In the summer of 1950, physicist Enrico Fermi posed a simple question to his colleagues over lunch: "Where is everybody?"
Fermi was referring to alien life in the universe.
Arguably, he said, in the 4.4 billion years it took for intelligent life to evolve on our planet, the rest of our galaxy should have been overrun with similarly smart, technologically advanced aliens. But despite decades of searching the Milky Way for signs of extraterrestrials, we haven't found anything or anyone.
This conundrum has come to be known as the Fermi Paradox.
Scientists have offered myriad potential answers to the question, including that aliens are hibernating or deliberating hiding from us. Some researchers have also suggested that highly advanced technological civilizations destroy themselves before they have the opportunity to get in contact with other intelligent life in the universe.