If the universe is infinite then even the smallest probability of life appearing on a planet and evolving intelligence would produce countless alien civilisations.
So Fermi asked the question:
Where are they?
And if they are not here now, then where are the remains of their passing?
Countless suns and solar systems have been created and destroyed even before our own sun existed. Even if a tiny percentage of all those worlds were able to support life they would still be enough to give birth to a large number of alien civilisations. And even if a fraction of those reached a high stage of technological development they would still have enough time until we came along to colonise the Galaxy and such high technology would mean that they would have built spaceships and space stations around the galaxy. Going even further than that, given the enormous lengths of time we are talking about here they would have theoretically been able to build mega-structures comparable to the size of something like our moon or even bigger And this ought to have happened over and over again by now.
But we can’t find any evidence of that. So far we have not discovered any clearly artificial structures with our telescopes – no Death Stars or Dyson Spheres, no spaceship junkyards with thousands of drifting space hulks. In perhaps the most famous failure we have not discovered any intelligent communication signals either. And most importantly of all, no alien spaceship has appeared in the sky – no ET has come to say hello.
As an aside, let me say here that I consider the whole Roswell mythos as pure nonsense, if only because it doesn’t make an ounce of scientific sense. A civilisation developed enough to be able to execute interstellar travel would have technology beyond even the dreams of our current scientists – in particular they would have been able to perform all monitoring tasks in our planet remotely, with no need to come within the atmosphere. If they did need for some reason to do that they would have sent robotic probes – hell, we are already doing it on Mars and we haven’t even colonised the moon. And even if they did need to send vessels with life forms in them – quite a stretch given all of the above – I do not believe that such high technology would somehow crash like a Cessna propeller plane – the machines of any technologically advanced civilisation would be much more robust and reliable than our own, with self healing abilities and automatic anti-gravitation abilities; i.e being able to stay on air without power solely on the strength of the materials with which it would have been made of.And finally, even if it did malfunction and crash are we seriously going to believe that there was no crew escape mechanism, a technology that we have since the 40s? Whatever that “event” was, it was surely not aliens landing on earth.
So going back to the original problem.
Where are they?
There are several ways to explain the paradox.
One is that our detection instruments are not powerful enough to detect remains of alien civilisations; we cannot tell if what we are looking is a planet or an artificial structure nor can we as yet detect disturbances in space time that could have an artificial source.
Another explanation is that all alien civilisations that would have been detectable by us have either evolved to a stage where they are no longer bound by physical reality and have left the Universe or they have destroyed themselves in some kind of massive event. The problem here is that even if they are long gone their artefacts should still be floating around us in space. One would then have to reach the conclusion that they had taken steps to erase their passing from the universe – bulldozed their cities and destroyed all their spaceships. This may make sense for civilisations that have departed – on accounts of safeguarding primitive races like us from stumbling upon such world-shaterring technology – but no so much for civilisations that have self-destructed unless that self-destruction was more like a carefully planned suicide.
A third explanation is that we are really alone, owing to the fact that the probability of intelligent life forming on its own anywhere around the universe is so small so that there can only ever be at most one such civilisation per galaxy and in this one it is us. While this appears to be the simplest solution to the problem – a mere application of probability – its foundations have already been shaken by the discovery of planets orbiting other suns in their habitable zones – zones where water can exist as a liquid and where life as we know it can survive. In the coming decades telescopes should be powerful enough to detect what the atmospheres of these planets are made of, and we should be able to see if the cocktail of gases has biological origins. Once signs of life are detected its evolution should more or less be guaranteed at least given our experience here on Earth. And if this happens then it will automatically have a retrospective application; if life is found now then there is no reason that it did not exist in the distant past nor any reason that it would not have been evolved into something intelligent and space-faring.
And finally, a fourth explanation for the paradox is that they are out there but they have either not stumbled upon as yet or they are keeping themselves invisible preferring instead to observe us as some sort of project rather than make contact with us. Again the age of the galaxy does not provide much basis for the first theory – any number of civilizations with advanced interstellar travel technology would have criss-crossed the galaxy several times with their probles and even if they did not reach every single solar system out there they would surely catalogue them via remote sensing – much as we are cataloguing them with our space and land telescopes. It cannot be a case of not being aware that we are here, like the ignorance of the existence of the Americas by Europeans. So if they are out there they know we are here.Which leads us to the second proposition, that they are keeping us isolated from any alien contact for their own purposes. There are of course parallels with the way our own scientific methods have been designed; scientists observing animals in the wild often remain hidden from view so that they do not disturb the habits and behaviour of their specimens i.e avoiding contamination. Packs of lions and antelopes can be observed from the air or through powerful telelenses on cameras. When our entire civilisation is the specimen then any aliens wishing to keep us ignorant of what is our there would do that by setting up a buffer zone around us preventing any form of alien spaceship from coming to our attention while doing their observation via remote sensing machines. It is of course impossible to theorise on the politics behind such an undertaking, that is whether this would be a venture between various civilizations or just one and whether the reasons would be merely academic or something more exploitative.
What is my own belief you might ask?
I cannot eliminate any of the above theories of course; with our current level of understanding I do not believe that any human can. But I have a hunch that the universe is too big for us and that there is life somewhere out there. Even if it is on a different galaxy. And sooner or later, we will either find it or they will find us. And perhaps then we will finally be able to give the definite answer to the Fermi Paradox.