Stephen Hawking once held a dinner party for time travelers. He announced the date and time of the party after he held it and invited anyone capable of time travel now or in the future to attend. No one did. This suggests that time travel, at least into the past, isn’t possible. (I think it could just be that Hawking is a total bore and all the time travelers were washing their hair that night.) But that still doesn’t stop Hollywood from playing with the idea.
Some light spoilers ahead.