The ten most important questions for astrobiology: Number 10

The final piece in this brief summary of what the most pressing questions are for astrobiology effectively brings us full circle. It is what ultimately motivates us, what we really want to know, perhaps even what we really need to know as a species. It is a question that humans have pondered for at least 2,000 years

Is there intelligent life elsewhere in the universe?

One of my favorite quotes in the long history of this question is attributable to the Greek philosopher Metrodorus of Chios in the 4th century BC, who was of the school of Democritus. Undoubtedly mangled over the centuries it nonetheless brilliantly summarizes a key part of the discussion:

"To consider the Earth as the only populated world in infinite space is as absurd as to assert that in an entire field of millet, only one grain will grow"

The universe may not be infinite but it is extremely large, containing as many as 10 to the power of 23 to 10 to the power of 24 stars, and perhaps equally as many planets of all varieties, as well as their moons and the rocky detritus of formation. It has existed for some 13 billion years and the first generations of stars formed almost as long ago and have been forming ever since. When faced with this enormity it is very hard to not imagine that there just has to be a place somewhere else where creatures like us, or at least with our capacity for self-awareness and curiosity, exist. For ten to hundreds of thousands of years Homo Sapiens, along with our genetic cousins, have thought, invented, drawn, painted, talked, sung, wondered, explored, built, rebuilt, modified, investigated, fought, loved, hated, struggled, enjoyed, and survived. What a remarkable thing that is. In the grand scope of life on Earth we are still just a fleeting quirk of evolution, but we have just begun. The dinosaurs, the insects, the fish, and the plants are shining examples of the potential longevity of complex organisms. Nothing really says we can't exist for another hundred million years if we are clever enough, and if that's correct then it seems more inevitable for the same to happen elsewhere.

If there is other recognizable intelligence out there amongst the stars how do we find it? In various posts I have discussed some of the issues, including whether it is even a safe thing to make this search. In very practical terms there are a few options. First, we can listen for the electromagnetic signs of life, whether serendipitous glimmers of structured communication or a specific, targeted communique designed to trigger the interest of other civilizations. Second, we can look for anything that smacks of the 'unnatural', whether it is a bizarre artifact that eclipses light from a distant star, or evidence of atmospheric chemistry that smells like industrial pollution, or even deliberate 'terraforming'. Third, we can send our machines, or eventually ourselves, out into the universe to explore and to carry the message that we would like to make contact. Finally, we can make ourselves sufficiently noisy and intriguing that at some point someone else, or their machines, show up on our doorstep.  Though it is of course quite likely that they'd get here a few thousand years later, long after we had lost interest.

Searching the skies for signals has not yet had any real success. Although the techniques have become better and better I don't think anyone would argue that there is data that looks even slightly suggestive of an artificial origin (except just possibly, perhaps, maybe, that infamous WOW! signal). It's a very tough challenge, and it is clear that enterprises such as SETI have a long way to go before exhausting all possibilities. I think the second option may actually be an interesting one, particularly the notion of finding chemical fingerprints of a planet dealing with either pollutants or deliberate geo-engineering. We do seem to be edging towards the telescopic capabilities required to sniff at Earth-type planets, with JWST or next-gen giant instruments on the ground, so can we equate any unusual environmental parameters with intelligent inhabitants? It would be a hugely tricky task, but it may be a lot easier than the other avenues of investigation.

There are also many arguments that seek to convince that we are a rare thing, and we have discussed those before. Some are extreme but even mild variants suggest a big problem for our attempts to answer question 10. Suppose that intelligent life comprehensible to us does indeed occur across the universe, and has done so for most of the past 13 billion years, but it's a bit thin on the ground. In cosmic terms even one such species per galaxy still fills the universe with something like a hundred billion of these brainy civilizations. The problem for those intelligences is that there is on average a colossal gulf of millions of light years between them and anyone else. Barring physical laws that allow the circumvention of inconveniences like the finite and absolute limit of light speed, as well as the passage of time, then they will remain in splendid isolation. It's sobering. However, the flip side is that equally good arguments can be made for intelligent, or at least complex, life to be common. While interstellar space is still a huge gulf, it is nothing compared to intergalactic space and the equation shifts quite dramatically. So much so in fact that issues such as Fermi's Paradox then raise their heads. No wonder that scientists keep coming back to question number 10, it's full of juicy points to argue endlessly over.

The good news is that barely 16 years ago we didn't know for sure that any planets existed around other normal stars. How strange that appears now. It seems almost absurd that we were ever cautious about whether the universe made planets efficiently. Now we are on the cusp of finding out just how many small rocky, even Earth-like, ones there are across the galaxy. This is arguably the biggest single advance towards dealing with question 10 in a real, non-speculative, fashion since Galileo and Copernicus opened the floodgates of astronomical reason. This is one thing that makes modern astrobiology such a compelling and exciting field. The fog is lifting on a scientific path that will eventually lead us to a census of worlds, and ultimately of their contents. Slowly we will push out further from Earth, and in doing so will further and further narrow the options for intelligent life.
 
Finally, one cannot help but feel in the most non-scientific way imaginable, that it would be so bleak and awful for such an extraordinary phenomenon as ourselves to be alone in the void that we must strive our greatest to find out the truth. Even if the ultimate answer is that yes, we are a singular event, then it would still seem that the mere act of looking, the scientific and technological effort required, would surely play some role in ensuring that we do not vanish into the gaping maw of evolutionary extinction. If we just 'are', with no rhyme or reason, then it behooves us to revel in our existence, embracing the cosmos as the very fiber of our being that it is.