If now

If nobody had any child how long it would take to decrease the population on planet Earth 20%? Would you live better or worse or the same with 20% less of population?. I am a psychologist and rational thinker and I help people survive. My truth is atheism is a logical fallacy that assumes God is the religious idea of the creator of the creation to conclude wrongly no creator exists because a particular idea of God doesn’t exist. Thank you.