The quantum mechanics of Avengers: Endgame touches on modern scientific ideas about quantum time travel and the possibility of wiping out the Grandfather Paradox.
Instead of time travel effecting your current future like the Grandfather Paradox, Avengers: Endgame goes with an alternative reality idea, which is based on the Many Worlds Theory.
Avengers: Endgame contains talk of quantum mechanics, Deutsch propositions, The Planck scale, eigenvalues, and inverted Mobius strips, which are all based on real science.
It’s no secret that the Quantum Realm was going to play a role in Avengers: Endgame.