However, Thorne solved an apparent problem that could arise due to time travel (within the limits of general relativity). The “grandfather paradox” involves going back in time and accidentally killing his grandfather before his father is conceived, preventing his own birth, making it impossible to go back in time and kill his grandfather. Thorne discovered that for point masses passing through a wormhole, there are no initial conditions that create this kind of paradox.
That’s good news for anyone concerned about people coming back and changing the past at will, but bad news for any Whovian hoping to reverse the decision to cancel the show in 1989 and avoid a 16-year hiatus. That would probably go beyond even the Doctor himself.