Abstract
The kinematical nature of the spectral shift in different types of spacetime, cosmological redshift and frequency shift in Schwarzschild spacetime being the most prominent representatives, has been a subject of recent interest. We demonstrate that the kinematical nature of the spectral shift is an inherent feature of the particular type of spacetimes. The general solution is found: necessary and sufficient conditions for the spectral shift arising from a kinematical origin are formulated. The status of the relative speed is discussed.
Highlights
Communication by means of the exchange of electromagnetic signals is accompanied by a frequency shift
In general the spectral shift may be expressed in terms of two parameters, the relative speed and another one, a quantity, referred to by Synge as a recession speed
Recent interests were associated with the particular case of a spectral shift being represented solely by relative speed
Summary
Communication by means of the exchange of electromagnetic signals is accompanied by a frequency shift This is a combined effect involving, in the general case, entangled contributions of kinematical and gravitational origins. The main issue of this paper is to establish how general this effect is, namely that the spectral shift has a kinematic origin We will discuss this question, providing what we hope will be a definitive answer. There is no invariant definition of such a quantity, one can find a suitable background for the discussion of the status of “relative speed” In this way one could validate the statements in [7] associated with the meaning of speeds in the expanding universe. A final discussion and conclusions will be given in the last section
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