With the universe so vast, why haven't we heard from the other intelligent life that must supposedly be out there?

Darwin's extraterrestrials, the Fermi paradox, all attempt to explain things, and are set forth quite nicely in this article. The comments are just as good as the article itself.

My take on this question is that what scientists define as " intelligent life" has only existed on the Earth for the past few thousand years, an absurdly short period of time. In addition, the ability to even listen for evidence or extraterrestrial life has existed for about a hundred years, generously defined. Is it any wonder that we haven't detected anything yet? We probably don't even know what to listen for, or how to listen.

After you chew on that one for a while, consider the proposition, gaining more and more favor among physicists, that the universe began as a one dimensional line!