How is Qur'an 13:15 justified?

> And unto Allah (Alone) falls in prostration whoever is in the heavens and the earth, willingly or unwillingly, and so do their shadows in the mornings and in the afternoons. 13:15 http://quran.com/13/15 http://tanzil.net/#13:15 But, there are a lot of people who don't care to fall in prostration to Allah. Taking the worst case example of atheists. So, where am I going wrong? Interested in Sunni explanation.