[time-nuts] Re: Project Great

[Magnus Danielson]

Hi,

There is an overemphasis on the atom being used, and especially on 
cesium as that is what is used for SI definition. However, actual 
implementation means actual physical devices, and the physical devices 
have a physics package, for which details will be important to the 
actual performance. Various atoms have been more or less well adapted to 
different types of physical package types. The beam type of device can 
be made to have very little perturbation, and cesium was well suited for 
that, while rubidium ended up being very well suited for the gas cell 
type. The CSAC is really a cesium based gas cell, but the original 
benefit of rubidium filtered optical pumping has been replaced with 
semiconductor lasers for pumping. Today both cesium and rubidium gas 
cells with the same mechanism exists. With gas cell you get wall shift 
from atoms banging around the wall, but also gas shift as buffer gas 
makes the atoms hit the buffer gas most of the times. With a bit of 
selection of gas mixture, these can be made to balance each other.

So, what is the claim to fame for CSAC? It's actually not being cesium, 
but for the stability it provides for the small amount of power it 
consumes. That's also where it finds actual applications. If you can 
afford more power, there is cheaper alternatives available.

Cheers,
Magnus

Den 2021-11-27 kl. 23:28, skrev Bob kb8tq:
> Hi
>
> The CSAC is not a cesium in the conventional sense. It is much closer to
> a telecom Rb than anything else. There likely are telecom Rb’s that would
> do a better job. Would they do a good enough job? …. likely not ….
>
> Bob
>
>> On Nov 27, 2021, at 5:11 PM, Lux, Jim <jim at luxfamily.com> wrote:
>>
>> On 11/27/21 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
>>>
>> I don't think a CSAC would be good enough.
>>
>> Tom's experiment was 22 ns out of 42 hours or about 1.45E-13. That's quite a bit smaller than a CSAC adev over that period.
>>
>> There's a variety of roads that go to ~12,000 ft in Colorado, about ~10,000 in CA (Tioga Pass isn't closed yet), so you can get about 3x change, but still you're talking <1E-12.
>>
>> Mammoth Mtn has a gondola to the top, but it's only 11,000. There may be a ski resort in CO that's higher.
>>
>>
>>>> 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
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