Our universe is 13.8 billion years old, with life on Earth only beginning around four billion years ago. The first life could have started about one to two billion years after that start of the universe, leaving a huge time period prior to signs of life on Earth where civilisations could have developed or wiped out. Could we, therefore, have missed a civilisation in the past or is there a civilisation yet to come that we could communicate with? Many feel we should be asking, why have we not come across intelligent alien yet?
It is critical to remember when scientists discuss alien life that there are two types – microbial and intelligent. When NASA talks about searching for life elsewhere in our solar system, they are referring to microbial life and not intelligent beings that have created something similar to our own world.
Then there is intelligent life. Intelligence does not necessarily mean human intelligence. It can be in diverse forms. On the Kardashev scale – a measure of a civilisation’s level of intelligence based on how technologically advanced it is – humankind is not really even at level one. The most advanced civilisation should have mastered interstellar travel and be able to harness and control the energy produced by an entire galaxy.
In the Milky Way alone, there are an estimated 100,000 million stars and 100 billion planets, many of which are possibly habitable, and therefore could have the right conditions for life to develop. Up to this point, we thought there were about two trillion galaxies in the universe, each containing hundreds of billions of stars and trillions of planets. However, new NASA research demonstrates there are presumably at least 10 times as many as this.
There have been countless potentially habitable planets forming over the history of the universe and that suggests that it is highly likely that life may have, or has, emerged on just one. On the off chance that only 0.1% of potentially habitable planets in our cosmic system harboured life, that would still, at present, be a million planets.
So why do we seem to be alone? That question is known as the Fermi paradox, and there are a few potential answers!
Fermi’s paradox is the contradiction between the high probability that alien civilisations exist and the lack of contact we have had with aliens. There are several hypothetic answers to Fermi’s paradox, some of which sound feasible, while others resemble big-budget sci-fi movie plots.
One hypothesis is that before intelligent life figures out how to spread past its original planet to other nearby planets, it keeps running into a kind of “Great Filter.”
This idea implies there are several “evolutionary transitions or steps” that life on an Earth-like planet needs to accomplish before it can communicate with civilisations in other star systems. Nonetheless, an interference or barrier may make it inconceivable for an intelligent species like our own to get through all those steps. That would explain why we have not heard from or seen any other life.
Simply put, the Great Filter states that “Civilisations rise, but there’s an environmental filter that makes them cease to exist again and vanish fairly fast”.
In a universe that is many billions of years old, with star systems isolated as much by time and space, civilisations might rise, develop, and consume themselves before ever being able to discover each other.
The consequences of human activity could also be the thing that keeps our civilisation from progressing much further. Climate change caused by the development of cutting edge human advancement could possibly be that filter in our situation. That may sound improbable, but it is the answer some researchers are providing to this puzzling question.
If you have a look at planet Earth, these past mass eradications have been the filtering. The mass extinction some argue that we are presently living through has apparently barely started; much more destruction and loss is coming.
Unchecked climate change would ultimately lead to widespread destruction on Earth. Rising seas would immerse coastal urban areas, searing heat would increase human mortality, and acidic oceans would become unwelcoming to fish and coral.
Researchers are currently debating whether we are amidst the Earth’s sixth mass-extinction event or moving towards it. In any case, the situation is critical. The existential dangers posed by the most pessimistic climate-change scenario are genuine.
Until our technology develops to the point where we can explore space on far shorter time scales, the ball of finding intelligent life is very much left in the aliens’ court. Additionally, in the event that those dangers become serious enough to act as humanity’s Great Filter, it may be too late for us to communicate with anyone else in our universe.