Why explore space ?

Knowledge of this, certainly, is not gonna feed you or me in our life time. But, I thought it worthwhile to know why billions of dollors go into space programs, when humanity has grave social problems right here on earth.

With Columbia having had its brush with doom, and as the debate rages over the future of space exploration, I came across www.spaext.com that gives compelling arguements of some great astronomers and thinkers like Stephen Hawking, about why space exploration has go on braving all failures and criticism.