# Is Time Dilation in Special Relativity Similar to the Doppler Effect?

• I
Does time dilation in Special Relativity relate to the Doppler effect? If you move near the speed of light you experience time differently and the sound is stretched. Are these similar phenomenon?

Mentor
Sometimes time dilation is called the transverse Doppler shift, so they are related. But the relativistic Doppler is a different formula than the classical Doppler, and the difference is precisely the time dilation. In other words, classical physics predicts no transverse Doppler, but relativity does.

Gold Member
2022 Award
One has to distinguish two cases: (a) Doppler effect for em. waves in the vacuum and (b) Doppler effect of other waves like sound waves. Case (a) is special, because here the Doppler effect only depends on the relative velocity beween transmitter and receiver, while in case (b) there is a preferred reference frame, the (local) rest frame of the medium the wave propagates in (for sound waves, e.g., the air). In all cases time dilation is part of the Doppler effect. In case (a) the transverse Doppler effect, i.e., the observer measures light emitted perpendicularly to the velocity of the source, is purely due to time dilation. For details, see

https://itp.uni-frankfurt.de/~hees/pf-faq/rela-waves.pdf

Dale
Staff Emeritus
Gold Member
"classical" Doppler effect is a result of the changing distance between observer and source (it also relies on a medium, so it makes a difference as to whether it is the source or observer which is moving relative to the medium.)
Relativistic Doppler effect also has a component which depends on the changing distance between observer and source. The difference is that with classical Doppler shift, if you factor out the effect caused by changing distance, you end up with no net time difference, but with Relativistic Doppler effect, when you factor the changing distance out, you are still left with a time difference, which is the time dilation.

vanhees71