# Communication at a near-light speed

• I
So, I've been wondering: how would time dilation affect communications?
For the sake of visualisation, imagine the Flash is running at 99% the speed of light in a circle around a fixed position. There's a building in this position, and inside this building are his friends. Due to time dilation, they should be experiencing time at different rates. Assuming the usual problems(wind muffling comms, drag etc.), are a non-issue, and that he is talking to his friends through conventional radio communications, would others perceive him to be talking much slower than normal, if, from his perspective, he was talking at a normal rate? If so, at what rate would he have to talk to be able to communicate with them?

If you'd prefer, you can swap the Flash for a spaceship and the building for an asteroid; like I said, it's just to help with visualisation.

Orodruin
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Well, to start off, his friends would have to tune their receiver differently as the radio signal would be affected by relativistic Doppler shift. Exactly what would be observed depends on the direction the Flash is running in.

phinds
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So, I've been wondering: how would time dilation affect communications?
For the sake of visualisation, imagine the Flash is running at 99% the speed of light in a circle around a fixed position. There's a building in this position, and inside this building are his friends. Due to time dilation, they should be experiencing time at different rates. Assuming the usual problems(wind muffling comms, drag etc.), are a non-issue, and that he is talking to his friends through conventional radio communications, would others perceive him to be talking much slower than normal, if, from his perspective, he was talking at a normal rate? If so, at what rate would he have to talk to be able to communicate with them?

If you'd prefer, you can swap the Flash for a spaceship and the building for an asteroid; like I said, it's just to help with visualisation.
Taking the spaceship case, the Lorentz factor for 99% of c is about 7. You take it from there.

robphy
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Draw a spacetime diagram with a sequence of periodic transmissions.
Note the receptions.
As mentioned by @Orodruin , this involves the Doppler Effect.

m4r35n357
Draw a spacetime diagram with a sequence of periodic transmissions.
Note the receptions.
Seriously, do this.

PAllen