Thursday NASA announced that they have identified another potentially habitable exoplanet (NASA’s Kepler Mission Discovers Bigger, Older Cousin to Earth). That makes it the 21st such extra-solar sorta Earth-ish planet on the list maintained by the Habitable Exoplanets Catalog. What makes this even more interesting is that we have just begun to scratch the surface of what might be out there.
Furthermore, on Monday of this week no less a stellar light than Stephen Hawking himself, along with Russian entrepreneur Yuri Milner, announced a new SETI project named Breakthrough Listen. Professor Hawking expressed the motivation for the project by stating, “We believe that life arose spontaneously on Earth. So in an infinite universe, there must be other occurrences of life.”
Of course, whenever such announcements are made it begs the question, “If there is life out there, why haven’t we found it yet?” This is known as the Fermi Paradox, named after physicist Enrico Fermi, the first person of consequence to pose the question to the right people. Those people happened to be a bunch of his physicist buddies shooting the breeze over tea in the 1940s.
Ever since then bright people all over the place have been trying to figure out the answer. For the most part, the proposed solutions tend to fall into one of two categories, Either (1) Advanced civilizations are out there and there are many good reasons we haven’t found them yet; or, (2) there may be life out there, but nothing advanced enough for us to see.
The first category of answers are favored by optimists, like SETI and the newly announced Breakthrough Listen initiative, who believe that if we just keep looking we will eventually find something. The second group is more pessimistic. They assert that either the Earth, and we humans, beat the odds somehow and are special; or, that intelligent life is relatively common, but tends to extinguish, or otherwise limit itself, before reaching the point where they would be noticeable across interstellar distances. This concept of the self limiting nature of intelligent life is known as the Great Filter.
The Great Filter theory says that at some stage along the evolutionary path from pre-life to galaxy spanning Kardashev Type III Civilization there is one great leap that is extremely unlikely or impossible for life to get past.
Depending on the solution in question, the Great Filter could either be behind us, in which case we are one of the lucky few (or one), or it is somewhere ahead of us, in which case we are doomed. I have given this some thought and have my own theory to throw into the mix.
The Bio-Compatibility Problem
People wonder why, if there are other advanced civilizations out there, why we haven’t seen or heard from any of them in all the time we’ve been looking. I know exactly why. It’s because expanding to other stars, even relatively close ones, is incredibly difficult. Not only do you have to find another planet with atmospheric and climatic conditions similar to the ol’ homestead, you also have to hope the biosphere is at least partially compatible. And that’s something you can’t determine easily until you get there.
So, imagine you pack your colony ship full of hopeful souls and venture forth. What happens when you get to Colony Alpha only to discover that, while the air is breathable, the climate is pleasantly temperate, and the gravity is tolerable, the local flora is poisonous. Or, perhaps it is merely indigestible. Worse yet, the seeds you thoughtfully brought along won’t grow because the soil lacks the requisite trace elements, chemical nutrients, or micro-organisms.
Let us not discount the very real possibility that if life on this brave new world has progressed to the level of micro-organisms, they may very well be deadly to visiting space aliens. War of the Worlds anyone?
The human body is a finely tuned system that relies on various complex chemical molecules to function. The odds of these exact same molecules occurring naturally in just the right combinations and quantities on a planet orbiting a distant star, and experiencing a significantly different geologic, meteorologic, and biologic history than our own are phenomenally low. It is reasonable to assume that any extra-solar beings would be likewise tuned to the conditions on their home planets.
In fact, it would be better if the destination planet were essentially barren. Then one could grow an ecology from the ground up, as it were. However, if a planet’s atmosphere, climate, gravity, composition, and such are at all conducive to the formation and/or support of organic life, then it stands to reason that such life will develop. In such a case, the arriving hopeful colonists have two options, either they adapt to the prevailing conditions or they play the invading species and bend the ecosystem to their needs.
Either option is exhausting and potentially disheartening. Neither possibility encourages further expansion. This, I submit, is the Great Filter that prevents the continual expansion of even exceedingly advanced species. They simply discover that the cosmos is a much harsher place than they imagined and give up on the whole notion of interstellar expansion all together. Restricted by their own finely tuned biology which enables them to really flourish only at home, they stay there and essentially stagnate at Kardashev Type II or eventually succumb to one of a number of possible extinction scenarios. Unless, of course, they happen to be just stubborn enough to forge on anyway,
Project 15 Tie-In
The limiting factor of home world biology, beyond things like breathable atmosphere, is something I’ve rarely seen addressed in outer space fiction. The notable exceptions that come to mind are H. G. Wells’ War of the Worlds and one Star Trek episode in which a supposed paradise planet turned out to be poisonous. I think this could make for an interesting wrinkle in the standard expansion into space scenario. It might also form a basis for interstellar trade. Planet B might have an abundance of Molybdenum whereas Planet G is entirely deficient, but has the Cobalt that B needs to make Vitamin B-12.