Do you believe in the existence of extraterrestrial beings? If you do, then you must be intrigued about their whereabouts and why we haven’t heard for them yet? It’s not just you, the question has troubled scientists and astrophysicists for decades.
Sometime in the year 1950, a conversation broke out between few colleagues at Los Alamos National Laboratory over lunch. Among them was physicist Enrico Fermi, noted for demonstrating first ever self-sustained nuclear chain reaction.
The conversation was not ordinary at all. As far as they can recall, the group discussed recent reports of UFO sightings and the possibility of finding evidence of the speed of light travel soon. In the middle of the conversation, Fermi came up with an unexpected, out of the blue question, “where are they“?
Even though Fermi didn’t explicitly mention extraterrestrial life, it was self-evident among his peers. The conversation that followed after the question became the basis of what we now know as the Fermi Paradox.
In simple words, the Fermi Paradox is the contradiction between the high probability estimates for the existence of extraterrestrial civilizations and the lack of evidence for it.
The Possibility of Finding an Earth-like Planet
It’s estimated that for 100 billion stars in our Milky Way galaxy, there is almost the 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’s believed to be about 5% to 20%. Let’s go with the lowest possible number, which is 5%, which gives us nearly 500 billion sun-like stars.
The next question is that what percentage of those sun-like stars is orbited by an Earth-like planet (a planet with similar terrestrial conditions, habitable temperature and abundant liquid water, which can harbor life as we know). The answer varies. Some say it’s about 50%, but according to research published in PNAS, it is 22%.
If we apply the same math to our galaxy, with an estimated 100 billion stars (lowest possible estimate), it will give us an estimated 1 billion Earth-like planets and 100,000 intelligent civilizations in our galaxy alone.
Assuming that our calculations are correct, even if a small fraction of these planets had sent signals, we should have already received them. But we didn’t. Why?
Where Are The Aliens?
A popular hypothesis regarding galactic colonization is that it could be achieved by a spaceship that can travel to nearby planets, spend a couple of centuries there, while self-replicating and then send those replicas to other worlds.
Concept Terrestrial Planet Finder | Image Courtesy: NASA
With this, even without traveling near the speed of light, a civilization would be able to colonize the entire galaxy in less than 4 million years, a relatively short time on the cosmic scale.
If we assume that only one percent of intelligent life survives long enough to become a galaxy-colonizing civilization, their presence would still be fairly noticeable. And yet, we see nothing, hear nothing, and we’re visited by no one.
This is the Fermi Paradox, in essence, at least. If 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. On a scale from 0 to 1, one being type I civilization, the EarthEarth is currently 0.7. We should be able to reach this level in the next century or so.
Type II Civilization: The type II civilization must harness all the energy from its home star.
Type III Civilization: The third and last type of civilization in the Kardashev Scale controls everything in its galaxy. A race this advance would be like a god to us.
If there is any civilization older than ours, which is able to survive all the way to type III then it is more or less likely that they have mastered intergalactic travel and possibly colonizing other planets.
The Great Filter
The concept of the “Great Filter” was first proposed by American economist Robin Hanson in 1998. He argued that the failure to find any extraterrestrial civilization so far suggests there is something fundamentally wrong with the scientific assumption that advanced intelligent life might arise.
The ‘Great Filter’ implies the existence of some kind of ridiculously hard-to-pass barrier that prevents civilization from becoming truly superior. It acts as a filter, which restricts an intelligent civilization from becoming a highly advanced one.
It further explains that almost all civilizations tend to destroy themselves before developing advanced space travel technology or colonizing other planets.
From our standpoint, the ‘Great Filter’ could lie either in our past or in our future. In other words, we could already have crossed the barrier (if that’s the case, then we might indeed be the only knowledgeable species in the Milky Way).
The other possibility is that our civilization is not advanced enough and is behind the Great Filter. Based on this hypothesis, many believe that our civilization will self-destruct in the future.
It is possible that we are not advanced enough to communicate with extraterrestrial beings and alien civilizations.
Image Courtesy: Kurz Gesagt
We Are Really Alone?
Are we really alone in the galaxy/universe? Even though it appears to be empty and dead, we cannot be sure that we are the only existing intelligent being in the universe. However, all the evidence we have so far indicates that it might indeed be the case.
Consider this, here on EarthEarth, we still haven’t figure out how multi-cellular life began on this planet, how it was able to move from a tiny cell to big, complex organisms. Not only that, but we also are not even sure how life began here in the first place or how water came into existence. There are many such questions, but no definite answer so maybe that our planet Earth is the only cosmic entity, which has allowed smart-species to evolve.
No one can deny the fact that where we live, the planet earth is unique and fascinating. It is the only planet, or cosmic entity we know of that harbors life.