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
1914
2015
1939
1983
2013
2021
1932
2019
1920
—
2008
2020
2005
2011