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.
2017
2013
2022
2007
2011
1910
1911
2021
2010
1984
2018
1976
2023
1953
1989