I decided to open my Pandora’s Box of thoughts with this simple question, which is often addressed by speculative fiction and science fiction novels, but as yet, has not really touched the real world outside the SETI community (SETI being the group of scientists actively seeking for signs of alien civilisations, primarily by monitoring the sky for artificial radio signals).
Of course this question can easily be answered by a simple: we haven’t contacted any aliens because there are no aliens to contact. This gets the job done but is rather dull, and might not be the definitive swipe of Occam’s Razor that it first seems to be, since you have to make nearly as many assumptions to reach such a negative conclusion as you do to reach a positive one.
Since I’m in the speculative fiction business; let’s assume that life is common throughout the universe and the Earth is not the only spec of dust that has any clinging to its surface. Soon, this will not be such an intellectual leap, because humanity is on the verge of being able to test this assumption. Or at least have the facts to make an educated guess. Within a few decades, we will have probes sampling the oceans of many different worlds and telescopes scrutinising the atmospheres of goldilocks planets around other starts. We will then be able to state, with confidence, whether or not alien life is common or not.
Personally, I’m prepared to speculate that life is common, if not very common. I don’t believe the existence of life is some billion-to-one chance occurrence or that it’s some deity’s Sunday school construction project. I think the emergence of life is a natural process that will occur wherever the conditions are right. Even if it is a billion-to-one chance then it still might have happened a few hundred times in our galaxy alone.
However, although I think life is common, intelligent life might not be. Given the Earth’s history, life existed as single celled organisms for billions of years before it got its act together and became interesting. Some use this as evidence that more complex life is unlikely, but basing an assumption on one example has its drawbacks. What if Earth based life seriously under achieved? What if the average time for an ecosphere to mature from primordial soup to sliced bread is more like a billion years or even less? We simply have no way of knowing, yet. As you can probably tell, I prefer to speculate that life is not only common but biological complexity will naturally occur.
Even if intelligent life is common, space is so vast, even within our own galaxy, that intelligent species separated by even a few dozen light-years will probably never meet. This assumption is often stated as one of the main reasons why any aliens that might exist haven’t shown up yet. However, even if technology limits interstellar travel to only 10% of the speed of light – something that should be achievable even for us, it would take only a million years for a species to traverse the entire Milky Way galaxy, perhaps a little more if you include time for setting up colonies and sight-seeing. That does sound like a very long time, and it is, but another intelligent species might have had a billion years head start; it would be reasonable to speculate that such a species would have visited everywhere in the galaxy, even here. It’s also possible that such a species would have found a way to circumvent the universal speed limit, shortening the exploration time even further. So, it would be reasonable to ask: where are they?
This is the Fermi paradox; if we think alien life is common, then where is it?
I think the question says more about us than it could do about any possible aliens. Presuming that life is common and aliens have the ability to travel the galaxy, then why would they bother to visit us, or make their presence known to us? Are we, as a species, really that arrogant? Surely, with these assumptions in mind, would we not be just pond scum to these alien space farers by comparison, dangerous pond scum that can’t even play nice in its own puddle.
Seriously, why would they bother?
I think life is common, and I think intelligent life is everywhere, and if the universal speed limit really cannot be broken by spaceships, I at least hope it can be broken by energy allowing distributed communities to stay in touch. If they are out there, and if they can be bothered they might be watching us, just in case we grow up, but until then I think they will keep their distance, turn away their beacons, shield their sitcom broadcasts and just hope we leave them alone.