Why Haven't We Heard From Aliens Yet?

During the summer of 1950, physicist Enrico Ferm posed a question to his colleagues over lunch, "Don't you ever wonder where everybody is?" Fermi was referring to alien life. In the 4.4 billion years it took a species capable of space travel to form on Earth, Fermi proposed that the galaxy should have been overrun with intelligent, technologically-advanced aliens. Yet, we have no evidence of this despite decades of searching. This conundrum became known as the Fermi Paradox. Scientists have proposed many theories over the decades, including planetary scientist, Alan Stern, who has the latest idea.