THE SPEED OF LIGHT VARIES WITH THE SPEED OF THE OBSERVER

When an observer starts moving towards a SOUND source with (small) speed u, the frequency he measures shifts from f=c/λ to f'=(c+u)/λ, where c is the speed of the waves relative to a stationary observer and λ is the wavelength.

Question: Why does the frequency shift from f=c/λ to f'=(c+u)/λ?

Answer: Because the speed of the waves relative to the observer shifts from c to c'=c+u:

http://faculty.washington.edu/wilkes...erference..pdf
"Sound waves have speed c, and f and λ are related by c=λf. For an observer moving relative to medium with speed u, apparent propagation speed c' will be different: c'=c±u. Wavelength cannot change - it's a constant length in the medium, and same length in moving coordinate system (motion does not change lengths). Observed frequency has to change, to match apparent speed and fixed wavelength: f'=c'/λ."

When an observer starts moving towards a LIGHT source with (small) speed u, the frequency he measures shifts from f=c/λ to f'=(c+u)/λ, where c is the speed of the waves relative to a stationary observer and λ is the wavelength.

Question: Why does the frequency shift from f=c/λ to f'=(c+u)/λ?

Answer 1 (fatal for Einstein's relativity): Because the speed of the waves relative to the observer shifts from c to c'=c+u.

Answer 2 (possibly saving Einstein's relativity): Because...

There is no reasonable statement that could become Answer 2.

Pentcho Valev