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It is my understanding that a Doppler shift is the result of a change in wave frequency due to a change in distance of a signal source, relative to the observer.

I assume that the change in distance must be continuous, in order to observe a Doppler effect:

frequency increase = decreasing distance / time

frequency decrease = increasing distance / time

Assuming this simple explanation is correct, and that the velocity of light is constant for all inertial frames of reference, then no Doppler shift should be observed. However, a Doppler shift (redshift) is apparent.

It is my understanding that the apparent cosmological redshift has given rise to the "expansion of space" hypothesis.

With this in mind I wish to ask what the difference is between:

- increasing distance between signal source and observer

and

- increasing space between signal source and observer

Thanks in advance,

B

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# Doppler shift, c, observation, recession, spacetime expansion

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