Do you believe in aliens? If you do, you must be intrigued with the question that where are they and why haven’t we heard from them yet? Well, it’s not just you as this question has also troubled space scientists and astrophysicists for a long time. Over the years, based on various calculations, scientists have been trying to find other life forms situated in far distant galaxies in the vast universe. Let’s try to understand this step-by-step.
The Gigantic Milky Way
It is estimated that for as many as 100 billion stars in our Milky way galaxy, there are almost a same number of galaxies in the observable universe. So technically, for every star in the Milky Way, there’s a whole galaxy somewhere.
There are conflicting views in the scientific community on how many of those stars are actually “sun-like”. It typically varies from around 5% to 20%. Let’s go with the lowest possibility, which is 5%, giving us nearly 500 billion billion sun-like stars. Now, the next question is that what percentage of those sun-like stars might be orbited by an Earth-like planet (a planet with similar terrestrial conditions, habitable temperature and abundant liquid water, which can ultimately harbor life). The answer varies, some even say it’s 50%, but let just go with 22%, according to a recent study by PNAS.
If we apply the same math to our galaxy, with estimated 100 billion stars (lowest possible estimate) in the Milky Way, it would give us an estimate 1 billion Earth-like planets and 100,000 intelligent civilizations in our galaxy. Assuming that we are correct with our calculations, even if a small fraction of these planets had sent signals, then we should have been able to pick up those signals. But we didn’t. Why? Where is everybody?
Image credit: Nasa
This is the Fermi Paradox, if the life exists on other planets, why have we never heard from anyone? To understand the paradox, we first have to learn about something called The Kardashev Scale. It groups intelligent civilizations in three different categories.
Type I Civilization: A type I civilization has the ability to use the entire energy available on their planet. We are currently not type I civilization, we are currently at 0.7 on the scale and we should be able to reach this in the next century or so.
Type II, Civilization: The type II civilization must harness all the energy from its home star. Right now we can just imagine this
Type III, Civilization: The third and last type of civilization basically controls everything in their galaxy. A race this advance would be like a god to us.
If a civilization on another Planet is much older than our Earth and were able to survive all the way to Type III, then it is more or less obvious that they’d probably have mastered intergalactic travel by now, and possibly colonizing other planets in their galaxy.
There is a popular hypothesis surrounding galactic colonization that it could be done by fabricating a spaceship that can travel to other planets, spend a couple of centuries or so in self-replicating using the raw materials on their new planet, and then send two replicas off to do the same. With this, even without traveling near the speed of light, that civilization would we able to colonize the whole galaxy in 3.75 million years, relatively a small dot on the time scale of billions of years
Even if assume that only 1% of intelligent life survives long enough to become a galaxy-colonizing Civilization, which should at-least 1000 according to our calculations then their presence would likely be pretty noticeable. And yet, we see nothing, hear nothing, and we’re visited by no one.
Well, there are few possibilities of why this is the case. Let’s take a brief look at them.
The Great Filter
The idea of the Great Filter was conceived in 1998 by Robin Hanson. It suggests that there is an existence of some kind of ridiculously difficult step in the evolution of life, which precludes it from becoming truly superior. Actually, the simple idea is that all civilization destroy themselves before developing any advanced space technologies and colonizing other planets. Therefore the empty universe.
It is based on this hypothesis that many believe we will destroy ourselves in the future. But, there is yet another possibility for this. It is also plausible that we have already crossed the great filter, and it is behind us, which means we might be the only knowledgeable-species in the Milky Way.
We are too primitive
There is also a possibility that we are not as advanced as our possible counterparts. Maybe there are ways to communicate that we are not aware of and alien civilization are waiting patiently for us to reach a certain level of technological advancement before they can make contact. If that’s the case we cannot do anything.
We Are Really Alone
This last explanation of the puzzle might be a more feasible one right now. As we are not aware of any other life form outside the Earth, the entire Universe appears to be empty and dead. Then perhaps we are alone in the universe. Consider this, here on earth we still can’t figure out how multi-cellular life actually begun on this planet, how it was able to move from a tiny cell to big, complex organisms.
Not only that, we are not even sure how life begun here in the first place or how water came into existence. Many more questions, but no definite answer, so may be that our planet Earth is the only cosmic entity, which has allowed smart-species to evolve.
One can’t deny that we are the only intelligent species known which makes humanity, and Earth, incredibly special, and we should preserve this fascinating and lonely life-harboring world we inhabit as hard as we can.