[time-nuts] GENIUS by Stephen Hawking (PBS TV), with 5071A cesium clocks

[Tom Van Baak]

Hi Peter,

Good question. And, yes, it would work to use GPS.

But we don't do it that way because it's a poor physics demonstration to use a highly complex system that *already* takes relativity, propagation delay, gravity and elevation into account (GPS) as a tool to then "detect" relativistic effects in a portable cesium clock at high altitude.

The clearest demonstration, one free from needing to know anything or everything about GPS, one that avoids circular proof, is just to use two identical synchronized portable clocks. So that's why and what we did.

Alternatively, a really nice *thought* experiment is -- if your GPS receiver firmware, and if the entire DoD infrastructure eliminated all notions of relativity for one day. Everyone would then get a wonderful lesson on why relativity is important in a satellite-based PNT system like GPS. Hint: it would screw up 1PPS timing and UTC by tens of microseconds, but as far as I can tell, it would distort positioning only by a small fraction of a meter.

The nearest we have to this thought experiment was the pre-GPS experiment done with NTS-2 in 1977. Read, or at least look at the plots at the end of:
http://leapsecond.com/history/Ashby-Relativity.htm
http://leapsecond.com/history/1978-PTTI-v9-NTS-2.pdf

/tvb

----- Original Message ----- 
From: "Peter Reilley" <preilley_454 at comcast.net>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Friday, May 20, 2016 8:24 AM
Subject: Re: [time-nuts] GENIUS by Stephen Hawking (PBS TV), with 5071A cesium clocks


> I have a question.   I, of small brain, am wondering: if the time 
> difference between the
> top of the mountain and the bottom of the mountain is 20 nS over 24 
> hours could you
> repeat the same experiment using GPS?    The time difference of 20 nS is 
> measurable
> using GPS.
> 
> The GPS clock must run faster on the mountain top than the GPS at the 
> mountain
> base and yet the two remain synchronized to the satellite reference.   
> Therefore
> the GPS 1 PPS signal (measurable to a few nS) must be wrong in in one of 
> the local
> frame references.
> 
> My brain hurts.
> 
> Pete.
>