While I'm here, I have another question that I don't know if has ever been adressed. I know the show has been on for 50 years. However, has it been established how long each incarnation of the Doctor has survived? If it's been real time, then the first Doctor would have lasted nearly 900 years, but the other 11 would have each lasted a fraction of 50 years each, which really isn't all that long. Of course, with all that pesky time travel, is there any way of knowing how long each particular Doctor lasted before regenerating?