What force can cause red shift other than stellar movement?

Question

 The force that can cause red shift.

Answer 1

In addition to the Doppler effect in relative motion, a red shift can be caused by a gravitational field, according to General Relativity.  It can be observed when light travels form a strong gravitational field to a weaker field.  This effect has been measured in electromagnetic waves, and must be accounted for in navigation satellites such as the GPS constellation.  

Answer 2

From the Internet:

Some redshifts are an example of the Doppler effect, familiar in the change of apparent pitches of sirens and frequency of the sound waves emitted by speeding vehicles.