Does the following argument prove that any method of faster than light communication is impossible? 1. A transmitter sends a signal at 12:00 from point A to B faster than light by some hypothetical method. 2. A transmitter at point B is moving at a high speed (but less than speed of light) relative to A. When it receives the signal, it sends a reply signal faster than light back to point A. 3. Receiver at A detects the reply at 11:00 - before original signal was transmitted. According to special relativity, this backward in time effect can always be set up using a pair of superluminal signals. 4. Electronic mechanism is set up to turn off the transmitter as soon as receiver detects a signal. 5. If a signal is received at 11:00, then no signal can be sent at 12:00. If no signal is received at 11:00, then a signal is sent at 12:00. A paradox is created. If no original signal is sent, then how can you get a reply? If no reply was received, then what happened to the original signal? This is a version of the "grandfather paradox". 6. If a theory has a logical contradiction in it, then it is not self-consistent. So it must be rejected on logic alone. No experiments are needed. Therefore, the theory that some form of faster than light signaling exists must be false. This argument would prove not only that all current ideas for superluminal signaling are impossible (wormholes, warp drives, quantum mechanisms) but also that all new clever ideas that will be thought of in the future must be impossible too. Did I make any mistake in logic? Did I make any unproven assumptions? What is your opinion??