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Do you have a cite for Brain Cox's claim about GPS?

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griffin2000
859134.  Mon Oct 24, 2011 4:21 pm Reply with quote

In the "Incomprehensible" episode featuring Brain Cox, he made a claim that when the GPS was first proposed to the US military's top brass, they very skeptical of this whole "relativity" thing and didn't really believe that time would run at different speed in orbit compared to an observer on the surface of the Earth.

This sounds rather apocryphal to me, or at least a serious distortion of a real event. Does anyone have a cite to back up Dr Cox's claim?

 
Moosh
859142.  Mon Oct 24, 2011 5:09 pm Reply with quote

Okay, so this is as far as I've got.

Between 1984 and 1986 (so after the launch of the first set of GPS satellites but before the military actually started using GPS operationally) there was an US Air Force committee called the Committee on Accuracy of Time Transfer in Satellite Systems which was chaired by Professor Clifford M. Will. One of the functions of the committee was to check that the relativistic effects had been correctly taken into account in the calculations.

Their report doesn't seem to be online anywhere (although there is evidence of it's existence here), and here, which gives the following abstract.
Quote:
Report evaluates and determines adequacy of corrections for relativistic effects in present Air Force programs to perform their mission, e.g., the global positioning system (GPS). Report determines adequacy of present methods for meeting Air Force mission needs and explains future uses and needs for time transfer, including use of time transfer to test the postulates of relativity theory. Keywords include: global positioning system, NAVSTAR, relativistic effects, and time transfer.

And according to this (not very authoritative) source the result was positive.

A report that is online is a 1996 report from The GPS Joint Program Office of the Aerospace Corporation here which says that basically everything is good but that's from far later than we need to look at. I only put it in because it's a nice explanation of how the calculations actually work.

Anyway, back to the '80s. So if we believe that Clifford Will decided it was okay, then Prof Cox's story was at least a little inaccurate, because he stated that when the GPS system was first used they had the option of not calculating for relativistic effects, which wouldn't make sense in the light of the committee reporting favourably on their use in 1986.

Anyone got anything better to go on?

 
griffin2000
859162.  Mon Oct 24, 2011 7:24 pm Reply with quote

This article was posted in the Straight Dope thread about this:
Quote:

There is an interesting story about this frequency offset. At the time of launch of the NTS-2 satellite (23 June 1977), which contained the first Cesium atomic clock to be placed in orbit, it was recognized that orbiting clocks would require a relativistic correction, but there was uncertainty as to its magnitude as well as its sign. Indeed, there were some who doubted that relativistic effects were truths that would need to be incorporated

 
CB27
859174.  Mon Oct 24, 2011 11:14 pm Reply with quote

Below is part of the initial report into the launch in 1977, which included a number of tests. It's quite technical, but from what I've been able to understand, they were testing to see whether the theory held up or not, suggesting they might not have been convinced beforehand.

Right at the outset it states:

Quote:
This paper discusses the launch and preliminary results which include verification of the relativistic clock effect.


http://www.leapsecond.com/history/1978-PTTI-v9-NTS-2.pdf

 
djgordy
859196.  Tue Oct 25, 2011 3:33 am Reply with quote

I was a bit supicious of it and had done some digging. I was hoping for a firm rebuttal of the story but hadn't found anything concrete. The thing that made me most suspicious was the fact that Mr. Cox said that the Dept of Defence had described Albert Einstein as a "funny looking Swiss bloke" (or words to that effect). Einstein was German, though he had lived and worked in Switzerland, and had been the most famous and respected scientist in the world. He had, effectively, delivered the atomic bomb and had worked as a consultant on ordnance with the US Navy during WWII. One might expect that there had been discussion as to whether relativistic effects should be taken account of but the idea that they would be dismissed out of hand seems a little far fetched.

One might suspect that is a story put about by non military scientists who have to beg for funding whilst the military just get just about anything they ask for.

 
dr.bob
859205.  Tue Oct 25, 2011 4:42 am Reply with quote

djgordy wrote:
Einstein was German, though he had lived and worked in Switzerland


Einstein wrote:
If my theory of relativity proves to be correct, Germany will claim me a German, and France will claim me a citizen of the world. However, if it proves wrong, France will say I'm a German, and Germany will say that I'm a jew.


djgordy wrote:
He had, effectively, delivered the atomic bomb


Had he?! That's rather belittling the efforts of all the people involved at Los Alamos.

 
griffin2000
859335.  Tue Oct 25, 2011 1:03 pm Reply with quote

djgordy wrote:
Mr. Cox said that the Dept of Defence had described Albert Einstein as a "funny looking Swiss bloke"

That part I assumed was added for humour value.

Basically the closest I've come is that snippet in an article by Neil Ashby. The source for that sentence is cited as:
"Proper time experiments in gravitational fields with atomic clocks, aircraft, and laser light pulses"
http://books.google.com/books/about/Proper_time_experiments_in_gravitational.html?id=QIFIQwAACAAJ

It's not available online.

 
CB27
859362.  Tue Oct 25, 2011 3:08 pm Reply with quote

Ashby also cites the report I linked to a couple of posts back, that's how I found it.

 
clack
859381.  Tue Oct 25, 2011 4:08 pm Reply with quote

I believe that bit of info is something Cox picked up when he toured a US military facility while presenting a Horizon episode on time (he also did one on gravity). I vaguely recall some uniformed person telling him something to that effect.

 
griffin2000
859406.  Tue Oct 25, 2011 6:45 pm Reply with quote

Is that the "Do you know what time it is?" episode of Horizon ? Is that available on DVD anywhere ?

 
djgordy
859482.  Wed Oct 26, 2011 4:19 am Reply with quote

dr.bob wrote:

Had he?! That's rather belittling the efforts of all the people involved at Los Alamos.


I don't wish to belittle their efforts at all. The point is, of course, that it was Einstein's work which provided the basis for the concept of the bomb and so if someone in the Dept of Defence were to say" who the hell is this Einstein anyway" the response would be "he was the guy who gave us the A bomb".

 
dr.bob
859499.  Wed Oct 26, 2011 5:41 am Reply with quote

djgordy wrote:
The point is, of course, that it was Einstein's work which provided the basis for the concept of the bomb


That's simply not true. Rutherford and Bohr did early work on the structure of the atom, Becquerel and the Curies worked on nuclear radiation. People like Hahn and Meitner examined the process of fission, and Otto Frisch proved that it was happening. Then a team of people at Columbia, including Enrico Fermi, measured the energy released by fission. All of this work paved the way for the concept of the bomb.

All Einstein did in this field was to predict how much energy would be released by the process of fission. Whilst this was, of course, important and impressive, the experimentalists would've found out how much energy was released with or without Einstein's predictions.

djgordy wrote:
and so if someone in the Dept of Defence were to say" who the hell is this Einstein anyway" the response would be "he was the guy who gave us the A bomb".


To which the DoD person would reply "no he didn't! Rutherford, Bohr, Curie, Meitner, Frisch, Fermi, and Oppenheimer gave us the A bomb. Stop talking such nonsense. As you well know, Einstein is that annoying pacifist who tried to convince the US government to stop developing the bomb and was actively barred from the Manhattan Project over security fears."

 
djgordy
859522.  Wed Oct 26, 2011 6:43 am Reply with quote

Well, if you wanted to give a lecture on the entire history of atomic physics followed by another lecture on the Los Alamos project down to the person who made the tea then I suppose you would say those things. But if you were in the Dept of Defence and someone said to you "who is this Einstein and why should we listen to him?" you woulld say "he is the man who gave us the atomic bomb".

Although I suppose you might instead say "how the hell are you working in the department of defence on these multi billion dollar projects and don't know who Albert Einstein is?"

 
dr.bob
859536.  Wed Oct 26, 2011 7:32 am Reply with quote

djgordy wrote:
But if you were in the Dept of Defence and someone said to you "who is this Einstein and why should we listen to him?" you woulld say "he is the man who gave us the atomic bomb".


I wouldn't, because I don't believe that to be true. I think the A bomb would've been developed whether or not Einstein had existed.

Einstein did many great things, and we have a lot to thank him for, but nuclear fission is not one of them.

 
clack
859580.  Wed Oct 26, 2011 10:00 am Reply with quote

griffin2000 wrote:
Is that the "Do you know what time it is?" episode of Horizon ? Is that available on DVD anywhere ?
Yes, that's the episode. I watched it on youtube, don't know if it's still on there.

 

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