Re: A little challenge for relativists.


"John Kennaugh" <JKNG@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:elT$tKFKQyhDFwfQ@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Harry wrote:
> >
> >"John Kennaugh" <JKNG@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
> >news:bRK+wMJuUFhDFwsj@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> >> Joe Fischer wrote:
> >> >On Tue, 22 Nov 2005 04:35:12 +0000, John Kennaugh
> >> ><JKNG@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> >> >
> >> >>Joe Fischer wrote:
> >> >>> Nature wants to "rnsure" that c is a constant?
> >> >>
> >> >>c is a constant speed whether it is constant w.r.t the ether as per
> >> >>Lorentz, constant w.r.t the source as per Ritz or constant w.r.t the
> >> >>observer observing it as per relativity although how an observer has
the
> >> >>power to influence the speed at which light leaves a source over vast
> >> >>distances and back through time no one has yet explained.
> >> >
> >> > No, I did not mention observer influence, what I have said
> >> >is the light is always measured as c.
> >> > This is a fact of experiment, I am not sure if any model
> >> >explains why it is always measured as c.
> >
> >Lorentz's model does that, depending --as always-- on how far one extends
> >the "why".
>
> Agreed
>
> >> You have to appreciate that a text book has to sell. It sells if it is
> >> recommended by an educator. An educator will recommend it if it doesn't
> >> land him in trouble with his students. The problem with relativity is
> >> that there is no direct logical path to it so a text book will use
> >> various semantic tricks to ease the educators path.
> >>
> >> You have just repeated one such trick - I suspect unknowingly. The text
> >> book will not actually say "the speed of light is always measured as c
> >> EVEN WHEN THE SOURCE IS MOVING." because that is a lie.
> >
> >Please explain! IMO it'd be merely an innocent
simplification/exaggeration.
> >According to experts (for I admit to never have calculated it myself),
such
> >measurements are implicitly done for radio waves with GPS, and GPS
usually
> >("always") works.
>
> Two different points here. If you are writing a text book you can hardly
> say that Einstein based his second postulate on something which wasn't
> going to happen for another 50 years. :o).

Physics text books rarely present a chronological account. Me thinks you
read too much into it.

> GPS does not 'measure' the speed of light at all. The assumption is that
> it would give the wrong results if the speed of light was not
> independent of the speed of the observer.

Not an just an assumption: an assertion by GPS specialists, even by one who
dislikes Einstein's ideas.

> I am not qualified to say
> whether or not that is valid but there is a tendency to assume that
> because something works with Relativity it shows that it would not work
> with an alternative theory.
>
> For example on Tom Roberts website "The Experimental basis of SR" it
> states:
> "In SR there is a non-zero Doppler effect for transverse motion, due to
> the relative time dilation of the source as seen by the detector.
> Measurements of Doppler shifts for sources moving with velocities
> approaching c can test the validity of SR's prediction for such
> observations, ... the experiments support SR and are in complete
> disagreement with non-relativistic predictions."

Here you deviated from the subject of source independency in a moving medium
and GPS, according to GPS specialists.

> This just isn't true. It _seems_ perfectly logical and a clear cut case.
> SR predicts time dilation source dependent theories don't. In relativity
> transverse Doppler comes from time dilation. Transverse Doppler is
> measured therefore time dilation is real. The only fly in the ointment
> is that source dependent theory predicts exactly the same frequency
> shift for a much less exotic reason - it is simply a velocity triangle.
>
> The maths of relativity and source dependent theory are not different in
> many cases when you think they should be and one would have to go far
> deeper into the subject of GPS than those who argue about it in this NG
> have, to come to any meaningful conclusion.
>
> To make one small point:
>
> A B
>
>
> O
>
>
> Satellites A and B observer O. The argument goes that as O fixes his
> position accurately Relativity must be right because if light was source
> dependent O would get a different answer. Looks good but it is flawed.
> Where is A? Where is B? Where is O? The height of A and B and their
> position have all been calculated from data using relativity as a model.
> There is no independent way of fixing their position. If you are going
> to test a different model you have to start by recalculating the
> position of A and B according to that model then check for consistency.

Sure. O is considered to be moving, together with the atmosphere; A and B
are moving too.

> As results as to the position of O are more consistent than terrestrial
> surveying methods O's position is now defined as being where GPS says it
> is. What you have is consistency not necessarily accuracy - the former
> is more important anyway. As I say I do not know enough to argue the
> case but neither do Henri Wilson and Paul Anderson but that does not
> stop them :o)

:)

Harald


.

Relevant Pages

  • Re: Question about relativity
    ... matter which you thought was moving and which not. ... it seemed that there was a certain frame of reference that was the ... and the Theory of Relativity was created. ... The GPS would not work if it did not use frames ...
    (sci.physics.relativity)
  • Re: A little challenge for relativists.
    ... The problem with relativity is ... >measurements are implicitly done for radio waves with GPS, ... Measurements of Doppler shifts for sources moving with velocities ... SR predicts time dilation source dependent theories don't. ...
    (sci.physics.relativity)
  • Re: to sam
    ... Real-World Relativity: The GPS Navigation System ... GPS satellites are not in geosynchronous or geostationary orbits). ... their clocks ticking more slowly (see the Special Relativity ...
    (sci.physics)
  • Re: to sam
    ... Einstein's Relativity and Everyday Life ... But GPS is an exception. ... twice per day, much faster than clocks on the surface of the Earth, ... The net result is that time on a GPS satellite clock advances ...
    (sci.physics)
  • Re: to sam
    ... Real-World Relativity: The GPS Navigation System ... GPS satellites are not in geosynchronous or geostationary orbits). ... their clocks ticking more slowly (see the Special Relativity ...
    (sci.physics)
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