Hi Dale:There is no universal clock because there is no frame-invariant definition of what "instant" means. That is an essential part of relativity regardless of if you have FTL or not.
I am not sure I am understanding this discussion, but I would like to ask a question.
Imagine a train of carriages, each with a technologically identical clock. Imagine this train is moving at a constant speed on a circular track. Assume the track itself is stationary. Imagine in the exact center of the track is another same kind of clock. The center clock periodically broadcasts a signal identifying the current time on the center's clock. When each carriage clock receives the broadcast, it makes an immediate acknowledgement response. The center clock checks that all of the acknowledgement returned signals arrive simultaneously, and also notes the time it took for the round trip of signals. The center clock includes with the time signal a message (1) confirming all of the round-trip times of the carriage returned signals are identical, and (2) that the message also communicates the time(on the center clock) the signal was sent, and (3) the amount of time the round trip signal took. Each of the carriage clocks for itself confirms for each received message, that the time on the carriage clock is exactly equal to the time given in message from the center clock plus one-half of he round trip message travel time.
Is it correct, or is it not-correct, to say that all of he clocks involved are synchronized?