Hollywood has made billions of dollars producing movies about aliens and potential intelligent life in space. And the US government has spent billions of dollars exploring our galaxy for signs of intelligent life.

We haven’t found it yet at least as far as we know. If we did find it, would it be a cause for celebration or concern?

Senior Astronomer at the Search for Extraterrestrial Intelligence Institute Seth Shostak joins William Shatner on this week's episode of 'I Don't Understand' to explain why haven't we found life in space.