It is inconceivable that we are the only intelligent life in the universe, nearly impossible to believe that we are alone even in our galaxy. But the distances involved are immense. The Milky Way is 100,000 light years across. Imagine receiving a radio signal from a civilization, say, just 10,000 light years away. The civilization producing the signal could be long gone by the time we received it. And our response would be received - if there was anyone left to receive it - 20,000 years after the original signal was sent. That's a long time between, "hi there" and "s'up?"

Not in my lifetime, but at some point. Hard to imagine that we're the only intelligent life.