(Original Review, 1980-12-03)
There is yet another possible method of time travel which was used in Williamson’s novel (made up of two novellas: “Legion of Time” and “After World’s End”). This version takes time travel to its logical conclusion when you take quantum mechanics into account. At any given point in time, there are several possible "futures". Each of these futures has a certain probability attached to it. As "time" progresses, one of these possible futures approaches 100% probability, and thus becomes "reality".
If you're into stuff like this, you can read the full review.