 13:59, 22 October 2015 (UTC)
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Does "a second in XXX million years" really make sense?
In the article, the accuracy of atomic clocks is stated in several places as "expected to neither gain nor lose a second in XXX million/billion years". I understand that this is only intended to be a more "layman friendly", or more "intuitive" way to state something like "an accuracy of XXX × 10-16". However, not only I doubt this way of describing the precision is really more intuitive (since a million years cannot be grasped by the imagination, it's kind of an abstract notion, except for a geologist), I fear it may be plain wrong.
My (limited) understanding is that the Allan deviation of most clocks tends to worsen at very long sample times due to random walk frequency modulation noise and aging effects. Then, it should not be expected for the clocks to achieve their rated accuracy over decades, let alone megayears.
I propose to reword those instances as "expected to neither gain nor lose XXX nanoseconds per month". I assume a month is, as least as an order of magnitude, a more realistic sample time than XXX megayears. I know the nanosecond is not really an "everyday life" unit. However, in today's highly technological world, it's closer to everyday life than a megayear. At least closer to the life of those reading Wikipedia on an electronic device clocked somewhere in the GHz range.
-- Edgar.bonet (talk) 16:19, 25 February 2016 (UTC)
Nuclear clock
Hi, nuclear clock redirects here while there is not mention of it within this article. Could someone says few words about it within this article or create another article for this kind of clock? Pamputt (talk) 16:56, 19 August 2016 (UTC)
"According to sources"?
@Francis Flinch: Thanks for checking my edits, when you removed the uncertainties from the frequency table in this edit with the edit comment "according to sources", I don't quite understand.
The uncertainties were all taken from the cited sources. For example, the rubidium uncertainty was taken from the cited source, converted by a simple WP:CALCulation from a relative uncertainty of ±3×10-15 to an absolute uncertainty of 6834682610.904324(20).
Just re-checking in case I made a mistake: 87Sr has a frequency of 429228004229873.4 Hz with a relative uncertainty of ±1×10-15, which is 0.43 Hz, so 429228004229873.4(4) is correct. (Unless you'd prefer 429228004229873.40(43), but I think that's excessive precision.)
And the hydrogen maser citation (available at http://cyber.sci-hub.ac/MTAuMTA4OC8wMDI2LTEzOTQvOS8zLzAwNA==/essen1973.pdf if you'd like to check) already says 1420405751.7662±0.003 Hz.
I thought the uncertainties were an informative contrast to the exact-by-definition caesium value, but I can see how someone could disagree. You might find them unhelpful or distracting for various reasons, but "according to sources" confuses me. Could you clarify? 71.41.210.146 (talk) 17:02, 5 September 2016 (UTC)
Attosecond as unit of precision
I think the unit "attosecond" is dubious in this passage:
In the future this might lead to redefine the caesium microwave based SI second and other new dissemination techniques to transfer clock signals will be required that can be used in both shorter-range and longer-range (frequency) comparisons between attosecond (sub-1 × 10-17 s) accurate clocks without significantly compromising their performance.
The passage seems to call for a unit of relative precision (10-17 to 1), not a unit of time. Can User:Francis Flinch supply a quote from one of the cited sources to justify this unit? Jc3s5h (talk) 18:16, 14 November 2016 (UTC)
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