[Physics] Gravitational Time Dilation and Gravitational Redshift - two separate things?

[Doug Marett]

Hi Ilja,

    Yes, I agree with you that " the only change in the frequency is
because of the clocks (which have to be used to measure the frequency of
the hand-waving", but the red-shift of the light can't be "the same thing"
in my mind because, as you say, from the "point of view of the background
time coordinate, there is no change in frequency".
So if there is no change in frequency from the source to the receiver,
there is no relativistic mechanism by which the EM wave is made to bend,
since the bending is supposed to be caused by the progressive change in
frequency through the gradient. Quite literally, for EM waves approaching
the earth at an angle, the portion of the wavefront closer to the earth
must contract compared to the portions further away, eliciting a
progressive bend towards the surface, and Einstein attributes this to a
change in frequency of the wave acted upon by the grav. gradient, which is
something physical independent of the clocks. Einstein's idea also creates
another paradox, that a receiver on the surface will receive more
wave-fronts than are emitted by the transmitter at altitude - if this were
true we would have a free-energy generating device!

I think the only way out of this is to argue that it is the change in the
speed of light with altitude and the associated change in wavelength that
causes light to bend in the gradient, and frequency remains preserved.
Einstein himself said in 1911 that this explanation was equivalent to his
own (except for the energy change). Then there is only the one frequency
effect due to the clocks and no problem with free energy. But then the
black hole theory has to be a fiction.

Doug


On Wed, Dec 5, 2018 at 3:52 PM Ilja Schmelzer <ilja.schmelzer at gmail.com>
wrote:

> No, the signal will be blue-shifted only once.
>
> This can be best seen if one replaces the wave by a hand-waving person
> and looks at the time when the light signal of "hand up" and "hand
> down" arrive.
>
> If we look at this in coordinates which are natural for a stable
> configuration, thus, a metric of the form g_mn (x^i) dx^m dx^n with
> the metric coefficients depending only on the spatial coordinates, and
> assume the handwaving guy as well as the observer at rest, the light
> rays for "hands up" and for "hands down" are the same trajectories,
> only with a shift in the time coordinate t.
>
> Thus, from point of view of the background time coordinate, there is
> no change in the frequency.  Thus, the only change in the frequency is
> because of the clocks (which have to be used to measure the frequency
> of the hand-waving).   So, they are the same thing.
>
> 2018-12-04 22:12 GMT+01:00, Doug Marett <dm88dm at gmail.com>:
> > Hi All,
> >
> >     This just came up in a question I had to my website - it has to do
> with
> > the Pound-Rebka experiment and whether gravitational time dilation of
> > clocks and gravitational redshift of EM are two different things or the
> > same thing. The problem is set out by L.B. Okun is plain language in an
> > article here: https://arxiv.org/pdf/hep-ph/0010256.pdf
> >    The essence of it is that if you take a clock and move it from the
> > ground to the top of a tower, the clock should speed up in it's rate at
> the
> > higher altitude. If you then send an EM signal from this clock back to
> the
> > ground, Einstein says that the EM should be blue-shifted. However, this
> > would mean that the signal sent to the ground has now been blue-shifted
> > TWICE, once due to the clock speeding up,  and once due to the fall of
> the
> > EM through the gravitational gradient.
> > However, the Pound-Rebka experiment finds that it is blue-shifted only
> > once. So which effect is redundant, gravitational time dilation of clocks
> > or gravitational red-shift of light? They can't be the same thing, since
> > the latter is an operation performed on the EM during transit, and is
> > supposed to make it bend. And the former is something which happens to
> > clocks independent of EM signals sent between them.
> > Interestingly, the experiment proposed by Okun to answer the question was
> > performed in a slightly different form by Tom Van Baak as described here:
> >
> > http://leapsecond.com/great2005/
> >
> > Another link that is useful is the paper here which examines the math
> used
> > in the Pound-Rebka experiment and finds it is full of errors!
> >
> > http://milesmathis.com/pound.html
> >
> > Just wondering if anyone else is aware of this apparent contradiction in
> > the relativistic thinking : )
> >
> > Doug
> >
>
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