How much of a chance do we have of finding alien life in the universe?
The idea of alien life in our universe has been one of the most popularly debated topics among the science community. But it is not just the scientific community nor the sci-fi geeks on the internet.
The notion that we may not be alone in this vast universe is astonishing because humankind has always been curious and looking for answers to its unique existence in the universe. And as of now, we still haven’t found one!
Although we do not have clear reasoning behind our existence, the science community, including cosmologists, believe that our existence is not just luck. On the contrary, we are ignorant of the numerous possibilities where life could evolve in our universe, just like it did on earth. To understand that, we need to take a detour back in time, all the way back to the Big Bang.
We know that our universe is about 14 billion years old. Over 14 billion years since the Big Bang, a hundred billion galaxies formed through natural combination, each of them gave rise to another hundred billion stars and star clusters. Each of these stars hosted an entire star system, which consisted of planets and their moons, just like our own solar system.
Now here is where things got interesting: one particular planet saw itself at a specific distance from its host star, right at a temperature where the simplest molecules combine to form life gases, giving rise to the first unicellular organisms. And before you know it, life gradually evolved on the planet, like our home planet! If we approach the evolution of the universe and life on earth, we inadvertently conclude that life on earth was just a coincidence. A bit of selfish inference from our side, isn’t it?
But there is a catch: from each one billion trillion stars in the universe, there exists at least one planet that lies in the Goldilocks zone, a zone where life, as we know it, is expected to evolve. So, if we take a rough estimate of all such planets that support life, then there would be more than 20 billion potentially habitable planets in our Milky Way galaxy alone! A recent report from NASA and the SETI Institute estimates that there might be about 300 million habitable planets in the Milky Way. The study also showed that these planets seem to have similar properties to the earth. The study used the data collected by the Kepler space telescope, which has been in operation for about twenty years now. The research also found that some of those habitable exoplanets are relatively nearer to our solar system, about 30 light-years from the sun.
From the above facts, we can infer that at least a hundred thousand planets may have survived habitual eradication of life by natural means. Habitual eradication of life can take up different forms, like an asteroid collision, an abrupt climate change, or even extinction of living organisms through natural selection. Our earth survived at least two of these catastrophes, a giant asteroid impact that wiped out the dinosaurs about 65 million years ago and a drastic climate change that shifted from the ice age to the much warmer conditions of the present. But there is a fair chance that out of a few hundred million habitable planets, the earth is not the only one that successfully managed to sustain and evolve into organisms. If only one of those exoplanets could host life, gradually giving rise to modified multicellular cerebral organisms like ourselves or even much-advanced species than us. Now, considering all of these possibilities regarding life on such habitable planets, the thought of an alien civilization in our galaxy or our galactic neighbourhood is pretty plausible and convincing!
However, in reality, we have not received nor detected a clue that there might be alien life in the universe. This inference is one of the core aspects of a famous paradox known as the Fermi paradox. The paradox is that if there are over a billion possibilities for an alien civilization to exist in the universe, and some of them can even turn into advanced intelligent species that can tamper with spacetime, we definitely should have discovered each other by now. This conclusion is apt because now the universe is about 14 billion years old, which is enough time for an alien civilization to expand its territories to their galactic neighbourhoods, just like our case. But in reality, there is no solid evidence to believe that such a civilization exists to this date. We still have not found a convincing solution to the paradox, even though we have high hopes that we might solve it in the coming decades.
There are a few speculations in the scientific community regarding the solutions to the Fermi paradox, but none of it is built based on proper scientific evidence. One such popular opinion is that alien life might have existed about a hundred thousand years ago and somehow underwent an abrupt mass extinction. Or there may be an intelligent alien civilization that already exists in the universe, and maybe we are all just a simulation in their supercomputers. Whatever the upcoming solutions may be, it seems like we are all by ourselves in the universe for now, which, scientists say, is a better situation. We cannot possibly imagine what would happen if an alien invasion did occur at the moment. As human beings, we know that coexisting with nature and other species is something that we are still working on, let alone aliens. So, leading a pleasant life with aliens in the picture would be too ambitious. With the advancement of technology and science, we can hope that these fundamental questions of the universe get resolved. The knowledge that we are close to figuring out the entire cosmos indicates that we are on the right track.