I must say this is the question of the week asked by Tamy (Canada), as usual I never thought about such question, I am not that great to come up with such great questions but lets look at this one and try to answer it.
I must say the question should have been “why the earth keeps spinning?”
Well Tamy this is one of those puzzling questions human race has been trying to solve for ages and ages. But to give this a try, there is nothing to stop the Earth from spinning. I do not know or in fact I should say, we do not know why it started. I think the matter that fell in to create the planet after the Supernova must have been spinning, as it fell in and the planet formed, may be the spinning increased gradually over time which is what we have today. Only the tides slow it down nothing else.
Will it spin forever? I am not sure, I guess that is left for the day to come when we will find answer to many puzzling questions related to our universe.