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We live in a big Universe, billions of light years across. There are hundreds of billions of galaxies, and each one contains hundreds of billions of stars. Life happened here on Earth, and with countless other stars out there, you would think life would have arisen somewhere else. And yet, we have no evidence there’s any other life in the Universe. If life is common in the Universe, where are all the aliens. This is the Fermi paradox.
The Fermi Paradox was first described by the physicist Enrico Fermi. Even if we aren’t visited by aliens, we should see some evidence for them out in the Universe, or be able to detect their radio transmissions. And yet, scientists haven’t found a single piece of technology that wasn’t created by humans, or found a life form doesn’t share a common heritage with all life on Earth. There hasn’t been a single intelligent signal detected from the Universe.
Astronomers and scientists have been working to solve the Fermi paradox, and the easiest way is to just find evidence of alien civilizations. The Search for Extraterrestrial Intelligence, or SETI, involves scanning distant planets to detect alien signals. This research has been going on for decades, and no clearly intelligent signals have been discovered.
In the coming decades, astronomers will have the ability to directly image Earth-sized planets orbiting other stars and detect the presence of life there. If life is found, it provides more evidence that life is out there in the Universe; otherwise, the evidence may build up that we’re all alone.It should also be possible for a single civilization to create a probe that could travel to different star systems, replicate itself and send probes all the nearby systems. In just a million years or so, a probe could be delivered to every planet in the Milky Way. So where’s our probe?
What are some reasons for the Fermi paradox? Obviously the simplest answer is that we’re just the first intelligent civilization to arise. That’s seems unlikely, but maybe civilizations are so rare that there’s only one for every few million galaxies. There’s no way we’d be able to find each other and communicate.
Perhaps intelligent civilizations are doomed to destroy themselves. They reach a certain level of technology, develop weapons of mass destruction, and bring about their own extinction. Or maybe intelligent civilizations will attempt to destroy each other. Maybe they’re out there, but communicating in some way that we haven’t learned about yet, like with beams of neutrinos.
Another possibility is that aliens know all about us, but they choose not to interact with us. We’re in some kind of galactic zoo, and the aliens have agreed to leave us alone until we reach some point in our evolution. Or maybe they’re just too alien, and we couldn’t understand them if we tried. Maybe they’re here on Earth in disguise, all around us.
The Fermi paradox puzzles us to this day. Where is everybody?
Here’s a good article about the Fermi paradox, and here’s another.
We have recorded an entire episode of Astronomy Cast just about this topic. Listen to it here: Episode 24: The Fermi Paradox.