The top of a tower of height h emits a light pulse downwards. According to Newton's theory, the pulse will reach the ground with speed

c' = c(1 + gh/c^2)

The frequency measured by an observer on the ground is, as shown by the Pound-Rebka experiment,

f' = f(1 + gh/c^2)

where f is the initial frequency (measured at the top of the tower).

We have

λ = c/f = c'/f'

That is, the wavelength of light is INVARIABLE in a gravitational field.

Pentcho Valev