John Stachel: "But this seems to be nonsense. How can it happen that the speed of light relative to an observer cannot be increased or decreased if that observer moves towards or away from a light beam? Einstein states that he wrestled with this problem over a lengthy period of time, to the point of despair." http://www.aip.org/history/exhibits/...relativity.htm

SEEMS to be nonsense? No, it IS nonsense:

Stationary emitter, moving observer (receiver): http://www.einstein-online..info/ima...ector_blue.gif

The speed of the light pulses as measured by the emitter is

c = df

where d is the distance between the pulses and f is the frequency measured by the emitter. The speed of the pulses as measured by the observer is

c'= df' c

where f' f is the frequency measured by the observer.

Pentcho Valev