Another thought. The verse says 'the fool has said in his heart' ...not his mind.
The verse doesn't only apply to atheists but theists who haven't accpeted Christ as Saviour. We can easily recognise God in our mind. The real foolishness comes when we welcome the interlectual ideas of God and don't bow to Him being Lord in our hearts. The opinion of our mind towards the reality of God doesn't make any difference. The heart and the mind must both testify to God.