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.
2025
2011
2023
2024
2005
1930
1990
1996
1995
2017
2022
—
2016
2002
1983