Dual atomic clock experiment - Page 1
Forum section: electronics / general

author: iMo
author_rank: Super Contributor
timestamp: April 25, 2025, 06:30:16 am
content: Curious Marc tries with his clocks:

author: Doctorandus_P
author_rank: Super Contributor
timestamp: April 25, 2025, 02:36:13 pm
content: I find it hilarious that these clocks which were advertised as "accurate to within one second in (several) million years", are all broken after 20 to 30 or so years.Edit:Nah, I'm perfectly aware of the difference between accuracy and longevity (See below). Still find it hilarious.

author: tggzzz
author_rank: Super Contributor
timestamp: April 25, 2025, 03:11:42 pm
content: Quote from: Doctorandus_P on April 25, 2025, 02:36:13 pmYou are confusing precision with longevityFor the latter, seehttps://en.wikipedia.org/wiki/Clock_of_the_Long_Nowandhttps://en.wikipedia.org/wiki/Long_Now_Foundation

author: iMo
author_rank: Super Contributor
timestamp: May 14, 2025, 05:15:42 pm
content: Now it looks better, but still..

author: SanderMTI
author_rank: Contributor
timestamp: May 18, 2025, 10:34:46 pm
content: Quote from: Doctorandus_P on April 25, 2025, 02:36:13 pmIt is indeed hilarious.I have old actual pictures of my parents when they were young.If they would have been digital, I likely could not look at them today.Over land en zee met...?Sander

author: Johnny B Good
author_rank: Frequent Contributor
timestamp: June 20, 2025, 11:28:28 pm
content: @iMo,thanks for posting that youtube link to the 2nd video which has now given me some idea of their frequency/phase stability. I don't know whether a phase drift of just 6ns in a 24 hour run ( frequency offset value of 694pHz) is typical of these secondary frequency standards or still a little short of what to expect with a new/factory refurbished unit.The reason for my interest in this being down to my pet project/obsession to convert an LPRO 101 into a "Poor Man's Cesium class frequency reference". At the moment, I'm seeing a stability about an order of magnitude worse with the current prototype.I'm in the middle of a major revamp to eliminate the issue of internal temperature gradient varying with ambient temperature. I have high hopes of limiting the phase wander to less than 10ns in 24 hours over an ambient temperaturet range that encompasses 0 to 33 degrees C (and obviously much less over the typically specified 23 +/- 5 deg C range) with the revamped version.It would be useful to have some idea as to when I can call this quest done and dusted.

author: iMo
author_rank: Super Contributor
timestamp: June 21, 2025, 07:07:23 am
content: ..it seems to me Marc has silently resigned in his attempt to repeat the relativistic experiment with his clocks, a pity..

author: dietert1
author_rank: Super Contributor
timestamp: June 21, 2025, 01:20:47 pm
content: For a cesium clock the usual number people tell you as accuracy is 1E-13. That is about 10 ns in 24 hours. Some special cesium fountain clock at the NIST reached 1E-16, but that's a different story.https://www.mdpi.com/2218-1997/9/3/133The introduction talks about modern atomic clocks and says: ".. near the surface of the Earth, a fractional frequency shift of 1.1E−18 corresponds to a height difference of 1 cm". In order to get a clear result comparing two cesium clocks one needs a height difference of several thousand meters. It can't be done at home, sorry.Regards, Dieter

author: Johnny B Good
author_rank: Frequent Contributor
timestamp: June 21, 2025, 02:01:17 pm
content: @iMo,That seems a pessimistic point of view. He seems to be a man after my own heart, only with more exotic (to me) bits of kit to play with.I've been working on my own pet project for just the past 4 1/2 years ever since I'd acquired my first LPRO 101 back in August 2020.Initially I took this on as a challenge to see just how far I could go in reducing the 0 to 50 deg C tempco effect to a vanishingly small value merely by shrinking this temperature range down 50mK or less. Over the following years, I kept maintaining progress and overcoming unexpected snags, every so often stepping back to admire my handiwork thus far and to contemplate my next step (a process most outside observers might well mistake for procrastination).I've no doubt Marc is merely taking pause to consider his options before resuming this project. "This project is not dead! It's merely resting" to misquote the pet shop proprietor in that famous Monty Python "Dead Parrot" sketch.I too, like you, thought it was rather a pity that his project had come to a (hopefully only temporary) stop, mainly I have to admit, due to my impatience in seeing the next installment.

author: iMo
author_rank: Super Contributor
timestamp: June 21, 2025, 06:43:55 pm
content: Quote from: dietert1 on June 21, 2025, 01:20:47 pmWhat Marc wanted, afaik, is to take one of his clock to a mountain top, the other will stay down in his lab.Not sure what specific summit he meant - we have to look in his first video above..PS: Mount Wilson (1740m, the top near LA accessible by car) perhaps ("..bringing it to an elevated altitude for couple of days..")??He targeted 20ns diff averaged during "couple of days" (he said it is 15x smaller diff as the guys saw in the famous 1971 experiment).

author: coppercone2
author_rank: Super Contributor
timestamp: June 21, 2025, 06:46:15 pm
content: if you shoot it out of a catapult can you get something else to measure from time like from rapid acceleration?Gravity static force, but acceleration is a rapid transient one with big magnitude.acceleration has something to do with relativityperhaps there is truth in the statement of time flyingI don't know many things that will get a giant jump like that other then catapults. maybe a rocket sled.

author: iMo
author_rank: Super Contributor
timestamp: June 21, 2025, 07:13:42 pm
content: Quote from: iMo on June 21, 2025, 06:43:55 pmAI made some math for me:Quote

author: dietert1
author_rank: Super Contributor
timestamp: June 21, 2025, 07:44:47 pm
content: If your "noise" is 10 nsec and the effect is 15.7 nsec in 24 hours, there is some chance. But you need to bring a clock up and down like 10 times to get the noise suppression of a lock-in. Maybe each time another clock. And assume losing some of the trips due to unexpected difficulties with the "mobile lab".How much is the power consumption of the cesium clock and the required air conditioning?Regards, Dieter

author: iMo
author_rank: Super Contributor
timestamp: June 21, 2025, 08:02:56 pm
content: There is an observatory on the Mount Wilson, so he may arrange an X day stay there in a controlled conditions.Say a week, that is ~100ns diff, that should be easily visible against 10ns noise..What could be an issue is the travel to the MWO and back by car, indeed..https://en.wikipedia.org/wiki/Mount_Wilson_Observatory

author: edpalmer42
author_rank: Super Contributor
timestamp: June 21, 2025, 08:22:47 pm
content: This experiment has been successfully done twice by one guy - with help from family & friends.http://leapsecond.com/great2005/The second time, Stephan Hawking (Yes, THAT Stephen Hawking) presented the experiment to the public on a TV show.http://leapsecond.com/great2016a/index.htm

author: dietert1
author_rank: Super Contributor
timestamp: June 21, 2025, 10:40:16 pm
content: Both experiments were using several clocks in order to reduce the measurement error, e.g. to 2 nsec in 24 hours. Probably with another even bigger set of clocks to stay for reference. And they expected an effect of 20 nsec. That makes more sense.The videos above mention completely different numbers, like the magnetic field tuning wasn't possible to better than 6 nsec per 24 hours. And for somebody with just two clocks he will go with one clock and the other one will stay. The error of the difference measurement will be 14 instead of 10 nsec per day and the 16 nsec on top of Mt. Wilson won't serve.Also to be a scientific experiment one needs to study how much time shift is caused by lower air pressure at high altitude. The pressurized plane cabin may be easier in that sense.Regards, Dieter

author: TimFox
author_rank: Super Contributor
timestamp: June 22, 2025, 02:43:57 am
content: Another way to look for the effect of gravity on timing uses the Moessbauer Effect to measure the frequency shift of60Co gammas (roughly 1 MeV) between source and detector at different altitudes. I believe the first successful test involved “dropping” the gammas down a tower at Harvard (22.5 m altitude).The interested reader can find accounts of the experiment, which can detect minuscule differences in photon energy, hence frequency shift.

author: Johnny B Good
author_rank: Frequent Contributor
timestamp: June 22, 2025, 01:27:42 pm
content: @dietert1Excuse me, are you telling me that these caesium beam secondary atomic standards also suffer air pressure induced frequency drifts like the rubidium atomic frequency references?

author: dietert1
author_rank: Super Contributor
timestamp: June 22, 2025, 03:04:37 pm
content: Quote from: Johnny B Good on June 22, 2025, 01:27:42 pmI can't tell you. Just wrote down a question that any physicist would ask. And the experimenter should have some number, i mean something more than an opinion.You mentioned rubidium clocks and i found this paper:https://apps.dtic.mil/sti/pdfs/ADA485423.pdfFrom their diagram i read about 1E-10 change after 200 days. So that could be 43 nsec in one day, or let's say a fraction of that for imperfect vacuum. And it's a dilatation effect, as the clocks are frequency aging faster at lower pressure. A pitty one can't tell the technical reason of the observed effect.Regards, Dieter

author: iMo
author_rank: Super Contributor
timestamp: June 22, 2025, 03:20:46 pm
content: Provided such helium penetration in/out the evacuated tube gets say "1000days time constant" it will have a negligible effect during the "couple of days long experiment", imho. And it has nothing to do with relativistic phenomenons, I would compare it to the humidity effect on an epoxy packaged reference..

author: Johnny B Good
author_rank: Frequent Contributor
timestamp: June 22, 2025, 04:45:33 pm
content: @dietert1Well, this experimenter did his own homework (see attached research paper and Datum's user guide for the Efratom LPRO 101 wherein they quote a rather wishy washy figure of "Altitude (operating) -200 ft. to 40,000 ft. <1E - 13/mbar").That Swiss Lab paper had arrived at a figure of 0.8 E - 13/mbar which, since it didn't violently disagree with Datum's rather vague figure, I took as my initial starting point to compensate for this effect until I could run my own verification tests to get an actual figure for the LPRO 101 oscillators.After figuring out a cost effective way to vacuum test one of my spare LPROs using a cheap 11 litre pressure cooker and vacuum pump, I purchased said items last February and ran my tests around the beginning of March. I eventually, after a few false starts, obtained Frequency shift delta figures of 0.607 E -13 and 0.587 E -13 per mBar on my final two test runs which I averaged to a value of 0.597 E -13/mBar to use as my barometric compensation factor.As far as I'm aware, the caesium beam tube in these secondary caesium atomic frequency standards aren't effected by this pressure effect to anywhere near what a typical rubidium vapor lamp pumped earthbound RFS has to endure, hence my response to your statement.[/* EDIT] Also worthy of note are the aging figures given in an entirely separate Datum datasheet (naturally!) which I've now attached which claims a 10 year figure of <1E -9 which, as best as I can figure it would by now correspond to a daily aging rate somewhere in the region of 1 to 2ns rather than your suggested figure of 43ns a day.[*/ EDIT]

author: dietert1
author_rank: Super Contributor
timestamp: June 22, 2025, 07:24:44 pm
content: In the report i linked above they measured a drift of -1,7E-13 per day in vacuum and about zero after taking the clocks out of vacuum. So the "surprise" when going to a high altitude with those rubidium clocks could amount to -1,7€-13, which is 15 nsec slowdown within one day, or a fraction of that. The 43 nsec overestimate was obtained as visual reading the difference of the slopes fitted in the diagram. The numbers are there.One would need a similar test of cesium clocks to give a limit on that systematic error.Regards, Dieter

author: Johnny B Good
author_rank: Frequent Contributor
timestamp: June 22, 2025, 10:48:08 pm
content: Quote from: iMo on June 22, 2025, 03:20:46 pmWhen I looked at that document, I had a strong feeling that I'd come across this in my earlier searches on the subject of Rubidium oscillator stability issues. Since it wasn't already in my 30 strong collection of downloaded pdfs, I assumed I'd dismissed it as being not really relevant enough at the time.Having downloaded it to facilitate a more relaxed perusal, I've added it to my collection despite it still not being as relevant as most of the other documentation (no firm conclusions, only interesting hypotheses on the subject of the aging phenomena).And, as you said, has no relevance to relativistic phenomena. As for the aging effect, I'll deal with that if I ever gain enough stability to be able to discern (and quantify) this effect. Like the proverbial Boy Scout, I've already got a strategy in mind to compensate even for that, involving the use of a battery backed RTC module.

author: edpalmer42
author_rank: Super Contributor
timestamp: June 22, 2025, 11:01:01 pm
content: John,Are you also stabilizing the temperature of the baseplate? It looks like temperature effects are larger than pressure effects. The LPRO User's Guide shows a graph (Fig. 1.4) of temperature vs. frequency on 19 random units. The spec (<3e-10 over 0 - 50C) suggests a value in the range of xE-12 per degree.

author: Johnny B Good
author_rank: Frequent Contributor
timestamp: June 23, 2025, 12:42:39 am
content: Quote from: edpalmer42 on June 22, 2025, 11:01:01 pmI certainly am (37.050 deg +/- 1mK).It was that which had inspired me to improve the frequency versus base plate temperature variations by simply reducing this temperature range to less than 1% to gain (in theory, all else aside) a 2 orders of magnitude improvement over the worst example's figure of +/- 5 E -11 over that 0 to 50 deg range.The implied x E-12 per degree totally ignores all the other tempco effects which, as far as its intended use as a telecoms GPS disciplined oscillator needing only to limit the 72 hour holdover drift to a whopping (by metrology standards) 140μs is concerned is regarded as inconsequential "noise".It's not as simple as merely stabilising the base plate temperature to within a milli Kelvin of a set point against a 20 to 30 degree variation in ambient temperature. The obvious measure of thermally insulating the hell out of the other 5 sides helps but I'd woefully underestimated just how (impracticably) much insulation would be required.Holding the base plate to a set temperature also requires a measure to eliminate variation in the temperature gradients within the LPRO itself. I'm in the middle of building a version where the heatsink exhaust is fed to the top cover to reduce this thermal gradient variation close to a vanishing point. I suspect I'll still need to add a couple of "after burners" to the heatsink exhaust to compensate for cooler ambient conditions (I think a watt or two each should do the trick).

author: EEVblog
author_rank: Unknown
timestamp: June 23, 2025, 04:13:05 am
content: I looked at one of the original flying atomic clocks:

author: dietert1
author_rank: Super Contributor
timestamp: June 23, 2025, 07:32:48 am
content: Mr. Daly mentioned how difficult the flying clock test was at the time, although they had several clocks for redundancy. Some results can be found here:http://www.hyperphysics.phy-astr.gsu.edu/hbase/Relativ/airtim.htmlMore detail:https://www.researchgate.net/publication/344428119_Hafele-Keating_Experiment_ReassessedThe data of their first flights were near useless, while the second attempt yielded pretty clear results.Regards, Dieter

author: Johnny B Good
author_rank: Frequent Contributor
timestamp: June 24, 2025, 01:56:36 pm
content: Prompted by this topic's subject a few days ago, to track down actual meaningful performance specifications for these secondary cesium frequency standards, I was surprised to see a rather modest frequency stability claim for the HP5061A of just 2.2 E -12.This afternoon, I thought I'd have another go at tracking down a more detailed specification list in regard of published "accuracy" and "stability" figures (apparently, two completely different animals according to my "Conversation" with duck.ai).Having had no better search results than my previous efforts at extracting this information, I decided to give duck.ai a crack at the problem. The results were to say, "rather interesting" which you can peruse for yourself.=====================================================================================================This conversation was generated with Duck.ai (https://duck.ai) using OpenAI's GPT-4o mini Model. AI chats may display inaccurate or offensive information (seehttps://duckduckgo.com/duckai/privacy-termsfor more info).====================User prompt 1 of 12:hp 5061a datasheetAssist:The HP 5061A is a cesium atomic clock that uses the radiation emitted by cesium-133 atoms to keep time accurately. It features advanced displays, adjustment controls, and significantly improved frequency measurement accuracy compared to earlier models.Relevant sources:-https://physicsmuseum.uq.edu.au/cesium-beam-frequency-standard-type-5061a=====================================================================================================[EDIT 2025-07-10]The rest of this AI Chat now expunged in favour of attaching the whole conversation as a plain text file.=====================================================================================================My frustration with the AI's answers shows in user response 10I'd only wanted a "Quick" sanity check of my own calculated figure of 2.77777777 μHz per ns per hour phase drift rate after seeing the AI's answer of a 1 E -15 stability figure expressed in terms of a 24 hour phase drift being out by 3 orders of magnitude (I'd already calculated this to be 86.4 psOf course, it can be all too easy to anthropomorphise the AI and vent your frustration on it's seemingly contrary responses. You need to step back and try to make your query absolutely crystal clear with no room for any ambiguity to avoid the GIGO trap.However, I find the >3 orders of magnitude disparity between a claimed frequency "accuracy" of 2.2 E -12 and a "stability" figure of 1 E -15 a little disconcerting (if not downright confusing), prompting me to ask if anyone here can offer some clarification or enlightenment regarding the AI's answers.It's the 1 E -15 stability figure I find a little hard to swallow - maybe it used a figure published for the primary cesium clocks operating in national time laboratories such as NIST?

author: Dr. Frank
author_rank: Super Contributor
timestamp: June 24, 2025, 03:35:01 pm
content: Johnny B Good,This whole thread is for me the final proof, that Artificial "Intelligence" does not exist, yet.Intelligence would mean that such a program would really UNDERSTAND the problem, the technology, or the questions, in contrast to just "knowing" something, i.e. not only collect random knowledge snippets from the internet.First off, "stability" is always "deviation" in relation to a given time span (or in relation to other physical parameters like Temperature, mangentic field, etc.).Therefore, a number of 2x10-12is no measure of stability at all.If you would simply look into the 5061B specification, there is a (probably fitting) stability parameter of:2x10-12over the lifetime of the tube, i.e. a max. deviation of 2x10-12over many years (usually 7.. 15 years for the different kind of tubes).Accuracy has no meaning in metrology, we only use "uncertainty" and "stability".The uncertainty of the 5061B, i.e. its initial deviation from the defined, fixed frequency of the Cs frequency is (1..0.7) x10-11.Then, the conversion from stability (1x10-15) over 24h to nsec deviation (within 24h) is wrong by a factor of 1000.1x10-15x 24 x 3600s gives 86.4 ps or 0.086ns.This 1x10-15stability over 24h is as well wrong, as you can derive from the Allan deviation diagram on the same page.Over a 105sec time constant, which is more than 24h, the stability is about 3x 10-14.That gives about 2.9ns deviation over 24h, which sounds much more reasonable.I suggest, that you as well should try to understand the specification and performance of the Cs clock technology.Frank

author: dietert1
author_rank: Super Contributor
timestamp: June 24, 2025, 03:42:29 pm
content: I stopped reading at the line "8.64×10−11 seconds=86.4 ns".An example Allan diagram i found shows the typical 1E-11 of a precision crystal oscillator at short time scales and the typical 1E-13 of the cesium beam device above about 1000 seconds (20 minutes). For a good clock (like "Clock C") that really goes down towards 1E-13, that should happen at time scales of some hours or more. So for an observation period of a day or two it can be about 1E-13, but the example diagram also shows two bad clocks that stay at 1E-12 or 6E-13.I also found a report of German PTB. Figure 4 shows how modern metrology cesium clocks with beam reversal support continue the Allan diagram down to 1E-14 at time scales of 5 days and may reach 5E-15 at longer time scales.The NIST cesium fountain device i mentioned above supports a longer observation time for the cesium atoms than industrial clocks. But that device isn't mobile.Regards, Dieterhttps://www.ptb.de/cms/fileadmin/internet/fachabteilungen/abteilung_4/4.4_zeit_und_frequenz/pdf/2003_Bauch_MST_CAC_VF_author_version.pdf

author: iMo
author_rank: Super Contributor
timestamp: June 24, 2025, 04:14:13 pm
content: Quote from: Dr. Frank on June 24, 2025, 03:35:01 pmMy experience with the "AI tool" is you have to navigate it a little bit, and, of course, re-formulation of your prompts sometimes helps as well.So a step by step iteration at both sides of the keyboard is perhaps the right way how to handle the AI tool as it is today.Artificial "Inteligence" does not exist, sure, no special proof for that is required, imho..

author: KE5FX
author_rank: Super Contributor
timestamp: June 24, 2025, 06:17:30 pm
content: Quote from: iMo on June 24, 2025, 04:14:13 pmSure, it exists. Try the same queries again with o3-pro.Would you call a student unintelligent for making rudimentary scale errors? No, you'd correct the mistake and the student would update their understanding. As will the AI model.The only real difference is that the model doesn't have a "sleep" phase where corrections are used to update the weights. Once someone figures out how to makethathappen -- and they will, because why wouldn't they -- yowza.We don't know what intelligence is, so it's hard to justify a conclusion that it can't be emulated. It's easy to state what intelligenceisn't, though, and using low-end models like o4-mini to try to state sweeping conclusions is a good example of what it's not.Quote from: Dr. Frank on June 24, 2025, 03:35:01 pmExactly, but that didn't stop people from using sigmas without accompanying taus in press releases and marketing literature for decades.Which is why the models are confused by it. GIGO as always.

author: Johnny B Good
author_rank: Frequent Contributor
timestamp: June 24, 2025, 08:08:12 pm
content: @Dr. FrankFunnily enough, I spotted that last figure of stability you mentioned written on the paper graph in his other repair video belowhttps://youtu.be/alQBsNx7t9o?t=1942You do have to bear in mind the limitations of AI in its current state of development. Notably its inability to correctly infer the meaning or context of a technical and or more complex type of enquirey such as this.Anyway, it looks like I've finally obtained the actual accuracy /stability figures I'm attempting to emulate with my RFS project.

author: iMo
author_rank: Super Contributor
timestamp: July 09, 2025, 08:35:56 am
content: ..perhaps the chase continues..

author: radiolistener
author_rank: Super Contributor
timestamp: July 09, 2025, 09:34:14 pm
content: Quote from: iMo on June 21, 2025, 06:43:55 pmCesium clocks are not perfectly isolated from their environment, and moving them into different conditions can easily affect their frequency, even before we consider any relativistic effects. For example, a difference in magnetic field between Marc's lab and the mountaintop could alter the atomic energy levels of cesium via the Zeeman effect, leading to a measurable shift in the output clock frequency. Environmental factors like temperature, pressure, and even vibration can also play a role. So, any observed difference in timekeeping between the two clocks might be due to these external influences rather than purely relativistic time dilation.This is similar to using a good DMM - in a controlled home lab environment, it may provide stable and accurate readings. But once you take it outside on a cold winter day or during hot weather, and its readings may start to drift. This has nothing to do with relativity - it’s simply that the change in temperature affects the measurement accuracy.

author: iMo
author_rank: Super Contributor
timestamp: July 09, 2025, 10:07:01 pm
content: As I wrote above, the closest summit reachable by car, with a hotel and a well-known Observatory is called Mount Wilson, 1740m asl.So if I were Marc I would call the people there and I will arrange a month long study stay there in their labs, under controlled environment (or I will stay with my clocks in the hotel room)..The only difficulty to solve will be the transport up hill/ down hill..PS: the hotel has been closed..Quote

author: coppercone2
author_rank: Super Contributor
timestamp: July 10, 2025, 12:11:58 am
content: does spinning an atomic clock like in a pilot g-trainer do anything?I am expected a rocket powered carousel with 3 clocks on it