What the Global Positioning System Tells Us about Relativity

http://www.metaresearch.org/cosmology/gps-relativity.asp

by six70one • 17 years ago

19 10 17 years ago

jacquesm• 17 years ago

The first GPS satellites had a switch to enable the correction for relativistic effects because there was some skepticism if it was needed to do so.

It didn't take very long before it was decided that the switch needed to be permanently in the 'on' position, and it was dropped from subsequent models.

EDIT: makes you wonder if Einstein had not made his predictions regarding relativity, this would have been the first real opportunity to find out in a 'natural' way, how long it would have taken them based on the observation that things did not work as intended.

jerf2• 17 years ago

No, there have been numerous other signs of relativity, going all the way back to the unexpected aberration of the orbit of Mercury that Einstein was aware of. Eventually somebody would have noticed the gravitational deflection of the stars during eclipses, too, though it could have been decades before that happened. (Not because of technology, of course, which clearly existed in Einstein's day, though just barely, but simply because nobody might have noticed.)

Einstein was definitely ahead of the curve, but wasn't running on zero data, even if we discount the purely mathematical issues, such as the inability to reconcile the lack of a reference frame in the Maxwell equations with the need for a reference frame for all other physics of the time.

(It might be worth pointing out here that relativity itself was not a new concept; now when we say "relativity" we mean Einsteinian relativity, but there is also, for instance, "Galilean relativity". Relativity wasn't a surprise, it's just nobody could make it all work out properly without contradictions until Einstein.)

I really recommend this online book: http://www.mathpages.com/rr/rrtoc.htm It is both a great (IMHO) introduction to relativity, Einsteinian and otherwise, and also has a lot about history of Einstein's theory and the general state of thought at the time. I do not mean to diminish Einstein's accomplishment, because like I said he legitimately was ahead of the curve, but it wasn't quite the "bolt from the blue" that it is often portrayed as. All the math pieces Einstein needed had been developed, and his genius was largely the combination of figuring out how to put them together in a way that explained reality, and doing so while discarding inappropriate assumptions that were holding back the physics community at large. I'm actually more impressed by the latter, lest you think I'm trying to diminish that accomplishment; that's a hard harder than that sentence may make it sound.

scott_s• 17 years ago

That's for special relativity. I've read claims that if Einstein hadn't developed general relativity, we'd probably still be waiting for it.

Luc2• 17 years ago

This looks interesting, but read carefully - while I haven't had the time to look at the article and the site in detail, it seems that it could be described as 'fringe science'...

stingraycharles• 17 years ago

I've actually seen a BBC Horizon documentary a while ago, "Do You Know What Time Is?" [http://www.bbc.co.uk/programmes/b00fyl5z], that also talks about this. On top of all the theoretical background, they interview people at the US Army that manage the GPS sattelites, and show how they have to resync the internal clocks every day because of this.

Worth a watch if you like this kind of material.

EDIT: Sorry, I believe it was a different episode: "What On Earth Is Wrong With Gravity?" [http://www.bbc.co.uk/sn/tvradio/programmes/horizon/broadband...]

Here are the online video links to both episodes:

http://www.youtube.com/watch?v=V3aYKAJEVfQ

http://video.google.com/videoplay?docid=-421765295887486158

Luc2• 17 years ago

Oh, I don't doubt the effect, it's just that this article seems to have an anti-Special Relativity viewpoint, and espouses a different explanation for the effect. But I have just scanned it quickly.

Thanks for the links by the way!

tilly• 17 years ago

The article is fine until it starts talking about Lorentzian Relativity vs Special Relativity. Then it starts making amateur errors and misses obvious points.

As a random example, the traditional exposition of special relativity depends on working in an INERTIAL reference frame. Hence the answer to Richard Keating's puzzlement is that the time dilation depends on absolute velocities relative to an inertial frame. A convenient inertial frame being approximately the vector sum of the Earth's rotation and the airplane speeds. (Approximately because the Earth still goes around the Sun, and the Sun around the Milky Way. And then there are the effects of gravity.) Calculating relative speeds in a rotating frame of reference gives an incorrect answer, and SR predicts that fact.

To address the more fundamental problem, nowhere does he address the point accepted by Lorentz himself that the Lorentz transformations with a preferred frame of reference causes every other inertial frame of reference to make absolutely identical calculations. Therefore there is no possible experimental difference between Lorentzian Relativity and Special Relativity. Or, put alternately, there is absolutely no way to single out any particular inertial reference frame as being preferred.

Furthermore Lorentzian Relativity has no theory of gravity. So it is intellectually dishonest to include corrections from GR in a discussion about LR. Fundamentally you can't discuss GR without accepting the idea of not only having no preferred inertial reference frames, but in fact having no inertial reference frames at all!

JabavuAdams• 17 years ago

> The accuracy of this comparison is limited mainly because atomic clocks change frequencies by small, semi-random amounts (of order 1 ns/day) at unpredictable times for reasons that are not fully understood

What?

What the Global Positioning System Tells Us about Relativity

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