Asymmetries in relativistic information flow

In the so-called "twin paradox" of relativity theory, one spaceship leaves another at velocity v = ftc and returns to find that the other ship has aged more by a factor . The asymmetry is first isolated in order to resolve the paradox. Then the principle of relativity is used to derive the relative aging factor and the relativistic Doppler shift. Using the Doppler factor, asymmetries in information transmission between moving spaceships are investigated. An additive white Gaussian noise channel with Shannon capacity is considered. After accounting for the effect of the relativistic Doppler shift on signal power and bandwidth, it is found that for a given transmission rate and bandwidth, the traveler needs times the energy of the stationary spaceship to transmit times as much information. The asymmetry in efficiency is thus . A simple proof is given that the round trip asymmetry in efficiency for constant-rate transmission is always the square of the relative aging factor for all trajectories regardless of accelerations and the presence of gravitational fields.