Message #104015

[Nyki2]

If they developed time travel (even unreliable time travel) in the early 22nd century, why didn't they have it further in the future?  Like the 25th century, when the Doctor met Vicki?  Or the 40th century?  Though they did have it by the 51st, of course. 

I know, I know, time is in flux, but still...