[time-nuts] Re: Project Great

[Wilko Bulte]

Being curious here: has anyone ever taken a Cs in a submarine? E.g. the Marianatrench or so?

As a native from a mountain-deprived country I could not help wondering.

Wilko

> On 28 Nov 2021, at 08:14, Tom Van Baak <tvb at leapsecond.com> wrote:
> 
> Hi Thomas,
> 
> Good to hear the experiment was contagious for you. If you have additional questions let me know.
> 
> Your suggestion about Mount Evans and Pikes Peak are excellent. You will enjoy this 2017 paper:
> 
> "An Undergraduate Test of Gravitational Time Dilation"
> https://arxiv.org/abs/1710.07381
> https://arxiv.org/pdf/1710.07381.pdf
> 
> ---
> 
> As for CSAC, the news is not so good. I've worked with several groups to explore CSAC for gravitational time dilation experiments. Those clocks are so cute and small, it's irresistible; but the numbers just don't add up. Over a day their stability is in the low e-12's vs. a "real" cesium clock like a 5071A in the low e-14's. So when you are doing a relativity experiment trying to detect a frequency shift that's on the order of e-13's you reach for a 5071A instead of a CSAC. The performance is nearly 100 to 1.
> 
> One solution is a taller mountain. The best on the planet is Mauna Kea (Big Island, Hawaii) where you can literally drive from sea level to the summit (13,800 ft, 4200 m) in a few hours. The frequency shift up there is 4.5e-13, which is 40 ns per day. But still, to have even the slightest chance of success you'd want your clocks to be good to 1e-13 or better. CSAC aren't even close, and probably neither are telecom Rb.
> 
> I'm currently involved with another solution -- a HAB (High Altitude Balloon) CSAC flight. Getting to 100,000 ft altitude is quite common. Up there, clocks run a whopping 3.3e-12 faster, which is 280 ns/day, or 12 ns/hour. This is a clear case where the amazing low mass and low power of a CSAC is a  critical advantage. However, the numbers still aren't working out and the logistic and environmental conditions are brutal. I won't say it's impossible, but it may take years and a huge bag of tricks before it works or it's proved too impractical.
> 
> ---
> 
> Jim, I'd be interested in any Cubesat / CSAC results. They don't exactly land in one piece so the typical round-trip clock comparison method wouldn't work. A direct frequency comparison might. In that case the drift and re-trace specs of a CSAC are probably more important than the stability.
> 
> /tvb
> 
> 
>> On 11/27/2021 12:37 PM, Thomas Valerio wrote:
>> I think that Tom's GREAT adventure is kind of what sealed the deal making
>> me a time-nut or at least a time-nuts lurker, a lot of this stuff is still
>> little over my head, but I keep reading.
>> 
>> If anyone is inclined and has the clocks and the kids ( I don't have
>> either ), there is always Mount Evans and Pikes Peak, although you may
>> have to leave the clocks behind overnight.  Mount Evans is still on my
>> bucket list but without clocks and two or three days of time to monitor
>> them, I don't think I will be doing the Mount Evans edition of GREAT.  For
>> anyone that is flush enough to afford or can beg, borrow or steal access
>> to a Microsemi chip scale atomic clock, I think a Mount Evans edition
>> would be an awesome addition to Tom's original work.
>> 
>>    Thomas Valerio
>> 
>> 
>>> For newcomers to time-nuts, Andy is asking about my DIY gravitational
>>> time dilation experiment(s).
>>> 
>>>  > What am I missing?
>>> 
>>> It looks like you used the wrong value (or wrong units) for "h".
>>> 
>>> The summit of Mt Rainier is 14411 ft (4400 m), but the highest point on
>>> Mt Rainier that is accessible by road is the Paradise visitors center at
>>> 5400 ft. Our house is at 1000 ft elevation so the net difference in
>>> elevation of the clocks was 4400 ft (1340 m).
>>> 
>>> The clock(s) on the mountain ran fast by gh/c² = 9.8 × 1340 / (3e8)² =
>>> 1.5e-13. Fast clocks gain time. We stayed for about 42 hours so the net
>>> time dilation was 42×3600 × gh/c² = 22 ns.
>>> 
>>> ----
>>> 
>>> For more information see the Project G.R.E.A.T. 2005 page:
>>> 
>>> http://leapsecond.com/great2005/
>>> 
>>> Better yet, these two recent talks from 2018 and 2020 cover all 3 GREAT
>>> experiments:
>>> 
>>> <http://web.stanford.edu/group/scpnt/pnt/PNT18/presentation_files/I08-VanBaak-GPS_Flying_Clocks_and_Relativity.pdf>
>>> 
>>> <http://leapsecond.com/ptti2020/2020-PTTI-tvb-Atomic-Timekeeping-Hobby.pdf>
>>> 
>>> Lots of time nutty photos in both of those!
>>> 
>>> /tvb
>>> 
>>> 
>>> On 11/27/2021 7:33 AM, Andy Talbot wrote:
>>>> Just been reading your adventures with 3 Cs clocks, a mountain and 3
>>>> kids,
>>>> but I can't make the estimate of time dilation work out.
>>>> You measured ~ 23ns and say it agrees with calculation
>>>> 
>>>> The equation quoted in a related reference, for "low elevations" is
>>>> g.h/c²
>>>> which if you plug in g = 9.81 m/s²  and h = 4300m for Mt Rainer gives
>>>> an
>>>> expected value of 4.7 * 10^-16.
>>>> Over 2 days, 2 * 86400s, that would be 81 ns in total, four times your
>>>> value
>>>> 
>>>> What am I missing?
>>>> 
>>>> Was just speculating what Ben Nevis at a mere 1340m height might offer
>>>> 
>>>> Andy
>>>> www.g4jnt.com
>>>> _______________________________________________
>>>> time-nuts mailing list --time-nuts at lists.febo.com  -- To unsubscribe
>>>> send an email totime-nuts-leave at lists.febo.com
>>>> To unsubscribe, go to and follow the instructions there.
>>> _______________________________________________
>>> time-nuts mailing list --time-nuts at lists.febo.com  -- To unsubscribe send
>>> an email totime-nuts-leave at lists.febo.com
>>> To unsubscribe, go to and follow the instructions there.
>>> 
>> _______________________________________________
>> time-nuts mailing list --time-nuts at lists.febo.com  -- To unsubscribe send an email totime-nuts-leave at lists.febo.com
>> To unsubscribe, go to and follow the instructions there.
>> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe send an email to time-nuts-leave at lists.febo.com
> To unsubscribe, go to and follow the instructions there.