“Space is big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space.”
Douglas Adams, The Hitchhiker’s Guide to the Galaxy
The observable universe has a radius of approximately 46.5 billion light-years and is nearly 14 billion years old. In the Milky Way alone, there are at least 40 billion Earth-like planets, many of which have been around for billions of years longer than our own. Given the enormity of this space and time, providing plenty of opportunity for life to flourish, why is it that we haven’t seen anyone or any-thing out there yet? This conundrum is known as the Fermi paradox. There are many proposed solutions to the Fermi paradox that range from interesting to existentially alarming. Regardless, their logic allows us to ask: are we alone? And what does that mean for us?
The interesting solutions
If there are many potentially life-supporting planets in our galaxy, many of which have been around for longer than Earth, one would assume that some planets would have developed life as least as complex as that on Earth. This may be true, but this complexity doesn’t mean that those life forms would be similarly expansionist or even as curious as we are. Aliens might be having enough fun on their home planets and star systems to be unconcerned with taking over other planets or making contact with them. The vastness of space also contributes to the lack of alien contact; interstellar travel (even at light speed) for war or diplomacy is likely not worth the material and time-based resources.
Given the vastness of space, it is entirely possible that no space-faring aliens have noticed us at all, even if they are looking for us. Human radio signals, including those we send out deliberately hoping to communicate with others, travel only a tiny fraction (~1/1000) of the diameter of the milky way and decay into unreadable noise rapidly. It may also be the case that advanced alien species don’t use the same communication channels as us, meaning that, even if they noticed our signals, they would have no way of decoding what they meant. Or if others have stumbled across us, perhaps they just aren’t interested in talking.
A final consideration is that we are the first to have developed life complex enough to even consider looking for others in the universe. It’s possible that overcoming the barriers to developing complex multicellular life, such as ourselves, is incredibly unlikely, and we have been lucky enough to be the first to make it through. We also know from our knowledge of evolution on Earth that large brains are biologically expensive and fragile. Perhaps developing them was only worth their costs for the very particular conditions of current-day Earth, and wouldn’t be beneficial on similar Earth-like planets.
The alarming solutions
Now, it’s time for the worrying hypotheses
There may be many other alien civilisations out there that could theoretically communicate with us and each other. However, we may not have noticed them because they are all deliberately hiding — and for good reason. Our history has proved time and time again that humanity (in particular, those in power who control the planet’s resources) can be dangerous. If alien civilisations are anything like ours, perhaps they are dangerous too. The first-strike advantage in conflict is even more pronounced on the galactic stage, where time and length scales are monumental. It may then be the case that all other societies which happily publicised their existence were eliminated pre-emptively by others hoping to snuff out possible threats.
The final solution which must be considered is that there have been many other planets and species like ours, but they are all gone. Perhaps the steps to achieving complex life similar to humanity is easy, but a substantial challenge to life still lies ahead. This challenge, whatever it may be (e.g. climate collapse or pandemics), may have eliminated all our would-be alien friends. It is conceivable that becoming the dominant species on a planet ultimately produces such a crisis, and every other species which reached this point failed to act in order to prevent mass extinction.
Regardless of the true answer to the Fermi paradox, it is clear that life of any sort is precious and its existence fragile. Whether there are malicious aliens eager to conquer Earth we cannot know, but there are many crises, most obviously the climate crisis, that we have the resources and know-how to solve. Whether we are the only life-harbouring planet or not, failing to protect the life we know exists would be a great shame. We ought to do what we can to protect life on our planet. If we succeed, maybe we’ll one day have the chance to share the joys and challenges of life on Earth with new-found intergalactic friends.