This goes back a bit before "our time", but... death. Or rather, the fear of death, and its first-born child, anxiety. All problems are derivations of this. Without it, what could possibly trouble a person?
GOOD ANSWER! Life goes on ... gloriously, if looked at from the correct angle (and it doesn't even have to be "correct")
That aside,... We can all easily dismiss the problems in the world by invoking the intergalactic prankster, my question was genuine, WHAT IS THE DEFINING PROBLEM OF OUR TIME, WHAT SAY YOU?