Fermi Paradox
Consciousness
Humans have always looked up at the sky and wondered at what might be up there. In the millennia we have been around, we have come to find that the sun is a star, and we live on one of the planets revolving around that star. In recent years, we have found thousands of planets orbiting other stars, and estimated that the total number of planets in the galaxy vastly outweighs the number of stars.
60 years ago, a bunch of physicists were having lunch and talking about the possibility of intelligent aliens, when one of the physicists, Enrico Fermi, burst out “Where are they?” If there are so many stars and so many planets in the universe, why have we not seen any sign of life from another world? No visits, no messages, nothing. This question became known as the Fermi Paradox.
The first question you might have is, why should we think we should have seen alien life? Space is really, really big, after all. Another physicist, Frank Drake, proposed an equation to calculate the number of intelligent civilizations in the galaxy. This became known famously as the Drake equation. It gives us the probable number of civilizations in the galaxy, given the rate of star formation, the fraction of those stars with planets that could support life, the fraction of those planets that give rise to life, and the fraction of those planets that evolves intelligent life. The problem, though, is that we have no idea what numbers we should plug into it.
Can we guess? We have to look at human life, the only example we have. Intelligent life arose on Planet Earth in 4 billion years. In the 100,000 years since we evolved intelligence, we have gone from hunter-gatherers to globally-connected space-exploring civilizations. Assuming we continue to develop and expand, we will be all over the galaxy a few million years from now. So the time it takes between the beginning of life and the colonization of the entire galaxy is, at least in our example, about 4 billion years.
But the universe is 14 billion years old, so civilizations have had plenty of time in which to develop. Life needs heavy elements, which are only produced in the most extreme environments like supernovae or colliding neutron stars, so the longer the universe has been around, the better the environment for life to arise. Still, some of the first stars exploded less than a billion years after the big bang, which means it would have been possible for the first forms of life to arise 13 billion years ago. If it evolved to intelligence, then it would have spread across the galaxy ten billion years ago, and only continued to advance since!
If humanity is any example, intelligent life advances fast, a mere blink of an eye compared to the age of the universe. In science fiction we see all kinds of alien life forms encountering each other at about the same technological level, but this is unrealistic. Given the vast amount of time the universe has been around, if life arose elsewhere, it would be much more likely to be ancient than our age.
Science enthusiast YouTuber Isaac Arthur has gone further and suggested that as humanity expands, we will create artificial habitats around each star until the star is completely obscured from outside view. These swarms of habitats are called Dyson Spheres, after the physicist Freeman Dyson who first proposed their possibility. They would still give off infrared radiation as a heat signature, so we would be able to detect them. So if intelligent life besides us arose in the Milky Way, it would most likely be old and have covered all the stars with Dyson Spheres, so we should not be able to see any stars in the sky. Furthermore, this logic applies to all galaxies. Since we see billions of galaxies in the sky, and have so far found none to have the heat signature of a Dyson Swarm, then we might be pressed to conclude that we are the only intelligent species in the observable universe; a lonely and depressing thought.
So if civilizations are rare, what might be the reason? Some say it is because when civilizations advance enough, they turn introspective, have a strict non-interference policy, die out by natural disaster, or wipe themselves out in wars. But in order to resolve the Fermi Paradox, these explanations would have to apply to all civilizations, setting a heavy burden of proof to meet.
A more favorable resolution is something called the Great Filter, which would be an event in the course of the development of life that is extremely improbable. Any Great Filter candidate would have to be something that have happened only once in the history of life. There are several key events that fit this criterion, but I will focus on two of them: abiogenesis and intelligence. Since we have only one example of each happening, we cannot assign probabilities to them, so either or both might be extremely improbable.
We still do not know how life began on Earth. Though we have created simple bacteria in the laboratory in extremely artificial conditions, we have not observed it in nature nor in laboratory-reproduced conditions of the early Earth. If the Great Filter is abiogenesis, then life may truly be rare in the universe.
The evolution of intelligence is a happier Great Filter possibility, because it would mean that the universe is teeming with bacteria, plants, animals, and perhaps other Kingdoms we do not have on Earth. Imagine sending probes to planets around other stars, only to get back pictures of wild forests and creatures, ripe for colonization!
On the other hand, it may be that intelligent life is quite common, and we simply have not been able to find it yet. After all, the fraction of our own galaxy we have searched is so small that, as Neil deGrasse Tyson puts it, to claim there is no other life in the universe is like scooping up a glass of water from the surf and proclaiming there are no whales in the ocean. Space is big, and we have a lot of exploring ahead of us, and with the new telescopes we are building we may be on the brink of answering this age-old question.
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