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Groups > sci.physics.relativity > #371188
| From | Thomas 'PointedEars' Lahn <PointedEars@web.de> |
|---|---|
| Newsgroups | sci.physics.relativity |
| Subject | Re: Where is the center of the universe? |
| Date | 2015-11-30 22:50 +0100 |
| Organization | PointedEars Software (PES) |
| Message-ID | <14494064.6kbgbgsuoQ@PointedEars.de> (permalink) |
| References | (17 earlier) <n3eitv$q9n$1@node1.news.atman.pl> <4204306.PgI3GLYfg2@PointedEars.de> <ec1ece41-a1c0-4df5-a7db-b1d92de4a6a6@googlegroups.com> <16637c99-e838-44a8-825d-a35b133c195f@googlegroups.com> <4f9f62bd-d6f6-4723-87a0-2c9c45c6c128@googlegroups.com> |
Your “Ingrid”, as it is called in the German-speaking Usenet at least, is
giving me opportunity to clarify your misconceptions in one posting. Thank
you for that.
Ross A. Finlayson wrote:
> On Sunday, November 29, 2015 at 5:49:01 AM UTC-8, Ross A. Finlayson wrote:
>> On Sunday, November 29, 2015 at 4:56:35 AM UTC-8, Ross A. Finlayson
>> wrote:
>> > On Sunday, November 29, 2015 at 2:45:09 AM UTC-8, Thomas 'PointedEars'
>> > Lahn wrote:
It is called attribution *line*, _not_ attribution novel.
>> > > Because it describes reality so well. For example, moving clocks,
>> > > such as on a satellite in orbit, *are* observed to tick slower, and
>> > > clocks on a higher gravitational potential (lower spacetime
>> > > curvature), such as in
>> > > orbit, *are* observed to tick faster. And those effects do not
>> > > cancel each
>> > > other out. So one has to compensate for those facts. Think of your
>> > > hubris now the next time you get lost in a foreign city and have only
>> > > your car navigation system/smartphone with
>> > > GPS/GLONASS/GALILEO/BeiDou-2 support to help you out.
>> > >
>> >
>> > Why isn't time skew symmetrical?
The effect I was talking about is properly called time _dilation_, and it
*is* symmetrical.
<https://en.wikipedia.org/wiki/Time_dilation#Due_to_relative_velocity_symmetric_between_observers>
>> > A body orbits, but the Earth spun around it,
>> > which is the master clock and why?
The observer is on the surface of Earth. The clocks onboard the GNSS
satellites tick *in total* faster relative to the observer’s clock (with
GPS, about 38 µs per day, which are 37'970 ns too many). So you could say
that the observer’s clock or, more generally, the observer’s proper time,
is the "master clock/time".
Why? We want to know the position of the observer on the surface of Earth,
and for that we need to know the distance between them and at least 3 GNSS
satellites (and one more for verification) for trilateration. Lacking a
tape measure that is up to 20'000 km long, the distance is measured
by comparing the time the signal is sent from a satellite (which is the
time encoded in the signal) to the time it is received, taking
relativistic effects into account. There are one observer and, with GPS,
about 4 to 12 GPS satellites in direct sight to them at any one time.
>> > (This is just a matter of acceleration
>> > of the inertial rest frame, then.)
*Inertial* frames of reference are _not_ accelerated frames.
<https://en.wikipedia.org/wiki/Inertial_frame_of_reference>
>> > Then for gravity, is that always the
>> > configuration of the clock or the cesium
>> > clock?
Probably the answers to all your questions, all ill-worded so far, can be
found in the resource cited on the bottom of my posting.
>> > Is it just the accel./decel. of
>> > taking up and bringing back the clock?
>> > What if you take the reference clock up
>> > instead of bringing the sample clock back?
No clocks are "brought back" with a GNSS. How did you get that idea?
>> > Are any of the ground referenced satellites
>> > truly dead-reckoning, or do they just point
>> > to landmarks and update their positions
>> > they encode over their signal?
No.
<http://www.catb.org/~esr/faqs/smart-questions.html>
>> "Clock-driven transmitters send out synchronous
>> time signals, tagged with the position and time
>> of the transmission event, so that a receiver near
>> the earth can determine its position and time by
>> decoding navigation messages from four satellites
>> to find the transmission event coordinates, and
>> then solving four simultaneous one-way signal
>> propagation equations."
AISB.
>> "Thus the Sagnac [...] the problem of path-dependent
^effect…
>> inconsistencies."
Do you even realize that your snipping has turned the original well-worded
text into gibberish?
>> "Conversely, the elapsed coordinate time can be
>> computed by integrating corrections to the proper time. "
Obviously. (Do you even know what “coordinate time” and “proper time” are?)
>> http://www.phys.lsu.edu/mog/mog9/node9.html
>>
>> GR might be never wrong,
There are strong indications, namely a century of confirmations, that it is
not. Or, as a popular professor of physics in Germany, Harald Lesch, likes
to put it: “If relativity is wrong, it is damn well wrong.”
>> but, uh, non-Newtonian corrections are what are applied to geo-
>> referenced satellites,
So what? It is obvious that Newton’s laws alone do not quite cut it.
>> because the path integral isn't solved
>> and solar neighbor effects are significant enough
>> that GR doesn't solve their n-body system yet.
You have no clue what you are talking about.
The n-body _problem_, and its only partial solution, has nothing to do with
this. And “solar neighbor effects”? Gimme a break.
<https://en.wikipedia.org/wiki/N-body_problem>
>> Quantum mechanics is never wrong....
There are strong indications, namely more than half of a century of
conformation, that it is not. The functionality of the device that you are
using to read this posting depends on the correctness of quantum
electrodynamics (QED), and therefore on special relativity. And that the
system time on your device is kept in sync with atomic clocks over a
computer network (via NTP) depends at least on the correctness of general
relativity, because clocks on different elevations already tick differently
(you do not have to go to orbit to see that).
When I say “correctness of X” I mean, of course, some theory X has been
confirmed by experiments/observation and not falsified by such.
> "At present one cannot easily perform
> tests of relativity with the system because
> the SV clocks are actively steered to be
> within 1 microsecond of Universal
> Coordinated Time (USNO). "
>
> So, thanks, GR, you're too complicated for
> GPS (with any further non-Newtonian
> adjustments or corrections).
>
> Also, _there
> are still offsets_, more of the non-Newtonian,
> just like GR's difference improves the estimate
> of orbits but is yet not _exact_.
Utter nonsense.
> "Even without this impetus, the GPS provides
> a rich source of examples for the applications
> of the concepts of relativity. "
A slightly less out of date, less second-hand resource (note that you are
citing a document by Prof. Jorge Pullin, last updated in 1997, which is
quoting a text by now-Professor *Emeritus* Neil Ashby [of the University of
Chicago] of unknown date and origin, but presumably not newer than 1995 when
he ceased to be a member the International Committee on General Relativity
and Gravitation):
<http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html>
(“Real-World Relativity: The GPS Navigation System” by Prof. Richard W.
Pogge; last updated “2015 October 25”)
PointedEars
--
Q: What did the nuclear physicist post on the laboratory door
when he went camping?
A: 'Gone fission'.
(from: WolframAlpha)
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Re: Where is the center of the universe? The Starmaker <starmaker@ix.netcom.com> - 2015-11-25 10:01 -0800
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Re: Where is the center of the universe? The Starmaker <starmaker@ix.netcom.com> - 2015-11-25 12:42 -0800
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