It is called the Time Traveler's Paradox. In which a scientist creates a Time Machine and kills their younger self. So now a man who should not- can not- exist, somehow does. That is the Paradox, and Paradoxes are impossible.
2016
1938
2019
2007
2017
1923
1918
1993
2018
1928
2024
1898
2001
2014
2022
