[time-nuts] Einstein Special on PBS
Tom Van Baak
tvb at LeapSecond.com
Fri Nov 27 13:17:44 EST 2015
It's a good question and I've wrestled with it too. I see two choices:
1) Time is stable and every ultra-precise timing measurement of atomic behavior appears to depend on gravity.
2) Every ultra-precise timing measurement of atomic behavior is stable, and Time appears to depend on gravity.
My impression is they are both equivalent and indistinguishable. Practical people like to use #1, for example, the SI second is defined as 9,192,631,770 Hz specifically and only at mean sea level on planet earth; national laboratories, and some time nuts, correct their clocks for elevation. By contrast, astronomers and physicists use #2 because it make everything simpler and universal.
So you can say that a cesium clock ticks at 9,192,631,770 Hz +/- some function of gravity and velocity, or you can say that a cesium clock always ticks at 9,192,631,770 Hz in its "own reference frame".
But either way, if you leave a clock on a mountain for a while, it comes back the same frequency it left. So what we measure is not the frequency, but the time (clock phase). The time the clock displays contains the sum total history of all frequency changes during the trip. You can't tell this during the trip, since the clock always thinks it is running at a constant and correct rate, wherever it is.
----- Original Message -----
From: "Mike Feher" <mfeher at eozinc.com>
To: "'Discussion of precise time and frequency measurement'" <time-nuts at febo.com>
Sent: Friday, November 27, 2015 7:37 AM
Subject: Re: [time-nuts] Einstein Special on PBS
>I just do not get it. I know that now I am 70 and my good smart days are behind me, but, this should be simple. In all these clocks mentioned, time is derived from the transition of a hyperfine line of a certain atom within some element, in this case cesium, In order for any of these clocks to deviate in relative time at different heights for example, it seems to me that the period of the hyperfine transitions must change as well, to make the defined second longer or shorter. So, in these examples the elevation does not change the time, but the way the atoms behave. What obvious item am I missing, besides maybe brain capacity? Thanks - Mike
> Mike B. Feher, EOZ Inc.
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> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Tim Shoppa
> Sent: Friday, November 27, 2015 9:19 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Einstein Special on PBS
> Would've been more fun to see Tom and his kids going to the top of Mt Ranier in 2005 with the ensemble :-). http://leapsecond.com/great2005/
> They mentioned some "6 miles per day" offset due to GPS relativity effects.
> I think this is the sum of both special relativity (time dilation) and general relativity (gravitational) effects. The GR correction is 45 microseconds a day fast; the SR correction is 7 microseconds slow. 38 microseconds seconds is 11 kilometers which is indeed 6 or 7 miles. While time drifts 38 microseconds a day, I'm not sure that GPS coordinates would drift that fast - aren't most of the corrections in the same direction?
> Seeing Kip Thorne describe black holes was a blast - he refused to use the word mass when describing them, just like when I took a course from him in 1990. When my advisor taught the same course, I pleaded with him, "please use coordinates!". (Kip Thorne loves coordinate-free notation, unfortunately my brain does not work that way!!! I would've failed the course if it was only GR; fortunately it also had plasma physics in the same quarter, and I was an ace at that due to some undergraduate work.)
> Tim N3QE
> On Fri, Nov 27, 2015 at 12:05 AM, Arthur Dent <golgarfrincham at gmail.com>
>> In the special it looks like they used two HP5071A standards, an
>> SRS620 counter, and a scope. They first made sure the stds were in
>> sync then took one to the building at the top of the ski lift on New
>> Hampshire's Mount Sunapee at 2726' elevation for 4 days where it would
>> be running a little faster because it would be slightly further from
>> the center of the spinning earth. After bringing the 5071A back from
>> the top of the mountain they checked the difference in the start of
>> square waves displayed on the scope and detected the 5071A at altitude
>> was now 20ns ahead of the 5071A kept at sea level, as predicted, if I
>> understood everything correctly. They explained that the clocks in the
>> GPS satellites traveling at a much higher speed had to correct for the
>> speed difference which also verified Einstein's theory.
>> My wife and I were on the top of Mt. Sunapee this summer where we
>> enjoyed the views but didn't run any experiments. ;-)
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