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
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