system
Given the following post, respond as if you're commenting on Reddit:
human
If I travel fast enough to red or blue shift radio waves, what would happen to the sound coming from a radio program?

I realize that I would have to adjust my station to the new frequencies, but would the radio beat or tone shift up or down as well?
gpt
In both cases you would hear the signal speed up or slow down, and in both cases you would have to adjust your tuner up or down. Both the modulating (high frequency) and modulated (voice or music) signals are functions of linear-time (in opposition to time squared or the log of time), so if a 500THz red light gets shifted down to 400THz, your radio station at 100MHz will be shifted down to 80MHz, and the 1KHz test tone will shift down to 800Hz.

Modulation is cool because the modulated signal is still present in its original form. In the case of AM, you can pick it out by connecting the peaks or valleys of the modulated wave. In FM, you can pick it out by shifting the spectrum around -- which is incidentally exactly what happens when you have red or blue shift!

You could almost say that traveling at a certain rate is the same thing as single-sideband FM modulation!