Are we the only intelligent life in the universe? Here's how we intend to find out.

The search for extraterrestrial intelligence (SETI) got a boost in July 2015, when investor Yuri Milner and physicist Stephen Hawking (left) announced a new $100 million SETI initiative called Breakthrough Listen.

The first serious, scientific attempt to listen for alien radio signals was Project Ozma in 1960, conducted by astronomer Frank Drake.

Since the invention of radio in 1900, researchers have occasionally detected unexplained signals that have led them to wonder about the possibility of life on other planets. In the 1960s, robotic probes revealed that the other planets of this solar system are not compatible with advanced civilizations. The many other planets and moons in the Milky Way galaxy and in billions of other galaxies in the universe still provide hope for the discovery of alien civilizations.

Popular culture often depicts unidentified flying objects (UFOs) as alien spacecraft and bizarre ancient artifacts as evidence that alien beings visited the Earth in the distant past. Scientists, however, have never found evidence that either of these things have ever occurred and do not take alien UFOs and ancient astronauts seriously.

Astronomer Frank Drake created an equation to estimate the number of intelligent, communicating civilizations currently living in the galaxy.