We’ve probably already been discovered by aliens, but they have some pretty good reasons to hide.

Neil deGrasse Tyson, an astronomer and science communicator, explores the issue of why extraterrestrial life hasn’t made contact with Earth in the sixth episode of Pop Mech Explains the Universe. The terrifying Fermi paradox suggests that aliens may have known about humans for a very, very long time.

It’s unlikely that an alien will greet you.
We could cross the Milky Way Galaxy in a million years if we could move at 10% the speed of light. It is conceivable that a highly developed alien society is already doing this while cruising through a sizable chunk of the galaxy. According to Tyson, who speaks to Popular Mechanics, “a million [years] is little, compared to the time life has been on Earth.”

So why have they not gotten in touch?

Enrico Fermi, an Italian scientist, speculated in the middle of the 20th century that if you learn how to travel among the stars, you might begin colonising other worlds. Once you do that, your population grows throughout the galaxy and you only get better at it.

He has a few ideas for remedies. One is that, regardless of how brilliant your species is, space travel may be a very tough task. Or, perhaps—and this is where we shift uncomfortably while nodding with wry smiles—they visited us but concluded that we weren’t smart enough to bother dropping a line.

There’s yet another chance. There may have been several groups who had made progress on other worlds, but, like human groups from various Earth nations seeking to settle the same exciting “new” regions, the aliens ran into people who had previously settled on those “new” planets. No alien ever really made it to Earth because of disputes and violence. Remember that there are likely more planets than stars in the galaxy, so the likelihood that you’ll find a specific one is low.

“The competition over property, or real estate, that we’ve witnessed on Earth might theoretically occur among aliens. The system collapses as a result of that. Since they are unable to get along, Tyson claims. He finds the result intriguing.