When processing GPS signals, one takes into account the influence of the speed of the satellites and the strength of the gravitational field in which they are located. I have read (Lisa Ranall) that one must also take into account the frequency shift of the photons ( in in this case a shift to blue higher frequency) of the electromagnetic signal from the satellite to the receiver on Earth. Why? the speed of the signal is the constant speed of light and the information transmitted is digital, right? Does it have to do with an increasing deflection as the signal approaches the earth and the energy of the photons increases and is thus deflected differently in the increasing gravitational field?
Answer
I’ve tried looking up Randall’s text, but can’t find it. I suspect there has been a little confusion.
The gravitationally induced effect that a clock runs faster or slower in a weaker than stronger gravitational field is generally referred to as redshift (via the equivalence principle, the time dilation in an accelerated frame of reference is linked to that in the gravitational field, hence the general term red or blueshift). So in my opinion it has nothing to do with the deflection of the photons by the gravitational field of the earth.
Piet Van Duppen
Institute for Nuclear and Radiation Physics
Department of Physics and Astronomy
University of Leuven (KU Leuven)
Answered by
Professor Walter Lauriks
Physics Acoustics
Old Market 13 3000 Leuven
https://www.kuleuven.be/
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