

What the Global Positioning System Tells Us about Relativity - six70one
http://www.metaresearch.org/cosmology/gps-relativity.asp

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jacquesm
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.

~~~
jerf
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
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.

~~~
jerf
I think those sorts of claims are an insult to the hundreds of smart people
who came after Einstein, including the many smart people who are still
practicing physics today. In fact, I think the whole idea of "If X hadn't done
it, it wouldn't be here today" is virtually useless beyond a 20-year timeline
at most.

Have you _seen_ those string theorists? I'm not a big fan of string theory,
but anyone who can even remotely navigate those things could work out GR in a
few afternoons, with all the advantages another 100 years of evidence and
developments would bring. (Sort of a weird thing to say since it's already
worked out, but still.)

You think all those smart people would just be diddling around, going, _gosh,
I sure wish I could reconcile this overwhelming data that points at a 100+
year-old mathematical formalism, but I guess we'll just have to dick around
for a while longer!_?

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tilly
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!

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Luc
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
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...](http://www.bbc.co.uk/sn/tvradio/programmes/horizon/broadband/tx/gravity/)]

Here are the online video links to both episodes:

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

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

~~~
Luc
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!

~~~
lnguyen
The discussion of the twin paradox and SR seems to be lacking. There's a focus
on only the time dilation effects and nothing on length contraction which
would resolve the issue. Instead it becomes a mess of confusion.

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JabavuAdams
> 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?

