So many stars in our local group alone yet we have received no signal nodding towards the existence of alien life. In 1974, Dr. Frank Drake (the creator of the Drake Equation), along with Carl Sagan and some others, wrote an interstellar radio transmission, the Arecibo message, as humanity's first attempt to contact unknown alien life. It contained 7 parts, each holding basic information about human life and was aimed at 25000 light years away towards the current location of M13, a cluster of stars.
At some point in life, we all have or will ask ourselves, “Why are we here?” It’s totally natural after all to ponder upon our existence, to think, “What is the purpose of life?” That moment when we have what is called the ‘existential crisis’, our mind forces us to question the blank thought of us being alone in this wide empty universe.
The universe is about 90 billion light years in diameter and has more than 100 billion galaxies each with 100 billion to 1000 billion stars. The Local Group, where we live in, is the cluster of galaxies in space, containing the Milky Way, that we can ever hope to reach but not beyond. Owing to the universe’s constant expansion it would take us billions of years to reach our neighboring group of stars, outside the Local Group, and that too while passing through the emptiest sectors of the universe. Yes, the universe is so big that venturing out towards our neighboring cluster of stars too is deemed improbable at the moment.
Let’s scale down to our Milky Way galaxy. There are 400 billion stars in it which accounts as 10 thousand stars for each grain of sand on Earth. Amongst those, there are 20 billion Sun-like stars and a fifth of them are thought to harbor an Earth-like planet meaning there are 4 billion Earth-like planets sheltering life and even if there was a 0.1% chance of life on any of them, there are still 400 million planets with life; but then, where are they?
The Milky Way is 13 billion years old but it wasn’t habitable right away. There followed up to 2 billion years of steamy hot gas explosions after which the planets cooled down. So even if there was a planet that started life around 3 billion years after that, comparing it with our 4.54 billion year old Earth, they would have had 3.46 billion years for extra development, more than us, giving them enough time to evolve into a Type III civilization. A Type III civilization is an example of a civilization that has harnessed the energy of its entire host galaxy and extended its reach either through settlements or annihilation across its entire galaxy as proposed by the Kardashev scale. In that case, their signs of existence would have been quite distinct.
This is the Fermi Paradox and no one has the answer to it. It questions alien life based on the low probability and lack of evidence. While mathematical structures like the Drake Equation predict the number of active alien civilizations, they are but mere statistics and the parameters entered into it are more or less round estimates questioning the authenticity of such experiments.
Every civilization has a fate; our remains unknown at the moment
Theories to the paradox exist. One says that at certain points in time every civilization has to pass through filters like Earth’s global warming or a nuclear fallout. Then there’s the Great Filter. Sometimes civilizations are just wiped out of existence once they reach the Great Filter, which is metaphorically a high level of advancement and sophistication, while only one in thousands or so make it through. Despite all logical contradictions and plausible theories, the only actual and definite way we can answer that question is to venture out there ourselves, perhaps when we have invented faster-than-light-travel and hopefully then we will find the truth to our woes.