C
cavemann
Guest
Alfred, Brian, Cindy & David are trying to violate causality.<br /><br />Alfred and Brian are sitting in their flying saucers in interstellar space. Cindy and David are flying their flying saucers in formation at a constant velocity towards Alfred and Brian respectively.<br /><br />Alfred pulls out his handy-dandy FTL communicator (yes I know that FTL violates the current understanding of all physical laws, but this is a thought exercise. It would be impossible for me to enjoy carnal knowledge of Kate Beckinsale and her two identical triplets too, but that doesn't prevent me from thinking about it!) and sends a 3 second message to Brian. <br /><br />Because Brian is 10 light minutes away from Alfred, the FTL communicator needs 15 seconds to reach Brian from Alfred's position. <br /><br />Brian receives Alfred's transmission and immediately retransmits it to David whose flying saucer is just now passing by Brian's. The transmission from Brian to David is another 3 seconds (since they are so close the time for the FTL to reach from Brian to David is small enough for us to ignore) and David immediately relays this message to Cindy. <br /><br />Since Cindy is just passing Alfred while David is passing Brian, and since Cindy and David are following parallel courses, the time the FTL needs to reach from David to Cindy is another 15 seconds. <br /><br />Cindy then relays the signal to Alfred (again with negligible signal travel time) adding another 3 seconds to the round about trip of this signal.<br /><br />So that's 18 seconds from Alfred to Brian, 3 seconds from Brian to David, 18 seconds from David to Cindy, and 3 seconds from Cindy to Alfred again for a total of 42 seconds (the answer's always 42 isn't it?).<br /><br />Could somebody please explain to me why using the mythical FTL communicator in this scenario will create the paradox of Cindy sending Alfred the signal before Alfred sends it to Brian?<br /><br />Much obliged <br />