Why Haven’t We Been Visited by Aliens Yet?

By Jameson O’Reilly, Applied Physics and Electrical Engineering 2019

The title of this article may sound a bit strange, but Earth is just one planet within one of billions of solar systems within one of billions of galaxies within one of billions of superclusters. There are many requirements for a planet to support life, let alone intelligent life, but even if only a tiny fraction of planets can support life, there are still billions of those planets out there.

Given the huge number of planets that should be able to support intelligent life, especially bearing in mind how many of them are much older than our Earth, it seems odd that we do not yet have any concrete proof of another intelligent species. This contradiction is known as the Fermi Paradox, after Nobel laureate Enrico Fermi.

There are two main possibilities that may be used to address the Fermi Paradox: either there really are no other intelligent species capable of communicating with us, or those species exist but choose not to communicate with us. The most popular explanation for the former possibility is known as the Great Filter.


The Great Filter is thought to be one of the many obstacles that a species must overcome before reaching the level of sophistication that would allow them to communicate with us. It could be the development of the very first self-replicating organisms, of the first multicellular organisms, or even of consciousness. It could even be climate change or something far in the future that we cannot predict. We just can’t know. The difference between the Great Filter and all of the other obstacles is that it is so unlikely for a species to make it past the Great Filter that it accounts the tiny amount of sophisticated civilizations we have seen compared to how many we would expect to see.

If we humans have already made it through the Great Filter, we can breathe a collective sigh of relief that the end is not immediately forthcoming. Unfortunately, it also means that other civilizations as or more advanced than we are either very few in number or totally non-existent.

We are the lucky few that made it over the greatest hurdle to intelligent life, whatever that may have been.

Alternatively, we could be going through the Great Filter right now. If climate change due to industrialization is the Great Filter, and it might be, then a species of intelligent life on another planet would have to be in a similar situation around the same time in order for humans and that other species to communicate with one another. Given the minuscule amount of time we have spent in this stage compared to the age of the universe, it seems unlikely that our timing would match up so well. That could explain why we have had no contact with other intelligent species.

The final possibility for the timeline of the Great Filter is that it is still in our future. If this were true, then we would expect a decent amount of other planets to support intelligent life capable of communicating with us because they would not have hit the Great Filter yet. Civilizations as advanced or more advanced than ours would still have plenty of time left, hopefully enough to communicate with us. We would not be the only ones sending satellites and transmitting messages into the universe. Even if all other intelligent species had reached the Great Filter before us, we should still be able to detect some of their messages floating about in space.

Then again, we have only had the technological capability to transmit and search for those signals for about a century. This seems like a long time, but it’s not long compared to the age of the universe or how long it would take for signals to travel between all of the Earth-like planets that we believe to be out there. There could be many different things going on that humans simply have not caught onto yet. We could be too primitive to interpret the signs being sent to us or to even be considered worthwhile for more advanced beings to contact. Maybe we are part of a galactic zoo and just don’t know it. Perhaps most frightening, some have suggested that there is a rogue species of “berserkers,” the fear of which have forced all of the other advanced civilizations to keep quiet.

All of this is incredibly speculative, of course, and at this point it is impossible to know anything for sure. Perhaps someday we will come into contact with another intelligent species, or perhaps we will just continue speculating in an attempt to assuage our fears of loneliness in a dark, cold universe.