I’m asking this because there is a scifi book I’m reading, and in the book there’s a scene where someone is communicating with a person in a spacecraft moving at lightspeed. I know their ability to communicate would probably not be possible, but let’s just put that aside for a second. Hypothetically, if you could communicate with someone moving lightspeed, would the time dilation make it so that they would appear to be moving and speaking very slowly relative to you?
That only works if you are speaking through the same medium. The sound waves compress or elongate. If you are talking to someone on a spaceship, the conversation would presumably be transferred from analog, to digital, back to analog, like a phone call. It’s not like if you call someone on an airplane you hear the Doppler Effect on their voice.
That gave me a hilarious image in my head thinking about a Doppler shifted phone call from a plane.