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? Not exactly. The idea that the observer starts moving towards light pulses and their speed relative to him remains unchanged IS nonsense. Brian Greene presents the nonsense quite well:

Brian Greene: What does it mean for the speed of light to be constant? https://www.youtube.com/watch?v=-Irlq3TFr8Q

The speed of light, as measured by Gracy (the receiver or observer), OBVIOUSLY VARIES with Gracy's speed. Here is Gracy running towards George (the emitter):

http://www.einstein-online.info/imag...ector_blue.gif

(Website: http://www.einstein-online.info/spotlights/doppler.html)

The speed of the light pulses as measured by George (the emitter) is

c = df

where d is the distance between the pulses and f is the frequency measured by George. The speed of the pulses as measured by Gracy (the receiver) is

c'= df' c

where f' f is the frequency measured by Gracy.

"Einstein wrestled with this problem over a lengthy period of time, to the point of despair"

means

"Einstein wrestled with his conscience over a lengthy period of time, to the point of despair".

And the conscience was defeated in the end.

Pentcho Valev