- #1
Jano L.
Gold Member
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It is often said that superluminal communication is prohibited by special theory of relativity.
Do you think this is true? I have doubts about this claim.
Imagine a communication between two astronauts in two distant inertial frames A,B with any mutual velocity.
Suppose that both astronauts have one part of a special communication device on their ship. One part is used in the same way as ordinary receiver and transmitter, but when A asks simple question that B can answer, like "What's the time in your ship?", A hears the answer, say "10 a.m." from B immediately, with no delay and with no speech slowing down; the debate goes on as if the two were in the same room. The same happens in B; the whole thing proceeds like subspace call in Star Trek.
Most of you will probably protest at this point, saying relativity does not allow this because when we look at things from a third moving frame C, everything becomes nonsense.
Let's see.
The simplest case to discuss is when A,B are distant but in mutual rest. Judging from this frame, the debate of A,B looks innocent.
Now imagine observer in frame C moving past both A,B with velocity u, who reconstructs the course of the dialogue in his temporal frame. How does the debate look to him? He will find that in HIS time coordinates the times of questions do not match times of answers, but are systematically shifted by some (perhaps long) time interval. The mutual synchronization will be lost; the events that were almost simultaneous in A, B will become separated by some delay. In particular, the answer "10 a.m." may be spoken BEFORE the corresponding question "what's the time" was asked.
Does this relativity of ordering look as a contradiction to STR to you? Or is it only contradiction to daily expectation that the answer occurs after the corresponding question?
Do you think this is true? I have doubts about this claim.
Imagine a communication between two astronauts in two distant inertial frames A,B with any mutual velocity.
Suppose that both astronauts have one part of a special communication device on their ship. One part is used in the same way as ordinary receiver and transmitter, but when A asks simple question that B can answer, like "What's the time in your ship?", A hears the answer, say "10 a.m." from B immediately, with no delay and with no speech slowing down; the debate goes on as if the two were in the same room. The same happens in B; the whole thing proceeds like subspace call in Star Trek.
Most of you will probably protest at this point, saying relativity does not allow this because when we look at things from a third moving frame C, everything becomes nonsense.
Let's see.
The simplest case to discuss is when A,B are distant but in mutual rest. Judging from this frame, the debate of A,B looks innocent.
Now imagine observer in frame C moving past both A,B with velocity u, who reconstructs the course of the dialogue in his temporal frame. How does the debate look to him? He will find that in HIS time coordinates the times of questions do not match times of answers, but are systematically shifted by some (perhaps long) time interval. The mutual synchronization will be lost; the events that were almost simultaneous in A, B will become separated by some delay. In particular, the answer "10 a.m." may be spoken BEFORE the corresponding question "what's the time" was asked.
Does this relativity of ordering look as a contradiction to STR to you? Or is it only contradiction to daily expectation that the answer occurs after the corresponding question?