[time-nuts] Re: Project Great

[Dave ZL3FJ]

Is the ISS a suitable platform?
I expect getting the experiment package on there would be quite another matter!
DaveB, NZ


-----Original Message-----
From: Tom Van Baak [mailto:tvb at LeapSecond.com] 
Sent: Sunday, November 28, 2021 20:09
To: time-nuts at lists.febo.com
Subject: [time-nuts] Re: Project Great

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-Hobb
>> y.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
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