Are we alone in the Universe?

Science fiction writer Arthur C. Clarke - the man who, in 1948, first conceived of the communications satellite - addressed the question of whether we are alone in the Universe. In the book Visions : How Science Will Revolutionize the Twenty-First Century (1999) by Michio Kaku, he is quoted as saying:

Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying.

I agree.