Here's why it's so weird that we haven't found aliens yet

In our observable universe there are about 100 billion galaxies, each with 100 to 1,000 billion stars - and based on what we've learned about planets, there are probably trillions and trillions of habitable ones out there.

So, to ask the question in the words of Nobel-prize winning physicist Enrico Fermi: "Where is everybody?"

Why haven't we encountered any evidence for extraterrestrial life? With so many potential places for it to arise, it might seem incredibly strange that we haven't found it - or that it hasn't found us.

This puzzling question, named the Fermi Paradox after our aforementioned physicist, isn't just strange - it's terrifying.

For an excellent explanation of the Fermi Paradox, check out this fantastic YouTube video by Kurz Gesagt, which we first spotted on io9:

Think about it. Even if life is incredibly rare, it should have arisen somewhere in our galaxy alone in the past 11 billion years. (Not 13 billion years, because the first 2 billion were very hostile to life.) As the video explains, if only 0.1% of potentially habitable planets in our galaxy harbored life, there should still be a million planets harboring life.

So if we haven't encountered life, what does that mean?

Is life much less likely to develop than we think? Was the early universe more hostile than we think?

Or have we just not hit the point yet where civilizations end up destroying themselves - something known as a "Great Filter" - to know any better?

Definitely watch the full video above, and you can check out some of the potential solutions to the Fermi Paradox in another Kurz Gesagt video, too.