http://www.newsweek.com/avengers-endgame-time-travel-quantum-mechanics-explained-scientist-1405522

At the end of Avengers: Infinity War half the people (including heroes and villains) in the universe were gone in the snap of a finger from Thanos (Josh Brolin).

So how can Avengers: Endgame (in cinemas from this week) try to bring them back?