I bet those guys are PhD's...which means this illustrates a temporal ...paradox...pair of docs
More accurately, those guys would no longer exist. Each of us are the result of billions to one odds.
Our mom and dad are the result of their moms and dads meeting which were the result of their moms and dads meeting and marrying.
Then, that exact spermatozoa had to permeate the exact egg in the exact day and time that it did for us to exist.
The odds against it are astronomical.
Something as disruptive as killing Hitler would change everything. The odds of recreating the scenario where your parents meet and marry and copulate on the same day with the same sperm meeting the same egg are infinity to one (basically zero odds).
So if you go back in time and kill Hitler, you would no longer exist.
And if you do not exist, then how did you manage to go back in time and kill Hitler?