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.
2010
2021
1973
—
2018
2020
2013
2019
2014
2005
1942
1914
2015
2023
2008