The Universe is a gigantic place, filled with potentially life-sustaining stars and, at latest estimate, trillions and trillions of habitable planets. So... where are all the aliens? This is what scientists call the Fermi Paradox, and this video created by design collective Kurz Gesagt provides the best explanation of it we've ever seen - in six minutes.
The reality is that, even if the Universe was teeming with alien civilisations, there's no way we'll ever know about them unless they exist in our Milky Way, thanks to the expansion of space. "Even if we had really fast spaceships, it would literally take billions of years to reach these places," the video above explains. So let's focus on the Milky Way.
Even here, in our own galactic neighbourhood, the chance of life is pretty high. There are roughly 10,000 stars in the Milky Way for every grain of sand on Earth, and one-fifth of them is estimated to host an Earth-like planet in the habitable zone. If only 0.1 percent of those planets harboured life? That's still 1 million planets with life in our very own galaxy. Why we haven't seen any signs of this life as yet is at the very crux of the Fermi Paradox, and it's something no one has managed to explain.
But there are some pretty good ideas out there, like the filter hypothesis, which predicts that there are large hurdles in the Universe that wipe out most life. We may have already passed these without noticing (which means we're pretty special), or perhaps we're yet to come up against them.
"For example, awesome future technology exists, but when activated it destroys the planet," the video suggests. "The last words of every advanced civilisation would be 'this new device will solve all of our problems once I push this button'. If this is true, then we're closer to the end than the beginning of human existence."
Yikes. But if you find that frightening, there's the alternative - in 90 billion light-years of Universe, maybe we're the only living organisms. Watch the video above to find out more about why that may be more likely than you'd care to think. And be prepared to feel insignificant.