The Fermi Paradox: Is there life out there?

Have you ever wondered if Star Trek is right—that there is life somewhere out there in the universe? And not just life, but intelligent life capable of creating civilisations and building technology beyond our imagination. I definitely had, so imagine my excitement when my 9am lecture brought discussion of aliens and their existence. Let me introduce you to The Fermi Paradox.

Credit: Greg Rakozy via Unsplash

Named after Enrico Fermi, a Nobel Prize winning physicist, the Fermi paradox is the discrepancy between the sheer magnitude of the universe, and thus the very high certainty that there is life out there, and the fact that we have not found any evidence of this life yet. This particular problem has baffled scientists since it was posed in the 1950s, and still, we do not have an answer.

The basis for this paradox is the high chance of the universe being peppered with life. To explain this, it’s helpful to look at the Drake equation. This famous equation uses a number of parameters to work out how many civilisations are in our galaxy with which humans could communicate. The equation amalgamates the rate of star formation, the fraction of stars with planets, and the fraction of those planets that could support life, have developed life, and have developed intelligence. It also incorporates the fraction of intelligent life that developed communication, and the length of time a civilisation can communicate for. All these parameters are multiplied together to give an idea of the number of communicating societies that are out there. These parameters are not ones we have actual numbers for so any “solutions” to the Drake equation are merely hypothetical. Nevertheless, scientists have put forward their estimates. These have a huge range from much less than 1 to over 25 million civilisations being present for us to communicate with in the Milky Way. If the Drake equation is correct, there is somewhere between 1 and 25 million civilisations out there, and because Earth is actually quite young (4.5 billion years old compared to the universe’s 14 billion years) and life on Earth is even younger, chances are that these intelligent civilisations have been around for a while. This gives them plenty of time to develop interstellar travel and come give us a visit; even at a slow pace, the Milky Way could be traversed in just a few million years. So, why have we not seen the aliens yet? This is a hotly debated topic, with most scientists having their own opinion of what may or may not be true. A first solution is simply that life is very rare. If life, even of the unicellular variety, does turn out to be a rarity in the universe then maybe there is no other life out there for us to find. A unique set of conditions are needed for life to develop. As far as we know (and the only basis we have for this is what life looks like on Earth), life needs an energy source, a liquid solvent to dissolve everything, and the correct molecular building blocks to form. Perhaps these exact conditions have not occurred anywhere else in the galaxy. To further that, if life did manage to evolve elsewhere it may not have managed to evolve to the point of intelligence and therefore cannot communicate with us. An alternate theory is that life is all around us, but we haven’t seen it yet. A lack of evidence does not mean an absence of any. One suggestion as to why we haven’t had any alien contact is that we are in the wrong place in the universe to see it. Imagine the Milky Way as a country and Earth being in the countryside. The rest of life is concentrated together “in the city” and just hasn’t ventured out to see us yet, and maybe has no plans of ever doing so.

The Drake Equation (Credit to Google)

Another theory along these lines is that super-intelligent life did exist, but it existed a long time ago before humans evolved, so we never got the chance to see it. This can be brought further saying that the alien life existed before the limit of recorded human history around 5,500 years ago. It seems like a long shot but maybe humans did see aliens and it’s just that no one wrote it down - this is sometimes referred to as the ancient astronaut theory.

Another option, a little more unorthodox, is that there is some technologically advanced predator civilisation that roams the universe. All the other civilisations in the Milky Way know better than to broadcast signals out into space that could alert this predatory society as to where they are. This would, in theory, explain why we have not heard any communication from extra-terrestrial life. The possible existence of this super-predator has led to heated debates regarding whether humanity should be broadcasting out into space. On the one hand, it would be exciting if we got a reply, but on the other, we don’t want some predator civilisation to find (and destroy) us.

Maybe Star Trek had it right with its prime directive, the aliens are not allowed, or just don’t wish, to make contact with us. Or maybe they don't want to be found by us so are bamboozling (a word used in this context by one of my professors) us to make us think they aren't there. Or maybe we are not yet technologically advanced enough to read or interpret the signals they are sending out. All of these explanations are technically just as valid as each other as we don’t know the true answer. In recent years, scientists have continued to look for life beyond our planet The Jupiter Icy Moons Explorer (JUICE) and Europa Clipper missions, for example, are set to investigate Jupiter’s icy moons, particularly Europa and Ganymede, for evidence of life in the coming years. Scientists at the SETI institute have had the aim of detecting extra-terrestrial life since as far back as 1984 and the Breakthrough Listen project, which has recently moved its headquarters to Oxford, is searching our galaxy for technosignatures (signals out in space that could only be created by technology, not natural phenomena) as we speak.

Despite this, and 60 years on, the famous Fermi paradox remains unsolved. As humanity continues to advance its technology and venture out into the universe maybe that will change. Or maybe humanity will not survive long enough to ever know the real answer. For now though, the topic remains one to spark debate amongst scientists, inspire sci-fi movies, and excite students in lecture theatres around the world.