Tennis Player Gets Public Confused With Autograph About The Fermi Paradox

People were, of course, confused. Atmane finished last year as number 158 in the world, but in Cincinnati, he has beaten two players in the top 10, Taylor Fritz (number 4) and Holger Rune (number 9). It is unclear if the comment was about his performance, the performance of his rivals, or if he just wanted to reflect on the possibility of life beyond Earth.

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What is the Fermi paradox?

Astronomy is underpinned by the idea that the conditions for the Sun, the Earth, and us are not unique. Just like we cannot consider the Earth or the Sun at the center of creation, we cannot imagine that the vast universe was made specifically for us and only us. Basically, we are not special. With that in mind, the conditions for life should be widespread.

This topic is brought up again and again in many conversations. There are billions of stars like the Sun, we know that planets are common and many orbit the habitable zone of their star. One particular conversation involved Enrico Fermi when he visited Emil Konopinski, Edward Teller, and Herbert York at the Los Alamos laboratory.

The four were talking about the possibility of flying saucers and faster-than-light travel, and it is reported that Fermi asked a very simple but very profound question: Where is everybody?

It is a fair question. If the conditions for life are common, and we need to assume nothing about us is special (including the ability for a civilization to develop technology), and given how many planets we expect exist in the Milky Way, then it is very legitimate to ask why we have not found an extraterrestrial civilization. We currently do not have a solution to this – it wouldn’t be a paradox otherwise – but several hypotheses have been put forward.

Possible solutions to the Fermi paradox

The Rare Earth hypothesis: Maybe we are special

The simplest explanation, and one that can take many possible forms, is that maybe we are special. This could mean that life in general, complex life, civilization, and the ability to develop technologies that would allow us to communicate and discover extraterrestrial civilizations could all be unique to us. So we might be alone for multiple reasons, or we might not, but they are not going to find us because we would be hard to discover.

The best test of this multifaceted hypothesis is to keep studying worlds in the Solar System and exoplanets. Whether we find conditions suitable for life or not, it might better refine what might make us special.

Aliens do not think about expanding or finding others

As far as we can tell, we can’t travel close to the speed of light or faster, which means it takes a very long time to visit another star system. It might be possible that there is undiscovered physics that would make that sci-fi dream a reality, but maybe it is simply not the case. 

If a civilization were serious about spreading around the galaxy, even with slow-moving ships, it could eventually be everywhere. If a generational ship were to be launched first from an original star system, then from every settled one, every 100,000 years, travelling no more than 10 light-years, it would only take 1 billion years for those aliens to be everywhere in the galaxy.

Sure, big numbers, but it shows the power of exponential spreading. So where is everyone? Maybe they do not want to travel and settle another world. If we wanted to do it, it would be an extremely costly, very dangerous, and difficult endeavor for an uncertain return.

Maybe aliens feel the same. Or maybe they just do not care about traveling into space to other star systems.

The Zoo Hypothesis: We are in a galactic zoo

For the fans of Star Trek out there, one of the solutions to the Fermi paradox is the Zoo Hypothesis. Basically, alien civilizations are non-interventionists, leaving civilization to develop past a certain threshold before the aliens make themselves known.

Thanks to hypothetical technological advantages, alien civilizations would make themselves invisible to us. To test this, we need to consider possible ways aliens might hide from us or ways they couldn’t hide from us and keep testing them – or just work out the standard to be finally admitted to the United Federation of Planets.

The Dark Forest hypothesis

This is a dark twist on the galactic Zoo Hypothesis, and it is also used in sci-fi. The name is based on Liu Cixin’s 2008 novel The Dark Forest, although this has been discussed long before. The idea is that any space-faring alien intelligence would consider the discovery of another not as a blessing (“woohoo, we are not alone!”) but as a threat. So there may be many civilizations out there, but they are all keeping very quiet to avoid possible repercussions.

If this is correct, it would be a rude awakening, because we are certainly not quiet. We are not sending deliberate messages, but our mobile phone mast signals might one day be visible (with technology similar to ours) up to 10 light-years. Our airport radars are discoverable from even further away, 200 light-years.

The Great Filter

Life is common, but reaching the level to be discovered or discoverable is not. Welcome to the Great Filter, another pretty dark solution. Basically, it claims that it is extremely rare for civilizations to develop to a level that would allow them to be discoverable and/or able to travel through the stars.

This could be something technology-related, how easy it is for a civilization to kill itself (think of us and atomic weapons, the climate crisis, and vaccine denialism), or that the odds are stacked against civilization simply because it is difficult to survive long enough due to natural events, from stellar flares to asteroid impacts.

The most terrifying aspect is that we do not know what this hypothetical barrier, the so-called Great Filter, is. It might be behind us, and we are a rare triumph. Or it might be ahead of us, something in our future that might end our civilization.