10 Infamous Movie Plot Holes That Have Simple Explanations

The "Plot Hole"

Why doesn't Harry (Daniel Radcliffe) just use a Time-Turner to go back and prevent Voldemort's (Ralph Fiennes) rise before he became a threat?

The Explanation

Though time travel is very much a device which is difficult to put back in the box once used, J.K. Rowling at least had the benefit of fantasy contrivance on her side.

Beyond both the books and the films making a pains to emphasise the dangers of using the Time-Turner, and Hogwarts' supply of Time-Turners being destroyed in The Order of the Phoenix, the Wizarding World is a deterministic universe, where the past is fixed and the Time-Turner can only be used to do things which were always going to happen anyway.

As such, attempting to use it to eliminate Voldemort would likely cause a nullifying paradox of some kind which stops it from happening.

The books further acknowledge that tampering with the laws of time can cause irreparable damage to the universe. According to Professor Croaker's law in The Cursed Child, "the furthest someone can go back in time without the possibility of serious harm to the traveller or time itself is five hours," even if the play does also admit the existence of illegal Time-Turners not bound by this restriction.

Basically, even stopping a being as destructive and powerful as Voldemort isn't worth potentially destroying the universe. In Rowling's own words:

"I solved the problem to my own satisfaction in stages. Firstly, I had Dumbledore and Hermione emphasise how dangerous it would be to be seen in the past, to remind the reader that there might be unforeseen and dangerous consequences as well as solutions in time travel. Secondly, I had Hermione give back the only Time-Turner ever to enter Hogwarts. Thirdly, I smashed all remaining Time-Turners during the battle in the Department of Mysteries, removing the possibility of reliving even short periods in the future."