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The synchronization of GPS clocks at two positions on earth

November 4, 2011

Mohan, mdashf


If you think the synchronization of clocks at different ends of the OPERA beseline is a cause of concern consider this. Synchronize two GPS receivers at both end. Then transport them midway of the baseline. Check their synchronization at the midpoint. (there will be no difference, note if there is any and correct for it) Then you think the two clocks traveled a different kind of path hence there may be concern. Now let the clock from CERN at midpoint go to Gransasso and the clock at gransasso at midpoint go to CERN. These two clocks have traveled the exact same path as matters and any difference in synch. will be equal. If they are not take note of them. Now the experiment can be performed with claims about complete synchronization. This cancels any such systematics people were raising a concern about …
a few weeks ago I had done a simple calculation that had shown Boeings flying a distance of ~10,000 kms on earth lose a time of the range of micro-second. I had done it without effects of gravity. A Boeing flies ~10 kms above earth surface for a good part of the flight so it would measure a smaller time effected by a smaller gravitational potential of it’s height. An airplane is synchronized by the GPS clocks. Two airports 10,000 kms apart if not synchronized properly by this GPS system would lose a big time even in an hr. In a 15 hr trip it could reflect really well. (one can do the calculation) SO for the OPERA baseline which is not even 1000 kms we can not allow as big an error as 60 nano-secs since we are covering that distance at speed of light. That is we are allowing ourselves ~2.5 milli-secs only for the entire flight. A 60 nano-sec error in 2.5 milli-secs becomes 1.3 seconds in 15 hr flight. (not to mention what error we accumulate for satelites which govern our daily routines such as a favorite TV show, two places such as Delhi and Bhubaneswar would see the show at very different times, eg people in one city may lose few minutes of the show because the satelites warned us much later as they are so far above us) Also note that a 2 second error in a day is not something even a dead-battery would do (joke).

You can do this experiment with your digital watch if your watch is not synchronized by a GPS satelite, if it says 2 seconds either way after you have fixed all other factors you would know that there is something wrong with GPS system, we do not need very precise experiments to claim GPS precision if we are to lack such in the first place …

Before you start at Narita airport, you ask your friends in the destination country to show you a watch over video conference. You fix your watch time. Then you fly and keep precise note of what time it is when you landed the airport according to airport clocks and your clock after you made your time correction as per airport announcement. (You know how much you adjusted) Then you go to your friend’s place and he would broadcast his time again which will be noted as per another friend in Japan who did not fly. You are done.

basically you have more than one clock, all fixed differently as per your need. (that is reference clocks at different points and experimental clocks)

To get honest clocks you have to be careful, you may install pre-arranged clocks from the lab with airports permission or someone may just be present with such a clock ..

SO this can also be done to test the actual syncronization of clocks at both ends of OPERA. If it gives you synch below 1 sec for a corresponding time-of-flight you have set an upper limit for the actual synch offset thereby making a very confident measurement when neutrinos are involved .

OPERA calibrated it’s clocks in 3 methods. 1. GPS clock, 2. Cs clocks on lab (these are world wide synched by GPS clocks hence only reflect GPS precision) 3. fiber optics cables It can have electric cables (they must already have) and send electric currents or something like that which travel much slower so a much longer TOF than a second is available. Once that is the case any errors of second level will be determined ..

Two computer servers pre-synched at one place and placed at two different labs will note the timing of these two clocks on their servers and in a 24 hrs they will show a 2 second difference. I think this they already did, suggestion: transport them by bullock carts since the relativists think 4 km/s will bring in a time dilation or even a flight transportation, then the debate will go onto oh we transported them via Grey Hound buses and these buses offer a bumpy ride hence that may also be the cause for time dilation.

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