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?
If you were stationary, and talking to someone moving at lightspeed, would they appear to be speaking in slow motion due to time dilation?
5 months ago by a_gee_dizzle to c/askscience
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shoomemer 5 points 5 months ago
If we assume that the person moving at light speed is going in circles about the stationary person instead of linearly away. Would the radio waves be doppler shifted if transmitted orthogonally?
Onomatopoeia 3 points 5 months ago
Ooh, interesting point.
I suspect all EM would be shifted according to the angle relative to the target - so at exactly 90° It would be "half shifted" - or zero. (Assumption based on blue/red shift of light).
I'm assuming the traveler is at a percentage of C, not at C (I think being at C is a completely different scenario, like would any EM escape the traveler?).
But I'm only an armchair quantum physicist (I've read a few books over the years). Look forward to what someone who understands Quantum Weirdness has to say.
frongt 0 points 5 months ago
One would have to be orbiting the other. I don't think you'd get any doppler shift in that signal, because the distance between transmitter and receiver remain constant.
The fun part of that scenario is that emitted photons carry momentum from your motion. If you're moving at a significant fraction of the speed of light, hopefully you're using an omnidirectional transmitter.
Edit: hmm. I wonder if Terrell rotation comes into play here. Probably not in terms of the actual transmission, but it certainly would in terms of placement of a transmitter on a spacecraft.
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So, I would assume that you would be communicating through radio waves. If an object broadcasting a signal moving at the speed light away from you, I would further assume you experience a severe Doppler effect. To the point that I don't think you would experience anything coherent. You would receive small packets of information at a time, scattered across several million years.
This is just my initial impression on the fly, do not take this as any sort of gospel. I also did some communcations work for a time. So, this is tickling my brain and I might spend the rest of my evening in my books.
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