Philosophy
The Metaphysics of Time Travel and the Grandfather Paradox
Quick fact
The grandfather paradox was formally discussed by philosophers like David Lewis in the 1970s, and the Novikov self-consistency principle—named after physicist Igor Novikov—suggests that the laws of physics would prevent any such contradiction from occurring.
Why this is interesting
What if you could travel back in time and stop your own grandfather from ever meeting your grandmother—but then how could you exist to do it?